- Email: [email protected]
Inherently safer mechanical material selection for process equipment
Accepted Manuscript Title: Inherently Safer Mechanical Material Selection for Process Equipment Authors: Muhammad Athar, Azmi Mohd Shariff, Azizul Buang, Heri Hermansyah PII: DOI: Reference:
S0957-5820(18)30842-5 https://doi.org/10.1016/j.psep.2018.09.008 PSEP 1512
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
9-2-2018 17-8-2018 6-9-2018
Please cite this article as: Athar M, Shariff AM, Buang A, Hermansyah H, Inherently Safer Mechanical Material Selection for Process Equipment, Process Safety and Environmental Protection (2018), https://doi.org/10.1016/j.psep.2018.09.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Inherently Safer Mechanical Material Selection for Process Equipment Muhammad Athar a, Azmi Mohd Shariff a, *, Azizul Buang a, Heri Hermansyah b a
Center of Advanced Process Safety (CAPS), Chemical Engineering Department, Universiti Teknologi
Petronas, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia. b
Industrial Bioprocess Engineering Laboratory, Department of Chemical Engineering, Faculty of Engineering,
IP T
Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia.
* Corresponding author:
SC R
Tel: +60 5 3687570 Fax: +60 5 3656176
N
U
E-mail Address: [email protected]
A
CC E
PT
ED
M
A
Graphical abstract
1
Highlights
Inherently safer mechanical material (ISMM) method is developed for basic design stage.
Newly established Mechanical integrity safety index (MISI) identifies the critical process equipment
Two-fold criteria is developed to select the inherently safer mechanical material for
IP T
process units
SC R
Substitution guide word helps to select the inherently safer mechanical material
Abstract
U
Hazards associated with chemical processes can lead to accidents, which can be managed through
N
process safety strategies. Inherent safety is a proactive tactic, capable of both identifying and
A
minimizing the hazard. Available inherent safety assessment (ISA) methods focus on route selection
M
only. Individual process equipment characteristics, especially the mechanical aspects are not reported
ED
for ISA. Subsequently, this paper presents a new technique for suitable material selection of process equipment at initial design stages. In inherently safer mechanical material (ISMM), process characteristics are coupled with the mechanical attributes for mechanical material selection of process
PT
equipment. The relative ranking of process equipment is used to highlight the critical process
CC E
equipment that is more prone to leak. This risky process unit is further studied to select the suitable mechanical material. Two-fold mechanical compatibility criteria are established, which needs to be satisfied for material selection. If the proposed material is found unsuitable, inherent safety theme is
A
used to propose the suitable material. The ISMM technique is verified by a case study of MMA-TBA process plant Hysys simulation. The technique is simple and identifies the crucial equipment in early design stages, which can help the design engineers to implement inherent safety at the basic design stage. Keywords: Basic design engineering, Indexing, Inherent safety, Mechanical material, Process simulation 2
Nomenclature
Alphabetical Symbols Magnifying Factor
d
vessel diameter (m)
IS
Stress Index
IC
Corrosion Index
P
vessel pressure (kPa)
t
vessel thickness (m)
T
vessel temperature (˚C)
ΔT
temperature difference (˚C)
WS
working stress (kPa)
yi
individual component fraction
pKa, i
relative acid strength of individual component
pKa, mix
relative acid strength of mixture
ED
M
A
N
U
SC R
IP T
A
Greek Symbols
thermal expansion coefficient (1/˚C)
δhoop
hoop stress (kPa)
δP
pressure stress (kPa)
CC E
PT
α
temperature stress (kPa)
δWS
working stress of vessel (kPa)
γ
young's modulus (kPa)
A
δT
1. INTRODUCTION
3
There is always a threat of inventory loss in the chemical process industry (CPI), which may create multiple accident scenarios. Different safety measures are employed to avoid such situations. Most of these are add-on safety actions, which require regular maintenance (Hendershot, 2006). Hazards associated with chemicals processing cannot be eliminated, nevertheless, controlling or reduction of hazard is conceivable up to a specific level. For this purpose, the hazard is enveloped in
IP T
multiple layers, as demonstrated in Fig. 1. These layers are named as layers of protection (LOP), also known as process safety strategies (Hendershot, 2006, 2010, 2011). For an accident to occur, hazard has to breach all the protection layers. The first layer of protection, inherent, is proactive in nature
SC R
with the objective to either minimize the hazard or its impacts (Kletz and Amyotte, 2010). The
remaining three layers are additional safety measures to control the process hazard. All these layers of
U
protection are necessary for a comprehensive safety management system.
N
To use these layers for hazard avoidance, safety studies are usually performed. For a chemical process plant life cycle, there are certain phases, and there are various safety studies, which can be
A
individually applied at a certain phase of process lifecycle (Shariff and Zaini, 2013). These safety
M
assessment methods with specific project phases are presented in Fig. 2. Most of the industrially
ED
practiced safety assessments are performed at later phases of the life cycle, and changes at these stages need additional capital contribution. This emphasizes applying inherent safety concepts at the
A
CC E
PT
earlier design phases.
Fig. 1 Process safety layers of protection
4
Conceptual
Basic
Detailed
Engineering
Engineering
Engineering
Preliminary Hazard Analysis
Equipment Procurement and Construction
Hazard and Operability (HAZOP) Study
Dow Fire & Explosion & Chemical Exposure Index
Pre-Startup Safety Review (PSSR) What-if Review
Review of Operating Procedures to identify hazards
SC R
Quantitative Risk Studies
Post Process Hazard Analysis
Check List Review
Failure Mode and Effect Analysis (FMEA)
Economic Risk Assessment
Operations
Commissioning
IP T
Research & Development & Feasibility Study
U
Fig. 2 Safety studies for project phases
N
Inherent safety is now acquiring more attention from researchers because of its remarkable
A
capabilities in risk management, and operational and capital investments. It minimizes the risk with least add-on safety measures. However, the inherent safety concept has not gained much
M
acknowledgment in the process industries. The recommendations regarding inherent safety
ED
implications are identified by analyzing the gaps and available in the literature (Gupta and Edwards, 2002). Inherent safety is usually applied through different strategies, which have been established by
PT
Center for Chemical Process Safety and other researchers (CCPS, 2010; Khan and Amyotte, 2002, 2003; Kletz and Amyotte, 2010), and are accessible in Fig. 3. Among inherent safety strategies, only
CC E
four are widely used namely, minimization, substitution, moderation, and simplification. Out of these four strategies, more frequent used inherent safety strategy is the minimization, while moderation,
A
simplification, and substitution are the next correspondingly (Hussin et al., 2015).
5
ERROR TOLERANCE
MINIMIZE
Improve equipment to handle variations
Less amount of material Reduced Equipment Size
SUBSTITUTE
SIMPLIFY
INHERENT SAFETY
IP T
Apply to materials, Chemistry or processes
SC R
Remove design complications
MODERATE
Change design Change Conditions (A form of moderation)
Reduced or modified process conditions
U
LIMITATION OF EFFECTS
N
Fig. 3 Inherent safety strategies
A
Several tactics are available to perform inherent safety assessment. These include indexing,
M
numerical, and graphical, which have been employed by researchers for assessing inherent safety level of chemical processes (Srinivasan and Natarajan, 2012). Indexing methodology is preferred over
ED
the others because of flexibility in the early design stages, as less information about the process is available (Srinivasan and Nhan, 2008). However, there are some limitations associated with indexing,
PT
such as subjective scaling, weighting factors, and limited perspectives for consideration (Ahmad et al., 2014; Srinivasan and Nhan, 2008).
CC E
As recognized in Fig. 2, various safety studies are available to use at different phases of the
process lifecycle. An appropriate methodology for safety studies at the preliminary design stage is missing. To deal with this issue, various methods have been proposed, which emphasized the inherent
A
safety assessment. Proto-type index for inherent safety (PIIS) is the first method (Lawrence, 1996), which identifies the safest process route focusing on assessment of several process parameters like temperature, pressure, etc. Some additional parameters like type of equipment, process structure, etc. have been introduced in inherent safety index (ISI) by Heikkilä, (1999) and Heikkilä et al., (1996) to achieve the same objective. Integrated Inherent Safety Index (I2SI) has amalgamated safety and cost 6
aspects in single methodology (Khan and Amyotte, 2004, 2005). It identifies the safer and economically viable process by aiming the hazard minimization rather than risk reduction. Anyhow, some limitations, i.e., manual data extraction of process parameters and individual chemicals have been identified for the aforementioned indices. These restrictions, however, have been removed in the integrated risk estimation tool (iRET) by linking process simulation software and
IP T
spreadsheet tool to evaluate the inherent safety (Shariff et al., 2006). Based on this idea, more methods for inherent safety assessment have been introduced by manipulating numerous process
information. These techniques include inherent safety index module (ISIM) and process route index
SC R
(PRI) by Leong and Shariff, (2008, 2009), inherent risk assessment (IRA) proposed by Shariff and
Leong, (2009), process stream index (PSI), toxic release consequence analysis tool (TORCAT) and
U
toxic release inherent risk assessment (TRIRA) proposed by Shariff et al., (2012) and Shariff and
N
Zaini, (2010, 2013) and inherent fire consequence estimation tool (IFCET) presented in Shariff and Wahab, (2013) and Shariff et al., (2016). These techniques differ in results, as some identify the
A
inherently safer route, while the others propose an improvement in the selected process route.
M
All of these specified methods are based on the indexing procedure, which has certain bottlenecks
ED
as described earlier. In order to overcome the limitations of indexing methods, many other safety techniques have been developed which include, i-Safe (Palaniappan et al., 2002), a simple graphical
PT
method for safer process route (Gupta and Edwards, 2003), inherent benign-ness indicator (IBI) (Srinivasan and Nhan, 2008), numerical descriptive inherent safety technique (NuDIST) (Ahmad et
CC E
al., 2014) and graphical descriptive technique for inherent safety assessment (GRAND) (Ahmad et al., 2016). Moreover, a few methods have integrated the environmental aspects with indexing to analyze the different process routes (Gunasekera and Edwards, 2003; Warnasooriya and Gunasekera, 2017).
A
The inherent safety concept has been divided among two regimes, i.e., 1st order inherent safety
and 2nd order inherent safety (Kidam et al., 2016). The first concept is regarding the hazard avoidance, whereas the other one is applied in the context of risk reduction by targeting either the likelihood or the severity. Hazard avoidance is usually performed by the comparison of flowsheets for the same process to select which one has the least hazard, i.e., 1st order inherent safety. All the aforementioned inherent safety methods have concentrated on the determination of the inherently safer route. Some of 7
the inherent safety assessment methods, however, have concentrated on the equipment safety without contemplating mechanical aspects (Gangadharan et al., 2013), i.e., missing the 2nd order inherent safety concept. The accidents in process industries happen due to the failure of the mechanical component leading towards either the rupture or small leak, which in turn is defined as the loss of inventory or leak (CCPS, 2000). Therefore, consideration of mechanical aspects for selection of the
which is in line with the concept of minimizing the likelihood of consequences.
IP T
material of construction at early design stages may help in designing an inherently safer process,
In this paper, a new method has been presented to select the appropriate mechanical material for
SC R
process equipment at the basic design stage to ensure the safer process. The technique is divided into two parts. Initially, all equipment in the process are compared with each other to prioritize and
U
identify the critical process equipment. Next, the material is proposed for the identified critical
N
equipment to investigate the integrity of that particular equipment. An appropriate criterion for mechanical material selection has been developed. In case the suggested material is unsuitable for the
A
equipment, the inherent safety concept is used to select a suitable material until material selection
M
criteria are satisfied. Process information from ASPEN HYSYS is linked with MS Excel, and all
ED
processing is performed in MS Excel via VBA coding. This tool is simple to use and can be readily adopted by industrial persons.
