In the present context of oil price down turn and enhanced competitiveness, cost saving becomes more important than ever. As part of cost reduction solutions in offshore projects, it may be envisaged to leave field joints bare on subsea pipelines instead of applying a field anticorrosion coating after welding of the joints on board the laying vessels. This approach would need to be applied to specific cases, where it would lead to reduction of cycle time and consequently laying rate improvement during offshore installation campaigns when field joint coating activities are on the critical path, like with pipeline J-laying method. Although cathodic protection is an efficient, reliable and field proven method for seawater corrosion prevention on steel exposed areas of subsea coated pipelines, a quantitative assessment of the long term behavior of the pipeline coating at the transition zone with the bare field joint is recommended in order to support such a radical change in the pipeline external corrosion protection philosophy. Therefore, a bespoke experimental setup was designed to simulate bare field joint configuration under cathodic protection over a long term exposure in seawater together with long term cathodic disbondment tests for comparative purpose. The bespoke experimental test was performed at full scale on 3LPE coated pipe section with a field joint area left bare and protected by galvanic anodes. The pipe was immersed in a vessel containing renewed seawater and half-buried in mud to reproduce actual pipelines exposure on seabed. It was heated also with an internal fluid at 65°C to simulate actual operating conditions. Long term cathodic disbondment tests were performed on 3LPE coated pipe samples with internal heating of the samples at 23°C and at 65°C. Reference samples without CP were also exposed to the same conditions. The two experimental works were conducted during 12 months. For each of the tests above, a visual assessment was performed at regular intervals together with a quantitative assessment of the disbonded area (removal and recording of disbonded coating area). With these tests, it was possible to characterize the influence, over the time (up to one year) of the temperature over the normalized cathodic disbondment test results. The effect of the cathodic protection was also evaluated. For the full scale test evaluation and characterization, comparison was made between the disbonded coating length in the mud and the seawater exposure conditions. Correlation between cathodic disbondment tests and full scale test was also drawn. In light of the results obtained so far in this study, these tests results conclude positively that the bare field joint alternative concept for subsea pipelines is possible upon certain operating temperature limitation.

The use of titanium plate heat exchangers is widespread for Offshore and Coastal installations where seawater cooling is required. Several years ago difficulties to supply titanium Grade 1 for this application triggered the need for qualification of other alloys for this application. Applications using passive alloys are especially susceptible to crevice corrosion when exposed to hot seawater. Since titanium is the most corrosion resistant alloy in seawater only highly corrosion resistant alloys could be considered for its replacement in plate heat exchangers. In addition since they need to be shaped into plates by cold pressing only alloys with a high formability could be selected. This narrowed even further candidate alloys for plate heat exchangers. In this study nickel chromium molybdenum alloys and a highly alloyed stainless steel were tested between 30 and 70°C in natural seawater with up to 1 ppm free chlorine. Rather than using short term electrochemical testing that is often difficult to compare with service performance long term exposure tests (up to 18 months) of real plate heat exchangers were carried out. These tests are considered to be more representative of actual service conditions. The results of these tests and their significance are discussed and compared with previous reported work.

Subsea umbilicals are used for control and operation of subsea oil and gas production facilities. Typically an umbilical consists of steel tubes, electrical cables, fiber optic cables, weight or strength elements and fillers. Super duplex stainless steel tube material has been used for almost 20 years within the umbilical industry. However, a recent failure on two orbital welds of 25Cr super duplex of an umbilical installed in the South China Sea was reported. From these results some umbilical end users recommended the use of thermoplastic coating to avoid crevice corrosion on 25Cr super duplex stainless steel above 20°C. However, this limit is based on results obtained for super duplex stainless steel in aerated natural seawater and very little is known on the micro-environment formed by the confined seawater between metallic tubes and polymer matrix of an umbilical. This work reports corrosion potential and oxygen content measurements in the confined zone between the metallic tubes and the polymer matrix of an umbilical. These measurements were performed using micro-electrodes on a 2 meter long real umbilical at 30°C in heated natural seawater. From the measurements, it is shown that the oxygen content in the confined zone is rapidly consumed probably due to the passive current on the stainless steel tubes and then remains below 2 ppm over one year exposure period. From the open-circuit potential measurements performed in the confined zone, it is clear that the open circuit potential remained below -150 mV/AgCl. This translates an absence of electrochemical effect of the biofilm in the confined zone. Visual and metallographic examinations of the tubes after exposure confirmed the results obtained by the microelectrodes and clearly indicate that no corrosion initiation occurred on superduplex stainless steel (base metal and welds) under these experimental conditions. The results are discussed in view of the validity of corrosion tests performed under aerated conditions and the need of further developments of new testing procedures to represent the confined situation in the umbilical design.

