- Email: [email protected]
Investigation of marine environmental related deterioration of coal tar epoxy paint on tubular steel pilings
DESALINATION Desalination 166 (2004) 295-304
ELSEVIER
www.elsevier.com/locate/desal
Investigation of marine environmental related deterioration of coal tar epoxy paint on tubular steel pilings A. Husain*, O. A1-Shamali, A. Abduljaleel Kuwait Institute for Scientific Research, Department of Buildings and Energy Technologies P.O. Box 24885, Safat 13109, Kuwait Tel. +965 483 6100 Ext. 4522; Fax+965 484 5763; [email protected] Received 22 February 2004; accepted 3 March 2004
Abstract
In the Arabian Gulf region, port and waterway authorities are becoming increasingly concemed about accelerated tidal and splash zone concentrated corrosion on marine tubular steel piles. The coating protection and maintenance of tubular steel pilings located in a marine environment can be difficult. The arid environment of Kuwait of the salt water and salt laden moisture and high temperature fluctuation with the marine growth on the marine structure creates a challenging maintenance problem. This premature failure investigation dealt with the delamination and peeling of coal tar epoxy coating system. The new pier project is around 2.5 km long with topside facilities supported by 2000 tubular steel pilings in two types 914 mm and 1016 mm in diameters. Prior to installation, the piles at vendor's premises in another country received a protective coal tar epoxy coating with a minimum dry film thickness of 450 microns. However, almost all of the coated steel pilings severely deteriorated after 4-8 weeks causing an estimated cost of maintenance work of $4 million. The failure case investigation was carried out to ascertain the cause of the aforementioned coating defect and to propose a possible solution to the coating failure. An accepted method of repair has been proposed, and therefore to create a barrier system in the form of jacket material with anti corrosion wraps, protecting the underwater or splash zone pilings and other structural elements from further deterioration. The failure analysis results along with laboratory evaluation of the effectiveness of four different types of jacket materials will be addressed. Keywords: Steel tubular piles; Oil and water piers; Tidal and splash zone corrosion; Coating delamination; Coal tar epoxy; Anti-corrosion wrap; Jacket material
*Corresponding author. Presented at the EuroMed 2004 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and Office National de l'Eau Potable, Marrakech, Morocco, 30 May-2 June, 2004. 0011-9164/04/$- See front matter © 2004 Elsevier B.V. All rights reserved doi; 10.1016/j.desal.2004.06.084
296
A. Husain et aL / Desalination 166 (2004) 295-304
1. Introduction
Kuwait Gulf seawater receives little fresh water with its huge shallow areas of black mud and high evaporation rate and its climate is considered one of the hottest in the world. The salinity from a cold December to a hot August varies between 44,000 ppm and 48,000 ppm. The Kuwaiti seawater analysis indicates 5% NaCI, which is higher than the normally designated seawater composition found elsewhere. Barnacle multiplies and grows rapidly in this warm water, which has a seasonal range between 8°C and 35°C. Whereas, the concentration of suspended solids may rise from a normal 5 ppm to over 50 ppm within a few hours. The relevance of this study pertains to coating material performance in the Middle East, and particularly in Kuwait, Saudi Arabia and other countries in the region, where atmospheric conditions offshore and the adjacent to shore are considered the most severe marine environment in the world. A structure in constant contact with water whether it is a ship, a pier, or an offshore oil platform is subject to corrosion [ 1]. The battle against this scourge of the underwater industry continues with the development of new coating and outer jacket technology. Prior to the 1950's, corrosion problems in this difficult marine exposure conditions were mitigated somewhat by conventional paints and coatings that were available at that time which included chlorinated rubber, bitumen's and coaltar mastics as well as ordinary metal primers and paint. In the early 60, other materials were available including zinc rich coatings, coal-tar epoxies, and there were developments in the so-called high performance coatings. Oil companies were required to stock as many as 200 items and suppliers in order to show progress in corrosion control regardless of their effectiveness. This requires a fresh look at and increased attention to coating material selection and coating performance evaluation for condition of immersion water and desalination plants service as well as splash, and tidal zone in marine environment of Kuwait.
In the Gulf region, coal tar epoxies are still among the most popular coatings. They are essentially a mix of coal tar and epoxy resins. Coal tar epoxies were at their peak of popularity in Europe in the 1960's through about 1990. After that, non-coal tar epoxies replaced coal tar epoxies due largely to health concerns over long term exposure and direct contact (by coating applicators) to the 'tar'. Where their use is permitted coal tar epoxies are suitable for protection from moisture, both in water immersion condition (such as barge hulls and pilings) and when buried underground pipelines and tanks. Moreover, a literature search made on the subject of coal tar epoxy coatings performance in Kuwait has indicated the occurrence of one major types of coal tar epoxy failure in Kuwait marine environment during the 80's [2]. The coating was coal tar epoxy mastic 356KT, which was applied to sheet piles used in the construction of piers at one of the power station south of Kuwait. The coating failure occurred after almost six months of marine exposure. The study was concluded that coating failure was attributed to the poor specification of the quality and composition of the coal tar epoxy coating materials, caused by an interlayer paint failure delamination. In August 2001 another major financial losses were reported in Kuwait marine industry due to coating failures of coal tar epoxy on tubular steel pilings. The second failure ease concerning coal tar epoxy reported after 4 weeks of installation in marine seawater. However, it has been observed that almost 450 coated steel pilings were severely deteriorated after approximately 4 weeks of in service installation in real marine seawater exposure condition (i.e. adjacent to the sea shore marine environment). The paint systems began to experience severe coating peeling damage in the inter-tidal zone and combined with intense accumulation of marine growth in the form of Barnacles (i.e. Balanus). It has been estimated that almost 2000 coated steel tubular pilings were severely damaged or under going the process of
A. Husain et al. / Desalination 166 (2004) 295-304
coating deterioration. Prior to installation, the contractor and owner did not found any nonconformity's either in the tubular steel pile or in the finished coating product. Moreover, after 8 weeks in service the paint system begins to fail. The most common feature of both failures found to be limited in the intertidal and splash zone. In addition to that, the coating offers no protection against marine fouling, as shown in Fig. 1. An accepted method of repair for the steel pile is to create a barrier system (jacket system), protecting the underwater or tidal and splash zone pilings and other structural elements from further deterioration, both above and below the water line. There are many jacket materials products available combined with petrolatum tape or wax, some that provide structural integrity, and others that are less costly and simply seal out air and moisture to stop corrosion.[7-9] The general aim of this investigation is to provide laboratory information and approach on the causes of failure of coal tar epoxy coating and for designing and selecting an outer jacket material approved as a replacement for protecting the existed steel piles under the prevailing condition
297
of Kuwait environment. The field study was limited to an examination to the peeled offlayers of coating and an onsite inspection. Whilst the laboratory aging testing program was initiated and consisted of exposing four types of commercial quality outer jacket materials to different types of severe aging environments in order to recommend the optimum jacket material suitable for failure remediation. The main reason for the evaluation is to select the best jacket material suitable for the inter-tidal zone for the surface protection of the steel pilings in Kuwait marine environment. In the laboratory, the deterioration behaviors of this paint system in addition to the proposed jacket materials were evaluated by utilizing the following methods: (a) Electrochemical surface potential corrosion mapping (SCM) (b) Electrochemical impedance spectroscopy (EIS) (c) ASTM aging tests for durability The combined electrochemical testing techniques of EIS together with SCM were used to generate comparative data on paint performance,
Fig. 1. Corrosionsituationof coal tar epoxy coatedpiles in marineenvironment.