PT
2. METHODOLOGY
CC E
The mechanical integrity of process equipment is an indispensable factor to characterize the safety level. Numerous materials are available to use for process equipment fabrication, and choice of the right material is the most critical decision. The reasons for mechanical failure in process
A
equipment can be classified as follows (Maleque and Salit, 2014): 1. poor selection of materials 2. fabrication defects 3. exceeding design limits 4. inadequate maintenance
8
The material of construction has been identified as one of the prominent design error, recognized from the investigation of past accidents (Kidam and Hurme, 2012a; Kidam et al., 2016). This design error is related with the basic design stage, while the others are related to later phases of process lifecycle (Kidam and Hurme, 2012a, b, 2013; Kidam et al., 2016). The detailed analysis of this design error has revealed that the chemical and mechanical suitability is required for the inherently safer material of
IP T
construction (Kidam and Hurme, 2012a, b; Kidam et al., 2015; Kidam et al., 2016). Furthermore, it is identified that these two suitability criteria are defined in terms of stress, corrosion, and wear, and applicable to all the reasons of failure and subsequently relevant for the material of construction
SC R
(Maleque and Salit, 2014). Corrosion is related to the acidity, which would define the chemical
suitability. While, stress is linked to temperature and pressure, and would highlight the mechanical
U
suitability. All this information of acidity, temperature, and pressure are available at the basic design
N
stage. While wear is related to removal of material by mechanical action and during initial design phases such information is missing. Therefore, stress and corrosion are the parameters available for
A
selection of materials during the early phase of process lifecycle. The methodology for mechanical
M
material selection, at the basic design stage, is explained in the next subsections and named as
A
CC E
PT
ED
Inherently Safer Mechanical Material (ISMM), and the relevant framework is available in Fig. 4.
9
INDEXING PART
START
Identification of Process Units
Select a Material of Construction
IP T
Process Data from ASPEN HYSYS
Mechanical Integrity Safety Index
M ED
SUBSTITUTION
CC E
PT
NON-RECOMMENDED
A
SC R
A
NO
Apply Suitable ISD Guideword
Working Stress Acceptable
YES
Corrosion Suitability
RECOMMENDED
MECHANICAL MATERIAL SUITABILITY & SELECTION PART
N
U
Identification of Critical Equipment
Components pKa Data
SATISFACTORY
Can Proceed with Design
Fig. 4 Framework for inherently safer mechanical material (ISMM) selection
Mechanical materials for process equipment
Diverse sort of materials are used in the process industry, i.e., metals, elastomers, and plastics. Each material class has particular characteristics. Some are more corrosion resistant, while others can bear high stresses. There are thousands of material compositions available, which can be used to 10
fabricate the process equipment. However, in this work, only a few materials have been chosen to present the idea. Three different mostly used materials are identified for each material class mentioned earlier. These selected materials are as follows:
Metals: Carbon Steel, Stainless Steel 316, Titanium
Elastomers: Viton, NBR (Nitrile rubber), Neoprene
IP T
Plastics: Poly chloro-tri-fluoro ethylene (Kel-F), Teflon, Polyvinylidene fluoride (KYNAR) Incorporation of stress at the basic design
SC R
As mentioned earlier, stress in process equipment is caused by temperature and pressure.
Information about these parameters is available from process simulation and can be used to define the magnitude of stresses.
U
2.2.1. Pressure stress
N
Most of the process equipment in process industry occur in the shape of the pressure vessel
A
(Dupen, 2016), and this theory can be used for the ISMM assessment at initial design stages. Further, pressure vessels occur either in the thick wall or thin wall. If the thickness of the wall is less than 10%
M
of the internal radius, then the pressure vessel is a thin wall pressure vessel. For a thick pressure
ED
vessel, the wall thickness is more than 10% of the internal radius. Most of the equipment in process industry has a thickness of less than 10% of the radius. In this context, at initial design stages, thin
PT
wall pressure vessels have been assumed for pressure stress estimation. Pressure vessels occur in spherical or cylindrical shape. For cylindrical vessels, only hoop stress is valid, while for spherical
CC E
vessels longitudinal stress is useful. As, most of the industrial vessels are cylindrical, so the hoop stress is considered in ISMM, and longitudinal stresses are eradicated. Hoop stress can be calculated by:
A
δ hoop =
Pd
(1)
2t
For this work, hoop stress is considered as pressure stress, i.e., δhoop = δP. 2.2.2.Temperature stress
The change in temperature influence the shape of the material, i.e., if the temperature is increased, the material expands and vice versa. The temperature stress is a function of the thermal expansion
11
coefficient, Young's modulus, and the change in temperature as per the following relation (Dupen, 2016):
δT = - α γ T
(2)
The thermal expansion coefficient, 𝛼, is material explicit property, which is the material expansion rate. Different materials expand at different rates. While, young's modulus 𝛾 is the measure of
IP T
material stiffness. The essential data for temperature stress calculation is given in Table 1. Initially, a material is proposed for calculation purposes, and then the temperature stresses in each process
SC R
equipment are estimated. For the negative thermal stress, the vessel is under compressive stress and if it is positive, the vessel is under tensile stress.
Table 1 - Material specific characteristics (Department, 2016; Elastomers, 2016; Ellis and Smith, 2008) Thermal expansion coefficient (1/˚C)
Young's modulus (GPa)
1.80 x 10-5
U
Material name
N
Material class
205
1.50 x 10-5
215
10-5
115
8.00 x 10-5
1.45
1.35 x 10-4
0.55
KYNAR
9.00 x
10-5
1.60
NBR
1.97 x 10-4
0.005
6.00 x 10-4
0.002
10-4
0.016
Metals
A
Stainless Steel 316
Titanium Kel-F Teflon
Elastomers
ED
Plastics
M
Carbon Steel
PT
Neo-prene (Nitrile rubber) Viton
1.28 x
2.16 x
CC E
2.2.3. Stress index calculations
The total working stress can be estimated by the following relationship:
δWS = δP + δT
(3)
A
The stress index for each process equipment based on relative ranking can be estimated by: IS =
Working Stress of Individual Equipment
(4)
Average Working Stress of All Equipment
Equipment with higher IS value is under high stress relatively and vice versa.
12
Corrosion for basic design Most of the process industry equipment are fabricated by iron and its alloys. These materials corrode in acidic and basic conditions, however, more prone to decay in an acidic environment (Negm et al., 2011). The reason for more corrosion in an acidic environment is that most acids tend to accept electrons, while bases donate electrons. Corrosion is done when the metal donates electrons, and the
IP T
solution is accepting the electrons (Landolt, 2007). For example, the electron transfer equations for iron are given below:
SC R
Fe Fe2+ +2e-
2H+ + 2e- H2
Therefore, acidic media tends to behave more corrosive than the basic environment. (Heikkilä, 1999)
U
in ISI method has considered the corrosion aspect, however, no criteria are available to quantify the
N
corrosion. Dow F&E index has also proposed penalties based on corrosion rate (AIChE, 2010),
A
whereas the corrosion rate is not linked to the chemicals being processed in the process equipment.
M
2.3.1. Acidity measurement
Acidity is usually measured by pH value; however, it is not available from the process simulation
ED
software i.e. ASPEN Hysys. An alternate method for acidity estimation is to determine the relative strength of an acid, pKa. An acid, which transfers hydrogen atoms close to 100% upon dissolution is a
PT
concentrated acid. The smaller the value of pKa, the stronger the acid and vice versa. The strengths of
CC E
different acids with their pKa values are furnished in Table 2 (College of Pharmacy, 2016). Briefly, if pKa is less than 3, the solution is strongly acidic; for 3 to 7 it is weakly acidic, range 7 to 11 indicates weak base and greater than 11, the solution is strongly basic. The pKa values of individual chemicals
A
are available in the literature, and pKa value for a mixture can be calculated through: pK a, mix =
1
yi pK a, i
(5)
2.3.2. Corrosion index estimation
The corrosion index is calculated by:
13
IC =
1
pK a, mix of individual Equipment Average pK a,mix of All Equipment
(6)
Highest pKa, mix value reveals a more basic solution, and without reciprocal, significant IC value indicates a strong base. If IC is calculated by reciprocal method, enormous IC translates into more
Table 2 - Strength of acids and bases (College of Pharmacy, 2016) pKa
Acid Strength
HI
-10
Strongest Acid
H2SO4
-9 -7
C6H5SO3H
-6.5
H3O+
-1.7
HNO3
-1.4 4.6
CH3CO2H
4.8
+
9.2
NH4
C6H5OH
9.9
CH3NH3+
10.6
H2O
15.7 16
ED
CH3CH2OH CH ≡ CH
25
NH3
38 44 50
Weakest Acid
Strong Base
CC E
PT
CH2 = CH2 CH3CH3
A
C6H5NH3
N
0.2
+
M
CF3CO2H
Weakest Base
U
HCl
Base Strength
SC R
Acid
IP T
acidic conditions, and it is easy to identify the equipment under more acidic conditions relatively.
Mechanical integrity safety index (MISI)
Initially, all process equipment in process flow sheet are identified. An initial material is proposed
A
for all the equipment, and stress and corrosion indices are then estimated through equations (4) and (6). These indices individually identify critical process equipment regarding stress and corrosion level. The equipment under combined conditions of stress and corrosion, however, can be determined by considering both factors at the same time. For this purpose, a new index is proposed, which is termed as mechanical integrity safety index (MISI). This concept of indexing has similar approach to the inherent safety index for shell and tube heat exchanger (ISISTHE) in identifying the critical 14
process equipment that has high potential of failure at the earlier design stages (Pasha et al., 2017). The MISI can be calculated through the following relation:
MISI = A × IS × IC
(7)
For small MISI magnitude, a magnifying factor A can be used to amplify the effect (Shariff et al., 2012). The higher the value of MISI, the more critical is the equipment and vice versa. This indexing
IP T
method aids the design engineer in identifying the most critical equipment during earlier design
phases, which is in line with the previously presented indexing method, such as inherent safety index
SC R
for shell and tube heat exchanger (ISISTHE) (Pasha et al., 2017). Material selection for critical process equipment
Once the critical process equipment is identified, next is the selection of suitable mechanical
U
material for the identified process equipment. The selected material should be able to withstand the
N
stresses created by process temperature and pressure, and corrosion imposed by the chemical mixture.
A
A criterion of acceptability has been developed for stress and corrosive environment. If both criteria
M
are satisfied for identified critical process equipment, then the selected material is considered suitable. Otherwise, inherent safety principle substitution is applied by replacing the material with better
ED
material. The loop is rerun and checked for stress and corrosion suitability until both conditions are satisfied.
PT
2.5.1. Stress suitability criteria
The working stress for critical process equipment is calculated using Eq. (2) mentioned earlier. If
CC E
the working stress of critical process equipment is below the ultimate tensile strength (UTS) of the selected material, the material is suitable. If the working stress is greater than the ultimate tensile strength of the chosen material, some material with high ultimate tensile strength is required. The
A
ultimate tensile strength is defined as the maximum stress that a material can withstand before it breaks or weakens (Dewolf et al., 2009). The ultimate tensile strength values of selected materials are given in Table 3. This table is prepared after reviewing the appropriate literature (Department, 2016; Elastomers, 2016; Ellis and Smith, 2008).