In natural seawater, surfaces will be rapidly covered by microorganisms which form a thin film called biofilm. It is now generally admitted that biofilms may affect the electrochemical behavior of metals and alloys and thereby may accelerate the corrosion of the material. Biofilms formed in seawater around the World does not necessarily present the same aggressiveness in terms of corrosion risk, and recently some high alloy stainless steel corrosion failures were attributed to the particular aggressiveness of biofilms which form in tropical seawaters. In deep sea, the biofilm activity as well as the corrosion risk induced by these phenomena has to be assessed. The objective of the present study was to develop an autonomous sensor able to characterize seawater biofilms through their electrochemical effects on stainless steel surface. The sensor is able to in-situ detect the potential ennoblement and to quantify the cathodic reduction efficiency of biofilmed stainless steel, which is a major parameter to quantify the risk of corrosion propagation on these alloys, as well as the bacterial presence and activity. This sensor will be able to be deployed down to 3000 m depth for long term measurements.

In natural seawater, many parameters might influence the cathodic protection current demand such as potential, temperature, dissolved oxygen content, biofilm and fouling activity, and calcareous deposit formation. The actual deepsea environment cannot be easily reproduced at laboratory scale. In this study, the influence of the depth on the cathodic protection criteria of carbon steel and stainless steel was investigated in intermediary (1020 m depth) and deep water (2020 m) at the same location. For this purpose, at set of corrosion and environmental sensors, as well as metallic coupons, were exposed during 11 months in Azores in the Atlantic Ocean. On stainless steel, a strong characteristic cathodic depolarization due to biofilm activity was observed in deep water and not in intermediary water. The biological-induced cathodic activity appears thus to be dependent on the environment, even in open seawater. In presence of an electroactive biofilm high and relatively stable current densities were measured. Under such conditions, an important structure depolarization appears, affecting thus the CP design and efficiency. For carbon steel, the cathodic protection data collected in-situ show that the initial and mean (after 11 months) current densities are higher than those recommended by the DNVGL RP B401 standard. Even if mean current densities are expected to continue to decrease slowly with further exposure time, so probably tending to the standard recommendations, the DNVGL RP B401 standard might not be conservative in terms of current densities criteria for these environments. 

In the context of the high-level radioactive waste disposal CIGEO, the corrosion rate due to microbially influenced corrosion (MIC) has to be evaluated. In France, it is envisaged to dispose of high- and intermediate-level long-lived radioactive waste at a depth of 500 m in a deep geological disposal, drilled in the Callovo-Oxfordian claystone (Cox) formation. To do so, a carbon steel casing will be inserted inside disposal cells, which are horizontal tunnels drilled in the Cox. A specific cement grout will be injected between the carbon steel casing and the claystone. A study was conducted to evaluate the possibility of MIC on carbon steel in the foreseeable high radioactive waste disposal. The corrosiveness of various environments was investigated at 50°C and 80°C with or without microorganisms enriched from samples of Andra's underground research laboratory. The monitoring of corrosion during the experiments was ensured using gravimetric method and real-time corrosion monitoring using sensors based on the measurements of the electrical resistance. The corrosion data were completed with microbiological analyses including cultural and molecular characterizations.

In the process industry, seawater is commonly used when available to cool process fluids. However chlorination of the seawater is widely used to limit any microbial activity; that makes the environment quite aggressive. Chlorination oxidizes and increases the corrosion potential to approximately +600mVSCE for stainless steels and leads to higher susceptibility to localized corrosion. Super duplex stainless steels, PRENw >40, in seawater-cooled heat exchangers can be used at limited temperatures otherwise Ti Gr.2 shall be used for equipment integrity over the service life. Recent results with combination of hyper duplex UNS S32707 tubes and super austenite UNS S31266 plate, with PRENw of 49 resp. 53, for seawater-cooled heat exchangers are presented. Testing is performed in seawater cooled scale model heat exchangers with 0.5 ppm residual chlorine during a period of 18 months. Thus, it shows a corrosion resistance of the materials at a heat flux representative to a tube skin temperature up to 95°C inside in the seawater. These new results also show a good correlation with the field service and help to challenge the use of Titanium in seawater-cooled heat exchangers.

The effects of cathodic polarisation switch-off on the passivation of AISI 304L stainless steel in air and its crevice corrosion susceptibility in 3.5 wt.% NaCl aqueous electrolyte were investigated. Scanning Kelvin probe (SKP) data showed that the oxide film is significantly destabilised and the rate of steel passivation in air is slowed down. Thermal desorption analysis (TDA) highlighted that hydrogen absorption is proportional to the applied cathodic current density. A special crevice corrosion set-up was designed to realise simultaneous reproducible monitoring of potential and galvanic current to study the impact of prior cathodic polarisation on crevice corrosion onset. © 2021 by the authors.

