- Email: [email protected]
Biofilm activity on corrosion of API 5L X65 steel weld bead
Accepted Manuscript Title: Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead Authors: V.S. Liduino, M.T.S. Lutterbach, E.F.C. S´ervulo PII: DOI: Reference:
S0927-7765(18)30558-7 https://doi.org/10.1016/j.colsurfb.2018.08.026 COLSUB 9558
To appear in:
Colloids and Surfaces B: Biointerfaces
Received date: Revised date: Accepted date:
27-3-2018 26-7-2018 14-8-2018
Please cite this article as: Liduino VS, Lutterbach MTS, S´ervulo EFC, Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead, Colloids and Surfaces B: Biointerfaces (2018), https://doi.org/10.1016/j.colsurfb.2018.08.026 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.
Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead
Short statistical summary of the article
A
CC E
PT
ED
M
A
N
U
SC R
IP T
5720 total number of words 2 Tables 6 Figures
Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead V.S. Liduino*a, M.T.S. Lutterbachb and E.F.C. Sérvuloa a
School of Chemistry, Federal University of Rio de Janeiro, Brazil b
Corresponding author
IP T
*
National Institute of Technology, Rio de Janeiro, Brazil
Universidade Federal do Rio de Janeiro
Av. Athos da Silveira Ramos, 149, Escola de Química, Sala 109 - Rio de Janeiro, RJ
E-mail: [email protected] | Phone: (+55 21) 3938 7619
CC E
PT
ED
M
A
N
U
Graphical Abstract
SC R
21941-909 | Brazil
Ms. Ref. No.: COLSUB-D-18-00542
A
Highlights
1) Welding with filler material creates conditions more favorable for biofilm development; 2) Microstructural modifications due to welding interfere little in microbial adhesion; 3) Pit occurrence and depth is more intense in HAZ than over weld bead.
Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead
ABSTRACT This work aimed to identify microbial colonization and biocorrosion in welded
IP T
seam areas of API 5L X65 carbon steel, since microorganisms are ubiquitous and there is
a lack of information on their biological and electrochemical interactions with these structures. In the present study, polished and unpolished welded coupons prepared by
SC R
shielded metal arc welding were assayed to identify the effect of surface roughness and
local changes in the metal microstructure on microbial colonization. Experiments were performed in glass cell vessels with fresh and sterile seawater to establish the presence or
U
absence of microorganisms. For comparison, nonwelded coupons were simultaneously
N
tested as a control. On the 15th day, both polished and unpolished welded coupons and the nonwelded coupons immersed in fresh seawater showed microbial colonization,
A
though the corrosion products were more abundant for the welded coupons. Nevertheless,
M
unpolished welded coupons showed a higher predominance of pitting around the beads than polished coupons. These results suggest that filler material creates conditions more
ED
favorable for biofilm development, thus intensifying the localized corrosion on the welds. It can be concluded that adhesion and subsequent biocorrosion are directly influenced by surface roughness, whereas microstructural modifications due to welding interfere little
PT
with microbial adhesion, regardless of the greater pit depths compared to those of nonwelded coupons. Additionally, although open circuit potential measurements
CC E
indicated that metal surfaces are protected when coated with biofilms, pitting corrosion was more pronounced in welded coupons immersed in fresh seawater than in those immersed in seawater without microorganisms. Therefore, the use of open circuit analysis
A
alone is not recommended for biocorrosion monitoring of welded coupons.
Keywords: Biocorrosion; Welding; Pitting; Carbon Steel X65; Seawater
1. Introduction The interactions between microorganisms and solid surfaces and their ability to trigger corrosion processes in diverse materials under different environmental conditions have been intensively studied over recent decades [1-4]. It is well documented that
IP T
biofilm formation on materials, particularly on metallic materials, contributes deeply to the deterioration of these materials by modifying the physical, chemical and
physicochemical characteristics of their surfaces [4-6]. Biofilm-mediated deterioration of
SC R
materials, a process known as microbiologically induced corrosion (MIC) [7,8], is common once microorganisms are widespread both in nature and in industrial environments. In general, MIC is associated with pitting by sulfate-reducing bacteria (SRB) and is the main cause of fast and unexpected equipment failure [9,10].
U
MIC has already been recognized as a major threat to many industries, particularly
N
the oil industry, whose activities depend heavily on metallic materials. The main
A
corrosion costs of oil facilities are a result of pipeline network failure that can lead to oil spills with economic and environmental damage. The economic data on MIC prevention
M
and control are still very scarce; however, it is generally considered that 20 to 30% of failures are related to microbial activity [11-13]. It should be emphasized that these data
ED
are out of date and do not reflect the intensive use of metal structures today. Currently, pipelines for petroleum industry applications are constructed according
PT
to the American Petroleum Institute (API) technical specifications [14]. The API 5L X65 specification is widely accepted as one of the most economical for seamless and welded
CC E
steel line pipes because of its high resistance, strength and weldability [15-17]. In fact, pipeline accidents have been reduced by the use of API steels but still occur due to the corrosion of welded joints [18]. The corrosion behavior of the welded seam areas is expected to account for the local microstructure changes that occur with welding thermal
A
cycles [19]. The heat-affected zone (HAZ) deserves special attention for its role in the reduced corrosion resistance, as the physical, mechanical and alloy chemistry properties differ from those observed in the parent metal area [20-22]. Although the corrosion of welded joints has been broadly reported [23-26], little is known about the influence of biofilms on the deterioration performance of weld beads and nearby zones. It is also worth noting that most published works only evaluate the
corrosion of the weld fusion boundary region of stainless steels exposed to artificial environments [23,24]. Thus, there is a research gap for investigating MIC on the welded area of carbon steels under naturally corrosive conditions. The present study aimed to evaluate the MIC attack on 5L X65 steel of a weldment (shielded metal arc welding). For comparison, polished weld bead coupons were also analyzed to check whether surface roughness and/or local changes in microstructure in the HAZ contribute to biofilm formation and MIC. The choice of the shielded metal arc
IP T
welding technique was due to its wide use in the construction and repair of metal
structures. The corrosive process of all coupons was evaluated comparatively in fresh and
SC R
sterile seawater by electrochemical, microbiological, weight loss and surface microscopy techniques.
U
2. Experimental procedure 2.1 Working electrodes
N
Rectangular flat coupons of API 5L X65 carbon steel with an area of 6 cm2 were
A
employed. Three different designs of coupons were used: (i) coupons with weld beads
M
generated by shielded metal arc (SMA) welding with the addition of E7018 filler metal, (ii) coupons with SMA weld beads ground to a polished finish and (III) coupons without
ED
welding. The weld beads, approximately 3.0 cm in length, were made in longitudinal and centralized orientation. Analysis of the chemical elements of API 5L X65 steel and the filler metal were performed using inductive coupled plasma atomic emission
CC E
PT
spectroscopy [27] and are given in Table 1.
Prior to the welding process, the surfaces of the coupons were glass-bead blasted
with 200 μm microspheres to remove impurities and mimic the inner surface of oil
A
pipelines. After welding, the coupons were degreased in acetone, sanitized by exposure to germicidal ultraviolet (UV) light for 30 minutes, settled in sterile Petri dishes and kept in a desiccator until the beginning of the tests. Moreover, the coupons used for the electrochemical test were connected to a copper wire to promote electrical bonding.
2.2 Corrosive fluid
Seawater collected from Guanabara Bay, Rio de Janeiro, Brazil (220 24' S and 430 33' W), was used. This fluid has been used before by our group because of its high microbial diversity, including microorganisms that are usually implicated in biocorrosion, caused by constant and undue disposal of sewage as well as industrial effluents [28-31]. Table 2 shows the values of the main chemical and physical parameters of the seawater samples used according to APHA (American Public Health Association) methodologies
IP T
[32].
SC R
2.3 Corrosion test systems
The unpolished and polished weld bead coupons and the nonwelded coupons were placed in 1 L glass vessels containing 800 mL of fresh seawater without nutrient
U
supplementation, taking into account its content of organic and inorganic matter (Table
N
2). Small ports located on the vessel lids were filled with hydrophobic cotton to allow the sufficient diffusion of oxygen to the aerobic microorganisms but to avoid external
A
contamination into the systems [31]. For abiotic tests, seawater was previously autoclaved
M
at 121°C for 20 minutes to sterilize it. Tests of seawater sterility were carried out prior to its use and at the end of abiotic experiments to guarantee the absence of microorganisms.
ED
In total, 12 vessels were tested simultaneously; system I: coupons immersed in fresh seawater for microbiological and surface characterization; system II: coupons immersed
PT
in sterile seawater for surface characterization; system III: coupons immersed in fresh seawater for electrochemical analysis; and system IV: coupons immersed in sterile seawater for electrochemical analysis.
CC E
Each system was installed on magnetic stirring plates to promote slow and constant
fluid rotation and favor microbial adhesion to the working surfaces of the coupons for 15 days. All systems were placed in an air-conditioned room with a temperature between
A
18°C and 20°C and tested in three replicates. 2.4 Bacterial quantification Quantitative determinations of different populations of planktonic and sessile bacteria were performed using the most probable number (MPN) technique in appropriate culture media [33]. The populations of aerobic heterotrophic bacteria, iron-oxidizing bacteria and sulfate-reducing bacteria were cultured in nutrient broth, ferric ammonium
citrate broth and Postgate E medium supplemented with 1.2% (m/v) sodium thioglycolate, respectively. All culture media were supplemented with 35 g L-1 NaCl to mimic the salinity of seawater. The conditions and incubation time of each culture medium inoculated with samples were ensured according to the requirements of each bacterial population [28]. The quantification of planktonic bacteria from the seawater was performed before and at the end of the assay. The quantification of sessile bacteria was performed only at the end of the experiment. All results are presented as the average value
IP T
from three independent trials.
SC R
2.5 Electrochemical analysis
The open circuit potential of the metal coupons of systems III and IV was measured using a saturated calomel electrode as the reference electrode and a portable multimeter [9]. The analyses were performed at 24-hour intervals during the experiment to observe
U
possible variations in the corrosion potential due to biofilm formation and abiotic
A
N
deposits.
M
2.6 Corrosion rate
The extent of corrosion was determined by measuring the weight loss using a high-
ED
accuracy mass balance (Gehaka AG-200, read-ability 0.0001 g). Then, the corrosion rate was calculated as indicated by ASTM standard G1–03 [34]: 86.7 𝑥 𝑤𝑒𝑖𝑔ℎ𝑡 𝑙𝑜𝑠𝑠 (𝑔) 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 (𝑔 𝑐𝑚−3 ) 𝑥 𝑎𝑟𝑒𝑎 (𝑐𝑚2 ) 𝑥 𝑡𝑖𝑚𝑒 (ℎ)
CC E
PT
𝐶𝑜𝑟𝑟𝑜𝑠𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (𝑚𝑚 𝑦 −1 ) =
2.7 Surface examination The surface roughness of the coupons was characterized in three different positions
A
of each coupon to calculate the average value using a profilometer (Bruker Contour GTK1). Pitting corrosion was investigated according to ASTM Standard G-46/94 [35] employing a 3D measurement system (Alicona Infinite Focus microscope). Scanning electron microscopy (FEI Company Quanta 200 SEM) and energy dispersive X-ray spectroscopy (Oxford Instruments Inca Penta FET x3 EDS) were used to observe biofilm morphology and to characterize the corrosion products.