15
Table 3 - Ultimate tensile strength of different materials (Department, 2016; Elastomers, 2016; Ellis and Smith, 2008)
Plastics
Elastomers
Ultimate Tensile Strength (MPa)
Stainless Steel 316
2,240
Carbon Steel
1,640
Titanium
1,625
Kel-F
40
Teflon
40
KYNAR
30
NBR
27
Neoprene (Nitrile rubber)
24
IP T
Metals
Material Name
SC R
Material Class
Viton
20
U
2.5.2. Corrosion Suitability Criteria
There is no particular value to decide about corrosion compatibility. Each chemical behaves in a
N
different way towards the various type of mechanical materials. Compatibility charts for a broad range
A
of mechanical materials with different chemicals are available in the literature (Corporation, 2017;
M
Emerson, 2016). For each acidic classification, three chemicals have been studied for their effect on
categories as below:
ED
selected mechanical materials. The effects of chemicals on mechanical materials are divided into three
PT
1. Recommended / Good for use 2. Satisfactory
CC E
3. Non-recommended
Numerical values are outlined for each category of effects, and average values of the response of selected chemicals are calculated, and a simple compatibility chart of mechanical material is prepared,
A
as shown in Table 4. Various material compatibility charts have been studied to formulate this table (Corporation, 2017; Emerson, 2016). This table is preferred over the Heikkila corrosion indexing because it is based on the actual interaction of chemicals with different mechanical materials rather than the expert judgment. However, the pattern of compatibility is not smooth because of the chemicals nature.
16
I N U SC R
Table 4 - Chemicals corrosion compatibility chart for mechanical materials (Corporation, 2017; Emerson, 2016) Metals Acidic Nature
Elastomers
Plastics
Carbon Steel
Stainless Steel 316
Titanium
Strong Acid
pKa < 3
3
3
2
3
3
1
2
1
1
Weak Acid
3 < pKa < 7
3
2
2
2
2
1
1
1
1
Weak Base
7 < pKa < 11
3
2
1
2
1
2
1
1
1
Strong Base
pKa > 11
1
1
1
1
2
2
2
1
1
PT
ED
M
A
pKa Range
NBR (Nitrile rubber)
A
CC E
1 - Recommended / Good for use 2 - Satisfactory 3 - Non-recommended
17
Neoprene
Viton
KYNAR
Teflon
Kel-F
3. RESULTS AND DISCUSSION Case study for MISI Methyl methacrylate (MMA) production has been the most studied process for validation of numerous inherent safety techniques. There are six different process routes to produce MMA (Lawrence, 1996) using the following raw materials:
IP T
1. Acetone Cyanohydrin (ACH) 2. Ethylene through methyl propionate (C2/MP)
SC R
3. Ethylene through propionaldehyde (C2/PA) 4. Propylene (C3) 5. Isobutylene (i-C4)
U
6. Tertiary butyl alcohol (TBA)
N
Numerous inherent safety assessment techniques for route selection have been compared by (Leong
A
and Shariff, 2009; Rahman et al., 2005), and TBA process route has been identified as the safer one
M
among all routes. This route has been selected to demonstrate the ISMM technique. The process simulation for the production of methyl methacrylate (MMA) from tertiary butyl alcohol (TBA) is
ED
given in Fig. 5 (Jha et al., 2016). In this process, TBA is oxidized to methacrolein which is further oxidized to methacrylic acid. The reaction of methacrylic acid with methanol leads to MMA.
PT
There are ten process units in this process as shown in Fig. 5. Initially, carbon steel has been selected as the mechanical material for all process units. Necessary process information has been
CC E
imported from ASPEN HYSYS to MS Excel through VBA programming. Information about the acidity of individual chemicals has been collected from the literature. Temperature, pressure and relative acidity have been processed in MS Excel via VBA coding to estimate the stress and corrosion
A
indices. Stress and corrosion indices have been calculated using equations (4) and (6), and the resulting values are provided in Table 5. These sub-indices values have been multiplied to calculate the MISI values as mentioned in equation (7). As MISI values of each equipment are appropriate in magnitude, the magnifying factor used in this calculation is 1. MISI for individual process units in descending order are available in Table 5. The individual indices have identified different process
18
equipment as critical about a particular mechanical aspect, i.e., highest stresses in E-100 and the most acidic environment in E-101. The reason for dissimilar critical process units for each individual parameter is different process conditions and compositions in each unit. However, for the combined effect of both aspects, E-101 has emerged as the most critical process unit. During the early design stages, we will focus on the most critical equipment only for material selection. Even though the E-
IP T
101 is selected based on the MISI value, however, the value is very close to the E-100. A better confirmation could be done by comparing the relevant cost of the equipment. However, the process
SC R
economics is not included in this paper, therefore it should be considered in future work.
Table 5 - Initial MISI values through relative ranking
E-101
2.0278
1.7169
E-100
4.1474
0.7533
CRV-102
0.9371
1.3845
T-101
0.3773
1.4733
T-100
0.7580
T-102
0.2919
E-102
0.2919
CRV-101
0.2343
CRV-103 V-101
MISI
Equipment Ranking based on MISI
3.4817
1
3.1242
2
1.2975
3
0.5559
4
0.5565
0.4218
5
1.0442
0.3048
6
0.9897
0.2889
7
0.7350
0.1722
8
0.0893
1.0009
0.0894
9
0.0353
1.0179
0.0359
10
A
N
U
IC
M
IS
A
CC E
PT
ED
Equipment Tag No.
19
I N U SC R A M ED PT CC E
A
Fig. 5 - Hysys process simulation of MMA-TBA process (Jha et al., 2016)
20
Proposed mechanical material suitability Next is the assessment of proposed material suitability for the critical process equipment as identified through MISI, i.e., E-101. Individual criteria for stress and corrosion needs to be assessed and fulfilled. For this study, the dimensions of vessels have been assumed as 36 inches in diameter and 1 inch in thickness. Ambient temperature is 25 ˚C, and as mentioned earlier, carbon steel is taken
IP T
as the initial mechanical material for this process equipment. The working stress has been estimated for E-101 using equations (1), (2) and (3). Total working stress is a combination of pneumatic and
SC R
thermal stresses. Total working stress has been estimated as 1,959 MPa. The ultimate tensile strength of carbon steel is found from Table 3 as 1,640 MPa. The selected material is not suitable concerning stress aspect, which suggests that a superior material is required for these process conditions. Before
U
substituting the carbon steel with a better material, a check for corrosion suitability has also been
N
performed. The pKa value for the chemical mixture has been calculated to be 6.17, i.e., a weak acid.
A
For a weak acid, carbon steel is not recommended. Therefore, carbon steel is not suitable to be used with this composition of the processing chemicals. Both stress and corrosion criteria are not satisfied
M
for the identified critical process equipment E-101 with the initially selected material i.e., carbon
ED
steel.
Mechanical material selection through IS Guide Word
PT
As carbon steel has been identified as non-suitable for E-101 and a better material is required. Applying the inherent safety guide word ‘substitute,' carbon steel has been replaced by stainless steel
CC E
316, and all parameters are recalculated. The vessel dimensions and atmospheric conditions have been the same. First of all, the stress and corrosion indices have been estimated with the substituted mechanical material. The MISI values for respective process equipment have been determined with
A
individual equipment sub-indices. The revised results of MISI and both sub-indices are given in Table 6. E-101 has emerged again as the most critical equipment in the revised analysis.
21
Table 6 - Revised MISI values through relative ranking Equipment Ranking based on MISI
IC
MISI
E-101
2.0353
1.7169
3.4945
1
E-100
4.1663
0.7533
3.1385
2
CRV-102
0.9000
1.3845
1.2461
3
T-101
0.3783
1.4733
0.5574
4
T-100
0.7608
0.5565
0.4234
5
T-102
0.2929
1.0442
0.3059
6
E-102
0.2929
0.9898
0.2899
CRV-101
0.2344
0.7351
0.1723
CRV-103
0.0888
1.0010
0.0888
V-101
0.0331
1.0180
0.0337
IP T
IS
7 8 9
10
SC R
Equipment Tag No.
The revised stresses for E-101 have been estimated as 2,239 MPa. Although the process
U
conditions have not changed, the stresses have increased. This phenomenon is because of the specific
N
properties of the stainless steel, i.e., thermal expansion coefficient and Young’s modulus. The
A
ultimate tensile strength from Table 3 for stainless steel 316 is 2,240 MPa. This material has passed
M
the stress criteria. Next is the corrosion criteria. pKa value has not changed with the substitution of mechanical material as it is dependent purely on the chemical mixture inside the process equipment.
ED
For a weak acid, stainless steel can be used satisfactorily. Consequently, the stainless steel 316 can be used for identified critical process equipment, E-101, as both stress and corrosion criteria have been
PT
satisfied. Results for initial and revised material suitability are given in Table 7. A further better material can be selected for this process equipment at later design stages with
CC E
more detailed information about the process. However, this method would serve as an initial indicator for process engineers to identify the critical process unit and narrow down the material of construction
A
choice for specified process equipment.
22
Table 7 - Initial and revised material suitability for E-101 Stress Material of Scenario Construction
𝛅𝐏
Corrosion 𝛅𝐓
𝛅𝐖𝐒
Initial
Carbon Steel
18,000 1,941,162 1,959,162
Revised
Stainless Steel 18,000 2,221,050 2,239,050
UTS
𝒑𝑲𝒂,𝒎𝒊𝒙
Remarks
NonRecommended 2,240,000 Recommended 1,640,000
Compatibility Remarks Value
6.17
3
6.17
2
IP T
4. CONCLUSION
NonRecommended Satisfactory
Many techniques have been proposed by many researchers for the conduct of inherent safety
SC R
assessment. Most of these techniques have focused on the selection of inherently safer process path. Individual equipment has never been taken into consideration to make them inherently safer.
Failure of most process equipment in many of the process accidents is caused by the mechanical
U
component failure. This paper has presented a new technique for inherently safer mechanical material
N
selection (ISMM) at the basic design stage. Mechanical and chemical suitability aspects, namely
A
stress and corrosion correspondingly, have been linked with the process parameters to assist in the
M
inherently safer mechanical material selection. ISMM technique has two parts i.e., identification of mechanically critical process unit through MISI and selection of suitable material for critical
ED
equipment. MISI has been developed to identify the mechanically critical equipment. Twofold criteria have been proposed to select the material of fabrication for process unit. Both criteria have to be
PT
satisfied before selecting the final material. For any unsatisfied criteria, inherent safety guide word
CC E
substitution has been considered to select the suitable material. The whole framework for mechanical material selection at the basic design stage has been demonstrated by a case study. The identified critical process unit has been made inherently safer by proposing a better material using substitution
A
idea. For the ease of process design engineers, only the most vital process unit has been suggested to be reviewed for material selection during the initial design phase. However, the choice of materials can also be applied to other process units by linking directly to the stream properties to select the appropriate material. For future studies, more materials can be included in the list for industrial use and more processes can be explored to enhance the idea. Furthermore, other factors such as the change in process variables and cost can also be combined with mechanical and chemical suitability 23
aspects for selection of the material of construction that can be developed using an optimization model.
Acknowledgement
The authors would like to gratitude Universiti Teknologi PETRONAS, Malaysia for providing
IP T
internal research funds to make this research possible.