Many oil and gas offshore facilities use heat exchangers cooled with seawater. Titanium is widely used for seawater plate heat exchangers, but its availability for this market depends on other large demand from other markets like the aerospace industry. Thus, it is vital to find alternative materials in seawater heat exchangers' applications. High-alloyed stainless steels and nickel-base alloys are used for different marine and offshore applications, but have not been widely used for seawater plate heat exchangers. Most of the corrosion data available in the literature on these alloys have been obtained from laboratory experiments. Thus, there is a need to determine the corrosion resistance of these alloys under real service conditions. This is important as heat transfer, flowing and geometrical conditions of plate heat exchangers may be difficult to simulate based upon simple laboratory exposure. Therefore, a test program has been developed to test selected materials in actual plate heat exchanger conditions using natural sea water during one year and more. These materials are nickel-based alloys UNS N06625, N10276, N06059, N06200 and N06686, along with a special steel UNS N08031. The study was performed in chlorinated natural sea water from 30°C up to 60°C. The result data from this test program are presented and discussed in this paper.

The galvanic corrosion of carbon steel (UNS G10150) and of copper-nickel 90/10 (UNS C70600) coupled to superduplex stainless steel (UNS S32750) in seawater was investigated from 6°C to 70°C, with different cathode to anode ratios. The effect of chlorination on galvanic corrosion rates was also studied. Continuous monitoring of the open-circuit potentials and galvanic currents were performed to measure the exact evolution and the contribution of the galvanic corrosion on the total corrosion. Results showed that formation of natural biofilms and precipitation of calcareous deposits on surfaces had a very significant impact on the cathodic efficiency, which is directly correlated to the rate of galvanic corrosion. For all the tested configurations, chlorination led to a significant decrease of the measured galvanic currents due to the low cathodic efficiency of surfaces in chlorinated media (i. e. no biofilm). The long term exposure of specimens allowed to draw realistic pseudo-polarization curves which were used in a boundary element modeling software.

Seawater desalination infrastructures require a careful material selection with high corrosion resistance. The high seawater temperatures in warm regions, where many desalination plants are developed, must be clearly considered regarding the corrosion of materials. To comply with the operational characteristics of seawater reverse osmosis (SWRO) process (high pressure, high chloride content and dissolved oxygen content at saturation values), the conventional material selection was stainless steel with sufficient pitting resistant equivalent number. However, many cases of corrosion failures of stainless steel in SWRO desalination units have been reported. In most cases the cause of the failures was attributed to the use of not enough alloyed grades. However, high alloy stainless steels are also susceptible to crevice and pitting corrosion in seawater. The operational corrosion risk will highly depend on the stainless steel composition, on the metallurgy (i.e. cast or wrought), on the service conditions, and on the geometrical configuration of the confined zones in contact with seawater. The present paper reviews the corrosion performance of metallic materials used for SWRO desalination plants. It focuses on the corrosion behaviour of several stainless steel grades. Recent corrosion failures of stainless steel pumps used in SWRO desalination plant in the Mediterranean Sea are also discussed.

Yamal LNG, one of the largest liquefied natural gas (LNG) projects in the world, processes natural gas from the giant onshore South Tambey gas and condensate field located on the Yamal Peninsula in the Arctic region of the Russian Federation. Yamal LNG will produce reserves of 4.6 billion bbl (731 billion L) of oil equivalent. The project includes an integrated gas treatment and liquefaction facility with three liquefaction trains (each with a capacity of 5.5 million tons per year), storage tanks, a port with 15 ARC 7 ice-class LNG carriers with a capacity of 170,000 m(3) each, and airport infrastructure.

Nickel-Aluminum Bronze (NAB) and Copper-Nickel alloys (CuNi) are commonly used in seawater environments due to their strength combined with a good corrosion resistance and a high resistance to biofouling. However, localized corrosion failures have been reported and are often attributed to abnormal service conditions. The effect of several service condition parameters on the localized corrosion of NAB (UNS C63000, CuAl10Ni5Fe4) and CuNi alloys 90/10 (UNS C70600) and 70/30 (UNS C71500) have been investigated in natural seawater. The results are compared with that of Aluminum-brass (UNS C68700). It includes flow conditions (flowing, quiescent and stagnant), chlorination, sulphide pollution, and crevice geometries. Exposures in both indoor (laboratory) and outdoor tanks (conditions promoting macro fouling) have been tested in temperate and in tropical seawaters. The corrosion stability of the protective oxide layer of the tested copper-based alloys was mainly affected by sulphide pollution in aerated seawater (general corrosion). Under the tested conditions, localized corrosion under-biodeposit clearly appeared as the critical failure for the tested alloys. The conditions for which biodeposit appeared critical for copper-nickel alloys was investigated. 