298
A. Husain et al. / Desalination 166 (2004) 295-304
which has been used successfully by the author for detection of various corroded metallic systems in order to facilitate decisions, development, screening, and grading of contemporary and new paint [3,4]. 2. Experimental method
Laboratory failure analysis tests on the failed section of the piles are being conducted in parallel with similar marine painted steel substrates samples of coal tar epoxy paint exposed for 3 months, under submerged and atmospheric conditions (intertidal zone) in the Gulf seawater (5% NaC1), in the State of Kuwait. The mild steel substrates (10 cm x 15 cm) were grit blasted, initially half masked and an area of (5 cm x 15 cm) was 'contaminated' with 3% NaC1, and the whole area subsequently sprayed with the multilayer coat. EIS was conducted on both salt contaminated and non contaminated areas using a measurement cell that consisted of, a working electrode (measurement area = 20 cm2), saturated calomel electrode (SCE) and a Pt or graphite counter electrode. The results were also compared with control specimens of modified epoxy MP2 and abrasion resistance epoxy MP3 materials of known durability in terms of EIS parameters of capacitance and impedance values. In SCM tests, a measurement area (1 cm x 1 cm) was scanned with the modified SCM probe with respect to a remote (SCE). Immersion solution for both tests was 5% seawater salt. EIS is widely used to characterize the behavior of coated metal immersed in aggressive solutions. The determination of EIS over a large frequency range (100 KHz to 0.01 Hz) provides cumulative information on processes involved in the protective coating. On the other hand, the SCM technique developed in this laboratory has been improved to scan over blistered surfaces without causing damage to the probe or the blister. In SCM tests, sequential measurement of areas of(1 cm x 1 cm) over the whole specimens surface were
scanned with the modified SCM probe with respect to a remote (SCE). Immersion solution for both tests was 5% seawater salt. Background details of the experimental setup for EIS and SCM are presented elsewhere in references [3--6]. The ASTM aging test used in this study for material screening criterion was based on exploring the ability of the outer jacket material to survive the aggressive aging attack in a quantitative manner by observing the minimal changes in its' mechanical properties in terms of tensile strength and maximum elongation percentage (%). Therefore, the recommended aging tests were consisted of the following ASTM test 1. Resistance to UV degradation, 2. Resistance to heat 3. Resistance to seawater immersion 4. Cyclic wetting and drying test in 5% seawater 5. Chemical resistance test. Selections of ASTM test condition are summarized below (Tables 1,2) along with details of test conditions and testing duration. 3. Results and discussion
On site inspection of the oil pier revealed that the extent of the coating defect was severe in areas located within the low and high tidal zone of the seawater. The paint film has experienced severe coating deterioration that was mainly associated with severe corrosion products and marine growth in the form of Barnacles. Visual observations have clearly indicated that all of the deteriorated paint films have developed a common type of failure with certain types of surface morphological features in terms of peelings, delaminations, and or flaking pattern (Fig. 1). The propagation direction of the deteriorated narrow region of the paint film has been found to show inclination or deflection at angel approximately 45 ° from the horizontal axes opposite the direction of the gravitational force. At this moment, the exact causes of the onset of paint defect can not be justified without proper
299
A. Husain et aL / Desalination 166 (2004) 295-304 Table 1 Specification of the ASTM standard tests for evaluation of the jacket system
Test No. ASTMstandard ASTM standard D638 ASTM standard D638 ASTM standard G53-96 4
ASTM D-3045
5
ASTM standard D453
Test description
Test duration Effect of continuous immersion in seawater at 40°C Two weeks 3 tests Two weeks 2 tensile tests Effect of cyclic wet/dry in seawater at 40°C QUV/UV-exposure Effect of intensive UV light via accelerated 5 tensile tests up to 500 h weathering test at 60°C Effect of resistance to temperature variations One week 3 tensile tests at T = 60°C, 80°C and 100°C Resistance to chemical attack, i.e., nitric acid, sulfuric acid detergent and NaOH
One week 4 tensile tests after immersion
Table 2 Outer jacket materials specification for aging test Sample code J1 J2 J3 J4
Jacket material specification Polypropylene High density polyethylene,HDPE Polyurethanematerialwith fabric Polypropylene
laboratory examination and chemical analysis on the failed section as well as on the as received steel piles. Presumably, the failure can be attributed to both the quality and composition of the coal tar epoxy material of the paint film or to the improper cleaning preparation of the steel substrate. After comprehensive examination and laboratory analysis of the failure morphology it was apparent that the areas of severe paint peelings are associated with the geometrical feature of the spiral weld beads of the steel tubing materials as shown in Fig. 1. Presumably, failure of the coated spiral weld beads may have been initiated at the junction between the weld bead and base metal (i.e. could be generated at the fusion line of the weld). The observations have clearly indicated that the exact causes of the damaged could be related to the insufficient surface preparation condition (i.e. post welding cleaning operation) or may be attributed to the quality of the underlying chemical composition of the spiral weld bead. It is very
Average thickness, mm 3.2 1.8 Multilayer (1.6 and 4.7) 2.2
common that almost 70% of paint failure in welded structure is always associated with low quality cleaning pretreatment of the weld bead adjacent to the parent metal or micro-cracking failure of the weldment. The spiral welded area is very widely accepted as the most common weakest point in any welded structure. The degradation of the paint film was also enhanced by the natural process of wet and dry cyclic effect of seawater low and high tide presented in marine environment. Technical personnel pointed out that during the month of August 2001 the local climatic temperature of Kuwait exceeded the acceptable record for that month. It has also been indicated that the aforementioned steel pilings have experienced a severe surface temperature of 76°C at the time when the seawater temperature was 34°C. It is also believed that the black colored nature of the coal tar epoxy coating enhanced the absorption of UV light and contributed to the deterioration process. The presence of coated spiral weld bead in the tubular steel
300
A. Husain et al. / Desalination 166 (2004) 295-304