SC R
References
Ahmad, S.I., Hashim, H., Hassim, M.H., 2014. Numerical descriptive inherent safety technique (NuDIST) for inherent safety assessment in petrochemical industry. Process Safety and Environmental
U
Protection 92, 379-389. doi: http://dx.doi.org/10.1016/j.psep.2014.03.009
N
Ahmad, S.I., Hashim, H., Hassim, M.H., 2016. A graphical method for assessing inherent safety
A
during research and development phase of process design. Journal of Loss Prevention in the Process
M
Industries 42, 59-69. doi: http://dx.doi.org/10.1016/j.jlp.2015.09.018 AIChE, American Institute of Chemical Engineers, 2010. Dow's Fire and Explosion Index Hazard
ED
Classification Guide, 7 ed. Wiley.
CCPS, Center for Chemical Process Safety, 2000. Guidelines for chemical process
PT
quantitative risk analysis. American Institute of Chemical Engineers AIChE. CCPS, Center for Chemical Process Safety, 2010. Inherently Safer Chemical Processes: A Life Cycle
CC E
Approach, 2 ed. John Wiley & Sons. College of Pharmacy, Health Professions Division, 2016. Acid-Base Properties of Drugs, Accessed, http://pharmacy.nova.edu/Pharmacodynamics/Modules/AcidsSaltsBases/Main_P3.html
A
Corporation, Quick Cut Gasket & Rubber, 2017. Chemical Resistance Chart, Accessed on 30/03/2017, http://www.quickcutgasket.com/pdf/Chemical-Resistance-Chart.pdf Department, Engineering, 2016. Materials Data Book, Accessed on 25/10/2016, http://wwwmdp.eng.cam.ac.uk/web/library/enginfo/cueddatabooks/materials.pdf Dewolf, J.T., Beer, F.P., Johnston, E.R., 2009. Mechanics Of Materials (In Si Units), 5 ed. McGraw24
Hill Education (India) Pvt Limited. Dupen, B., 2016. Applied Strength of Materials for Engineering Technology. Elastomers, DuPont Dow, 2016. Viton® fluoroelastomer: A Product of DuPont Dow Elastomers, Accessed on 23/11/2016, http://www.rainbowrubber.com/VB.pdf Ellis, B., Smith, R., 2008. Polymers: A Property Database, 2 ed. CRC Press.
IP T
Emerson, 2016. Chemical Compatability of Elastomers and Metals, Accessed on 18/10/2016, http://www.documentation.emersonprocess.com/groups/public/documents/reference/d351798x012_06 .pdf
SC R
Gangadharan, P., Singh, R., Cheng, F., Lou, H.H., 2013. Novel methodology for inherent safety
assessment in the process design stage. Industrial & Engineering Chemistry Research 52, 5921-5933.
U
doi: http://dx.doi.org/10.1021/ie303163y
Gunasekera, M.Y., Edwards, D.W., 2003. Estimating the Environmental Impact of Catastrophic
A
http://dx.doi.org/10.1205/095758203770866638
N
Chemical Releases to the Atmosphere. Process Safety and Environmental Protection 81, 463-474. doi:
M
Gupta, J.P., Edwards, D.W., 2002. Inherently Safer Design—Present and Future. Process Safety and
ED
Environmental Protection 80, 115-125. doi: http://dx.doi.org/10.1205/095758202317576210 Gupta, J.P., Edwards, D.W., 2003. A simple graphical method for measuring inherent safety. Journal
PT
of Hazardous Materials 104, 15-30. doi: http://doi.org/10.1016/S0304-3894(03)00231-0 Heikkilä, A.-M., 1999. Inherent safety in process plant design: an index-based approach. (PhD), VTT
CC E
Technical Research Centre of Finland. Heikkilä, A.-M., Hurme, M., Järveläinen, M., 1996. Safety considerations in process synthesis. Computers & chemical engineering 20, S115-S120. doi: https://doi.org/10.1016/0098-1354(96)00030-
A
0
Hendershot, D.C., 2006. An overview of inherently safer design. Process safety progress 25, 98-107. doi: http://dx.doi.org/10.1002/prs.10121 Hendershot, D.C., 2010. A summary of inherently safer technology. Process Safety Progress 29, 389392. doi: http://dx.doi.org/10.1002/prs.10395 Hendershot, D.C., 2011. Inherently safer design: an overview of key elements, Professional Safety, p. 25
48. Hussin, N.A.E., Kidam, K., Suhaili, S., 2015. Lessons learned from process equipment failures in the chemical process industry. Jurnal Teknologi 10, 43-52. doi: http://dx.doi.org/10.11113/jt.v75.5184 Jha, V., Pasha, M., Zaini, D., 2016. Enhanced inherent safety intervention framework. Procedia Engineering 148, 1051-1057. doi: https://doi.org/10.1016/j.proeng.2016.06.589
IP T
Khan, F.I., Amyotte, P.R., 2002. Inherent safety in offshore oil and gas activities: a review of the present status and future directions. Journal of Loss Prevention in the Process Industries 15, 279-289. doi: http://dx.doi.org/10.1016/S0950-4230(02)00009-8
SC R
Khan, F.I., Amyotte, P.R., 2003. How to make inherent safety practice a reality. The Canadian Journal of Chemical Engineering 81, 2-16. doi: http://dx.doi.org/10.1002/cjce.5450810101
U
Khan, F.I., Amyotte, P.R., 2004. Integrated inherent safety index (I2SI): a tool for inherent safety evaluation. Process safety progress 23, 136-148. doi: http://dx.doi.org/10.1002/prs.10015
N
Khan, F.I., Amyotte, P.R., 2005. I2SI: a comprehensive quantitative tool for inherent safety and cost
M
http://dx.doi.org/10.1016/j.jlp.2005.06.022
A
evaluation. Journal of Loss Prevention in the Process Industries 18, 310-326. doi:
ED
Kidam, K., Hurme, M., 2012a. Design as a contributor to chemical process accidents. Journal of Loss Prevention in the Process Industries 25, 655-666. doi: http://dx.doi.org/10.1016/j.jlp.2012.02.002
PT
Kidam, K., Hurme, M., 2012b. Origin of equipment design and operation errors. Journal of Loss Prevention in the Process Industries 25, 937-949. doi: http://dx.doi.org/10.1016/j.jlp.2012.05.005
CC E
Kidam, K., Hurme, M., 2013. Method for identifying contributors to chemical process accidents. Process Safety and Environmental Protection 91, 367-377. doi: http://dx.doi.org/10.1016/j.psep.2012.02.001
A
Kidam, K., Sahak, H.A., Hassim, M.H., Hashim, H., Hurme, M., 2015. Method for identifying errors in chemical process development and design base on accidents knowledge. Process Safety and Environmental Protection 97, 49-60. doi: http://dx.doi.org/10.1016/j.psep.2015.06.004 Kidam, K., Sahak, H.A., Hassim, M.H., Shahlan, S.S., Hurme, M., 2016. Inherently safer design review and their timing during chemical process development and design. Journal of Loss Prevention in the Process Industries 42, 47-58. doi: http://dx.doi.org/10.1016/j.jlp.2015.09.016 26
Kletz, T.A., Amyotte, P., 2010. Process plants: A handbook for inherently safer design. CRC Press. Landolt, D., 2007. Corrosion and Surface Chemistry of Metals. EFPL Press. Lawrence, D., 1996. Quantifying inherent safety of chemical process routes. (PhD), Loughborough University. Leong, C.T., Shariff, A.M., 2008. Inherent safety index module (ISIM) to assess inherent safety level
IP T
during preliminary design stage. Process Safety and Environmental Protection 86, 113-119. doi: http://dx.doi.org/10.1016/j.psep.2007.10.016
Leong, C.T., Shariff, A.M., 2009. Process route index (PRI) to assess level of explosiveness for
SC R
inherent safety quantification. Journal of Loss Prevention in the Process Industries 22, 216-221. doi: http://dx.doi.org/10.1016/j.jlp.2008.12.008
U
Maleque, A., Salit, M.S., 2014. Materials Selection and Design. Springer My Copy UK.
Negm, N., Ghuiba, F., Tawfik, S., 2011. Novel isoxazolium cationic Schiff base compounds as
A
http://dx.doi.org/10.1016/j.corsci.2011.06.029
N
corrosion inhibitors for carbon steel in hydrochloric acid. Corrosion Science 53, 3566-3575. doi:
M
Palaniappan, C., Srinivasan, R., Tan, R.B., 2002. Expert system for the design of inherently safer
ED
processes. 2. Flowsheet development stage. Industrial & engineering chemistry research 41, 67116722. doi: http://dx.doi.org/10.1021/ie0201765
PT
Pasha, M., Zaini, D., Mohd Shariff, A., 2017. Inherently safer design for heat exchanger network. Journal of Loss Prevention in the Process Industries 48, 55-70. doi:
CC E
http://doi.org/10.1016/j.jlp.2017.04.002 Rahman, M., Heikkilä, A.-M., Hurme, M., 2005. Comparison of inherent safety indices in process concept evaluation. Journal of Loss Prevention in the Process Industries 18, 327-334. doi:
A
http://doi.org/10.1016/j.jlp.2005.06.015 Shariff, A.M., Leong, C.T., 2009. Inherent risk assessment—a new concept to evaluate risk in preliminary design stage. Process Safety and Environmental Protection 87, 371-376. doi: http://dx.doi.org/10.1016/j.jlp.2009.07.005 Shariff, A.M., Leong, C.T., Zaini, D., 2012. Using process stream index (PSI) to assess inherent safety level during preliminary design stage. Safety science 50, 1098-1103. doi: 27
http://dx.doi.org/10.1016/j.ssci.2011.11.015 Shariff, A.M., Rusli, R., Leong, C.T., Radhakrishnan, V., Buang, A., 2006. Inherent safety tool for explosion consequences study. Journal of Loss Prevention in the Process Industries 19, 409-418. doi: http://dx.doi.org/10.1016/j.jlp.2005.10.008 Shariff, A.M., Wahab, N.A., 2013. Inherent fire consequence estimation tool (IFCET) for preliminary
IP T
design of process plant. Fire Safety Journal 59, 47-54. doi: http://dx.doi.org/10.1016/j.firesaf.2013.03.015
Shariff, A.M., Wahab, N.A., Rusli, R., 2016. Assessing the hazards from a BLEVE and minimizing its
SC R
impacts using the inherent safety concept. Journal of Loss Prevention in the Process Industries 41, 303-314. doi: http://dx.doi.org/10.1016/j.jlp.2016.01.001
U
Shariff, A.M., Zaini, D., 2010. Toxic release consequence analysis tool (TORCAT) for inherently safer design plant. Journal of hazardous materials 182, 394-402. doi:
N
http://dx.doi.org/10.1016/j.jhazmat.2010.06.046
A
Shariff, A.M., Zaini, D., 2013. Inherent risk assessment methodology in preliminary design stage: a
M
case study for toxic release. Journal of Loss Prevention in the Process Industries 26, 605-613. doi:
ED
http://dx.doi.org/10.1016/j.jlp.2012.12.003
Srinivasan, R., Natarajan, S., 2012. Developments in inherent safety: A review of the progress during
PT
2001–2011 and opportunities ahead. Process Safety and Environmental Protection 90, 389-403. doi: http://doi.org/10.1016/j.psep.2012.06.001
CC E
Srinivasan, R., Nhan, N.T., 2008. A statistical approach for evaluating inherent benign-ness of chemical process routes in early design stages. Process Safety and Environmental Protection 86, 163174. doi: http://dx.doi.org/10.1016/j.psep.2007.10.011
A
Warnasooriya, S., Gunasekera, M.Y., 2017. Assessing inherent environmental, health and safety hazards in chemical process route selection. Process Safety and Environmental Protection 105, 224236. doi: http://doi.org/10.1016/j.psep.2016.11.010
28
S0957-5820(18)30842-5 https://doi.org/10.1016/j.psep.2018.09.008 PSEP 1512
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
9-2-2018 17-8-2018 6-9-2018
Please cite this article as: Athar M, Shariff AM, Buang A, Hermansyah H, Inherently Safer Mechanical Material Selection for Process Equipment, Process Safety and Environmental Protection (2018), https://doi.org/10.1016/j.psep.2018.09.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Inherently Safer Mechanical Material Selection for Process Equipment Muhammad Athar a, Azmi Mohd Shariff a, *, Azizul Buang a, Heri Hermansyah b a
Center of Advanced Process Safety (CAPS), Chemical Engineering Department, Universiti Teknologi
Petronas, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia. b
Industrial Bioprocess Engineering Laboratory, Department of Chemical Engineering, Faculty of Engineering,
IP T
Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia.