To comply with the demanding operational conditions of seawater reverse osmosis (SWRO) process, both in terms of corrosion resistance and mechanical properties, the conventional metallic material selection was often stainless steel for seawater and brines handling units (e.g. pumps, valves and piping). However, many cases of corrosion failures of stainless steel in SWRO desalination units have been reported often attributed to un-adapted stainless steel grade selection and/or to the particular aggressive conditions in "warm" regions where many recent desalination plants are built (high ambient temperature, severe biofouling, etc.). The operational corrosion risk will actually highly depend on the material composition, on the metallurgy (i.e. cast or wrought), on the service conditions and on the geometrical configuration of the concerned units in contact with seawater. Considering all these parameters, a proper material selection should avoid corrosion issue. For existing corrosion, cathodic protection (CP) may be an efficient solution to stop or to control the propagation of the degradation. However, the CP for materials used in SWRO desalination plants and in its specific operational conditions (i.e. high pressure, velocity and confinements) is not well documented; as a result, an adapted CP design is not always possible from existing data. The present paper reviews some corrosion cases of stainless steel and copper-based alloys in SWRO desalination plants. Solutions to manage existing corrosion of metallic materials in SWRO plants are discussed and focus is done on CP of stainless steel elements. Some results of an ongoing investigation about the CP for the specific operational conditions of SWRO desalination plant are presented and discussed.

The exploration and exploitation of deep seawater present promising prospects for many industries. Hence, the use of reliable materials resistant to corrosion in deep seawater conditions is required. In natural seawater, many parameters can influence the kinetics of corrosion such as: temperature, oxygen content, biofilm and fouling activity, flow rates and hydrostatic pressure. For passive materials such as Cr Ni Mo stainless steels and nickel-based alloys, the specificity of the above parameters in deep sea environment might have an impact on both initiation and propagation phases of localized corrosion (e.g. pitting and crevice corrosion), and no or limited field data obtained in deep sea can be found in the literature. Currently, there are still many questions on the corrosion behavior of metallic materials in deep seawater since the results obtained in laboratory or from near-surface seawater cannot be extrapolated to deep seawater environments, especially in terms of bacterial activity which can significantly impact the localized corrosion resistance of passive alloys (cf. biofilm-induced ennoblement). In this study, 13-Cr Ferritic, Austenitic, Lean Duplex, Duplex, Super Duplex, Super Austenitic, Hyper Duplex Stainless Steels and Nickel based alloys were exposed during 11 months at 1020 and 2020 m water depth in the Atlantic Ocean to evaluate their corrosion behavior. Structural carbon steel S355 was also exposed under similar conditions. Polyvinylidene difluoride (PVDF) crevice gaskets according to ISO18070:2015 were used to assess the crevice corrosion at two different gasket pressures, namely 3 and 20 N/mm2. Potential monitoring was performed in-situ (at both 1020 m and 2020 m) in order to characterize the formation of electroactive biofilms at the surface of passive alloys in these environments. At each exposure depth, the environment was characterized using environmental sensors, e.g. temperature, flow velocity, dissolved oxygen, salinity. The obtained results allowed i) ranking the passive material in terms of resistance to pitting and crevice corrosion in deep water at 4°C, ii) comparing biofilm electroactivity and corrosion rates at 1020 and 2020 m depth.

Abstract: Stainless steel is widely used in seawater reverse osmosis units (SWRO) for both good mechanical and corrosion resistance properties. However, many corrosion failures of stainless steel in SWRO desalination units have been reported. These failures may often be attributed to un-adapted stainless steel grade selection and/or to the particular aggressive seawater conditions in “warm” regions (high ambient temperature, severe biofouling, etc.). Cathodic protection (CP) is a well-known efficient system to prevent corrosion of metallic materials in seawater. It is successfully used in the oil and gas industry to protect carbon steel structures exposed in open-sea. However, the specific service conditions of SWRO units may seriously affect the efficiency of such anti-corrosion system (high flow rates, large stainless steel surfaces affected by biofouling, confinement limiting protective cathodic current flow, etc.). Hence, CP in SWRO units should be considered with special care and modeling appears as useful tool to assess an appropriate CP design. However, there is a clear lack of CP data that could be transposed to SWRO service conditions (i.e. stainless steel, effect of biofouling, high flow rate, etc.). From this background a Join Industry Program was initiated including laboratory exposures, field measurements in a full scale SWRO desalination plant, and modeling work using PROCOR software. The present paper reviews the main parameters affecting corrosion of stainless steel alloys in seawater reverse osmosis units. CP on specific stainless steel devices was investigated in order to assess its actual efficiency for SWRO units. Severe environmental conditions were intentionally used to promote corrosion on the tested stainless steel products in order to evaluate the efficiency of CP. The study includes a modeling work aiming at predicting and designing adapted CP protection to modeled stainless steel units. An excellent correlation between modeling work and field measurements was found.