2.8 Statistical analysis The average results for the bacterial quantification and electrochemical data were submitted to analysis of variance (ANOVA) and multiple comparison of means (Tukey’s test) with significance at 5% by using Statistica software (StatSoft Inc.).
IP T
3. Results and discussion
Surface differences of API X65 carbon steel were evidenced between the three
SC R
working coupons employed prior to installation in the reactors (Fig. 1). The coupons with a linear weld bead made by shielded metal arc welding had an average roughness (Ra) value of approximately 8.3 ± 1.2 μm, while a smaller roughness of 0.8 ± 0.3 μm was determined for the polished weld bead coupons. Moreover, metallic spatter also existed
U
on the coupon surfaces due to high-speed welding circumstances. For comparison, the
N
average surface roughness value for nonwelded coupons was 0.5 ± 0.2 μm. The much
A
large surface roughness of unpolished welded coupons was expected because the shielded metal arc welding is a technique based on the use of filler metal to join parts [36].
M
FIGURE 1
ED
Additionally, the welded and nonwelded coupons were analyzed by electron microscopy at 15 days of immersion in fresh or sterile seawater (Fig. 2). All coupons
PT
exhibited intense corrosion products; however, the amount of corrosion products was higher on surface of coupons exposed to fresh seawater than on those under sterile
CC E
conditions. The highest level of corrosion of steel carbon in the marine environment indicates that beyond the high chloride content [37], the main cause of corrosiveness of
A
fresh seawater is due to bacterial cells and their metabolites.
FIGURE 2
The presence of microorganisms on solid surfaces was confirmed by MEV/EDS. By analyzing the surfaces during the biotic assays, Figures 2A and 2B, it is noted that biofilm formation throughout the analyzed areas of both welded coupons occurred in a short interval (3 days). This behavior was previously reported for other different metallic
materials [28,29]. Besides oxygen (O) and iron (Fe) detected for corrosion products on coupons under sterile conditions, carbon (C) and sulfur (S) were observed when the coupons were exposed to microorganisms. It should be noted that among the coupons immersed in fresh seawater, the unpolished welded coupons had a slightly higher carbon content and a lower oxygen content, which may indicate a higher density and activity of adhered aerobic microorganisms than on the polished welded coupons. Sulfur is normally a result of metabolic sulfate reduction by SRB in seawater [31,38]. Biogenic sulfide may
IP T
react with iron-forming compounds such as iron (II) sulfide, which intensifies metal deterioration [39-41]. Other recent works have shown that iron sulfides and iron oxides
SC R
are easily detected on API steel exposed to seawater [42-44]. Under sterile conditions (Figures 2FC and 2D), the coupons were covered by a compact and cracked layer of corrosion products, probably formed only by iron compounds. The EDS analysis did not show diffraction peaks of carbon and sulfur in these samples, indicating the absence of
U
microorganisms.
N
Figure 2 suggests the predominance of rod-shaped cells in biofilms. This morphology is characteristic of most sulfate-reducing bacteria as well as primary
A
colonizing species found in environments with MIC occurrence [3,38,39]. In addition,
M
the viability of cells in the biofilms at the end of the test was evidenced through analysis of preparations of samples stained with a LIVE/DEAD Baclight Bacteria Viability Kit
ED
and confocal microscopy (image not shown in this document). Therefore, even without nutrient supplementation, the cells remained metabolically active throughout the test
PT
period and did not compromise the microbiologically induced corrosion process. The main bacterial groups involved in MIC were quantified in the fluid and biofilms, and their results are shown in Figure 3. The microbiological analysis of seawater
CC E
before the corrosion assays revealed low concentrations of iron-oxidizing bacteria (FeB) and sulfate-reducing bacteria (SRB), but mostly aerobic heterotrophic bacteria (AHB). In general, the higher the cell concentration is, the greater is the likelihood that
A
microorganisms will adhere to the exposed surfaces [45]. The AHB population comprises extracellular polymeric substances (EPS) producing strains of great importance to the colonization of solid surfaces and thus biofilm formation [46,47]. In contrast, the average of SRB in seawater samples was small (2.2 x 102 MPN mL-1). Similar data were reported by other authors for samples collected previously from distinct sites of Guanabara Bay [28,29]. However, these studies demonstrated that the low concentration of SRB in the
planktonic phase was not an obstacle to the intense activity of these microorganisms in the biofilms, with an effective occurrence of MIC.
FIGURE 3
At the end of assay, the number of planktonic iron-bacteria increased by 3 orders of magnitude reaching 105 MPN mL-1 at the end of assay (Fig. 3). Most likely, their
IP T
growth may have been stimulated by the release of iron to the surrounding fluid due to
carbon steel degradation and/or detachment of cells from the biofilm. A similar density
SC R
increase was observed for the AHB population in the planktonic phase, although FeB
present chemolithotrophic metabolism. On the other hand, there was no change in SRB concentration, which demonstrates the ability of this microbial group to survive temporary aerobiosis [48].
U
As shown in Figure 3, bacterial colonization was similar in the nonwelded coupons
N
and in those with polished weld beads, while larger numbers of bacteria were observed in the coupons with unpolished weld beads. This may be due to the high surface roughness
A
of shielded metal arc welding, which facilitates microbial adhesion and subsequent
M
proliferation [49]. Additionally, regarding the coupons with unpolished weld beads, the aerobic heterotrophic bacteria population reached a value of 4.0 x 1011 MPN cm-2. This
ED
number was slightly superior that detected for the iron-oxidizing bacteria, revealing also an intense activity of FeB in this condition. This group is largely responsible for the
PT
generation of abiotic and biotic deposits in pipelines, which can cause clogging, especially in the oil extraction industry [50,51]. Even in this biofilm sample, the number of SRB reached 2.5 x 106 MPN cm-2 at the end of the assays. Javed, Stoddart and Wade
CC E
[52] suggest that high concentrations of ferrous ions in the medium may favor the adhesion of SRB to carbon steel surfaces. Biofilms with the presence of SRB have been reported as a cause of pitting corrosion in iron-carbon alloys and even stainless steels,
A
mainly due to the production of reactive metabolites such as sulfur compounds, as evidenced by the EDS analysis [53,54]. Thus, the results suggest that increased bacterial colonization is truly due to the influence of surface roughness and is not due to local changes in microstructure. Monitoring microbial colonization and biofilm development in metallic coupons over short intervals of time by confocal microscopy could show the real influence of microstructural changes on the primary adhesion of bacteria in parental metal, HAZ and
weld bead areas. However, the intense generation of corrosion products of API X65 steel immersed in fresh seawater hid the adhered cells, which made this effect impossible to observe. Figure 4 shows the surface images of the coupons obtained by 3D microscopy. In general, coupons exposed to sterile seawater showed uniform corrosion, although the deterioration was more intense in welded coupons, both unpolished and polished, with a few shallow pits observed even in the absence of microorganisms. The average pit depth
IP T
for coupons with unpolished weld beads was higher than that for polished weld bead
coupons (12.5 ± 4 μm and 5.0 ± 3 μm, respectively). It should be noted that the filler
SC R
metal and the parent metal have distinct chemical and metallurgical properties, even
though they are both carbon steel. Therefore, a galvanic cell could be formed and consequently aggravate the deterioration of the weld region even without microbial
N
FIGURE 5
U
activity [55].
Comparatively, pitting corrosion was higher for the coupons immersed in fresh
A
seawater regardless of the coupon tested. However, a greater severity of the localized
M
corrosion was once again observed in coupons with unpolished weld beads. The average pit depth in these coupons reached 35.2 ± 9.3 μm. The density and depth of pits observed
ED
around the weld bead reinforce the seriousness of the occurrence of microbiological corrosion in carbon steel parts joined by this welding technique. The biofilm formed on
PT
the metal surface and in contact with the medium may cause a reduction in the corrosion potential to a value close to the pitting potential, resulting in the occurrence of localized corrosion [56]. In this work, this phenomenon can be corroborated by the high number of
CC E
cells adhered to the coupons, whereas in the abiotic tests, the incidence of pits was significantly lower. Although bacterial adhesion was similar in polished weld bead coupons and nonwelded coupons, the observation of pits was most frequently observed
A
in the first coupons. This result is due to all local changes that reduce the corrosion resistance in welded areas and MIC occurrence, even in areas of very low roughness. Chaves and Melchers [57] investigated the occurrence of pits in API X56 carbon steel welded by an autogenous technique and exposed to seawater from the Pacific Ocean for 3.5 years. The authors verified that no difference in pitting density was observed in the parent metal zone, in the heat-affected zone (HAZ) or in the weld zone in the first two months. However, at the end of the trial, they reported that the pitting density was much
higher in the HAZ than in the other areas. Although some results found in our study are consistent with those obtained by Chaves and Melchers, it should be noted that the total time of the test was only 15 days, a period much shorter than that tested by those authors. One reason for this may be the higher concentration of microorganisms present in the Guanabara Bay seawater in relation to the concentration of cells in the water of the Pacific Ocean. Corrosion rates for each coupon under the two conditions tested were measured and
IP T
are compiled in Figure 5. All coupons exposed to sterile seawater showed moderate
corrosion according to Standard NACE RP-07-75 recommendations, although the
SC R
corrosion rates ranged from 0.0623 to 0.1057 mm y-1 for nonwelded coupons and coupons with unpolished weld beads, respectively. This same corrosion grade was also observed for nonwelded coupons exposed to fresh seawater. High corrosion rates were reached
when welded coupons were immersed in fresh seawater (0.1286 mm y-1 for polished weld
U
bead coupons and 0.1501 mm y-1 for unpolished weld bead coupons). Thus, our results
N
corroborate that the severe incidence of pits can cause significant weight loss, which is fairly crucial for welded joints exposed to environments where microorganisms cause
M
A
deterioration of the metal.
ED
FIGURE 5
Figure 6 shows the open circuit potential (OCP) variation over 360 hours (15 days)
PT
for different coupons immersed in seawater. All potentials decreased in the first 24 hours of exposure, being more pronounced for coupons immersed in sterile seawater, reaching values of -775 mVSCE. This initial behavior was due to the chloride ion content in
CC E
seawater, which directly increased the electrical conductivity and accelerated the electron flow on the coupon surfaces [36], especially on cell-free surfaces (sterile test). Then, the potentials increased until 96 hours, probably because of iron compound deposition (Fig.