piling is believed to have exerted a certain degree of residual stresses on the coating at weld junction with respect to the coated parent metal of the surrounding. Prior to installation it has been found that the adhesion strength of the coating system to the steel substrate was found to be within the acceptable limit of the specification as indicated by company engineers. Therefore, coating degradation in Fig. 2b was due mainly to seawater effect of wet dry cycle and strong susceptibility of the epoxy material to degradation by UV light. It has been also observed that the density of the marine Barnacles followed a narrow band when attached to the direction of the spiral weld bead beneath the coated layer. In contrast to the spiral weld zone no appreciable amount of Barnacles were found in the surrounding areas away from the weld. These finding will clearly indicate that the surfaces of the coated layer beneath the marine fouling were having certain degree of surface roughness or coating microcracks that were favorable sites for the nucleation of Barnacles when compared to the surrounding areas with coating of smooth surface nature. Issues here can include solvents in the product, andpoor resistance to UV (becoming more brittle and chalky), are the ones that come to mind. There
Laboratory EIS and SCM investigation (Fig. 3) on the exposed specimens coating material has indicated the tolerance level of this type &coating to dust and grit is low after removal from seawater as shown in Figs. 3a and 3b. It is therefore essential to ensure complete removal of any dust or grit particles when the surface of the steel pilings are prepared by shot or grit blasting. Moreover, strong evidence has indicated by SEM/EDX analysis that the failure initiation could be attributed to the poor specification of the quality and cleans less of the steel substrate and composition of the multi-layer coal tar epoxy coating system. The SCM map for the contaminated coal tar epoxy Fig. 3d determines the distribution of potential (E) corresponding to current flowing between local anodes and local cathodes for MP1 paints displayed here [6]. The SCM map shows red spot of defect embedded in the paint film due to dust particles. Table 3 illustrates paint specification and comparative results of EIS obtained on coal tar epoxy
(a)
(b)
are also reports that weathered coal tar is difficult to recoat. 4. EIS/SCM and SEM/EDX analysis
Fig. 2. (a) Coal tar epoxy paint after 3 month of Kuwait seawater immersionin the tidal zone, (b) SEM image showing MP 1 paint crack initiation.
A. Husain et al. / Desalination 166 (2004) 295-304 ~.~"~;
~'
. .~v.,. • ~
~s=z~5 (a)
301 v.,~,n,- . ~ , m ~ ¢
3,~72
~e~J
6,0 >i
(b)
"" ~ . ¢ a C t
i i
i/
e
,g/ d
/ b2
/
}
g
?
5
r U
(c) Fig. 3. (a) SEM image sand particle embedded in the paint film (b) EDX analysis of the same particles (c) EIS spectrum for MP1, MP2, and MP3, (d) SCM.
Table 3 Specification of the coating and EIS tests results Paint system
Paint code
Color
Coal tar epoxy Modified epoxy Abrasion epoxy
MP1 MP2 MP3
Black White Red brown
Thickness dft., ~tm 450 500 1000
E . . . . mV
Rpo, Ohm ~ n
-390 -184 -289
4.86× 109 1.05x10 ~ 8.82× 108
2
C1~~Fcm -2 3.29× I0 -l° 15x10 9 1.74× 10 l0
302
A. Husain et aL / Desalination 166 (2004) 295-304
MP 1 and two other marine paints used as reference or control samples, (MP2, MP3). The paint systems were exposed in the tidal zone of Kuwaiti seawater for 3 months, and were evaluated by EIS and SCM in our laboratory. The resulting impedance are interpreted in order to determine the individual parameters of paint film capacitance ( C ) , pore resistance (R o), and warburg diffusion or c~hargetransfer resis~nce ( Z ) of an equivalent electrical circuit that best approximates the behavior of the painted metal solution interface. Nyquist plots in Fig. 3c show the difference between the three paints displayed here after three month of marine exposure in the tidal zone. Coal tar epoxy paint system MP 1 has a higher film resistance as compared to MP2 and MP3. However, MP 1 and MP3 systems maintain higher resistance for a longer time and deteriorate slower than MP2. The EIS results correlates well with surface corrosion mapping for the three paint systems. It can be indicated that the greater the red spot densities the higher the level ofanodic activity, and such areas are more likely to correlate to actual pits pores or defects in the paint film. However, in some localized areas, the coal tar epoxy coating did not behave as a dielectric, but more or less exhibited electrolytic conductivitybecause of polymer breakdown. This is because the electrolyte has dissolved within a hydrolyzed region or due to penetrationby the electrolytethrough pores aided by the presence of dust particles and the natural condition of cyclic wetting and drying condition of the seawater tidal zone as indicated in the SEM photomicrograph Fig. 2 and EDX analysis Fig. 3b. The degree of fouling of the failed coal tar epoxy coating by marine life is quite extensive considering the pilings have only been in position for about 6 weeks. The coating seems to offer no anti-fouling protection and, for some of the pilings, peeling of the coating appears to have been exacerbated by sheer weight and volume of marine life. Coatings might fail for a number of reasons, the most common being moisture, dirt and con-
taminants, and natural breakdown, and weathering. Under the prevailing marine environment of Kuwait many coatings will fail because they cannot handle the expansion/contraction (or movement) of the underlying surface due to thermal expansion, or they may crack when struck or exposed to the intense UV degradation. Brittleness is measured in terms of elongation. Brittle coal tar epoxies traditionally have elongations of only 2-3%. Once a coating cracks, even a tiny micro fracture, that crack becomes a pathway for moisture and corrosion. It is the beginning of failure for the coating. Look for coatings that have good elongation. Some products, like the abrasion epoxies mentioned above (MP3), are reinforced with glass flake pigments or fiber and iron oxide. These materials act like rip-stop nylon or rebar in concrete. They help keep tiny microfractures in the coating from spreading and growing. Coal tar epoxies yellow, chalk (or more commonly least lose their gloss), in direct sunlight (UV). However, steel surfaces in saltwater environments can be a problem. It is best to use epoxies with a mix ratio close to 1 to 1 as opposed to something 4-1, 5-1, etc. because errors in the mix ratios can be more pronounced with the latter. 5. Material aging test results
The most cost-effective solution to protect the steelwork from the corrosive marine environment during the installation stage would be to use the jacket system with the anti corrosion tape wrap designed for tubular steel protection system [79]. The steel piling should be prepared by stripping off and removing all the damaged coatings. These areas then should be cleaned thoroughly with water jet pressure. (i.e. high pressure water washing up to 10,000 psi or by manual wire-brushing. Then primed with special type of priming paste, and completely wrapped with petrolatum or wax tape. Infra radiation spectroscopy (IR) analysis, have identified the chemical composition of the
A. Husain et aL / Desalination 166 (2004) 295-304
four jacket materials, subsequently as polypropylene (J1), polyethylene (HDPE) (J2), polyurethane reinforced fabric (J3), and polypropylene (J4) Periodic inspections of other completed projects in the world confirm [9] that state-of-the-art jacket materials or polymer composites are the answer to corrosion protection for the inter-tidal or splash zones. A system that remains tightly bonded in severe offshore environments and
=--II--700~ i .