With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred. 

With lower alloying costs and higher mechanical properties, lean duplex stainless steels can be a good alternative to the more commonly used austenitic stainless steels. A study was initiated to define the limits of the use of lean duplex stainless steels for urban wastewater treatment (WWT) units. This paper gives and discusses the corrosion results in an aerated wet atmosphere containing H2S at different levels. Exposures were performed both at laboratory scale and in the field WWT plant for 1 year. A specific probe was also designed to study the corrosion process below water condensate film contaminated with H2S. Under such conditions, the properties of stainless steel were strongly modified with an enhanced risk of localized corrosion. The results obtained on lean duplex materials (UNS S32101, S32202, and S32304) are compared with austenitic UNS S30403 and UNS S31603 and with the more standard duplexes UNS S82441 and UNS S32205. The results show that lean duplexes can be used in aerated wet atmospheres in case of moderate contamination of H2S (<10 ppm) and chloride (<200 ppm). For higher contaminations (e.g., H2S around 100 ppm/chloride around 1000 ppm) the duplex S32205 should be preferred.

The corrosion risk for stainless steel components is not the same in all seawaters, with more failures generally reported in tropical seas. In this study, the influence of biofilm on electrochemical behavior and corrosion resistance of passive films of high-grade alloys was studied in different seawaters, including temperate seawater (France-Brest, North Atlantic Ocean), tropical seawater (Malaysia-Kelatan, Meridional China Sea), and intermediate conditions in terms of temperature (Brazil-Arraial do Cabo, South Atlantic Ocean). The stabilized open-circuit potentials and the polarization behavior of high-grade stainless steels were measured as a function of temperature in all of the tested field marine stations, providing quantified data and direct comparison of the biofilm-enhanced corrosion risks. Significant differences were measured in tropical and in temperate seawaters in heated conditions. Above 37°C, the biofilm activity was much more pronounced in tropical seawater compared to Atlantic Ocean sites, leading to much higher localized corrosion risk. Crevice corrosion of eight high-grades passive alloys was also studied with the use of crevice formers specifically developed for tube geometries. Duplex UNS S32205, superduplex UNS S32750, hyperduplex UNS S33207 and S32707, and 6Mo stainless steels UNS S31266 have been evaluated together with Ni-based alloys UNS N06845 and N06625. In the more severe conditions, the high-grade alloys UNS S32707 and the 6%Mo UNS S31266, both with pitting resistant equivalent number (PREN) around 50, showed better performance than commonly used superduplex UNS S32750 and UNS S39274 (PREN 40). The corrosion results are discussed regarding the monitored biofilm-induced depolarization measured in the different test conditions.

Chlorination is widely used in seawater systems to avoid fouling and associated microbial-induced corrosion. Free chlorine is a strong oxidizing agent that prevents biofilm formation on immersed surfaces when used above a certain content. However, the presence of residual chlorine associated with the relatively high chloride content in seawater significantly increases the risk of localized corrosion for most stainless steels. In the present study, a module initially developed to quantify the formation of electroactive biofilms on stainless steels has been used to assess the corrosiveness of chlorinated seawater. Both the electrochemical potential and the cathodic current were measured on super-duplex stainless steel as a function of residual chlorine levels and seawater temperatures. In parallel, long-term localized corrosion tests have been performed in simulated environments to assess the environmental limits for the safe use of high-grade stainless steels in chlorinated seawater. It includes crevice corrosion exposure tests using adapted ISO 18070:2015 crevice formers and internal tube pitting corrosion exposure tests in model tube heat exchangers simulating heat flux from 35°C to 170°C. The synergetic effect of residual chlorine content and temperature on the risk of localized corrosion has been quantified. Corrosion resistance properties are correlated to the electrochemical monitoring data, and the environmental limits of selected base materials stainless steels have been established for duplex stainless steel UNS S32205, super-duplex stainless steel UNS S32750, hyper-duplex stainless steels UNS S32707 and UNS S33207, and the high-grade austenitic stainless steel UNS S31266.