* Corresponding author:
SC R
Tel: +60 5 3687570 Fax: +60 5 3656176
N
U
E-mail Address: [email protected]
A
CC E
PT
ED
M
A
Graphical abstract
1
Highlights
Inherently safer mechanical material (ISMM) method is developed for basic design stage.
Newly established Mechanical integrity safety index (MISI) identifies the critical process equipment
Two-fold criteria is developed to select the inherently safer mechanical material for
IP T
process units
SC R
Substitution guide word helps to select the inherently safer mechanical material
Abstract
U
Hazards associated with chemical processes can lead to accidents, which can be managed through
N
process safety strategies. Inherent safety is a proactive tactic, capable of both identifying and
A
minimizing the hazard. Available inherent safety assessment (ISA) methods focus on route selection
M
only. Individual process equipment characteristics, especially the mechanical aspects are not reported
ED
for ISA. Subsequently, this paper presents a new technique for suitable material selection of process equipment at initial design stages. In inherently safer mechanical material (ISMM), process characteristics are coupled with the mechanical attributes for mechanical material selection of process
PT
equipment. The relative ranking of process equipment is used to highlight the critical process
CC E
equipment that is more prone to leak. This risky process unit is further studied to select the suitable mechanical material. Two-fold mechanical compatibility criteria are established, which needs to be satisfied for material selection. If the proposed material is found unsuitable, inherent safety theme is
A
used to propose the suitable material. The ISMM technique is verified by a case study of MMA-TBA process plant Hysys simulation. The technique is simple and identifies the crucial equipment in early design stages, which can help the design engineers to implement inherent safety at the basic design stage. Keywords: Basic design engineering, Indexing, Inherent safety, Mechanical material, Process simulation 2
Nomenclature
Alphabetical Symbols Magnifying Factor
d
vessel diameter (m)
IS
Stress Index
IC
Corrosion Index
P
vessel pressure (kPa)
t
vessel thickness (m)
T
vessel temperature (˚C)
ΔT
temperature difference (˚C)
WS
working stress (kPa)
yi
individual component fraction
pKa, i
relative acid strength of individual component
pKa, mix
relative acid strength of mixture
ED
M
A
N
U
SC R
IP T
A
Greek Symbols
thermal expansion coefficient (1/˚C)
δhoop
hoop stress (kPa)
δP
pressure stress (kPa)
CC E
PT
α
temperature stress (kPa)
δWS
working stress of vessel (kPa)
γ
young's modulus (kPa)
A
δT
1. INTRODUCTION
3
There is always a threat of inventory loss in the chemical process industry (CPI), which may create multiple accident scenarios. Different safety measures are employed to avoid such situations. Most of these are add-on safety actions, which require regular maintenance (Hendershot, 2006). Hazards associated with chemicals processing cannot be eliminated, nevertheless, controlling or reduction of hazard is conceivable up to a specific level. For this purpose, the hazard is enveloped in
IP T
multiple layers, as demonstrated in Fig. 1. These layers are named as layers of protection (LOP), also known as process safety strategies (Hendershot, 2006, 2010, 2011). For an accident to occur, hazard has to breach all the protection layers. The first layer of protection, inherent, is proactive in nature
SC R
with the objective to either minimize the hazard or its impacts (Kletz and Amyotte, 2010). The
remaining three layers are additional safety measures to control the process hazard. All these layers of
U
protection are necessary for a comprehensive safety management system.
N
To use these layers for hazard avoidance, safety studies are usually performed. For a chemical process plant life cycle, there are certain phases, and there are various safety studies, which can be
A
individually applied at a certain phase of process lifecycle (Shariff and Zaini, 2013). These safety
M
assessment methods with specific project phases are presented in Fig. 2. Most of the industrially
ED
practiced safety assessments are performed at later phases of the life cycle, and changes at these stages need additional capital contribution. This emphasizes applying inherent safety concepts at the
A
CC E
PT
earlier design phases.
Fig. 1 Process safety layers of protection
4
Conceptual
Basic
Detailed
Engineering
Engineering
Engineering
Preliminary Hazard Analysis
Equipment Procurement and Construction
Hazard and Operability (HAZOP) Study
Dow Fire & Explosion & Chemical Exposure Index
Pre-Startup Safety Review (PSSR) What-if Review
Review of Operating Procedures to identify hazards
SC R
Quantitative Risk Studies
Post Process Hazard Analysis
Check List Review
Failure Mode and Effect Analysis (FMEA)
Economic Risk Assessment
Operations
Commissioning
IP T
Research & Development & Feasibility Study
U
Fig. 2 Safety studies for project phases
N
Inherent safety is now acquiring more attention from researchers because of its remarkable
A
capabilities in risk management, and operational and capital investments. It minimizes the risk with least add-on safety measures. However, the inherent safety concept has not gained much
M
acknowledgment in the process industries. The recommendations regarding inherent safety
ED
implications are identified by analyzing the gaps and available in the literature (Gupta and Edwards, 2002). Inherent safety is usually applied through different strategies, which have been established by
PT
Center for Chemical Process Safety and other researchers (CCPS, 2010; Khan and Amyotte, 2002, 2003; Kletz and Amyotte, 2010), and are accessible in Fig. 3. Among inherent safety strategies, only
CC E
four are widely used namely, minimization, substitution, moderation, and simplification. Out of these four strategies, more frequent used inherent safety strategy is the minimization, while moderation,
A
simplification, and substitution are the next correspondingly (Hussin et al., 2015).
5
ERROR TOLERANCE
MINIMIZE
Improve equipment to handle variations
Less amount of material Reduced Equipment Size
SUBSTITUTE
SIMPLIFY
INHERENT SAFETY
IP T
Apply to materials, Chemistry or processes
SC R
Remove design complications
MODERATE
Change design Change Conditions (A form of moderation)
Reduced or modified process conditions
U
LIMITATION OF EFFECTS
N
Fig. 3 Inherent safety strategies
A
Several tactics are available to perform inherent safety assessment. These include indexing,
M
numerical, and graphical, which have been employed by researchers for assessing inherent safety level of chemical processes (Srinivasan and Natarajan, 2012). Indexing methodology is preferred over
ED
the others because of flexibility in the early design stages, as less information about the process is available (Srinivasan and Nhan, 2008). However, there are some limitations associated with indexing,
PT
such as subjective scaling, weighting factors, and limited perspectives for consideration (Ahmad et al., 2014; Srinivasan and Nhan, 2008).
CC E
As recognized in Fig. 2, various safety studies are available to use at different phases of the
process lifecycle. An appropriate methodology for safety studies at the preliminary design stage is missing. To deal with this issue, various methods have been proposed, which emphasized the inherent
A
safety assessment. Proto-type index for inherent safety (PIIS) is the first method (Lawrence, 1996), which identifies the safest process route focusing on assessment of several process parameters like temperature, pressure, etc. Some additional parameters like type of equipment, process structure, etc. have been introduced in inherent safety index (ISI) by Heikkilä, (1999) and Heikkilä et al., (1996) to achieve the same objective. Integrated Inherent Safety Index (I2SI) has amalgamated safety and cost 6
aspects in single methodology (Khan and Amyotte, 2004, 2005). It identifies the safer and economically viable process by aiming the hazard minimization rather than risk reduction. Anyhow, some limitations, i.e., manual data extraction of process parameters and individual chemicals have been identified for the aforementioned indices. These restrictions, however, have been removed in the integrated risk estimation tool (iRET) by linking process simulation software and
IP T
spreadsheet tool to evaluate the inherent safety (Shariff et al., 2006). Based on this idea, more methods for inherent safety assessment have been introduced by manipulating numerous process
information. These techniques include inherent safety index module (ISIM) and process route index
SC R
(PRI) by Leong and Shariff, (2008, 2009), inherent risk assessment (IRA) proposed by Shariff and
Leong, (2009), process stream index (PSI), toxic release consequence analysis tool (TORCAT) and
U
toxic release inherent risk assessment (TRIRA) proposed by Shariff et al., (2012) and Shariff and
N
Zaini, (2010, 2013) and inherent fire consequence estimation tool (IFCET) presented in Shariff and Wahab, (2013) and Shariff et al., (2016). These techniques differ in results, as some identify the
A
inherently safer route, while the others propose an improvement in the selected process route.
M
All of these specified methods are based on the indexing procedure, which has certain bottlenecks
ED
as described earlier. In order to overcome the limitations of indexing methods, many other safety techniques have been developed which include, i-Safe (Palaniappan et al., 2002), a simple graphical
PT
method for safer process route (Gupta and Edwards, 2003), inherent benign-ness indicator (IBI) (Srinivasan and Nhan, 2008), numerical descriptive inherent safety technique (NuDIST) (Ahmad et
CC E
al., 2014) and graphical descriptive technique for inherent safety assessment (GRAND) (Ahmad et al., 2016). Moreover, a few methods have integrated the environmental aspects with indexing to analyze the different process routes (Gunasekera and Edwards, 2003; Warnasooriya and Gunasekera, 2017).
A
The inherent safety concept has been divided among two regimes, i.e., 1st order inherent safety
and 2nd order inherent safety (Kidam et al., 2016). The first concept is regarding the hazard avoidance, whereas the other one is applied in the context of risk reduction by targeting either the likelihood or the severity. Hazard avoidance is usually performed by the comparison of flowsheets for the same process to select which one has the least hazard, i.e., 1st order inherent safety. All the aforementioned inherent safety methods have concentrated on the determination of the inherently safer route. Some of 7
the inherent safety assessment methods, however, have concentrated on the equipment safety without contemplating mechanical aspects (Gangadharan et al., 2013), i.e., missing the 2nd order inherent safety concept. The accidents in process industries happen due to the failure of the mechanical component leading towards either the rupture or small leak, which in turn is defined as the loss of inventory or leak (CCPS, 2000). Therefore, consideration of mechanical aspects for selection of the
which is in line with the concept of minimizing the likelihood of consequences.
IP T
material of construction at early design stages may help in designing an inherently safer process,
In this paper, a new method has been presented to select the appropriate mechanical material for
SC R
process equipment at the basic design stage to ensure the safer process. The technique is divided into two parts. Initially, all equipment in the process are compared with each other to prioritize and
U
identify the critical process equipment. Next, the material is proposed for the identified critical
N
equipment to investigate the integrity of that particular equipment. An appropriate criterion for mechanical material selection has been developed. In case the suggested material is unsuitable for the
A
equipment, the inherent safety concept is used to select a suitable material until material selection
M
criteria are satisfied. Process information from ASPEN HYSYS is linked with MS Excel, and all
ED
processing is performed in MS Excel via VBA coding. This tool is simple to use and can be readily adopted by industrial persons.