expected to provide unprecedented long-term service, wherever it is installed. The results of the testing program in Figs. 4 and 5 show that the jacket materials J2 based on high density polyethylene HDPE composition maintained a very stable mechanical and physical behavior under different aging condition. The screening criteria was based on comparing aged samples to its original unexposed materials and with respect to the other jacketing materials in 7oo i
J1
=
303
6O0
J2
500 1 F . "
-A-- o .A-- - - ~ ,
400 -
"G-. 400i
~
o
-
. . . . . . . .
~.~ . . . .
o
°G--
"O-
.
~ "
"-'~
J3
30O . . . .
.,
20O
"O
J4
6
J1
I-., - - . B,,., ~"
100
i"
""B"'
""ID"
~
0E
5
0 0
100
(a)
2(]0
300
400
500
100
200
300
400
500
600
600
~ i r ~ period (h)
(b)
Aging period (h)
Fig. 4. (a) Effect o f UV aging on tensile strength; (b) Effect of UV aging on elongation.The polyethylene material (J2) is very stable after 500 h o f UV aging exposure.
800
550
700
55O
600
450
o ~, 350
~) 400
e~
~ 250
~ 3oo
150
~ 200 b-
too
50
0 ,
1 (a)
2
3 Sample r~urrber
4
.50 i .....................,t....................................... 2 .......................................... 3............................................... 4..................... Sample number
Co)
Fig. 5. (a) Effect of different aging conditions on tensile strength for all jacket samples. (b) Effect of different aging conditions on maximum percentage elongation for all jacket samples. The tensile strength and elongation properties of the jacket materials before and after aging test, showing good stability of the polyethylene material (J2).
304
A. Husain et al. / Desalination 166 (2004) 295-304
terms of changes in tensile strength and maximum elongation percentage to break after aging test. In addition, the HDPE (J2)jacket material did not show any significant changes due to the effect of intense UV aging test after 500 h in QUV cabinet exposure chamber. The tensile properties of the J2 material showed a very stable system when compared with its original unexposed material. This effect is attributed to the presence of good amount of UV stabilizers elements and excellent mechanical properties of the polyethylene materials constituent.
anti corrosion petrolatum wax tape and by installing stainless steel strapping system to secure the outer jacket cover. Secondly, the outer cover can be manufactured from 1.8 to 3 m m in thickness, which is the most durable pile protection available in the industry. Moreover, most importantly, the steel piles receive a long service life without corrosion. Moreover, the jacket system can be installed on concrete pile and it is compatible with cathodic protection system. It can be concluded that coal tar epoxy paint is not suitable for tidal zone under Kuwait marine environment.
6. Conclusion
References
Based on the aging test results the high-density polyethylene (HDPE) J2 is the most recommended jacket material for the surface protection of the present tubular steel piling in the splash and intertidal zone. From the investigations of piles in water, it can be concluded that in all cases the most severe corrosion effect could be found at or in the vicinity of the water level. Below the water level, corrosion is usually less deep. At the bottom sediment level, corrosion is small and of the same order of magnitude as in soil on land. In the aerated zone, corrosion is typically lower, but not without significance. Steel tube piles can be protected effectively by application of a polyethylene (HDPE) jacket system of a few m m thicknesses. This cover can be applied to the steel tube piles in seawater, where the mechanical wear is low, it can in this way be protected for long time. There are many benefits inherent to the use of polyethylene jacket system. First, installation time can be reduced by 50% or more combined with an
[1] S. Al-Bahar and E. Attiobe, Proc. Int. Conf. CONSEC'95, Sapporo, Japan, 1 (1995) 564-573. [2] J Carew andA. Hadi, Delamination of coal tar epoxy mastic paint on steel pilings, Technical Report, KISR 1900, 1985. [3] A. Husain and A. Fakhraldeen, In-situ surface potential characterization of cathodically polarized coating, Desalination, 158 (2003) 29-34. [4] A. Husain, Precise determination of surface microgalvanic behavior, Desalination, 139 (2001) 333340. [5] A. Husain, Proc. 13th International Corrosion Congress, Melbourne, Australia, Nov.25-29, 1996, pp. 215/1-215/6. [6] H.S. Isaacs andY. Ishikawa, Proc. NACE Corrosion 83 Conference, Anaheim, CA, 1983, p.25. [7] V. Chaker, Proc. NACE Corrosion 90 Conference, Las Vegas, Nevada, 1990, pp. 376/2-376/16. [8] M.F. Bird, H.M. Smith and C.V. ~Bowley, Proc. NACE Corrosion 89 Conference, New Orleans, Louisiana, 1989, pp. 213/1-213/10. [9] M. Smith, C. Bowley and L. Williams, Proc. NACE Corrosion 2002 Conference, Denver, CO., pp. 02214/1-02214/10.