A
2), which may function as a barrier on the steel surface, promoting a lower contact between the corrosive electrolyte and the metal.
FIGURE 6
After 96 hours, all coupons showed an increasing tendency to oxidize, as corrosion potentials continued to decrease, even slightly, until the end of the experimental period.
The potentials of the welded and nonwelded coupons exposed to fresh seawater showed slightly more positive values than the potentials of coupons immersed in sterile seawater. This fact must be due to the thick barrier created by the formation of the biofilm on the coupons, which can reduce the flow of electrons on the metal surface. Unlike the open-circuit corrosion potential, which indicated a slight protection of the biofilm on coupons against corrosion, causing the so-called ennoblement of the steel, the current density values calculated by TAFEL extrapolation suggest that the
IP T
microorganisms of the biofilm presented high metabolic activity and promoted
degradation of the metal (data not shown in this document). As a brief example, at 15
SC R
days of assay, the current density for the unpolished welded coupons almost doubled in
the presence of adhered microorganisms, reaching 0.2610 ± 0.0475 μA cm-2. This fact was also corroborated by the pitting analysis, which means that the biofilm layer may not
U
be considered protective.
N
Conclusions
A
This study contributes new knowledge about the biocorrosion of welded regions of
M
metallic structures. It is highlighted that weld beads with filler metal favor an intense development of biofilms than those on nonwelded areas, not because of microstructural
ED
changes in the heat affected zone (HAZ) but greatly associated with the surface roughness. Moreover, the occurrence and depth of pits at the HAZ of unpolished welded
PT
coupons were greater than those seen on the polished welded coupons, even in the absence of microorganisms (sterile seawater). Effectively, to prevent MIC our research encourages the employment of welding without filler metal (autogenous techniques) or
CC E
polishing rough weld beads in structures exposed to environments where sulfate-reducing bacteria and iron-oxidizing bacteria are found.
A
Acknowledgments The authors would like to acknowledge the support received from SENAI-Solda
and the Programa de Recursos Humanos da Petrobras - PRH13. The authors declare no conflict of interest.
References
[1] Garret TR, Bhakoo M, Zhang Z. Bacterial adhesion and biofilms on surfaces. Prog Nat Sci. 2008,18:1049-1056. doi.org/10.1016/j.pnsc.2008.04.001 [2] Wang H, Sodagari M, Chen Y, He H, Newby BZ, Ju LK. Initial bacterial attachment in slow flowing systems: Effects of cell and substrate surface properties. Colloids Surf. 2011, 87:415-422. doi.org/10.1016/j.colsurfb.2011.05.053
IP T
[3] Feng G, Cheng Y, Wang SY, Borca-Tasciuc DA, Worobo RW, Moraru CI. Bacterial attachment and biofilm formation on surfaces are reduced by small-diameter
nanoscale pores: how small is small enough? Biofilms and Microbiomes. 2015,1:1-
SC R
9.
[4] Krishman M, Dahms HU, Seeni P, Gopalan S, Sivanandham V, Hyoung KJ, James RA. Multi metal assessment on biofilm formation in offshore environment. Mater Sci Eng C. 2017,73:743-755. doi.org/10.1016/j.msec.2016.12.062
U
[5] An D, Dong X, An A, Park HS, Strous M, Voordouw G. Metagenomic analysis
injected
with
bisulfite.
doi.org/10.3389/fmicb.2016.00028
Front
Microbiol.
2016,7-28.
A
pipelines
N
indicates Epsilonproteobacteria as a potential cause of microbial corrosion in
M
[6] Huang H, Yu Q, Ren H, Geng J, Xu K, Zhang Y, Ding L. Towards physicochemical and biological effects on detachment and activity recovery of aging biofilm by
ED
enzyme and surfactant treatments. Bioresour Technol. 2018,247:319-326. doi.org/10.1016/j.biortech.2017.09.082
PT
[7] Wang LW, Liu ZY, Cui ZY, Du CW, Wang XH, Li XG. In situ corrosion characterization of simulated weld heat affected zone on API X80 pipeline steel. Corr
CC E
Sci. 2014,85:401–410. doi.org/10.1016/j.corsci.2014.04.053 [8] Skovhus TL, Eckert RB, Rodrigues E. Management and control of microbiologically induced corrosion (MIC) in the oil and gas industry – Overview and a North See case study. J Biotechnol. 2017,256:31-45. doi.org/10.1016/j.jbiotec.2017.07.003
A
[9] Liu H, Cheng F. Mechanism of microbiologically induced corrosion of X52 pipeline steel in a wet soil containing sulfate-reduced bacteria. Electrochim Acta. 2017,253:368-378. doi.org/10.1016/j.electacta.2017.09.089 [10] Xu D, Li Y, Gu T. Mechanistic modeling of biocorrosion caused by biofilms of sulfate reducing bacteria and acid producing bacteria. Bioelectrochemistry. 2016,110:52-58. doi.org/10.1016/j.bioelechem.2016.03.003
[11] Koch GH, Brongers MPH, Thompson NG, Virmani YP, Payer JH (Eds). Corrosion Cost and Preventive Strategies in the United States. National Technical Reports Library (2001). [12] United States Department of Energy: The Mitigation and Detection of Microbial Corrosion (1999). [13] Flemming HC (Eds), Economical and Technical Overview, in Microbially Influenced Corrosion of Materials, Springer-Verlag, Heidelberg, Germany, 1996.
IP T
[14] API Specification 20A. Carbon steel, alloy steel, stainless steel, and nickel base alloy castings for using in petroleum and natural gas industry, 2nd edition, 2017.
SC R
[15] Oliveira MC, Figueiredo RM, Acciari HA, Codaro EN. Corrosion behavior of API 5L X65 steel subject to plastic deformation. J Mater Res Technol. 2018. doi.org/10.1016/j.jmrt.2018.02.006
[16] Arora KS, Pandu SR, Shajan N, Pathak P, Shome M. Microstructure and impact
U
toughness of reheated coarse grain heat affected zones of API X65 and API X80 line
N
pipe steels. Int J Pres Ves Pip. 2018,163:36-44. doi.org/10.1016/j.ijpvp.2018.04.004 [17] Farelas F, Choi YS, Nesic S. Corrosion behavior of API 5L X65 carbon steel under
A
supercritical and liquid CO2 phases in the presence of H2O and SO2. Corrosion.
M
2013,69:243-250. doi.org/10.5006/0739
[18] Shabani H, Goudarzi N, Shabani M. Failure analysis of a natural gas pipeline. Eng
ED
Fail Anal. 2018,84:167-184. doi.org/10.1016/j.engfailanal.2017.11.003 [19] Natividad C, García R, López VH, Contreras A, Salazar M. Metallurgical
PT
characterization of API X65 steel joint welded by MIG welding process with axial magnetic field. Mater Res. 2017. doi.org/10.1590/1980-5373-mr-2016-0182 [20] Wang LW, Liu ZY, Cui ZY, Du CW, Wang XH, Li XG. In situ corrosion
CC E
characterization of simulated weld heat affected zone on API X80 pipeline steel. Corr Sci. 2014,85:401–410. doi.org/10.1016/j.corsci.2014.04.053
[21] Geng H, Xia Z, Zhang X, Li G, Cui J. Microstructure and mechanical properties of
A
the welded AA5182/HC340LA joints by magnetic pulse welding. Mater Charact. 2018,138:229-237. doi.org/10.1016/j.matchar.2018.02.018
[22] Li G, Lu X, Zhu X, Huang J, Liu L, Wu Y. The interface microstructure, mechanical properties and corrosion resistance of dissimilar joints during multipass laser welding for
nuclear
power
plants.
Opt
doi.org/10.1016/j.optlastec.2017.12.002
Laser
Technol.
2018,101:479-490.
[23] Borenstein SW. Microbiologically influenced corrosion failures of austenitic stainless-steel welds. Mater Perform. 1988,27:62–66. [24] Ramkumar KD, Dagur AH, Kartha AA, Subodh MA, Vishnu C, Arun D, Kumar MGV, Abraham WS, Chatterjee A, Abraham J, Abraham J. Microstructure, mechanical properties and biocorrosion behavior of dissimilar welds of AISI 904L and
UNS
S32750.
J
Manuf
Process.
2017,30:27-40.
doi.org/10.1016/j.jmapro.2017.09.001
Today. 2018,5:7476-7485. doi.org/10.1016/j.matpr.2017.11.419
IP T
[25] Beeharry P, Surnam BYR. Atmospheric corrosion of welded mild steel. Mater
SC R
[26] Toppo A, Pujar MG, Sreevidya N, Philip J. Pitting and stress corrosion cracking
studies on AISI type 316N stainless steel weldments. Def Technol. 2018,14:226-237. doi.org/10.1016/j.dt.2018.03.004
[27] Ghosh S, Prasanna VL, Sowjanya B, Srivani, P, Alagaraja M, Banji D. Inductively
U
coupled plasma – optical emission spectroscopy: a review. Asian J Pharm Ana.
N
2013,3:24-33.
[28] De França FP, Lutterbach MT. Variation in sessile microflora during biofilm
A
formation on AISI-304 stainless steel coupons. J Ind Microbiol. 1996,17:6-10.
M
doi.org/10.1590/S0104-66321997000100007
ED
[29] Araújo LCA., Reznik LY, Lutterbach MTS, Carvalho LJ, Servulo EFC (Eds.). Biocorrosion of AISI 1020 carbon steel protected with the base coat of niobium
PT
oxide. Nace International Conference, Orlando, 2013. [30] Liduino VS, Lutterbach MTS, Ferreira AA, Ribeiro JW, Sérvulo EFC (Eds.). Biofouling and biocorrosion in carbon steel welds. The European Corrosion
CC E
Congress, Graz, 2015.
[31] Liduino VS, Lutterbach MTS, Sérvulo EFC. Corrosion behavior of carbon steel API 5L X65 exposed to seawater. Int J Eng Tech Res. 2017,7:70-74.
A
[32] American Public Health Association (APHA). Standard methods for the examination of water and wastewater, 22nd edition, Washington, 2012.
[33] Harrison AP. Microbial succession and mineral leaching in an artificial coal spoil. Appl Environ Microbiol. 1978,36:861-869. [34] ASTM G1-03, Standard Practice for Preparing, Cleaning and Evaluating Corrosion Test Specimens (2011).
[35] ASTM G46-94, Standard Guide for Examination and Evaluation of Pitting Corrosion (2005). [36] Bitharas I, McPherson NA, McGhie W, Roy D, Moore AJ. Visualization and optimization of shielding gas coverage during gas metal arc welding. J Mater Process Thech. 2018,255:451-462. doi.org/10.1007/BF03321146 [37] Zakowski Z, Narozny M, Szocinski M, Darowicki K. Influence of water salinity on corrosion risk – the case of the southern Baltic Sea Cost. Environ Monit Assess.