PT
2. METHODOLOGY
CC E
The mechanical integrity of process equipment is an indispensable factor to characterize the safety level. Numerous materials are available to use for process equipment fabrication, and choice of the right material is the most critical decision. The reasons for mechanical failure in process
A
equipment can be classified as follows (Maleque and Salit, 2014): 1. poor selection of materials 2. fabrication defects 3. exceeding design limits 4. inadequate maintenance
8
The material of construction has been identified as one of the prominent design error, recognized from the investigation of past accidents (Kidam and Hurme, 2012a; Kidam et al., 2016). This design error is related with the basic design stage, while the others are related to later phases of process lifecycle (Kidam and Hurme, 2012a, b, 2013; Kidam et al., 2016). The detailed analysis of this design error has revealed that the chemical and mechanical suitability is required for the inherently safer material of
IP T
construction (Kidam and Hurme, 2012a, b; Kidam et al., 2015; Kidam et al., 2016). Furthermore, it is identified that these two suitability criteria are defined in terms of stress, corrosion, and wear, and applicable to all the reasons of failure and subsequently relevant for the material of construction
SC R
(Maleque and Salit, 2014). Corrosion is related to the acidity, which would define the chemical
suitability. While, stress is linked to temperature and pressure, and would highlight the mechanical
U
suitability. All this information of acidity, temperature, and pressure are available at the basic design
N
stage. While wear is related to removal of material by mechanical action and during initial design phases such information is missing. Therefore, stress and corrosion are the parameters available for
A
selection of materials during the early phase of process lifecycle. The methodology for mechanical
M
material selection, at the basic design stage, is explained in the next subsections and named as
A
CC E
PT
ED
Inherently Safer Mechanical Material (ISMM), and the relevant framework is available in Fig. 4.
9
INDEXING PART
START
Identification of Process Units
Select a Material of Construction
IP T
Process Data from ASPEN HYSYS
Mechanical Integrity Safety Index
M ED
SUBSTITUTION
CC E
PT
NON-RECOMMENDED
A
SC R
A
NO
Apply Suitable ISD Guideword
Working Stress Acceptable
YES
Corrosion Suitability
RECOMMENDED
MECHANICAL MATERIAL SUITABILITY & SELECTION PART
N
U
Identification of Critical Equipment
Components pKa Data
SATISFACTORY
Can Proceed with Design
Fig. 4 Framework for inherently safer mechanical material (ISMM) selection
Mechanical materials for process equipment
Diverse sort of materials are used in the process industry, i.e., metals, elastomers, and plastics. Each material class has particular characteristics. Some are more corrosion resistant, while others can bear high stresses. There are thousands of material compositions available, which can be used to 10
fabricate the process equipment. However, in this work, only a few materials have been chosen to present the idea. Three different mostly used materials are identified for each material class mentioned earlier. These selected materials are as follows:
Metals: Carbon Steel, Stainless Steel 316, Titanium
Elastomers: Viton, NBR (Nitrile rubber), Neoprene
IP T
Plastics: Poly chloro-tri-fluoro ethylene (Kel-F), Teflon, Polyvinylidene fluoride (KYNAR) Incorporation of stress at the basic design
SC R
As mentioned earlier, stress in process equipment is caused by temperature and pressure.
Information about these parameters is available from process simulation and can be used to define the magnitude of stresses.
U
2.2.1. Pressure stress
N
Most of the process equipment in process industry occur in the shape of the pressure vessel
A
(Dupen, 2016), and this theory can be used for the ISMM assessment at initial design stages. Further, pressure vessels occur either in the thick wall or thin wall. If the thickness of the wall is less than 10%
M
of the internal radius, then the pressure vessel is a thin wall pressure vessel. For a thick pressure
ED
vessel, the wall thickness is more than 10% of the internal radius. Most of the equipment in process industry has a thickness of less than 10% of the radius. In this context, at initial design stages, thin
PT
wall pressure vessels have been assumed for pressure stress estimation. Pressure vessels occur in spherical or cylindrical shape. For cylindrical vessels, only hoop stress is valid, while for spherical
CC E
vessels longitudinal stress is useful. As, most of the industrial vessels are cylindrical, so the hoop stress is considered in ISMM, and longitudinal stresses are eradicated. Hoop stress can be calculated by:
A
δ hoop =
Pd
(1)
2t
For this work, hoop stress is considered as pressure stress, i.e., δhoop = δP. 2.2.2.Temperature stress
The change in temperature influence the shape of the material, i.e., if the temperature is increased, the material expands and vice versa. The temperature stress is a function of the thermal expansion
11
coefficient, Young's modulus, and the change in temperature as per the following relation (Dupen, 2016):
δT = - α γ T
(2)
The thermal expansion coefficient, 𝛼, is material explicit property, which is the material expansion rate. Different materials expand at different rates. While, young's modulus 𝛾 is the measure of
IP T
material stiffness. The essential data for temperature stress calculation is given in Table 1. Initially, a material is proposed for calculation purposes, and then the temperature stresses in each process
SC R
equipment are estimated. For the negative thermal stress, the vessel is under compressive stress and if it is positive, the vessel is under tensile stress.
Table 1 - Material specific characteristics (Department, 2016; Elastomers, 2016; Ellis and Smith, 2008) Thermal expansion coefficient (1/˚C)
Young's modulus (GPa)
1.80 x 10-5
U
Material name
N
Material class
205
1.50 x 10-5
215
10-5
115
8.00 x 10-5
1.45
1.35 x 10-4
0.55
KYNAR
9.00 x
10-5
1.60
NBR
1.97 x 10-4
0.005
6.00 x 10-4
0.002
10-4
0.016
Metals
A
Stainless Steel 316
Titanium Kel-F Teflon
Elastomers
ED
Plastics
M
Carbon Steel
PT
Neo-prene (Nitrile rubber) Viton
1.28 x
2.16 x
CC E
2.2.3. Stress index calculations
The total working stress can be estimated by the following relationship:
δWS = δP + δT
(3)
A
The stress index for each process equipment based on relative ranking can be estimated by: IS =
Working Stress of Individual Equipment
(4)
Average Working Stress of All Equipment
Equipment with higher IS value is under high stress relatively and vice versa.
12
Corrosion for basic design Most of the process industry equipment are fabricated by iron and its alloys. These materials corrode in acidic and basic conditions, however, more prone to decay in an acidic environment (Negm et al., 2011). The reason for more corrosion in an acidic environment is that most acids tend to accept electrons, while bases donate electrons. Corrosion is done when the metal donates electrons, and the
IP T
solution is accepting the electrons (Landolt, 2007). For example, the electron transfer equations for iron are given below:
SC R
Fe Fe2+ +2e-
2H+ + 2e- H2
Therefore, acidic media tends to behave more corrosive than the basic environment. (Heikkilä, 1999)
U
in ISI method has considered the corrosion aspect, however, no criteria are available to quantify the
N
corrosion. Dow F&E index has also proposed penalties based on corrosion rate (AIChE, 2010),
A
whereas the corrosion rate is not linked to the chemicals being processed in the process equipment.
M
2.3.1. Acidity measurement
Acidity is usually measured by pH value; however, it is not available from the process simulation
ED
software i.e. ASPEN Hysys. An alternate method for acidity estimation is to determine the relative strength of an acid, pKa. An acid, which transfers hydrogen atoms close to 100% upon dissolution is a
PT
concentrated acid. The smaller the value of pKa, the stronger the acid and vice versa. The strengths of
CC E
different acids with their pKa values are furnished in Table 2 (College of Pharmacy, 2016). Briefly, if pKa is less than 3, the solution is strongly acidic; for 3 to 7 it is weakly acidic, range 7 to 11 indicates weak base and greater than 11, the solution is strongly basic. The pKa values of individual chemicals
A
are available in the literature, and pKa value for a mixture can be calculated through: pK a, mix =
1
yi pK a, i
(5)
2.3.2. Corrosion index estimation
The corrosion index is calculated by:
13
IC =
1
pK a, mix of individual Equipment Average pK a,mix of All Equipment
(6)
Highest pKa, mix value reveals a more basic solution, and without reciprocal, significant IC value indicates a strong base. If IC is calculated by reciprocal method, enormous IC translates into more
Table 2 - Strength of acids and bases (College of Pharmacy, 2016) pKa
Acid Strength
HI
-10
Strongest Acid
H2SO4
-9 -7
C6H5SO3H
-6.5
H3O+
-1.7
HNO3
-1.4 4.6
CH3CO2H
4.8
+
9.2
NH4
C6H5OH
9.9
CH3NH3+
10.6
H2O
15.7 16
ED
CH3CH2OH CH ≡ CH
25
NH3
38 44 50
Weakest Acid
Strong Base
CC E
PT
CH2 = CH2 CH3CH3
A
C6H5NH3
N
0.2
+
M
CF3CO2H
Weakest Base
U
HCl
Base Strength
SC R
Acid
IP T
acidic conditions, and it is easy to identify the equipment under more acidic conditions relatively.
Mechanical integrity safety index (MISI)
Initially, all process equipment in process flow sheet are identified. An initial material is proposed
A
for all the equipment, and stress and corrosion indices are then estimated through equations (4) and (6). These indices individually identify critical process equipment regarding stress and corrosion level. The equipment under combined conditions of stress and corrosion, however, can be determined by considering both factors at the same time. For this purpose, a new index is proposed, which is termed as mechanical integrity safety index (MISI). This concept of indexing has similar approach to the inherent safety index for shell and tube heat exchanger (ISISTHE) in identifying the critical 14
process equipment that has high potential of failure at the earlier design stages (Pasha et al., 2017). The MISI can be calculated through the following relation:
MISI = A × IS × IC
(7)
For small MISI magnitude, a magnifying factor A can be used to amplify the effect (Shariff et al., 2012). The higher the value of MISI, the more critical is the equipment and vice versa. This indexing
IP T
method aids the design engineer in identifying the most critical equipment during earlier design
phases, which is in line with the previously presented indexing method, such as inherent safety index
SC R
for shell and tube heat exchanger (ISISTHE) (Pasha et al., 2017). Material selection for critical process equipment
Once the critical process equipment is identified, next is the selection of suitable mechanical
U
material for the identified process equipment. The selected material should be able to withstand the
N
stresses created by process temperature and pressure, and corrosion imposed by the chemical mixture.
A
A criterion of acceptability has been developed for stress and corrosive environment. If both criteria
M
are satisfied for identified critical process equipment, then the selected material is considered suitable. Otherwise, inherent safety principle substitution is applied by replacing the material with better
ED
material. The loop is rerun and checked for stress and corrosion suitability until both conditions are satisfied.
PT
2.5.1. Stress suitability criteria
The working stress for critical process equipment is calculated using Eq. (2) mentioned earlier. If
CC E
the working stress of critical process equipment is below the ultimate tensile strength (UTS) of the selected material, the material is suitable. If the working stress is greater than the ultimate tensile strength of the chosen material, some material with high ultimate tensile strength is required. The
A
ultimate tensile strength is defined as the maximum stress that a material can withstand before it breaks or weakens (Dewolf et al., 2009). The ultimate tensile strength values of selected materials are given in Table 3. This table is prepared after reviewing the appropriate literature (Department, 2016; Elastomers, 2016; Ellis and Smith, 2008).