ELSEVIER
www.elsevier.com/locate/desal
Investigation of marine environmental related deterioration of coal tar epoxy paint on tubular steel pilings A. Husain*, O. A1-Shamali, A. Abduljaleel Kuwait Institute for Scientific Research, Department of Buildings and Energy Technologies P.O. Box 24885, Safat 13109, Kuwait Tel. +965 483 6100 Ext. 4522; Fax+965 484 5763; [email protected] Received 22 February 2004; accepted 3 March 2004
Abstract
In the Arabian Gulf region, port and waterway authorities are becoming increasingly concemed about accelerated tidal and splash zone concentrated corrosion on marine tubular steel piles. The coating protection and maintenance of tubular steel pilings located in a marine environment can be difficult. The arid environment of Kuwait of the salt water and salt laden moisture and high temperature fluctuation with the marine growth on the marine structure creates a challenging maintenance problem. This premature failure investigation dealt with the delamination and peeling of coal tar epoxy coating system. The new pier project is around 2.5 km long with topside facilities supported by 2000 tubular steel pilings in two types 914 mm and 1016 mm in diameters. Prior to installation, the piles at vendor's premises in another country received a protective coal tar epoxy coating with a minimum dry film thickness of 450 microns. However, almost all of the coated steel pilings severely deteriorated after 4-8 weeks causing an estimated cost of maintenance work of $4 million. The failure case investigation was carried out to ascertain the cause of the aforementioned coating defect and to propose a possible solution to the coating failure. An accepted method of repair has been proposed, and therefore to create a barrier system in the form of jacket material with anti corrosion wraps, protecting the underwater or splash zone pilings and other structural elements from further deterioration. The failure analysis results along with laboratory evaluation of the effectiveness of four different types of jacket materials will be addressed. Keywords: Steel tubular piles; Oil and water piers; Tidal and splash zone corrosion; Coating delamination; Coal tar epoxy; Anti-corrosion wrap; Jacket material
*Corresponding author. Presented at the EuroMed 2004 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and Office National de l'Eau Potable, Marrakech, Morocco, 30 May-2 June, 2004. 0011-9164/04/$- See front matter © 2004 Elsevier B.V. All rights reserved doi; 10.1016/j.desal.2004.06.084
296
A. Husain et aL / Desalination 166 (2004) 295-304
1. Introduction
Kuwait Gulf seawater receives little fresh water with its huge shallow areas of black mud and high evaporation rate and its climate is considered one of the hottest in the world. The salinity from a cold December to a hot August varies between 44,000 ppm and 48,000 ppm. The Kuwaiti seawater analysis indicates 5% NaCI, which is higher than the normally designated seawater composition found elsewhere. Barnacle multiplies and grows rapidly in this warm water, which has a seasonal range between 8°C and 35°C. Whereas, the concentration of suspended solids may rise from a normal 5 ppm to over 50 ppm within a few hours. The relevance of this study pertains to coating material performance in the Middle East, and particularly in Kuwait, Saudi Arabia and other countries in the region, where atmospheric conditions offshore and the adjacent to shore are considered the most severe marine environment in the world. A structure in constant contact with water whether it is a ship, a pier, or an offshore oil platform is subject to corrosion [ 1]. The battle against this scourge of the underwater industry continues with the development of new coating and outer jacket technology. Prior to the 1950's, corrosion problems in this difficult marine exposure conditions were mitigated somewhat by conventional paints and coatings that were available at that time which included chlorinated rubber, bitumen's and coaltar mastics as well as ordinary metal primers and paint. In the early 60, other materials were available including zinc rich coatings, coal-tar epoxies, and there were developments in the so-called high performance coatings. Oil companies were required to stock as many as 200 items and suppliers in order to show progress in corrosion control regardless of their effectiveness. This requires a fresh look at and increased attention to coating material selection and coating performance evaluation for condition of immersion water and desalination plants service as well as splash, and tidal zone in marine environment of Kuwait.
In the Gulf region, coal tar epoxies are still among the most popular coatings. They are essentially a mix of coal tar and epoxy resins. Coal tar epoxies were at their peak of popularity in Europe in the 1960's through about 1990. After that, non-coal tar epoxies replaced coal tar epoxies due largely to health concerns over long term exposure and direct contact (by coating applicators) to the 'tar'. Where their use is permitted coal tar epoxies are suitable for protection from moisture, both in water immersion condition (such as barge hulls and pilings) and when buried underground pipelines and tanks. Moreover, a literature search made on the subject of coal tar epoxy coatings performance in Kuwait has indicated the occurrence of one major types of coal tar epoxy failure in Kuwait marine environment during the 80's [2]. The coating was coal tar epoxy mastic 356KT, which was applied to sheet piles used in the construction of piers at one of the power station south of Kuwait. The coating failure occurred after almost six months of marine exposure. The study was concluded that coating failure was attributed to the poor specification of the quality and composition of the coal tar epoxy coating materials, caused by an interlayer paint failure delamination. In August 2001 another major financial losses were reported in Kuwait marine industry due to coating failures of coal tar epoxy on tubular steel pilings. The second failure ease concerning coal tar epoxy reported after 4 weeks of installation in marine seawater. However, it has been observed that almost 450 coated steel pilings were severely deteriorated after approximately 4 weeks of in service installation in real marine seawater exposure condition (i.e. adjacent to the sea shore marine environment). The paint systems began to experience severe coating peeling damage in the inter-tidal zone and combined with intense accumulation of marine growth in the form of Barnacles (i.e. Balanus). It has been estimated that almost 2000 coated steel tubular pilings were severely damaged or under going the process of
A. Husain et al. / Desalination 166 (2004) 295-304
coating deterioration. Prior to installation, the contractor and owner did not found any nonconformity's either in the tubular steel pile or in the finished coating product. Moreover, after 8 weeks in service the paint system begins to fail. The most common feature of both failures found to be limited in the intertidal and splash zone. In addition to that, the coating offers no protection against marine fouling, as shown in Fig. 1. An accepted method of repair for the steel pile is to create a barrier system (jacket system), protecting the underwater or tidal and splash zone pilings and other structural elements from further deterioration, both above and below the water line. There are many jacket materials products available combined with petrolatum tape or wax, some that provide structural integrity, and others that are less costly and simply seal out air and moisture to stop corrosion.[7-9] The general aim of this investigation is to provide laboratory information and approach on the causes of failure of coal tar epoxy coating and for designing and selecting an outer jacket material approved as a replacement for protecting the existed steel piles under the prevailing condition
297
of Kuwait environment. The field study was limited to an examination to the peeled offlayers of coating and an onsite inspection. Whilst the laboratory aging testing program was initiated and consisted of exposing four types of commercial quality outer jacket materials to different types of severe aging environments in order to recommend the optimum jacket material suitable for failure remediation. The main reason for the evaluation is to select the best jacket material suitable for the inter-tidal zone for the surface protection of the steel pilings in Kuwait marine environment. In the laboratory, the deterioration behaviors of this paint system in addition to the proposed jacket materials were evaluated by utilizing the following methods: (a) Electrochemical surface potential corrosion mapping (SCM) (b) Electrochemical impedance spectroscopy (EIS) (c) ASTM aging tests for durability The combined electrochemical testing techniques of EIS together with SCM were used to generate comparative data on paint performance,
Fig. 1. Corrosionsituationof coal tar epoxy coatedpiles in marineenvironment.