IP T
2014,186:4871-4879. doi.org/10.1007/s10661-014-3744-3
[38] Miranda E, Bethencourt M, Botana JF, Cano MJ, Amaya JMS, Corzo A, Lomas JG,
SC R
Fardeau LM, Ollivier L. Biocorrosion of carbon steel alloys by a hydrogenotrophic
sulfate-reducing bacterium Desulfovibrio capillatus isolated from a Mexican oil field separator. Corr Sci. 2006,48:2417-2431. doi.org/10.1016/j.corsci.2005.09.005 [39] Videla H, Herrera LKJ. Microbiologically influenced corrosion: looking to the
U
future. Int Microbiol. 2005,8:169-180.
N
[40] Xu J, Sun C, Yan M, Wang F. Effects of sulfate reducing bacteria on corrosion of carbon steel Q235 in soil-extract solution. Int J Electrochem Sci. 2012,7:11281-
A
11296.
M
[41] Guan F, Zhai X, Duan J, Zhan M, Hou B. Influence of sulfate reducing bacteria on the corrosion behavior of high strength steel EQ70 under cathodic polarization. Plos
ED
One. 2016,11: e0162315. doi.org/10.1371/journal.pone.0162315 [42] Oliveira EDS, Pereira RFC, Melo IR, Lima MAG, Urtiga-Filho SL. Corrosion
PT
behavior of API 5L X80 steel in the produced water of onshore oil recovery facilities. 2017,20. doi.org/10.1590/1980-5373-mr-2016-0954 [43] Li Q, Wang J, Xing X, Hu W. Corrosion behavior of X65 steel in seawater containing reducing
CC E
sulfate
bacteria
under
aerobic
conditions.
Bioelectrochemistry.2018,122:40-50. doi.org/10.1016/j.bioelechem.2018.03.003
[44] Jia R, Tan JL, Jin P, Blackwood DJ, Xu D, Gu T. Effects of biogenic H 2S on the
A
microbiologically influenced corrosion of C1018 carbon steel by sulfate reducing Desulfovibrio
vulgaris
biofilm.
Corros
Sci.
2018,130:1–11.
doi.org/10.1016/j.corsci.2017.10.023 [45] Zeraik AE, Nitschke M. Influence of growth media and temperature on bacteria adhesion
to
polystyrene
surfaces.
Braz
doi.org/10.1590/S1516-89132012000400012
Arch
Biol
Technol.
2012.
[46] Bautista BET, Wikiel AJ, Datsenko I, Vera M, Sand W, Seyeux A, Zanna S, Frateur I, Marcus P. Influence of extracellular polymeric substances (EPS) from Pseudomonas NCIMB 2021 on the corrosion behaviour of 70Cu–30Ni alloy in seawater. J
Electroanal
Chem
Interfac Electrochem.
2015,737:184-197.
doi.org/10.1016/j.jelechem.2014.09.024 [47] Abdolahi A, Hamza E, Ibrahim Z, Hashim S. Microbially influenced corrosion of steels
by
Pseudomonas
aeruginosa.
Corros
Rev.
IP T
doi.org/10.1515/corrrev-2013-0047
2014,32:129-141.
[48] Brioukhanov AL, Netrusov AI. Aerotolerance of strictly anaerobic microorganisms
2007,43:567-582.
SC R
and factors of defense against oxidative stress: a review. Appl Biochem Microbial.
[49] Abdoli L, Suo X, Li H. Distinctive colonization of Bacillus sp. bacteria and the influence of the bacterial biofilm on electrochemical behaviors of aluminum Colloids
Surf
B.
U
coatings.
N
doi.org/10.1016/j.colsurfb.2016.05.075
2016,145:688-694.
[50] Beimeng QI, Chongwei C, Yixing Y. Effects of iron bacteria on cast iron pipe
M
2015,10:545-558.
A
corrosion and water quality in water distribution systems. Int J Electrochem Sci.
[51] Little BJ, Gerke TL, Lee JS. Mini-review: the morphology, mineralogy and
ED
microbiology of accumulated iron corrosion products. Biofoul. 2014,30:941-948. doi.org/10.1080/08927014.2014.951039
PT
[52] Javed MA, Stoddart PR, Wade SA. Corrosion of carbon steel by sulphate reducing bacteria: Initial attachment and the role of ferrous ions. Corros Sci. 2015,93:48-57. doi.org/10.1016/j.corsci.2015.01.006
CC E
[53] Enning E, Garrelfs J. Corrosion of iron by sulfate-reducing bacteria: new views of an
old
problem.
Appl
Environ
Microbiol.
2014,80:1226-1236.
doi.org/10.1128/AEM.02848-13
A
[54] Castaneda H, Benetton XD. SRB-biofilm influence in active corrosion sites formed at the steel-electrolyte interface when exposed to artificial seawater conditions. Corros Sci. 2008,50:1169-1183. doi.org/10.1016/j.corsci.2007.11.032 [55] Gentil V (Eds). Corrosão, Livros Técnicos e Científicos Editora S.A., 6th edition, Rio de Janeiro, 2011.
[56] Javaherdashti R. Impact of sulphate-reducing bacteria on the performance of engineering
materials.
Appl
Microbiol
Biotechnol.
2011,91:1507-1517.
doi.org/10.1007/s00253-011-3455-4 [57] Chaves IA, Melchers RE. Pitting corrosion in pipeline steel weld zones. Corros Sci.
A
CC E
PT
ED
M
A
N
U
SC R
IP T
2011,53:4026-4032. doi.org/10.1016/j.corsci.2011.08.005
FIGURE CAPTIONS
Figure 1. Illustration of the working coupons: weld bead generated by shielded metal arc welding (unpolished), polished weld bead (control for surface roughness) and nonwelded coupon (control for microstructure changes). The surface of the coupons is highlighted in 1.5x of magnitude.
IP T
Figure 2. Results of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of the corrosion products at 15 days of testing: polished coupons (A)
SC R
and unpolished coupons (B) immersed in fresh seawater and polished coupons (C) and unpolished coupons (D) immersed in sterile seawater.
Figure 3. Quantification of the different groups of bacteria investigated. The number of
U
cells adhered to all coupons was determined at 15 days of testing. Identical letters indicate
N
no significant differences according to the Tukey test (p > 0.05).
A
Figure 4. Localized corrosion on the surface of the coupons at 15 days of immersion in
M
seawater. Letter A indicates coupons immersed in sterile seawater (without microorganisms), and letter B indicates coupons immersed in fresh seawater (with
ED
microorganisms). The red circle indicates the region of pit investigation.
Figure 5. Corrosion rate of API X65 carbon steel calculated from the results of weight
PT
loss at 15 days of immersion in sterile seawater [▲] or fresh seawater [●]. Identical letters
CC E
indicate no significant differences according to the Tukey test (p > 0.05).
Figure 6. Open circuit potential of the welded coupons (polished and unpolished) and
A
nonwelded coupons immersed in sterile seawater [▲] and fresh seawater [●].
FIGURES
Figure 1)
IP T
NONWELDED
A
CC E
PT
ED
M
A
N
U
SC R
UNPOLISHED POLISHED WELD BEAD WELD BEAD
Figure 2) cps/eV
A
Wt % Au = 5.8 Fe = 47.0 C = 7.8 O = 36.7 S = 2.7
7
6
5
Au Au S O SC O Fe C Fe
4
AuAuSS
Fe Fe
Au
3
IP T
2
1
0 0
2
4
6
cps/eV 5
4
O Au Au S SC OFe Fe C
Au
Au S S
SiSi
U
3
Wt % Au = 8.3 Fe = 53.3 C = 8.6 O = 25.7 S = 3.5 Si = 0.6
SC R
B
10
Fe
Fe
Au
N
2
8
keV
A
1
0
2
4
M
0
ED
C
6
keV
8
10
Wt % Au = 5.0 Fe = 55.1 O = 39.9 O Fe
Au
Fe
CC E
PT
Au
A
D
cps/eV 2.5
cps/eV 2.5
2.0
2.0
Mn 1.5 Au O C Fe
1.5
1.0
1.0
0.5
0.5
Mn O Fe
Mn Au O Au C Fe
Au
Au Au
Mn
Wt % Au = 7.2 Fe = 71.7 O = 20.7 Mn = 0.4 Fe
Mn Mn
Fe
Fe
Au
Au
0.0
0.0 0
0 2
42
6
4
keV
8
6
10 keV
8
12
10
Figure 3)
1E+13
c d c
c,d
1E+09
1E+07
c a
b
1E+05
1E+03
a
a
b
b
a
1E+01
Nonwelded
Unpolished weld bead
U
Planktonic Final time
A
CC E
PT
ED
M
A
N
Planktonic Initial time
AHB
c
c
IP T
b
SC R
Cell number (MPN cm-2)
1E+11
Polished weld bead
FeB SRB
Figure 4)
IP T
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20
B
SC R
NONWELDED
A
U N M
A A
PT
ED
B
A
CC E
UNPOLISHED WELD BEAD
POLISHED WELD BEAD
A
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20
5
0 -5
-10 -15 -20
-25 -30
5 0 -5
-10 -15 -20 -25 -30
B
10 0 -5
-10 -15 -20 -30 -40
Figure 5) d
0,16 0.16
c
b
b
IP T
b
0,08 0.08
a
0,04 0.04
SC R
Corrosion rate (mm y-1)
0.12 0,12
00
Polished Polished Unpolished Unpolished weld bead [▲] weld bead [●] weld bead [▲] weld bead [●]
A
N
U
Nonwelded [▲] Nonwelded [●]
M
Figure 6)
ED
-730
PT
-760
-770 -780
Nonwelded [▲] Polished weld bead [▲] Unpolished weld bead [▲] Nonwelded [●] Polished weld bead [●] Unpolished weld bead [●]
CC E
-750
A
Potential (mV vs. SCE)
-740
-790
0
24
96
168
Time (h)
264
360
Table Table 1. Chemical composition of API X65 steel and E7018 filler metal (weight %) C
Mn
Si
P
API X65
0.1
1.4
0.7
E7018
0.07
0.1
0.61 0.02
S
0.45 0.002 0.02
Ni
Cr
Nb
Mo
Cu
Fe
0.3
0.05 0.04 0.01 0.1 0.06 0.06 0.01
Bal.
0.02
0.1
Bal.
-
0.01
Al
-
V
0.05
Mg
-
-
Value
Salinity
32.5 ± 0.02 g L-1
Conductivity
56.8 ± 0.05 mS cm
Total sulfide
8.5 ± 0.4 µg L-1
pH
7.6 ± 0.2
Temperature
21.8 ± 0.01°C
Dissolved oxygen
3.7 ± 0.3 mg L-1
Turbidity
CC E
PT
ED
M
Total suspended solids
A
11.8 ± 2.7 mg L-1 1.21 ± 0.1 NTU
A
Biochemical oxygen demand
N
U
SC R
Parameter
IP T
Table 2. Main chemical and physicochemical parameters of seawater samples
380 ± 52 mg L-1
S0927-7765(18)30558-7 https://doi.org/10.1016/j.colsurfb.2018.08.026 COLSUB 9558
To appear in:
Colloids and Surfaces B: Biointerfaces
Received date: Revised date: Accepted date:
27-3-2018 26-7-2018 14-8-2018
Please cite this article as: Liduino VS, Lutterbach MTS, S´ervulo EFC, Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead, Colloids and Surfaces B: Biointerfaces (2018), https://doi.org/10.1016/j.colsurfb.2018.08.026 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.
Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead
Short statistical summary of the article
A
CC E
PT
ED
M
A
N
U
SC R
IP T
5720 total number of words 2 Tables 6 Figures
Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead V.S. Liduino*a, M.T.S. Lutterbachb and E.F.C. Sérvuloa a
School of Chemistry, Federal University of Rio de Janeiro, Brazil b
Corresponding author
IP T
*
National Institute of Technology, Rio de Janeiro, Brazil
Universidade Federal do Rio de Janeiro
Av. Athos da Silveira Ramos, 149, Escola de Química, Sala 109 - Rio de Janeiro, RJ
E-mail: [email protected] | Phone: (+55 21) 3938 7619
CC E
PT
ED
M
A
N
U
Graphical Abstract
SC R
21941-909 | Brazil
Ms. Ref. No.: COLSUB-D-18-00542
A
Highlights
1) Welding with filler material creates conditions more favorable for biofilm development; 2) Microstructural modifications due to welding interfere little in microbial adhesion; 3) Pit occurrence and depth is more intense in HAZ than over weld bead.
Biofilm Activity on Corrosion of API 5L X65 Steel Weld Bead
ABSTRACT This work aimed to identify microbial colonization and biocorrosion in welded
IP T
seam areas of API 5L X65 carbon steel, since microorganisms are ubiquitous and there is
a lack of information on their biological and electrochemical interactions with these structures. In the present study, polished and unpolished welded coupons prepared by
SC R
shielded metal arc welding were assayed to identify the effect of surface roughness and
local changes in the metal microstructure on microbial colonization. Experiments were performed in glass cell vessels with fresh and sterile seawater to establish the presence or
U
absence of microorganisms. For comparison, nonwelded coupons were simultaneously
N
tested as a control. On the 15th day, both polished and unpolished welded coupons and the nonwelded coupons immersed in fresh seawater showed microbial colonization,
A
though the corrosion products were more abundant for the welded coupons. Nevertheless,
M
unpolished welded coupons showed a higher predominance of pitting around the beads than polished coupons. These results suggest that filler material creates conditions more
ED
favorable for biofilm development, thus intensifying the localized corrosion on the welds. It can be concluded that adhesion and subsequent biocorrosion are directly influenced by surface roughness, whereas microstructural modifications due to welding interfere little
PT
with microbial adhesion, regardless of the greater pit depths compared to those of nonwelded coupons. Additionally, although open circuit potential measurements
CC E
indicated that metal surfaces are protected when coated with biofilms, pitting corrosion was more pronounced in welded coupons immersed in fresh seawater than in those immersed in seawater without microorganisms. Therefore, the use of open circuit analysis
A
alone is not recommended for biocorrosion monitoring of welded coupons.
Keywords: Biocorrosion; Welding; Pitting; Carbon Steel X65; Seawater
1. Introduction The interactions between microorganisms and solid surfaces and their ability to trigger corrosion processes in diverse materials under different environmental conditions have been intensively studied over recent decades [1-4]. It is well documented that
IP T
biofilm formation on materials, particularly on metallic materials, contributes deeply to the deterioration of these materials by modifying the physical, chemical and
physicochemical characteristics of their surfaces [4-6]. Biofilm-mediated deterioration of
SC R
materials, a process known as microbiologically induced corrosion (MIC) [7,8], is common once microorganisms are widespread both in nature and in industrial environments. In general, MIC is associated with pitting by sulfate-reducing bacteria (SRB) and is the main cause of fast and unexpected equipment failure [9,10].
U
MIC has already been recognized as a major threat to many industries, particularly
N
the oil industry, whose activities depend heavily on metallic materials. The main
A
corrosion costs of oil facilities are a result of pipeline network failure that can lead to oil spills with economic and environmental damage. The economic data on MIC prevention
M
and control are still very scarce; however, it is generally considered that 20 to 30% of failures are related to microbial activity [11-13]. It should be emphasized that these data
ED
are out of date and do not reflect the intensive use of metal structures today. Currently, pipelines for petroleum industry applications are constructed according
PT
to the American Petroleum Institute (API) technical specifications [14]. The API 5L X65 specification is widely accepted as one of the most economical for seamless and welded
CC E
steel line pipes because of its high resistance, strength and weldability [15-17]. In fact, pipeline accidents have been reduced by the use of API steels but still occur due to the corrosion of welded joints [18]. The corrosion behavior of the welded seam areas is expected to account for the local microstructure changes that occur with welding thermal
A
cycles [19]. The heat-affected zone (HAZ) deserves special attention for its role in the reduced corrosion resistance, as the physical, mechanical and alloy chemistry properties differ from those observed in the parent metal area [20-22]. Although the corrosion of welded joints has been broadly reported [23-26], little is known about the influence of biofilms on the deterioration performance of weld beads and nearby zones. It is also worth noting that most published works only evaluate the
corrosion of the weld fusion boundary region of stainless steels exposed to artificial environments [23,24]. Thus, there is a research gap for investigating MIC on the welded area of carbon steels under naturally corrosive conditions. The present study aimed to evaluate the MIC attack on 5L X65 steel of a weldment (shielded metal arc welding). For comparison, polished weld bead coupons were also analyzed to check whether surface roughness and/or local changes in microstructure in the HAZ contribute to biofilm formation and MIC. The choice of the shielded metal arc
IP T
welding technique was due to its wide use in the construction and repair of metal
structures. The corrosive process of all coupons was evaluated comparatively in fresh and
SC R
sterile seawater by electrochemical, microbiological, weight loss and surface microscopy techniques.
U
2. Experimental procedure 2.1 Working electrodes
N
Rectangular flat coupons of API 5L X65 carbon steel with an area of 6 cm2 were
A
employed. Three different designs of coupons were used: (i) coupons with weld beads
M
generated by shielded metal arc (SMA) welding with the addition of E7018 filler metal, (ii) coupons with SMA weld beads ground to a polished finish and (III) coupons without
ED
welding. The weld beads, approximately 3.0 cm in length, were made in longitudinal and centralized orientation. Analysis of the chemical elements of API 5L X65 steel and the filler metal were performed using inductive coupled plasma atomic emission
CC E
PT
spectroscopy [27] and are given in Table 1.
Prior to the welding process, the surfaces of the coupons were glass-bead blasted
with 200 μm microspheres to remove impurities and mimic the inner surface of oil
A
pipelines. After welding, the coupons were degreased in acetone, sanitized by exposure to germicidal ultraviolet (UV) light for 30 minutes, settled in sterile Petri dishes and kept in a desiccator until the beginning of the tests. Moreover, the coupons used for the electrochemical test were connected to a copper wire to promote electrical bonding.
2.2 Corrosive fluid
Seawater collected from Guanabara Bay, Rio de Janeiro, Brazil (220 24' S and 430 33' W), was used. This fluid has been used before by our group because of its high microbial diversity, including microorganisms that are usually implicated in biocorrosion, caused by constant and undue disposal of sewage as well as industrial effluents [28-31]. Table 2 shows the values of the main chemical and physical parameters of the seawater samples used according to APHA (American Public Health Association) methodologies
IP T
[32].
SC R
2.3 Corrosion test systems
The unpolished and polished weld bead coupons and the nonwelded coupons were placed in 1 L glass vessels containing 800 mL of fresh seawater without nutrient
U
supplementation, taking into account its content of organic and inorganic matter (Table
N
2). Small ports located on the vessel lids were filled with hydrophobic cotton to allow the sufficient diffusion of oxygen to the aerobic microorganisms but to avoid external
A
contamination into the systems [31]. For abiotic tests, seawater was previously autoclaved
M
at 121°C for 20 minutes to sterilize it. Tests of seawater sterility were carried out prior to its use and at the end of abiotic experiments to guarantee the absence of microorganisms.
ED
In total, 12 vessels were tested simultaneously; system I: coupons immersed in fresh seawater for microbiological and surface characterization; system II: coupons immersed
PT
in sterile seawater for surface characterization; system III: coupons immersed in fresh seawater for electrochemical analysis; and system IV: coupons immersed in sterile seawater for electrochemical analysis.
CC E
Each system was installed on magnetic stirring plates to promote slow and constant
fluid rotation and favor microbial adhesion to the working surfaces of the coupons for 15 days. All systems were placed in an air-conditioned room with a temperature between
A
18°C and 20°C and tested in three replicates. 2.4 Bacterial quantification Quantitative determinations of different populations of planktonic and sessile bacteria were performed using the most probable number (MPN) technique in appropriate culture media [33]. The populations of aerobic heterotrophic bacteria, iron-oxidizing bacteria and sulfate-reducing bacteria were cultured in nutrient broth, ferric ammonium
citrate broth and Postgate E medium supplemented with 1.2% (m/v) sodium thioglycolate, respectively. All culture media were supplemented with 35 g L-1 NaCl to mimic the salinity of seawater. The conditions and incubation time of each culture medium inoculated with samples were ensured according to the requirements of each bacterial population [28]. The quantification of planktonic bacteria from the seawater was performed before and at the end of the assay. The quantification of sessile bacteria was performed only at the end of the experiment. All results are presented as the average value
IP T
from three independent trials.
SC R
2.5 Electrochemical analysis
The open circuit potential of the metal coupons of systems III and IV was measured using a saturated calomel electrode as the reference electrode and a portable multimeter [9]. The analyses were performed at 24-hour intervals during the experiment to observe
U
possible variations in the corrosion potential due to biofilm formation and abiotic
A
N
deposits.
M
2.6 Corrosion rate
The extent of corrosion was determined by measuring the weight loss using a high-
ED
accuracy mass balance (Gehaka AG-200, read-ability 0.0001 g). Then, the corrosion rate was calculated as indicated by ASTM standard G1–03 [34]: 86.7 𝑥 𝑤𝑒𝑖𝑔ℎ𝑡 𝑙𝑜𝑠𝑠 (𝑔) 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 (𝑔 𝑐𝑚−3 ) 𝑥 𝑎𝑟𝑒𝑎 (𝑐𝑚2 ) 𝑥 𝑡𝑖𝑚𝑒 (ℎ)
CC E
PT
𝐶𝑜𝑟𝑟𝑜𝑠𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (𝑚𝑚 𝑦 −1 ) =
2.7 Surface examination The surface roughness of the coupons was characterized in three different positions
A
of each coupon to calculate the average value using a profilometer (Bruker Contour GTK1). Pitting corrosion was investigated according to ASTM Standard G-46/94 [35] employing a 3D measurement system (Alicona Infinite Focus microscope). Scanning electron microscopy (FEI Company Quanta 200 SEM) and energy dispersive X-ray spectroscopy (Oxford Instruments Inca Penta FET x3 EDS) were used to observe biofilm morphology and to characterize the corrosion products.