15
Table 3 - Ultimate tensile strength of different materials (Department, 2016; Elastomers, 2016; Ellis and Smith, 2008)
Plastics
Elastomers
Ultimate Tensile Strength (MPa)
Stainless Steel 316
2,240
Carbon Steel
1,640
Titanium
1,625
Kel-F
40
Teflon
40
KYNAR
30
NBR
27
Neoprene (Nitrile rubber)
24
IP T
Metals
Material Name
SC R
Material Class
Viton
20
U
2.5.2. Corrosion Suitability Criteria
There is no particular value to decide about corrosion compatibility. Each chemical behaves in a
N
different way towards the various type of mechanical materials. Compatibility charts for a broad range
A
of mechanical materials with different chemicals are available in the literature (Corporation, 2017;
M
Emerson, 2016). For each acidic classification, three chemicals have been studied for their effect on
categories as below:
ED
selected mechanical materials. The effects of chemicals on mechanical materials are divided into three
PT
1. Recommended / Good for use 2. Satisfactory
CC E
3. Non-recommended
Numerical values are outlined for each category of effects, and average values of the response of selected chemicals are calculated, and a simple compatibility chart of mechanical material is prepared,
A
as shown in Table 4. Various material compatibility charts have been studied to formulate this table (Corporation, 2017; Emerson, 2016). This table is preferred over the Heikkila corrosion indexing because it is based on the actual interaction of chemicals with different mechanical materials rather than the expert judgment. However, the pattern of compatibility is not smooth because of the chemicals nature.
16
I N U SC R
Table 4 - Chemicals corrosion compatibility chart for mechanical materials (Corporation, 2017; Emerson, 2016) Metals Acidic Nature
Elastomers
Plastics
Carbon Steel
Stainless Steel 316
Titanium
Strong Acid
pKa < 3
3
3
2
3
3
1
2
1
1
Weak Acid
3 < pKa < 7
3
2
2
2
2
1
1
1
1
Weak Base
7 < pKa < 11
3
2
1
2
1
2
1
1
1
Strong Base
pKa > 11
1
1
1
1
2
2
2
1
1
PT
ED
M
A
pKa Range
NBR (Nitrile rubber)
A
CC E
1 - Recommended / Good for use 2 - Satisfactory 3 - Non-recommended
17
Neoprene
Viton
KYNAR
Teflon
Kel-F
3. RESULTS AND DISCUSSION Case study for MISI Methyl methacrylate (MMA) production has been the most studied process for validation of numerous inherent safety techniques. There are six different process routes to produce MMA (Lawrence, 1996) using the following raw materials:
IP T
1. Acetone Cyanohydrin (ACH) 2. Ethylene through methyl propionate (C2/MP)
SC R
3. Ethylene through propionaldehyde (C2/PA) 4. Propylene (C3) 5. Isobutylene (i-C4)
U
6. Tertiary butyl alcohol (TBA)
N
Numerous inherent safety assessment techniques for route selection have been compared by (Leong
A
and Shariff, 2009; Rahman et al., 2005), and TBA process route has been identified as the safer one
M
among all routes. This route has been selected to demonstrate the ISMM technique. The process simulation for the production of methyl methacrylate (MMA) from tertiary butyl alcohol (TBA) is
ED
given in Fig. 5 (Jha et al., 2016). In this process, TBA is oxidized to methacrolein which is further oxidized to methacrylic acid. The reaction of methacrylic acid with methanol leads to MMA.
PT
There are ten process units in this process as shown in Fig. 5. Initially, carbon steel has been selected as the mechanical material for all process units. Necessary process information has been
CC E
imported from ASPEN HYSYS to MS Excel through VBA programming. Information about the acidity of individual chemicals has been collected from the literature. Temperature, pressure and relative acidity have been processed in MS Excel via VBA coding to estimate the stress and corrosion
A
indices. Stress and corrosion indices have been calculated using equations (4) and (6), and the resulting values are provided in Table 5. These sub-indices values have been multiplied to calculate the MISI values as mentioned in equation (7). As MISI values of each equipment are appropriate in magnitude, the magnifying factor used in this calculation is 1. MISI for individual process units in descending order are available in Table 5. The individual indices have identified different process
18
equipment as critical about a particular mechanical aspect, i.e., highest stresses in E-100 and the most acidic environment in E-101. The reason for dissimilar critical process units for each individual parameter is different process conditions and compositions in each unit. However, for the combined effect of both aspects, E-101 has emerged as the most critical process unit. During the early design stages, we will focus on the most critical equipment only for material selection. Even though the E-
IP T
101 is selected based on the MISI value, however, the value is very close to the E-100. A better confirmation could be done by comparing the relevant cost of the equipment. However, the process
SC R
economics is not included in this paper, therefore it should be considered in future work.
Table 5 - Initial MISI values through relative ranking
E-101
2.0278
1.7169
E-100
4.1474
0.7533
CRV-102
0.9371
1.3845
T-101
0.3773
1.4733
T-100
0.7580
T-102
0.2919
E-102
0.2919
CRV-101
0.2343
CRV-103 V-101
MISI
Equipment Ranking based on MISI
3.4817
1
3.1242
2
1.2975
3
0.5559
4
0.5565
0.4218
5
1.0442
0.3048
6
0.9897
0.2889
7
0.7350
0.1722
8
0.0893
1.0009
0.0894
9
0.0353
1.0179
0.0359
10
A
N
U
IC
M
IS
A
CC E
PT
ED
Equipment Tag No.
19
I N U SC R A M ED PT CC E
A
Fig. 5 - Hysys process simulation of MMA-TBA process (Jha et al., 2016)
20
Proposed mechanical material suitability Next is the assessment of proposed material suitability for the critical process equipment as identified through MISI, i.e., E-101. Individual criteria for stress and corrosion needs to be assessed and fulfilled. For this study, the dimensions of vessels have been assumed as 36 inches in diameter and 1 inch in thickness. Ambient temperature is 25 ˚C, and as mentioned earlier, carbon steel is taken
IP T
as the initial mechanical material for this process equipment. The working stress has been estimated for E-101 using equations (1), (2) and (3). Total working stress is a combination of pneumatic and
SC R
thermal stresses. Total working stress has been estimated as 1,959 MPa. The ultimate tensile strength of carbon steel is found from Table 3 as 1,640 MPa. The selected material is not suitable concerning stress aspect, which suggests that a superior material is required for these process conditions. Before
U
substituting the carbon steel with a better material, a check for corrosion suitability has also been
N
performed. The pKa value for the chemical mixture has been calculated to be 6.17, i.e., a weak acid.
A
For a weak acid, carbon steel is not recommended. Therefore, carbon steel is not suitable to be used with this composition of the processing chemicals. Both stress and corrosion criteria are not satisfied
M
for the identified critical process equipment E-101 with the initially selected material i.e., carbon
ED
steel.
Mechanical material selection through IS Guide Word
PT
As carbon steel has been identified as non-suitable for E-101 and a better material is required. Applying the inherent safety guide word ‘substitute,' carbon steel has been replaced by stainless steel
CC E
316, and all parameters are recalculated. The vessel dimensions and atmospheric conditions have been the same. First of all, the stress and corrosion indices have been estimated with the substituted mechanical material. The MISI values for respective process equipment have been determined with
A
individual equipment sub-indices. The revised results of MISI and both sub-indices are given in Table 6. E-101 has emerged again as the most critical equipment in the revised analysis.
21
Table 6 - Revised MISI values through relative ranking Equipment Ranking based on MISI
IC
MISI
E-101
2.0353
1.7169
3.4945
1
E-100
4.1663
0.7533
3.1385
2
CRV-102
0.9000
1.3845
1.2461
3
T-101
0.3783
1.4733
0.5574
4
T-100
0.7608
0.5565
0.4234
5
T-102
0.2929
1.0442
0.3059
6
E-102
0.2929
0.9898
0.2899
CRV-101
0.2344
0.7351
0.1723
CRV-103
0.0888
1.0010
0.0888
V-101
0.0331
1.0180
0.0337
IP T
IS
7 8 9
10
SC R
Equipment Tag No.
The revised stresses for E-101 have been estimated as 2,239 MPa. Although the process
U
conditions have not changed, the stresses have increased. This phenomenon is because of the specific
N
properties of the stainless steel, i.e., thermal expansion coefficient and Young’s modulus. The
A
ultimate tensile strength from Table 3 for stainless steel 316 is 2,240 MPa. This material has passed
M
the stress criteria. Next is the corrosion criteria. pKa value has not changed with the substitution of mechanical material as it is dependent purely on the chemical mixture inside the process equipment.
ED
For a weak acid, stainless steel can be used satisfactorily. Consequently, the stainless steel 316 can be used for identified critical process equipment, E-101, as both stress and corrosion criteria have been
PT
satisfied. Results for initial and revised material suitability are given in Table 7. A further better material can be selected for this process equipment at later design stages with
CC E
more detailed information about the process. However, this method would serve as an initial indicator for process engineers to identify the critical process unit and narrow down the material of construction
A
choice for specified process equipment.
22
Table 7 - Initial and revised material suitability for E-101 Stress Material of Scenario Construction
𝛅𝐏
Corrosion 𝛅𝐓
𝛅𝐖𝐒
Initial
Carbon Steel
18,000 1,941,162 1,959,162
Revised
Stainless Steel 18,000 2,221,050 2,239,050
UTS
𝒑𝑲𝒂,𝒎𝒊𝒙
Remarks
NonRecommended 2,240,000 Recommended 1,640,000
Compatibility Remarks Value
6.17
3
6.17
2
IP T
4. CONCLUSION
NonRecommended Satisfactory
Many techniques have been proposed by many researchers for the conduct of inherent safety
SC R
assessment. Most of these techniques have focused on the selection of inherently safer process path. Individual equipment has never been taken into consideration to make them inherently safer.
Failure of most process equipment in many of the process accidents is caused by the mechanical
U
component failure. This paper has presented a new technique for inherently safer mechanical material
N
selection (ISMM) at the basic design stage. Mechanical and chemical suitability aspects, namely
A
stress and corrosion correspondingly, have been linked with the process parameters to assist in the
M
inherently safer mechanical material selection. ISMM technique has two parts i.e., identification of mechanically critical process unit through MISI and selection of suitable material for critical
ED
equipment. MISI has been developed to identify the mechanically critical equipment. Twofold criteria have been proposed to select the material of fabrication for process unit. Both criteria have to be
PT
satisfied before selecting the final material. For any unsatisfied criteria, inherent safety guide word
CC E
substitution has been considered to select the suitable material. The whole framework for mechanical material selection at the basic design stage has been demonstrated by a case study. The identified critical process unit has been made inherently safer by proposing a better material using substitution
A
idea. For the ease of process design engineers, only the most vital process unit has been suggested to be reviewed for material selection during the initial design phase. However, the choice of materials can also be applied to other process units by linking directly to the stream properties to select the appropriate material. For future studies, more materials can be included in the list for industrial use and more processes can be explored to enhance the idea. Furthermore, other factors such as the change in process variables and cost can also be combined with mechanical and chemical suitability 23
aspects for selection of the material of construction that can be developed using an optimization model.
Acknowledgement
The authors would like to gratitude Universiti Teknologi PETRONAS, Malaysia for providing
IP T
internal research funds to make this research possible.