The corrosion resistance of copper-nickel 90/10 and 70/30 tubes for heat exchangers was evaluated in 0.5 ppm-chlorinated seawater, under controlled service conditions in a bespoke test loop. The results were compared to Al-Brass tubes tested under the same conditions. Copper-Nickel 90/10 tubes were tested with two different geometries: internal smooth surface and internal finned surface (helix geometry). Internal pitting corrosion resistance was evaluated under simulated heat transfer conditions at two controlled skin temperatures from the internal and the external parts of the tubes for 6 months, at 50°C (Tskin-in)/35°C (Tseawater) and 70°C (Tskin-in)/35°C (Tseawater). For all the tested copper alloys, the uniform corrosion was very low and negligible. For both temperatures, CuNi 90/10 was globally more resistant to localized corrosion than CuNi70/30. The most corrosion resistant configuration was the CuNi 90/10 with the internal finned geometry. The best corrosion resistance compared to the smooth geometry might be attributed to different hydrodynamic conditions at the seawater/metal interface.

For most projects, cathodic protection (CP) design can be performed using CP standards or existing data from literature and field feed-back. It was not the case for the particular environment of the YAMAL gas carrier terminal project, planned in Sabetta (Siberia - Federation of Russia). This particular area is located between the Kara sea and a river mouth in Yamal peninsula (Artic region). It involves very different conditions in terms of salinity, temperature, liquid/ice phases, all depending on icing/deicing seasons and on the water depth. These very specific conditions can hardly be simulated at laboratory scale and required a specific corrosion and CP study with measurements on site. The global aim of this quantitative study was to collect field data to help at defining an adapted corrosion protection system for carbon steel immerged structure (e. g. berths), and to forecast the related corrosion risks. Regarding the extreme conditions of the site, the main challenge was to design adapted arrays containing corrosion and CP sensors (to be deployed on site), to get representative quantitative data. All systems have been qualified at laboratory scale before use on field site. The deployment was successful and allowed getting actual polarization curves, and local initial corrosion data. In parallel, the stability of zinc galvanic anodes has been evaluated in this resistive environment. For both corrosion and CP data, different results have been highlighted for surface and bottom waters, and for ice & liquid phases. Modelling can now be used to assess the efficiency and select the CP system (i. e. galvanic anode or impressed current)

Crevice corrosion is one of the main corrosion problems for metallic alloys used in reverse osmosis (RO) desalination plants. This type of corrosion depends on many factors, that is, alloy composition and/or metallurgy, seawater location, biofilm, temperature, service conditions and crevice geometry. Corrosivity of gulf seawater was compared with the heated Brest seawater (France) for different stainless steels and nickel-based alloy. Maintaining the same experimental conditions, similarity of crevice corrosion performance in both sites relied on the tested alloys. Both crevice corrosion initiation and propagation were evaluated and compared with previous studies. Duplex S32205 and nickel-based N06625 suffered from crevice corrosion contrary to the superaustenitic S31266. However, corrosion results of superduplex S32750 and superaustenitic S31254 were reported very randomly, confirming the “borderline” behavior of these grades in some seawater applications. The impact of the results on the RO plants materials selection is outlined. 

Some unit operations in wastewater treatment plants (WWTPs), such as settling tanks and pipes for aeration or sludge transfer, are composed of austenitic stainless steel (EN 1.4307 or EN 1.4404) instead of galvanised or painted carbon steel to reduce the maintenance costs. The sensitivity to pitting and crevice corrosion of austenitic grades in certain WWTP environments has also led to the use of duplex grades. The purpose of this study is to evaluate the maintenance of piping systems (WWTPs) and its effect on their life cycle environmental impacts and costs (LCC) for both austenitic and duplex stainless steel grades. The final objective is to aid grade selection for piping in a WWTP environment. The considered functional unit (FU) is a complete piping system. Conventional austenitic stainless steel grades (e.g., EN 1.4404) are studied alongside duplex ones (e.g., EN 1.4362 and EN 1.4462). The calculated environmental impacts are the Global Warming Potential (GWP) and Primary Energy Demand (PED). The production, manufacturing, transport, use including maintenance activities, and end-of-life (burdens and credits) phases are included in the life cycle assessment (LCA). The maintenance activities consist of the required replacements of stainless steel piping during the lifespan of the WWTP. Thus, the service lives of the pipes included in the considered WWTP environment are determined based on long-term corrosion prediction models (power law), which predict the evolution of pit or crevice depth as a function of time. The model parameters are estimated based on own experimental results, supplemented by the existing literature. The corrosion rates determine the number and frequency of replacements, i.e., define the different scenarios of maintenance. The LCA, LCC and corrosion prediction models are then combined into a user-friendly tool, which can be used in industry for an appropriate grade selection for pipes in a WWTP environment. The tool includes several degrees of freedom such as piping distribution, water pressure, chloride content, replacement criteria, etc. The results show that using duplex stainless steel grade EN 1.4462 leads to lower GWP and PED at the end of the WWTP's service life of 40 years. This is mainly due to multiple replacements of the system's parts in wastewater with high levels of chloride (>3000 ppm) if more conventional austenitic stainless steel alloys such as EN 1.4404 are used. Leaner duplex stainless steel grades were also included in this LCC assessment. The duplex grade EN 1.4062 showed the lowest total LCC, thanks to its leaner chemical composition (i.e., lower nickel content) combined with good localized corrosion resistance.