2.8 Statistical analysis The average results for the bacterial quantification and electrochemical data were submitted to analysis of variance (ANOVA) and multiple comparison of means (Tukey’s test) with significance at 5% by using Statistica software (StatSoft Inc.).
IP T
3. Results and discussion
Surface differences of API X65 carbon steel were evidenced between the three
SC R
working coupons employed prior to installation in the reactors (Fig. 1). The coupons with a linear weld bead made by shielded metal arc welding had an average roughness (Ra) value of approximately 8.3 ± 1.2 μm, while a smaller roughness of 0.8 ± 0.3 μm was determined for the polished weld bead coupons. Moreover, metallic spatter also existed
U
on the coupon surfaces due to high-speed welding circumstances. For comparison, the
N
average surface roughness value for nonwelded coupons was 0.5 ± 0.2 μm. The much
A
large surface roughness of unpolished welded coupons was expected because the shielded metal arc welding is a technique based on the use of filler metal to join parts [36].
M
FIGURE 1
ED
Additionally, the welded and nonwelded coupons were analyzed by electron microscopy at 15 days of immersion in fresh or sterile seawater (Fig. 2). All coupons
PT
exhibited intense corrosion products; however, the amount of corrosion products was higher on surface of coupons exposed to fresh seawater than on those under sterile
CC E
conditions. The highest level of corrosion of steel carbon in the marine environment indicates that beyond the high chloride content [37], the main cause of corrosiveness of
A
fresh seawater is due to bacterial cells and their metabolites.
FIGURE 2
The presence of microorganisms on solid surfaces was confirmed by MEV/EDS. By analyzing the surfaces during the biotic assays, Figures 2A and 2B, it is noted that biofilm formation throughout the analyzed areas of both welded coupons occurred in a short interval (3 days). This behavior was previously reported for other different metallic
materials [28,29]. Besides oxygen (O) and iron (Fe) detected for corrosion products on coupons under sterile conditions, carbon (C) and sulfur (S) were observed when the coupons were exposed to microorganisms. It should be noted that among the coupons immersed in fresh seawater, the unpolished welded coupons had a slightly higher carbon content and a lower oxygen content, which may indicate a higher density and activity of adhered aerobic microorganisms than on the polished welded coupons. Sulfur is normally a result of metabolic sulfate reduction by SRB in seawater [31,38]. Biogenic sulfide may
IP T
react with iron-forming compounds such as iron (II) sulfide, which intensifies metal deterioration [39-41]. Other recent works have shown that iron sulfides and iron oxides
SC R
are easily detected on API steel exposed to seawater [42-44]. Under sterile conditions (Figures 2FC and 2D), the coupons were covered by a compact and cracked layer of corrosion products, probably formed only by iron compounds. The EDS analysis did not show diffraction peaks of carbon and sulfur in these samples, indicating the absence of
U
microorganisms.
N
Figure 2 suggests the predominance of rod-shaped cells in biofilms. This morphology is characteristic of most sulfate-reducing bacteria as well as primary
A
colonizing species found in environments with MIC occurrence [3,38,39]. In addition,
M
the viability of cells in the biofilms at the end of the test was evidenced through analysis of preparations of samples stained with a LIVE/DEAD Baclight Bacteria Viability Kit
ED
and confocal microscopy (image not shown in this document). Therefore, even without nutrient supplementation, the cells remained metabolically active throughout the test
PT
period and did not compromise the microbiologically induced corrosion process. The main bacterial groups involved in MIC were quantified in the fluid and biofilms, and their results are shown in Figure 3. The microbiological analysis of seawater
CC E
before the corrosion assays revealed low concentrations of iron-oxidizing bacteria (FeB) and sulfate-reducing bacteria (SRB), but mostly aerobic heterotrophic bacteria (AHB). In general, the higher the cell concentration is, the greater is the likelihood that
A
microorganisms will adhere to the exposed surfaces [45]. The AHB population comprises extracellular polymeric substances (EPS) producing strains of great importance to the colonization of solid surfaces and thus biofilm formation [46,47]. In contrast, the average of SRB in seawater samples was small (2.2 x 102 MPN mL-1). Similar data were reported by other authors for samples collected previously from distinct sites of Guanabara Bay [28,29]. However, these studies demonstrated that the low concentration of SRB in the
planktonic phase was not an obstacle to the intense activity of these microorganisms in the biofilms, with an effective occurrence of MIC.
FIGURE 3
At the end of assay, the number of planktonic iron-bacteria increased by 3 orders of magnitude reaching 105 MPN mL-1 at the end of assay (Fig. 3). Most likely, their
IP T
growth may have been stimulated by the release of iron to the surrounding fluid due to
carbon steel degradation and/or detachment of cells from the biofilm. A similar density
SC R
increase was observed for the AHB population in the planktonic phase, although FeB
present chemolithotrophic metabolism. On the other hand, there was no change in SRB concentration, which demonstrates the ability of this microbial group to survive temporary aerobiosis [48].
U
As shown in Figure 3, bacterial colonization was similar in the nonwelded coupons
N
and in those with polished weld beads, while larger numbers of bacteria were observed in the coupons with unpolished weld beads. This may be due to the high surface roughness
A
of shielded metal arc welding, which facilitates microbial adhesion and subsequent
M
proliferation [49]. Additionally, regarding the coupons with unpolished weld beads, the aerobic heterotrophic bacteria population reached a value of 4.0 x 1011 MPN cm-2. This
ED
number was slightly superior that detected for the iron-oxidizing bacteria, revealing also an intense activity of FeB in this condition. This group is largely responsible for the
PT
generation of abiotic and biotic deposits in pipelines, which can cause clogging, especially in the oil extraction industry [50,51]. Even in this biofilm sample, the number of SRB reached 2.5 x 106 MPN cm-2 at the end of the assays. Javed, Stoddart and Wade
CC E
[52] suggest that high concentrations of ferrous ions in the medium may favor the adhesion of SRB to carbon steel surfaces. Biofilms with the presence of SRB have been reported as a cause of pitting corrosion in iron-carbon alloys and even stainless steels,
A
mainly due to the production of reactive metabolites such as sulfur compounds, as evidenced by the EDS analysis [53,54]. Thus, the results suggest that increased bacterial colonization is truly due to the influence of surface roughness and is not due to local changes in microstructure. Monitoring microbial colonization and biofilm development in metallic coupons over short intervals of time by confocal microscopy could show the real influence of microstructural changes on the primary adhesion of bacteria in parental metal, HAZ and
weld bead areas. However, the intense generation of corrosion products of API X65 steel immersed in fresh seawater hid the adhered cells, which made this effect impossible to observe. Figure 4 shows the surface images of the coupons obtained by 3D microscopy. In general, coupons exposed to sterile seawater showed uniform corrosion, although the deterioration was more intense in welded coupons, both unpolished and polished, with a few shallow pits observed even in the absence of microorganisms. The average pit depth
IP T
for coupons with unpolished weld beads was higher than that for polished weld bead
coupons (12.5 ± 4 μm and 5.0 ± 3 μm, respectively). It should be noted that the filler
SC R
metal and the parent metal have distinct chemical and metallurgical properties, even
though they are both carbon steel. Therefore, a galvanic cell could be formed and consequently aggravate the deterioration of the weld region even without microbial
N
FIGURE 5
U
activity [55].
Comparatively, pitting corrosion was higher for the coupons immersed in fresh
A
seawater regardless of the coupon tested. However, a greater severity of the localized
M
corrosion was once again observed in coupons with unpolished weld beads. The average pit depth in these coupons reached 35.2 ± 9.3 μm. The density and depth of pits observed
ED
around the weld bead reinforce the seriousness of the occurrence of microbiological corrosion in carbon steel parts joined by this welding technique. The biofilm formed on
PT
the metal surface and in contact with the medium may cause a reduction in the corrosion potential to a value close to the pitting potential, resulting in the occurrence of localized corrosion [56]. In this work, this phenomenon can be corroborated by the high number of
CC E
cells adhered to the coupons, whereas in the abiotic tests, the incidence of pits was significantly lower. Although bacterial adhesion was similar in polished weld bead coupons and nonwelded coupons, the observation of pits was most frequently observed
A
in the first coupons. This result is due to all local changes that reduce the corrosion resistance in welded areas and MIC occurrence, even in areas of very low roughness. Chaves and Melchers [57] investigated the occurrence of pits in API X56 carbon steel welded by an autogenous technique and exposed to seawater from the Pacific Ocean for 3.5 years. The authors verified that no difference in pitting density was observed in the parent metal zone, in the heat-affected zone (HAZ) or in the weld zone in the first two months. However, at the end of the trial, they reported that the pitting density was much
higher in the HAZ than in the other areas. Although some results found in our study are consistent with those obtained by Chaves and Melchers, it should be noted that the total time of the test was only 15 days, a period much shorter than that tested by those authors. One reason for this may be the higher concentration of microorganisms present in the Guanabara Bay seawater in relation to the concentration of cells in the water of the Pacific Ocean. Corrosion rates for each coupon under the two conditions tested were measured and
IP T
are compiled in Figure 5. All coupons exposed to sterile seawater showed moderate
corrosion according to Standard NACE RP-07-75 recommendations, although the
SC R
corrosion rates ranged from 0.0623 to 0.1057 mm y-1 for nonwelded coupons and coupons with unpolished weld beads, respectively. This same corrosion grade was also observed for nonwelded coupons exposed to fresh seawater. High corrosion rates were reached
when welded coupons were immersed in fresh seawater (0.1286 mm y-1 for polished weld
U
bead coupons and 0.1501 mm y-1 for unpolished weld bead coupons). Thus, our results
N
corroborate that the severe incidence of pits can cause significant weight loss, which is fairly crucial for welded joints exposed to environments where microorganisms cause
M
A
deterioration of the metal.
ED
FIGURE 5
Figure 6 shows the open circuit potential (OCP) variation over 360 hours (15 days)
PT
for different coupons immersed in seawater. All potentials decreased in the first 24 hours of exposure, being more pronounced for coupons immersed in sterile seawater, reaching values of -775 mVSCE. This initial behavior was due to the chloride ion content in
CC E
seawater, which directly increased the electrical conductivity and accelerated the electron flow on the coupon surfaces [36], especially on cell-free surfaces (sterile test). Then, the potentials increased until 96 hours, probably because of iron compound deposition (Fig.
A
2), which may function as a barrier on the steel surface, promoting a lower contact between the corrosive electrolyte and the metal.