SC R
References
Ahmad, S.I., Hashim, H., Hassim, M.H., 2014. Numerical descriptive inherent safety technique (NuDIST) for inherent safety assessment in petrochemical industry. Process Safety and Environmental
U
Protection 92, 379-389. doi: http://dx.doi.org/10.1016/j.psep.2014.03.009
N
Ahmad, S.I., Hashim, H., Hassim, M.H., 2016. A graphical method for assessing inherent safety
A
during research and development phase of process design. Journal of Loss Prevention in the Process
M
Industries 42, 59-69. doi: http://dx.doi.org/10.1016/j.jlp.2015.09.018 AIChE, American Institute of Chemical Engineers, 2010. Dow's Fire and Explosion Index Hazard
ED
Classification Guide, 7 ed. Wiley.
CCPS, Center for Chemical Process Safety, 2000. Guidelines for chemical process
PT
quantitative risk analysis. American Institute of Chemical Engineers AIChE. CCPS, Center for Chemical Process Safety, 2010. Inherently Safer Chemical Processes: A Life Cycle
CC E
Approach, 2 ed. John Wiley & Sons. College of Pharmacy, Health Professions Division, 2016. Acid-Base Properties of Drugs, Accessed, http://pharmacy.nova.edu/Pharmacodynamics/Modules/AcidsSaltsBases/Main_P3.html
A
Corporation, Quick Cut Gasket & Rubber, 2017. Chemical Resistance Chart, Accessed on 30/03/2017, http://www.quickcutgasket.com/pdf/Chemical-Resistance-Chart.pdf Department, Engineering, 2016. Materials Data Book, Accessed on 25/10/2016, http://wwwmdp.eng.cam.ac.uk/web/library/enginfo/cueddatabooks/materials.pdf Dewolf, J.T., Beer, F.P., Johnston, E.R., 2009. Mechanics Of Materials (In Si Units), 5 ed. McGraw24
Hill Education (India) Pvt Limited. Dupen, B., 2016. Applied Strength of Materials for Engineering Technology. Elastomers, DuPont Dow, 2016. Viton® fluoroelastomer: A Product of DuPont Dow Elastomers, Accessed on 23/11/2016, http://www.rainbowrubber.com/VB.pdf Ellis, B., Smith, R., 2008. Polymers: A Property Database, 2 ed. CRC Press.
IP T
Emerson, 2016. Chemical Compatability of Elastomers and Metals, Accessed on 18/10/2016, http://www.documentation.emersonprocess.com/groups/public/documents/reference/d351798x012_06 .pdf
SC R
Gangadharan, P., Singh, R., Cheng, F., Lou, H.H., 2013. Novel methodology for inherent safety
assessment in the process design stage. Industrial & Engineering Chemistry Research 52, 5921-5933.
U
doi: http://dx.doi.org/10.1021/ie303163y
Gunasekera, M.Y., Edwards, D.W., 2003. Estimating the Environmental Impact of Catastrophic
A
http://dx.doi.org/10.1205/095758203770866638
N
Chemical Releases to the Atmosphere. Process Safety and Environmental Protection 81, 463-474. doi:
M
Gupta, J.P., Edwards, D.W., 2002. Inherently Safer Design—Present and Future. Process Safety and
ED
Environmental Protection 80, 115-125. doi: http://dx.doi.org/10.1205/095758202317576210 Gupta, J.P., Edwards, D.W., 2003. A simple graphical method for measuring inherent safety. Journal
PT
of Hazardous Materials 104, 15-30. doi: http://doi.org/10.1016/S0304-3894(03)00231-0 Heikkilä, A.-M., 1999. Inherent safety in process plant design: an index-based approach. (PhD), VTT
CC E
Technical Research Centre of Finland. Heikkilä, A.-M., Hurme, M., Järveläinen, M., 1996. Safety considerations in process synthesis. Computers & chemical engineering 20, S115-S120. doi: https://doi.org/10.1016/0098-1354(96)00030-
A
0
Hendershot, D.C., 2006. An overview of inherently safer design. Process safety progress 25, 98-107. doi: http://dx.doi.org/10.1002/prs.10121 Hendershot, D.C., 2010. A summary of inherently safer technology. Process Safety Progress 29, 389392. doi: http://dx.doi.org/10.1002/prs.10395 Hendershot, D.C., 2011. Inherently safer design: an overview of key elements, Professional Safety, p. 25
48. Hussin, N.A.E., Kidam, K., Suhaili, S., 2015. Lessons learned from process equipment failures in the chemical process industry. Jurnal Teknologi 10, 43-52. doi: http://dx.doi.org/10.11113/jt.v75.5184 Jha, V., Pasha, M., Zaini, D., 2016. Enhanced inherent safety intervention framework. Procedia Engineering 148, 1051-1057. doi: https://doi.org/10.1016/j.proeng.2016.06.589
IP T
Khan, F.I., Amyotte, P.R., 2002. Inherent safety in offshore oil and gas activities: a review of the present status and future directions. Journal of Loss Prevention in the Process Industries 15, 279-289. doi: http://dx.doi.org/10.1016/S0950-4230(02)00009-8
SC R
Khan, F.I., Amyotte, P.R., 2003. How to make inherent safety practice a reality. The Canadian Journal of Chemical Engineering 81, 2-16. doi: http://dx.doi.org/10.1002/cjce.5450810101
U
Khan, F.I., Amyotte, P.R., 2004. Integrated inherent safety index (I2SI): a tool for inherent safety evaluation. Process safety progress 23, 136-148. doi: http://dx.doi.org/10.1002/prs.10015
N
Khan, F.I., Amyotte, P.R., 2005. I2SI: a comprehensive quantitative tool for inherent safety and cost
M
http://dx.doi.org/10.1016/j.jlp.2005.06.022
A
evaluation. Journal of Loss Prevention in the Process Industries 18, 310-326. doi:
ED
Kidam, K., Hurme, M., 2012a. Design as a contributor to chemical process accidents. Journal of Loss Prevention in the Process Industries 25, 655-666. doi: http://dx.doi.org/10.1016/j.jlp.2012.02.002
PT
Kidam, K., Hurme, M., 2012b. Origin of equipment design and operation errors. Journal of Loss Prevention in the Process Industries 25, 937-949. doi: http://dx.doi.org/10.1016/j.jlp.2012.05.005
CC E
Kidam, K., Hurme, M., 2013. Method for identifying contributors to chemical process accidents. Process Safety and Environmental Protection 91, 367-377. doi: http://dx.doi.org/10.1016/j.psep.2012.02.001
A
Kidam, K., Sahak, H.A., Hassim, M.H., Hashim, H., Hurme, M., 2015. Method for identifying errors in chemical process development and design base on accidents knowledge. Process Safety and Environmental Protection 97, 49-60. doi: http://dx.doi.org/10.1016/j.psep.2015.06.004 Kidam, K., Sahak, H.A., Hassim, M.H., Shahlan, S.S., Hurme, M., 2016. Inherently safer design review and their timing during chemical process development and design. Journal of Loss Prevention in the Process Industries 42, 47-58. doi: http://dx.doi.org/10.1016/j.jlp.2015.09.016 26
Kletz, T.A., Amyotte, P., 2010. Process plants: A handbook for inherently safer design. CRC Press. Landolt, D., 2007. Corrosion and Surface Chemistry of Metals. EFPL Press. Lawrence, D., 1996. Quantifying inherent safety of chemical process routes. (PhD), Loughborough University. Leong, C.T., Shariff, A.M., 2008. Inherent safety index module (ISIM) to assess inherent safety level
IP T
during preliminary design stage. Process Safety and Environmental Protection 86, 113-119. doi: http://dx.doi.org/10.1016/j.psep.2007.10.016
Leong, C.T., Shariff, A.M., 2009. Process route index (PRI) to assess level of explosiveness for
SC R
inherent safety quantification. Journal of Loss Prevention in the Process Industries 22, 216-221. doi: http://dx.doi.org/10.1016/j.jlp.2008.12.008
U
Maleque, A., Salit, M.S., 2014. Materials Selection and Design. Springer My Copy UK.
Negm, N., Ghuiba, F., Tawfik, S., 2011. Novel isoxazolium cationic Schiff base compounds as
A
http://dx.doi.org/10.1016/j.corsci.2011.06.029
N
corrosion inhibitors for carbon steel in hydrochloric acid. Corrosion Science 53, 3566-3575. doi:
M
Palaniappan, C., Srinivasan, R., Tan, R.B., 2002. Expert system for the design of inherently safer
ED
processes. 2. Flowsheet development stage. Industrial & engineering chemistry research 41, 67116722. doi: http://dx.doi.org/10.1021/ie0201765
PT
Pasha, M., Zaini, D., Mohd Shariff, A., 2017. Inherently safer design for heat exchanger network. Journal of Loss Prevention in the Process Industries 48, 55-70. doi:
CC E
http://doi.org/10.1016/j.jlp.2017.04.002 Rahman, M., Heikkilä, A.-M., Hurme, M., 2005. Comparison of inherent safety indices in process concept evaluation. Journal of Loss Prevention in the Process Industries 18, 327-334. doi:
A
http://doi.org/10.1016/j.jlp.2005.06.015 Shariff, A.M., Leong, C.T., 2009. Inherent risk assessment—a new concept to evaluate risk in preliminary design stage. Process Safety and Environmental Protection 87, 371-376. doi: http://dx.doi.org/10.1016/j.jlp.2009.07.005 Shariff, A.M., Leong, C.T., Zaini, D., 2012. Using process stream index (PSI) to assess inherent safety level during preliminary design stage. Safety science 50, 1098-1103. doi: 27
http://dx.doi.org/10.1016/j.ssci.2011.11.015 Shariff, A.M., Rusli, R., Leong, C.T., Radhakrishnan, V., Buang, A., 2006. Inherent safety tool for explosion consequences study. Journal of Loss Prevention in the Process Industries 19, 409-418. doi: http://dx.doi.org/10.1016/j.jlp.2005.10.008 Shariff, A.M., Wahab, N.A., 2013. Inherent fire consequence estimation tool (IFCET) for preliminary
IP T
design of process plant. Fire Safety Journal 59, 47-54. doi: http://dx.doi.org/10.1016/j.firesaf.2013.03.015
Shariff, A.M., Wahab, N.A., Rusli, R., 2016. Assessing the hazards from a BLEVE and minimizing its
SC R
impacts using the inherent safety concept. Journal of Loss Prevention in the Process Industries 41, 303-314. doi: http://dx.doi.org/10.1016/j.jlp.2016.01.001
U
Shariff, A.M., Zaini, D., 2010. Toxic release consequence analysis tool (TORCAT) for inherently safer design plant. Journal of hazardous materials 182, 394-402. doi:
N
http://dx.doi.org/10.1016/j.jhazmat.2010.06.046
A
Shariff, A.M., Zaini, D., 2013. Inherent risk assessment methodology in preliminary design stage: a
M
case study for toxic release. Journal of Loss Prevention in the Process Industries 26, 605-613. doi:
ED
http://dx.doi.org/10.1016/j.jlp.2012.12.003
Srinivasan, R., Natarajan, S., 2012. Developments in inherent safety: A review of the progress during
PT
2001–2011 and opportunities ahead. Process Safety and Environmental Protection 90, 389-403. doi: http://doi.org/10.1016/j.psep.2012.06.001
CC E
Srinivasan, R., Nhan, N.T., 2008. A statistical approach for evaluating inherent benign-ness of chemical process routes in early design stages. Process Safety and Environmental Protection 86, 163174. doi: http://dx.doi.org/10.1016/j.psep.2007.10.011
A
Warnasooriya, S., Gunasekera, M.Y., 2017. Assessing inherent environmental, health and safety hazards in chemical process route selection. Process Safety and Environmental Protection 105, 224236. doi: http://doi.org/10.1016/j.psep.2016.11.010
28