The corrosion of lean duplex stainless steel alloys is examined when applied as a construction material in advanced oxidation processes. Both electrochemical and immersion experiments have been carried out when subjecting wastewater to ozone or Fenton oxidation. The electrochemical experiments suggest that the presence of dissolved ozone at the levels tested does not result in an increased pitting susceptibility for none of the alloys included in the research. However, the application of Fenton reagents induces pitting corrosion to the studied lean duplex alloys. The immersion experiments highlight that crevice corrosion occurs during wastewater treatment with both ozone and Fenton reagents. 

In seawater handling systems, the available well tubing materials are Glass Reinforced Epoxy lined low alloy steel or Corrosion Resistant Alloy's (CRA) such as super duplex stainless steel. However, in treated seawater the corrosion risk can be controlled so that lower grade alloys can be considered. Recent efforts have focused attention on better dissolved oxygen controls which permits the investigation and possible use of more cost effective materials such as the duplex stainless steel UNS S82551. Full scale corrosion testing of tubes joined together with a proprietary premium threaded connection was performed in controlled seawater loops simulating service conditions at 30° C. The flow rate and dissolved oxygen were controlled at 5 m/s and <20ppb, respectively. Weekly dissolved oxygen excursions corresponding to 24h at 100ppb followed by 1 hour at 300ppb were included during the 5 months exposure. Corrosion results of UNS S82551 tubing were compared to UNS S31803 and UNS S39274. In parallel, laboratory exposures of coupons were performed in dissolved oxygen controlled cells with and without CREVCORR crevice formers, allowing the measurement of electrochemical potentials as function of dissolved oxygen content (e. g. biofilm ennoblement monitoring) and the related corrosion resistance. The results showed that dissolved oxygen content should be properly controlled below critical values to avoid crevice corrosion of the lesser alloyed duplex stainless steels. In the full scale loop test, UNS S82551 tubes did not exhibit crevice corrosion at threaded connection interfaces under the defined test conditions. 

The use of organic coatings in conjunction with cathodic protection (CP) for buried structures is the usual method for protecting steel against corrosion. When the organic coating loses its protective ability, regardless of the reason, the CP becomes the active protection, leading to a specific local environment. This environment can be characterized by high alkalinity, which can be detrimental for the coated structure, either by weakening the steel–coating interface or by the chemical aging of the coating. Thus, the coating must be compatible with CP and able to sustain aging under an alkaline environment. In this study, the susceptibility to alkaline aging and its consequences in regards to coating performance have been investigated for two commercial coatings used for buried structures—fusion bonded epoxy (FBE) and liquid epoxy (LE)—in free membrane and coated steel configurations. The results showed a clear impact of alkaline aging on the studied LE, leading to a significant reduction in coating resistance and ultimately, failure of the steel–coating interface, whereas the studied FBE remained stable. The presented results relate to a precise formulation of LE and FBE; however, the proposed chemical method appears to be relevant and shows the necessity of considering such specific aging results for coating specifications and improvements.

Anticorrosive coatings are widely used to protect steel against corrosion. Different standards exist to access the corrosion performance of anticorrosive paints. Among them, the so-called neutral salt spray test (NSST-ISO 9227) or cycling corrosion tests ISO 12944-6, ISO 12944-9, NACE TM0304, or NACE TM0404 can be named. It is well-known that some accelerated corrosion tests are not fully representative of the field exposure results. However, a lack in the literature exists correlating accelerated tests to field exposure, especially when long-term durations are considered. In this study, 11 different organic coatings have been investigated in terms of coating resistance to corrosion creep in two types of field exposure sites, namely a stationary site and an operating ship, and their performance was compared to two accelerated tests (ISO 12944-9 and modified ASTM D5894 standard). The results showed differences in the sites&rsquo; corrosivity and the coating systems&rsquo; performance as a function of the exposure sites. A lack of correlation exists between the ISO 12944-9 standard and the stationary site, due to the latter&rsquo;s high corrosivity, while, to the contrary, a satisfying correlation with the operating ship was demonstrated; whereas, the modified ASTM D5894 standard showed a satisfying correlation with both types of sites.