298
A. Husain et al. / Desalination 166 (2004) 295-304
which has been used successfully by the author for detection of various corroded metallic systems in order to facilitate decisions, development, screening, and grading of contemporary and new paint [3,4]. 2. Experimental method
Laboratory failure analysis tests on the failed section of the piles are being conducted in parallel with similar marine painted steel substrates samples of coal tar epoxy paint exposed for 3 months, under submerged and atmospheric conditions (intertidal zone) in the Gulf seawater (5% NaC1), in the State of Kuwait. The mild steel substrates (10 cm x 15 cm) were grit blasted, initially half masked and an area of (5 cm x 15 cm) was 'contaminated' with 3% NaC1, and the whole area subsequently sprayed with the multilayer coat. EIS was conducted on both salt contaminated and non contaminated areas using a measurement cell that consisted of, a working electrode (measurement area = 20 cm2), saturated calomel electrode (SCE) and a Pt or graphite counter electrode. The results were also compared with control specimens of modified epoxy MP2 and abrasion resistance epoxy MP3 materials of known durability in terms of EIS parameters of capacitance and impedance values. In SCM tests, a measurement area (1 cm x 1 cm) was scanned with the modified SCM probe with respect to a remote (SCE). Immersion solution for both tests was 5% seawater salt. EIS is widely used to characterize the behavior of coated metal immersed in aggressive solutions. The determination of EIS over a large frequency range (100 KHz to 0.01 Hz) provides cumulative information on processes involved in the protective coating. On the other hand, the SCM technique developed in this laboratory has been improved to scan over blistered surfaces without causing damage to the probe or the blister. In SCM tests, sequential measurement of areas of(1 cm x 1 cm) over the whole specimens surface were
scanned with the modified SCM probe with respect to a remote (SCE). Immersion solution for both tests was 5% seawater salt. Background details of the experimental setup for EIS and SCM are presented elsewhere in references [3--6]. The ASTM aging test used in this study for material screening criterion was based on exploring the ability of the outer jacket material to survive the aggressive aging attack in a quantitative manner by observing the minimal changes in its' mechanical properties in terms of tensile strength and maximum elongation percentage (%). Therefore, the recommended aging tests were consisted of the following ASTM test 1. Resistance to UV degradation, 2. Resistance to heat 3. Resistance to seawater immersion 4. Cyclic wetting and drying test in 5% seawater 5. Chemical resistance test. Selections of ASTM test condition are summarized below (Tables 1,2) along with details of test conditions and testing duration. 3. Results and discussion
On site inspection of the oil pier revealed that the extent of the coating defect was severe in areas located within the low and high tidal zone of the seawater. The paint film has experienced severe coating deterioration that was mainly associated with severe corrosion products and marine growth in the form of Barnacles. Visual observations have clearly indicated that all of the deteriorated paint films have developed a common type of failure with certain types of surface morphological features in terms of peelings, delaminations, and or flaking pattern (Fig. 1). The propagation direction of the deteriorated narrow region of the paint film has been found to show inclination or deflection at angel approximately 45 ° from the horizontal axes opposite the direction of the gravitational force. At this moment, the exact causes of the onset of paint defect can not be justified without proper
299
A. Husain et aL / Desalination 166 (2004) 295-304 Table 1 Specification of the ASTM standard tests for evaluation of the jacket system
Test No. ASTMstandard ASTM standard D638 ASTM standard D638 ASTM standard G53-96 4
ASTM D-3045
5
ASTM standard D453
Test description
Test duration Effect of continuous immersion in seawater at 40°C Two weeks 3 tests Two weeks 2 tensile tests Effect of cyclic wet/dry in seawater at 40°C QUV/UV-exposure Effect of intensive UV light via accelerated 5 tensile tests up to 500 h weathering test at 60°C Effect of resistance to temperature variations One week 3 tensile tests at T = 60°C, 80°C and 100°C Resistance to chemical attack, i.e., nitric acid, sulfuric acid detergent and NaOH
One week 4 tensile tests after immersion
Table 2 Outer jacket materials specification for aging test Sample code J1 J2 J3 J4
Jacket material specification Polypropylene High density polyethylene,HDPE Polyurethanematerialwith fabric Polypropylene
laboratory examination and chemical analysis on the failed section as well as on the as received steel piles. Presumably, the failure can be attributed to both the quality and composition of the coal tar epoxy material of the paint film or to the improper cleaning preparation of the steel substrate. After comprehensive examination and laboratory analysis of the failure morphology it was apparent that the areas of severe paint peelings are associated with the geometrical feature of the spiral weld beads of the steel tubing materials as shown in Fig. 1. Presumably, failure of the coated spiral weld beads may have been initiated at the junction between the weld bead and base metal (i.e. could be generated at the fusion line of the weld). The observations have clearly indicated that the exact causes of the damaged could be related to the insufficient surface preparation condition (i.e. post welding cleaning operation) or may be attributed to the quality of the underlying chemical composition of the spiral weld bead. It is very
Average thickness, mm 3.2 1.8 Multilayer (1.6 and 4.7) 2.2
common that almost 70% of paint failure in welded structure is always associated with low quality cleaning pretreatment of the weld bead adjacent to the parent metal or micro-cracking failure of the weldment. The spiral welded area is very widely accepted as the most common weakest point in any welded structure. The degradation of the paint film was also enhanced by the natural process of wet and dry cyclic effect of seawater low and high tide presented in marine environment. Technical personnel pointed out that during the month of August 2001 the local climatic temperature of Kuwait exceeded the acceptable record for that month. It has also been indicated that the aforementioned steel pilings have experienced a severe surface temperature of 76°C at the time when the seawater temperature was 34°C. It is also believed that the black colored nature of the coal tar epoxy coating enhanced the absorption of UV light and contributed to the deterioration process. The presence of coated spiral weld bead in the tubular steel
300
A. Husain et al. / Desalination 166 (2004) 295-304