FIGURE 6
After 96 hours, all coupons showed an increasing tendency to oxidize, as corrosion potentials continued to decrease, even slightly, until the end of the experimental period.
The potentials of the welded and nonwelded coupons exposed to fresh seawater showed slightly more positive values than the potentials of coupons immersed in sterile seawater. This fact must be due to the thick barrier created by the formation of the biofilm on the coupons, which can reduce the flow of electrons on the metal surface. Unlike the open-circuit corrosion potential, which indicated a slight protection of the biofilm on coupons against corrosion, causing the so-called ennoblement of the steel, the current density values calculated by TAFEL extrapolation suggest that the
IP T
microorganisms of the biofilm presented high metabolic activity and promoted
degradation of the metal (data not shown in this document). As a brief example, at 15
SC R
days of assay, the current density for the unpolished welded coupons almost doubled in
the presence of adhered microorganisms, reaching 0.2610 ± 0.0475 μA cm-2. This fact was also corroborated by the pitting analysis, which means that the biofilm layer may not
U
be considered protective.
N
Conclusions
A
This study contributes new knowledge about the biocorrosion of welded regions of
M
metallic structures. It is highlighted that weld beads with filler metal favor an intense development of biofilms than those on nonwelded areas, not because of microstructural
ED
changes in the heat affected zone (HAZ) but greatly associated with the surface roughness. Moreover, the occurrence and depth of pits at the HAZ of unpolished welded
PT
coupons were greater than those seen on the polished welded coupons, even in the absence of microorganisms (sterile seawater). Effectively, to prevent MIC our research encourages the employment of welding without filler metal (autogenous techniques) or
CC E
polishing rough weld beads in structures exposed to environments where sulfate-reducing bacteria and iron-oxidizing bacteria are found.
A
Acknowledgments The authors would like to acknowledge the support received from SENAI-Solda
and the Programa de Recursos Humanos da Petrobras - PRH13. The authors declare no conflict of interest.
References
[1] Garret TR, Bhakoo M, Zhang Z. Bacterial adhesion and biofilms on surfaces. Prog Nat Sci. 2008,18:1049-1056. doi.org/10.1016/j.pnsc.2008.04.001 [2] Wang H, Sodagari M, Chen Y, He H, Newby BZ, Ju LK. Initial bacterial attachment in slow flowing systems: Effects of cell and substrate surface properties. Colloids Surf. 2011, 87:415-422. doi.org/10.1016/j.colsurfb.2011.05.053
IP T
[3] Feng G, Cheng Y, Wang SY, Borca-Tasciuc DA, Worobo RW, Moraru CI. Bacterial attachment and biofilm formation on surfaces are reduced by small-diameter
nanoscale pores: how small is small enough? Biofilms and Microbiomes. 2015,1:1-
SC R
9.
[4] Krishman M, Dahms HU, Seeni P, Gopalan S, Sivanandham V, Hyoung KJ, James RA. Multi metal assessment on biofilm formation in offshore environment. Mater Sci Eng C. 2017,73:743-755. doi.org/10.1016/j.msec.2016.12.062
U
[5] An D, Dong X, An A, Park HS, Strous M, Voordouw G. Metagenomic analysis
injected
with
bisulfite.
doi.org/10.3389/fmicb.2016.00028
Front
Microbiol.
2016,7-28.
A
pipelines
N
indicates Epsilonproteobacteria as a potential cause of microbial corrosion in
M
[6] Huang H, Yu Q, Ren H, Geng J, Xu K, Zhang Y, Ding L. Towards physicochemical and biological effects on detachment and activity recovery of aging biofilm by
ED
enzyme and surfactant treatments. Bioresour Technol. 2018,247:319-326. doi.org/10.1016/j.biortech.2017.09.082
PT
[7] Wang LW, Liu ZY, Cui ZY, Du CW, Wang XH, Li XG. In situ corrosion characterization of simulated weld heat affected zone on API X80 pipeline steel. Corr
CC E
Sci. 2014,85:401–410. doi.org/10.1016/j.corsci.2014.04.053 [8] Skovhus TL, Eckert RB, Rodrigues E. Management and control of microbiologically induced corrosion (MIC) in the oil and gas industry – Overview and a North See case study. J Biotechnol. 2017,256:31-45. doi.org/10.1016/j.jbiotec.2017.07.003
A
[9] Liu H, Cheng F. Mechanism of microbiologically induced corrosion of X52 pipeline steel in a wet soil containing sulfate-reduced bacteria. Electrochim Acta. 2017,253:368-378. doi.org/10.1016/j.electacta.2017.09.089 [10] Xu D, Li Y, Gu T. Mechanistic modeling of biocorrosion caused by biofilms of sulfate reducing bacteria and acid producing bacteria. Bioelectrochemistry. 2016,110:52-58. doi.org/10.1016/j.bioelechem.2016.03.003
[11] Koch GH, Brongers MPH, Thompson NG, Virmani YP, Payer JH (Eds). Corrosion Cost and Preventive Strategies in the United States. National Technical Reports Library (2001). [12] United States Department of Energy: The Mitigation and Detection of Microbial Corrosion (1999). [13] Flemming HC (Eds), Economical and Technical Overview, in Microbially Influenced Corrosion of Materials, Springer-Verlag, Heidelberg, Germany, 1996.
IP T
[14] API Specification 20A. Carbon steel, alloy steel, stainless steel, and nickel base alloy castings for using in petroleum and natural gas industry, 2nd edition, 2017.
SC R
[15] Oliveira MC, Figueiredo RM, Acciari HA, Codaro EN. Corrosion behavior of API 5L X65 steel subject to plastic deformation. J Mater Res Technol. 2018. doi.org/10.1016/j.jmrt.2018.02.006
[16] Arora KS, Pandu SR, Shajan N, Pathak P, Shome M. Microstructure and impact
U
toughness of reheated coarse grain heat affected zones of API X65 and API X80 line
N
pipe steels. Int J Pres Ves Pip. 2018,163:36-44. doi.org/10.1016/j.ijpvp.2018.04.004 [17] Farelas F, Choi YS, Nesic S. Corrosion behavior of API 5L X65 carbon steel under
A
supercritical and liquid CO2 phases in the presence of H2O and SO2. Corrosion.
M
2013,69:243-250. doi.org/10.5006/0739
[18] Shabani H, Goudarzi N, Shabani M. Failure analysis of a natural gas pipeline. Eng
ED
Fail Anal. 2018,84:167-184. doi.org/10.1016/j.engfailanal.2017.11.003 [19] Natividad C, García R, López VH, Contreras A, Salazar M. Metallurgical
PT
characterization of API X65 steel joint welded by MIG welding process with axial magnetic field. Mater Res. 2017. doi.org/10.1590/1980-5373-mr-2016-0182 [20] Wang LW, Liu ZY, Cui ZY, Du CW, Wang XH, Li XG. In situ corrosion
CC E
characterization of simulated weld heat affected zone on API X80 pipeline steel. Corr Sci. 2014,85:401–410. doi.org/10.1016/j.corsci.2014.04.053
[21] Geng H, Xia Z, Zhang X, Li G, Cui J. Microstructure and mechanical properties of
A
the welded AA5182/HC340LA joints by magnetic pulse welding. Mater Charact. 2018,138:229-237. doi.org/10.1016/j.matchar.2018.02.018
[22] Li G, Lu X, Zhu X, Huang J, Liu L, Wu Y. The interface microstructure, mechanical properties and corrosion resistance of dissimilar joints during multipass laser welding for
nuclear
power
plants.
Opt
doi.org/10.1016/j.optlastec.2017.12.002
Laser
Technol.
2018,101:479-490.
[23] Borenstein SW. Microbiologically influenced corrosion failures of austenitic stainless-steel welds. Mater Perform. 1988,27:62–66. [24] Ramkumar KD, Dagur AH, Kartha AA, Subodh MA, Vishnu C, Arun D, Kumar MGV, Abraham WS, Chatterjee A, Abraham J, Abraham J. Microstructure, mechanical properties and biocorrosion behavior of dissimilar welds of AISI 904L and
UNS
S32750.
J
Manuf
Process.
2017,30:27-40.
doi.org/10.1016/j.jmapro.2017.09.001
Today. 2018,5:7476-7485. doi.org/10.1016/j.matpr.2017.11.419
IP T
[25] Beeharry P, Surnam BYR. Atmospheric corrosion of welded mild steel. Mater
SC R
[26] Toppo A, Pujar MG, Sreevidya N, Philip J. Pitting and stress corrosion cracking
studies on AISI type 316N stainless steel weldments. Def Technol. 2018,14:226-237. doi.org/10.1016/j.dt.2018.03.004
[27] Ghosh S, Prasanna VL, Sowjanya B, Srivani, P, Alagaraja M, Banji D. Inductively
U
coupled plasma – optical emission spectroscopy: a review. Asian J Pharm Ana.
N
2013,3:24-33.
[28] De França FP, Lutterbach MT. Variation in sessile microflora during biofilm
A
formation on AISI-304 stainless steel coupons. J Ind Microbiol. 1996,17:6-10.
M
doi.org/10.1590/S0104-66321997000100007
ED
[29] Araújo LCA., Reznik LY, Lutterbach MTS, Carvalho LJ, Servulo EFC (Eds.). Biocorrosion of AISI 1020 carbon steel protected with the base coat of niobium
PT
oxide. Nace International Conference, Orlando, 2013. [30] Liduino VS, Lutterbach MTS, Ferreira AA, Ribeiro JW, Sérvulo EFC (Eds.). Biofouling and biocorrosion in carbon steel welds. The European Corrosion
CC E
Congress, Graz, 2015.
[31] Liduino VS, Lutterbach MTS, Sérvulo EFC. Corrosion behavior of carbon steel API 5L X65 exposed to seawater. Int J Eng Tech Res. 2017,7:70-74.
A
[32] American Public Health Association (APHA). Standard methods for the examination of water and wastewater, 22nd edition, Washington, 2012.
[33] Harrison AP. Microbial succession and mineral leaching in an artificial coal spoil. Appl Environ Microbiol. 1978,36:861-869. [34] ASTM G1-03, Standard Practice for Preparing, Cleaning and Evaluating Corrosion Test Specimens (2011).
[35] ASTM G46-94, Standard Guide for Examination and Evaluation of Pitting Corrosion (2005). [36] Bitharas I, McPherson NA, McGhie W, Roy D, Moore AJ. Visualization and optimization of shielding gas coverage during gas metal arc welding. J Mater Process Thech. 2018,255:451-462. doi.org/10.1007/BF03321146 [37] Zakowski Z, Narozny M, Szocinski M, Darowicki K. Influence of water salinity on corrosion risk – the case of the southern Baltic Sea Cost. Environ Monit Assess.