Crevice corrosion resistance is one of the main criteria for the selection of a given stainless steel grade for seawater applications. Crevice corrosion resistance can be evaluated using different techniques that are described in standards and in the literature. However, the proposed assemblies are often restricted to plate geometry specimens. Some crevice assemblies for tube geometry have been proposed and used during the last ten years, but they showed a large dispersion of the results due to the difficulty to control crevice geometries on curved surfaces. From this background, an optimized crevice assembly was proposed to allow a better control of the reproducibility of crevice corrosion tests on stainless steel tubes. Finite element modelling and laboratory testing have shown that the new proposed design provides a better control of gasket pressure and consequently a better reproducibility than previous existing assemblies. The proposed assembly can be adapted and used for fit-for-purpose testing (e. g. evaluation of different gasket materials, different gasket pressures, etc.). 

The open-circuit potential is one of the main driving forces of galvanic corrosion when two dissimilar metals are in electrical continuity in an electrolyte. From the existing literature, the galvanic series which provides averaged potential of metallic materials in seawater is generally restricted to ambient/ standard conditions or to a limited number of alloys. However, advanced materials have been developed in the last decade and the corrosion potential of any alloy immersed in seawater may be strongly affected by environmental factors. There is a lack of information on these purposes (e.g., effect of dissolved oxygen content, temperatures, chlorination at different levels, or recently developed alloys, etc.). In this work, the open-circuit potential of different stainless steel grades, as well as nickel-based and copper-based alloys, has been systematically measured in seawater under different experimental conditions. In particular, the effect of temperature (from 30°C to 70°C), oxygen content (from 10 ppb to saturation), and chlorination level (from 0 ppm to 0.5 ppm) have been studied. The work can also be used for material selection in terms of risk of bi-metallic corrosion when coupling two materials under these conditions. 

Microorganisms can increase the open-circuit potential of stainless steel immersed in seawater of several hundred millivolts in a phenomenon called ennoblement. It raises the chance of corrosion as the open-circuit potential may go over the pitting corrosion potential. Despite the large impact of the ennoblement, no unifying mechanisms have been described as responsible for the phenomenon. Here we show that the strict electrotroph bacterium "Candidatus Tenderia electrophaga" is detected as an ennoblement biomarker and is only present at temperatures at which we observe ennoblement. This bacterium was previously enriched in biocathode systems. Our results suggest that "Candidatus Tenderia electrophaga," and its previously described extracellular electron transfer metabolism coupled to oxygen reduction activity, could play a central role in modulating stainless steel open-circuit potential and consequently mediating ennoblement.

The installation of metallic coupons in the vicinity of buried pipes under cathodic protection (CP) allows theoretically to measure the potential and the current density through the simulated coating defect. Nevertheless, this type of monitored coupon does not provide direct information on the actual efficiency of the CP and corrosion rates that could be caused by a CP failure over time or not adapted CP design. According to the soil resistivity and the corrosion potential in absence of CP, a protection potential is generally targeted following the standard recommendations. However, the soil resistivity as well as the corrosion potential might depend on the seasonal fluctuations and the protection potential might vary as function of the considered standard. Moreover, all soils parameters cannot be considered in recommendations from standards and cathodic protection criteria can be sometimes debatable. In this study, very sensitive electrical resistance (ER) sensors, used for obtaining precise corrosion data in real-time, were adapted for soil applications. They were used in the selected soils and conditions to determine the off potential and current density corresponding to a corrosion rate of 10 µm/year, which corresponds to the maximal corrosion rate of buried structures considered as protected according the standard ISO 15589-1:2015. The adapted ER sensors appeared to be particularly suitable for determining the protection potential and CP criteria in a relatively short time. For the tested soils and conditions, the results showed that the cathodic protection criteria recommended in ISO 15589-1: 2015 are conservative compared to those measured experimentally. This method therefore seems particularly relevant for the determination of the protection potential in complex or polluted media, in the absence of data in the literature.

Under operating conditions, alternated loading and fatigue are encountered, controlling the durability and safety of components and structures made of super duplex stainless steel (SDSS). In particular, the use of a cathodic protection (CP) system to protect the structure against corrosion can induce hydrogen charging of the SDSS. Thus, the aim of this study was to investigate the sensitivity of some industrial products made of SDSS 2507 (UNS S32750), without artificial thermal aging, under test conditions as close as possible to real environments. In situ fatigue tests under alternated 4-point bending conditions were conducted in natural seawater with and without CP. The fatigue behavior was evaluated as a function of environmental parameters, such as temperature, and material parameters, particularly the austenite spacing and microstructure around orbital welds by Tungsten Inert Gas (TIG) welding and stress concentrations, through the presence of surface defects. The fatigue life obtained in air or in seawater at the open circuit potential (OCP) was rather similar. Fatigue life enhancement was systematically observed under CP particularly in the range of low applied load, despite evidence of brittle failure on the fracture surfaces of samples tested under CP. The data suggest immunity of the SDSS to hydrogen embrittlement under the present experimental conditions of fatigue testing. Copyright © 2022 Vucko, Ringot, Thierry and Larché.