piling is believed to have exerted a certain degree of residual stresses on the coating at weld junction with respect to the coated parent metal of the surrounding. Prior to installation it has been found that the adhesion strength of the coating system to the steel substrate was found to be within the acceptable limit of the specification as indicated by company engineers. Therefore, coating degradation in Fig. 2b was due mainly to seawater effect of wet dry cycle and strong susceptibility of the epoxy material to degradation by UV light. It has been also observed that the density of the marine Barnacles followed a narrow band when attached to the direction of the spiral weld bead beneath the coated layer. In contrast to the spiral weld zone no appreciable amount of Barnacles were found in the surrounding areas away from the weld. These finding will clearly indicate that the surfaces of the coated layer beneath the marine fouling were having certain degree of surface roughness or coating microcracks that were favorable sites for the nucleation of Barnacles when compared to the surrounding areas with coating of smooth surface nature. Issues here can include solvents in the product, andpoor resistance to UV (becoming more brittle and chalky), are the ones that come to mind. There
Laboratory EIS and SCM investigation (Fig. 3) on the exposed specimens coating material has indicated the tolerance level of this type &coating to dust and grit is low after removal from seawater as shown in Figs. 3a and 3b. It is therefore essential to ensure complete removal of any dust or grit particles when the surface of the steel pilings are prepared by shot or grit blasting. Moreover, strong evidence has indicated by SEM/EDX analysis that the failure initiation could be attributed to the poor specification of the quality and cleans less of the steel substrate and composition of the multi-layer coal tar epoxy coating system. The SCM map for the contaminated coal tar epoxy Fig. 3d determines the distribution of potential (E) corresponding to current flowing between local anodes and local cathodes for MP1 paints displayed here [6]. The SCM map shows red spot of defect embedded in the paint film due to dust particles. Table 3 illustrates paint specification and comparative results of EIS obtained on coal tar epoxy
(a)
(b)
are also reports that weathered coal tar is difficult to recoat. 4. EIS/SCM and SEM/EDX analysis
Fig. 2. (a) Coal tar epoxy paint after 3 month of Kuwait seawater immersionin the tidal zone, (b) SEM image showing MP 1 paint crack initiation.
A. Husain et al. / Desalination 166 (2004) 295-304 ~.~"~;
~'
. .~v.,. • ~
~s=z~5 (a)
301 v.,~,n,- . ~ , m ~ ¢
3,~72
~e~J
6,0 >i
(b)
"" ~ . ¢ a C t
i i
i/
e
,g/ d
/ b2
/
}
g
?
5
r U
(c) Fig. 3. (a) SEM image sand particle embedded in the paint film (b) EDX analysis of the same particles (c) EIS spectrum for MP1, MP2, and MP3, (d) SCM.
Table 3 Specification of the coating and EIS tests results Paint system
Paint code
Color
Coal tar epoxy Modified epoxy Abrasion epoxy
MP1 MP2 MP3
Black White Red brown
Thickness dft., ~tm 450 500 1000
E . . . . mV
Rpo, Ohm ~ n
-390 -184 -289
4.86× 109 1.05x10 ~ 8.82× 108
2
C1~~Fcm -2 3.29× I0 -l° 15x10 9 1.74× 10 l0
302
A. Husain et aL / Desalination 166 (2004) 295-304
MP 1 and two other marine paints used as reference or control samples, (MP2, MP3). The paint systems were exposed in the tidal zone of Kuwaiti seawater for 3 months, and were evaluated by EIS and SCM in our laboratory. The resulting impedance are interpreted in order to determine the individual parameters of paint film capacitance ( C ) , pore resistance (R o), and warburg diffusion or c~hargetransfer resis~nce ( Z ) of an equivalent electrical circuit that best approximates the behavior of the painted metal solution interface. Nyquist plots in Fig. 3c show the difference between the three paints displayed here after three month of marine exposure in the tidal zone. Coal tar epoxy paint system MP 1 has a higher film resistance as compared to MP2 and MP3. However, MP 1 and MP3 systems maintain higher resistance for a longer time and deteriorate slower than MP2. The EIS results correlates well with surface corrosion mapping for the three paint systems. It can be indicated that the greater the red spot densities the higher the level ofanodic activity, and such areas are more likely to correlate to actual pits pores or defects in the paint film. However, in some localized areas, the coal tar epoxy coating did not behave as a dielectric, but more or less exhibited electrolytic conductivitybecause of polymer breakdown. This is because the electrolyte has dissolved within a hydrolyzed region or due to penetrationby the electrolytethrough pores aided by the presence of dust particles and the natural condition of cyclic wetting and drying condition of the seawater tidal zone as indicated in the SEM photomicrograph Fig. 2 and EDX analysis Fig. 3b. The degree of fouling of the failed coal tar epoxy coating by marine life is quite extensive considering the pilings have only been in position for about 6 weeks. The coating seems to offer no anti-fouling protection and, for some of the pilings, peeling of the coating appears to have been exacerbated by sheer weight and volume of marine life. Coatings might fail for a number of reasons, the most common being moisture, dirt and con-
taminants, and natural breakdown, and weathering. Under the prevailing marine environment of Kuwait many coatings will fail because they cannot handle the expansion/contraction (or movement) of the underlying surface due to thermal expansion, or they may crack when struck or exposed to the intense UV degradation. Brittleness is measured in terms of elongation. Brittle coal tar epoxies traditionally have elongations of only 2-3%. Once a coating cracks, even a tiny micro fracture, that crack becomes a pathway for moisture and corrosion. It is the beginning of failure for the coating. Look for coatings that have good elongation. Some products, like the abrasion epoxies mentioned above (MP3), are reinforced with glass flake pigments or fiber and iron oxide. These materials act like rip-stop nylon or rebar in concrete. They help keep tiny microfractures in the coating from spreading and growing. Coal tar epoxies yellow, chalk (or more commonly least lose their gloss), in direct sunlight (UV). However, steel surfaces in saltwater environments can be a problem. It is best to use epoxies with a mix ratio close to 1 to 1 as opposed to something 4-1, 5-1, etc. because errors in the mix ratios can be more pronounced with the latter. 5. Material aging test results
The most cost-effective solution to protect the steelwork from the corrosive marine environment during the installation stage would be to use the jacket system with the anti corrosion tape wrap designed for tubular steel protection system [79]. The steel piling should be prepared by stripping off and removing all the damaged coatings. These areas then should be cleaned thoroughly with water jet pressure. (i.e. high pressure water washing up to 10,000 psi or by manual wire-brushing. Then primed with special type of priming paste, and completely wrapped with petrolatum or wax tape. Infra radiation spectroscopy (IR) analysis, have identified the chemical composition of the
A. Husain et aL / Desalination 166 (2004) 295-304
four jacket materials, subsequently as polypropylene (J1), polyethylene (HDPE) (J2), polyurethane reinforced fabric (J3), and polypropylene (J4) Periodic inspections of other completed projects in the world confirm [9] that state-of-the-art jacket materials or polymer composites are the answer to corrosion protection for the inter-tidal or splash zones. A system that remains tightly bonded in severe offshore environments and
=--II--700~ i .