IP T
2014,186:4871-4879. doi.org/10.1007/s10661-014-3744-3
[38] Miranda E, Bethencourt M, Botana JF, Cano MJ, Amaya JMS, Corzo A, Lomas JG,
SC R
Fardeau LM, Ollivier L. Biocorrosion of carbon steel alloys by a hydrogenotrophic
sulfate-reducing bacterium Desulfovibrio capillatus isolated from a Mexican oil field separator. Corr Sci. 2006,48:2417-2431. doi.org/10.1016/j.corsci.2005.09.005 [39] Videla H, Herrera LKJ. Microbiologically influenced corrosion: looking to the
U
future. Int Microbiol. 2005,8:169-180.
N
[40] Xu J, Sun C, Yan M, Wang F. Effects of sulfate reducing bacteria on corrosion of carbon steel Q235 in soil-extract solution. Int J Electrochem Sci. 2012,7:11281-
A
11296.
M
[41] Guan F, Zhai X, Duan J, Zhan M, Hou B. Influence of sulfate reducing bacteria on the corrosion behavior of high strength steel EQ70 under cathodic polarization. Plos
ED
One. 2016,11: e0162315. doi.org/10.1371/journal.pone.0162315 [42] Oliveira EDS, Pereira RFC, Melo IR, Lima MAG, Urtiga-Filho SL. Corrosion
PT
behavior of API 5L X80 steel in the produced water of onshore oil recovery facilities. 2017,20. doi.org/10.1590/1980-5373-mr-2016-0954 [43] Li Q, Wang J, Xing X, Hu W. Corrosion behavior of X65 steel in seawater containing reducing
CC E
sulfate
bacteria
under
aerobic
conditions.
Bioelectrochemistry.2018,122:40-50. doi.org/10.1016/j.bioelechem.2018.03.003
[44] Jia R, Tan JL, Jin P, Blackwood DJ, Xu D, Gu T. Effects of biogenic H 2S on the
A
microbiologically influenced corrosion of C1018 carbon steel by sulfate reducing Desulfovibrio
vulgaris
biofilm.
Corros
Sci.
2018,130:1–11.
doi.org/10.1016/j.corsci.2017.10.023 [45] Zeraik AE, Nitschke M. Influence of growth media and temperature on bacteria adhesion
to
polystyrene
surfaces.
Braz
doi.org/10.1590/S1516-89132012000400012
Arch
Biol
Technol.
2012.
[46] Bautista BET, Wikiel AJ, Datsenko I, Vera M, Sand W, Seyeux A, Zanna S, Frateur I, Marcus P. Influence of extracellular polymeric substances (EPS) from Pseudomonas NCIMB 2021 on the corrosion behaviour of 70Cu–30Ni alloy in seawater. J
Electroanal
Chem
Interfac Electrochem.
2015,737:184-197.
doi.org/10.1016/j.jelechem.2014.09.024 [47] Abdolahi A, Hamza E, Ibrahim Z, Hashim S. Microbially influenced corrosion of steels
by
Pseudomonas
aeruginosa.
Corros
Rev.
IP T
doi.org/10.1515/corrrev-2013-0047
2014,32:129-141.
[48] Brioukhanov AL, Netrusov AI. Aerotolerance of strictly anaerobic microorganisms
2007,43:567-582.
SC R
and factors of defense against oxidative stress: a review. Appl Biochem Microbial.
[49] Abdoli L, Suo X, Li H. Distinctive colonization of Bacillus sp. bacteria and the influence of the bacterial biofilm on electrochemical behaviors of aluminum Colloids
Surf
B.
U
coatings.
N
doi.org/10.1016/j.colsurfb.2016.05.075
2016,145:688-694.
[50] Beimeng QI, Chongwei C, Yixing Y. Effects of iron bacteria on cast iron pipe
M
2015,10:545-558.
A
corrosion and water quality in water distribution systems. Int J Electrochem Sci.
[51] Little BJ, Gerke TL, Lee JS. Mini-review: the morphology, mineralogy and
ED
microbiology of accumulated iron corrosion products. Biofoul. 2014,30:941-948. doi.org/10.1080/08927014.2014.951039
PT
[52] Javed MA, Stoddart PR, Wade SA. Corrosion of carbon steel by sulphate reducing bacteria: Initial attachment and the role of ferrous ions. Corros Sci. 2015,93:48-57. doi.org/10.1016/j.corsci.2015.01.006
CC E
[53] Enning E, Garrelfs J. Corrosion of iron by sulfate-reducing bacteria: new views of an
old
problem.
Appl
Environ
Microbiol.
2014,80:1226-1236.
doi.org/10.1128/AEM.02848-13
A
[54] Castaneda H, Benetton XD. SRB-biofilm influence in active corrosion sites formed at the steel-electrolyte interface when exposed to artificial seawater conditions. Corros Sci. 2008,50:1169-1183. doi.org/10.1016/j.corsci.2007.11.032 [55] Gentil V (Eds). Corrosão, Livros Técnicos e Científicos Editora S.A., 6th edition, Rio de Janeiro, 2011.
[56] Javaherdashti R. Impact of sulphate-reducing bacteria on the performance of engineering
materials.
Appl
Microbiol
Biotechnol.
2011,91:1507-1517.
doi.org/10.1007/s00253-011-3455-4 [57] Chaves IA, Melchers RE. Pitting corrosion in pipeline steel weld zones. Corros Sci.
A
CC E
PT
ED
M
A
N
U
SC R
IP T
2011,53:4026-4032. doi.org/10.1016/j.corsci.2011.08.005
FIGURE CAPTIONS
Figure 1. Illustration of the working coupons: weld bead generated by shielded metal arc welding (unpolished), polished weld bead (control for surface roughness) and nonwelded coupon (control for microstructure changes). The surface of the coupons is highlighted in 1.5x of magnitude.
IP T
Figure 2. Results of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of the corrosion products at 15 days of testing: polished coupons (A)
SC R
and unpolished coupons (B) immersed in fresh seawater and polished coupons (C) and unpolished coupons (D) immersed in sterile seawater.
Figure 3. Quantification of the different groups of bacteria investigated. The number of
U
cells adhered to all coupons was determined at 15 days of testing. Identical letters indicate
N
no significant differences according to the Tukey test (p > 0.05).
A
Figure 4. Localized corrosion on the surface of the coupons at 15 days of immersion in
M
seawater. Letter A indicates coupons immersed in sterile seawater (without microorganisms), and letter B indicates coupons immersed in fresh seawater (with
ED
microorganisms). The red circle indicates the region of pit investigation.
Figure 5. Corrosion rate of API X65 carbon steel calculated from the results of weight
PT
loss at 15 days of immersion in sterile seawater [▲] or fresh seawater [●]. Identical letters
CC E
indicate no significant differences according to the Tukey test (p > 0.05).
Figure 6. Open circuit potential of the welded coupons (polished and unpolished) and
A
nonwelded coupons immersed in sterile seawater [▲] and fresh seawater [●].
FIGURES
Figure 1)
IP T
NONWELDED
A
CC E
PT
ED
M
A
N
U
SC R
UNPOLISHED POLISHED WELD BEAD WELD BEAD
Figure 2) cps/eV
A
Wt % Au = 5.8 Fe = 47.0 C = 7.8 O = 36.7 S = 2.7
7
6
5
Au Au S O SC O Fe C Fe
4
AuAuSS
Fe Fe
Au
3
IP T
2
1
0 0
2
4
6
cps/eV 5
4
O Au Au S SC OFe Fe C
Au
Au S S
SiSi
U
3
Wt % Au = 8.3 Fe = 53.3 C = 8.6 O = 25.7 S = 3.5 Si = 0.6
SC R
B
10
Fe
Fe
Au
N
2
8
keV
A
1
0
2
4
M
0
ED
C
6
keV
8
10
Wt % Au = 5.0 Fe = 55.1 O = 39.9 O Fe
Au
Fe
CC E
PT
Au
A
D
cps/eV 2.5
cps/eV 2.5
2.0
2.0
Mn 1.5 Au O C Fe
1.5
1.0
1.0
0.5
0.5
Mn O Fe
Mn Au O Au C Fe
Au
Au Au
Mn
Wt % Au = 7.2 Fe = 71.7 O = 20.7 Mn = 0.4 Fe
Mn Mn
Fe
Fe
Au
Au
0.0
0.0 0
0 2
42
6
4
keV
8
6
10 keV
8
12
10
Figure 3)
1E+13
c d c
c,d
1E+09
1E+07
c a
b
1E+05
1E+03
a
a
b
b
a
1E+01
Nonwelded
Unpolished weld bead
U
Planktonic Final time
A
CC E
PT
ED
M
A
N
Planktonic Initial time
AHB
c
c
IP T
b
SC R
Cell number (MPN cm-2)
1E+11
Polished weld bead
FeB SRB
Figure 4)
IP T
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20
B
SC R
NONWELDED
A
U N M
A A
PT
ED
B
A
CC E
UNPOLISHED WELD BEAD
POLISHED WELD BEAD
A
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20
5
0 -5
-10 -15 -20
-25 -30
5 0 -5
-10 -15 -20 -25 -30
B
10 0 -5
-10 -15 -20 -30 -40
Figure 5) d
0,16 0.16
c
b
b
IP T
b
0,08 0.08
a
0,04 0.04
SC R
Corrosion rate (mm y-1)
0.12 0,12
00
Polished Polished Unpolished Unpolished weld bead [▲] weld bead [●] weld bead [▲] weld bead [●]
A
N
U
Nonwelded [▲] Nonwelded [●]
M
Figure 6)
ED
-730
PT
-760
-770 -780
Nonwelded [▲] Polished weld bead [▲] Unpolished weld bead [▲] Nonwelded [●] Polished weld bead [●] Unpolished weld bead [●]
CC E
-750
A
Potential (mV vs. SCE)
-740
-790
0
24
96
168
Time (h)
264
360
Table Table 1. Chemical composition of API X65 steel and E7018 filler metal (weight %) C
Mn
Si
P
API X65
0.1
1.4
0.7
E7018
0.07
0.1
0.61 0.02
S
0.45 0.002 0.02
Ni
Cr
Nb
Mo
Cu
Fe
0.3
0.05 0.04 0.01 0.1 0.06 0.06 0.01
Bal.
0.02
0.1
Bal.
-
0.01
Al
-
V
0.05
Mg
-
-
Value
Salinity
32.5 ± 0.02 g L-1
Conductivity
56.8 ± 0.05 mS cm
Total sulfide
8.5 ± 0.4 µg L-1
pH
7.6 ± 0.2
Temperature
21.8 ± 0.01°C
Dissolved oxygen
3.7 ± 0.3 mg L-1
Turbidity
CC E
PT
ED
M
Total suspended solids
A
11.8 ± 2.7 mg L-1 1.21 ± 0.1 NTU
A
Biochemical oxygen demand
N
U
SC R
Parameter
IP T
Table 2. Main chemical and physicochemical parameters of seawater samples
380 ± 52 mg L-1