expected to provide unprecedented long-term service, wherever it is installed. The results of the testing program in Figs. 4 and 5 show that the jacket materials J2 based on high density polyethylene HDPE composition maintained a very stable mechanical and physical behavior under different aging condition. The screening criteria was based on comparing aged samples to its original unexposed materials and with respect to the other jacketing materials in 7oo i
J1
=
303
6O0
J2
500 1 F . "
-A-- o .A-- - - ~ ,
400 -
"G-. 400i
~
o
-
. . . . . . . .
~.~ . . . .
o
°G--
"O-
.
~ "
"-'~
J3
30O . . . .
.,
20O
"O
J4
6
J1
I-., - - . B,,., ~"
100
i"
""B"'
""ID"
~
0E
5
0 0
100
(a)
2(]0
300
400
500
100
200
300
400
500
600
600
~ i r ~ period (h)
(b)
Aging period (h)
Fig. 4. (a) Effect o f UV aging on tensile strength; (b) Effect of UV aging on elongation.The polyethylene material (J2) is very stable after 500 h o f UV aging exposure.
800
550
700
55O
600
450
o ~, 350
~) 400
e~
~ 250
~ 3oo
150
~ 200 b-
too
50
0 ,
1 (a)
2
3 Sample r~urrber
4
.50 i .....................,t....................................... 2 .......................................... 3............................................... 4..................... Sample number
Co)
Fig. 5. (a) Effect of different aging conditions on tensile strength for all jacket samples. (b) Effect of different aging conditions on maximum percentage elongation for all jacket samples. The tensile strength and elongation properties of the jacket materials before and after aging test, showing good stability of the polyethylene material (J2).
304
A. Husain et al. / Desalination 166 (2004) 295-304
terms of changes in tensile strength and maximum elongation percentage to break after aging test. In addition, the HDPE (J2)jacket material did not show any significant changes due to the effect of intense UV aging test after 500 h in QUV cabinet exposure chamber. The tensile properties of the J2 material showed a very stable system when compared with its original unexposed material. This effect is attributed to the presence of good amount of UV stabilizers elements and excellent mechanical properties of the polyethylene materials constituent.
anti corrosion petrolatum wax tape and by installing stainless steel strapping system to secure the outer jacket cover. Secondly, the outer cover can be manufactured from 1.8 to 3 m m in thickness, which is the most durable pile protection available in the industry. Moreover, most importantly, the steel piles receive a long service life without corrosion. Moreover, the jacket system can be installed on concrete pile and it is compatible with cathodic protection system. It can be concluded that coal tar epoxy paint is not suitable for tidal zone under Kuwait marine environment.
6. Conclusion
References
Based on the aging test results the high-density polyethylene (HDPE) J2 is the most recommended jacket material for the surface protection of the present tubular steel piling in the splash and intertidal zone. From the investigations of piles in water, it can be concluded that in all cases the most severe corrosion effect could be found at or in the vicinity of the water level. Below the water level, corrosion is usually less deep. At the bottom sediment level, corrosion is small and of the same order of magnitude as in soil on land. In the aerated zone, corrosion is typically lower, but not without significance. Steel tube piles can be protected effectively by application of a polyethylene (HDPE) jacket system of a few m m thicknesses. This cover can be applied to the steel tube piles in seawater, where the mechanical wear is low, it can in this way be protected for long time. There are many benefits inherent to the use of polyethylene jacket system. First, installation time can be reduced by 50% or more combined with an
[1] S. Al-Bahar and E. Attiobe, Proc. Int. Conf. CONSEC'95, Sapporo, Japan, 1 (1995) 564-573. [2] J Carew andA. Hadi, Delamination of coal tar epoxy mastic paint on steel pilings, Technical Report, KISR 1900, 1985. [3] A. Husain and A. Fakhraldeen, In-situ surface potential characterization of cathodically polarized coating, Desalination, 158 (2003) 29-34. [4] A. Husain, Precise determination of surface microgalvanic behavior, Desalination, 139 (2001) 333340. [5] A. Husain, Proc. 13th International Corrosion Congress, Melbourne, Australia, Nov.25-29, 1996, pp. 215/1-215/6. [6] H.S. Isaacs andY. Ishikawa, Proc. NACE Corrosion 83 Conference, Anaheim, CA, 1983, p.25. [7] V. Chaker, Proc. NACE Corrosion 90 Conference, Las Vegas, Nevada, 1990, pp. 376/2-376/16. [8] M.F. Bird, H.M. Smith and C.V. ~Bowley, Proc. NACE Corrosion 89 Conference, New Orleans, Louisiana, 1989, pp. 213/1-213/10. [9] M. Smith, C. Bowley and L. Williams, Proc. NACE Corrosion 2002 Conference, Denver, CO., pp. 02214/1-02214/10.