Atmospheric Stress Corrosion Cracking Research Articles

Insights from electrochemical crack tip modeling of atmospheric stress corrosion cracking

Crack tip electrochemical conditions are explored utilizing a reactive transport Finite Element Method model for stainless steel 304 exposed to 3 M NaCl. Under simulated full immersion conditions, a steady state pH of 3 and metal chloride concentration of 1.4 M were calculated. It was determined that an increase in cathode length and a decrease in water layer thickness increases total cathodic current per unit thickness, metal chloride concentrations, and decreases crack tip pH. The presented results and discussion call into question whether electrochemical similitude is achieved between different specimens, crack lengths, and between laboratory specimen and field relevant samples.

Predicting Stress Corrosion Crack Tip Electrochemical Conditions and the Influence of Exposure Environment

Metallic structures are commonly exposed to marine atmospheric conditions in real world conditions, characterized by thin water layers (WL) allowing for corrosion to occur. For austenitic stainless steels in such atmospheric environments, pitting and stress corrosion cracking (SCC) are potential degradation mechanisms. The rate and extent of corrosion and SCC on the alloy surface is dictated by the combination of environmental, physicochemical, and geometric variables, which include relative humidity, temperature, electrolyte conductivity, electrolyte film thickness, in addition to the electrochemical kinetics on the alloy surface. Due to the large potential variation in environmental conditions, modeling can serve as an important tool to evaluate environmental effects on the corrosion and SCC of alloys and galvanic couples.In this study, Finite Element Modeling approaches are used to evaluate chemical and electrochemical conditions present in a crack exposed to marine, thin film environments. A full reactive transport model, incorporating metal hydrolysis and salt formation, is built to evaluate SCC crack tip conditions. The influence of WL thickness, stress intensity level, crack length, and specimen geometry are evaluated. Specifically, crack tip pH and equilibrium potential among other variables will be compared between the various atmospheric factors both spatially and temporally. The modeling results will be compared to atmospheric SCC experiments and help give insight into critical experimental and testing phenomena. Acknowledgements Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This document is SAND2021-5051 A.

The effect of build direction and heat treatment on atmospheric stress corrosion cracking of laser powder bed fusion 316L austenitic stainless steel

Austenitic stainless steels are susceptible to stress corrosion cracking (SCC) when exposed to chloride ions and tensile stresses. For laser powder bed fusion (LPBF) components, high residual tensile stresses exist from the large thermal gradients during solidification. While post fabrication heat treatments can relieve residual stresses, their effectiveness in improving SCC resistance of LPBF material is undetermined. The effects of different heat treatments (i.e. temperature and cooling method) and build orientations on SCC susceptibility of LPBF 316L were explored. Samples were exposed to MgCl 2 and maintained at 75 °C and 70% RH for the test duration. Cracks were highly branched and propagated perpendicularly to build direction even in the presence of an applied perpendicular 60 MPa stress. Vertical as-built specimens exhibited higher cracking densities than horizontal ones, due to higher surface residual stresses. SCC and corrosion favoured one side for horizontal specimens while the distribution was random for vertical specimens. After 750 °C (2 h, furnace cooled) heat treatment, SCC susceptibility reduced for vertical 316L but increased for horizontal 316L. This was attributed to competing effects: reduction in residual surface tensile stresses (beneficial) and loss of non-equilibrium microstructure (detrimental). Encapsulation to prevent oxidation during heat treatment negatively impacted SCC resistance of LPBF 316L, likely due to changes to surface oxide condition. No SCC was observed after 900 °C (0.5 h) heat treatments within the test duration, however, pitting corrosion persisted.

Atmospheric stress corrosion crack growth rates of 316 L stainless steel for nuclear waste containment

Atmospheric stress corrosion cracking (SCC) tests were conducted for a 316 L stainless steel (SS) at an applied stress of 1.1 σ0.2 with a chloride deposition density of approximately 100 μg/cm2 deposited as MgCl2 from solution. The test specimens were exposed in an atmospheric chamber at a constant temperature of 40 °C with initial relative humidity (RH) of 40 %, followed by an increase to 60 % RH, then 80 % RH, and finally a decrease to 60 % RH. The total exposure period was 6500 h (about 9 months). The stress corrosion crack growth rate decreased with increasing RH and with increasing crack depth.

Atmospheric Stress Corrosion Cracking of Stainless Steel Rock Climbing Anchors, Part 1

Austenitic stainless steels Cr-Ni (Types 304, 304L, 321, and similar) and Cr-Ni-Mo (Types 316, 316L, 316 Ti, and similar) are susceptible to atmospherically-induced stress corrosion cracking (AISCC) at ambient temperatures if hygroscopic salts such as MgCl2or CaCl2are present on the surface and the air relative humidity (RH) is in a critical range. This phenomenon has been responsible for incidents of rock climbing anchors breaking under minimal load in seaside areas, putting climbers lives at stake. A systematic failure analysis of anchors collected from various seaside locations throughout the world, namely from Portugal, Azores, Hong Kong, Taiwan, South Africa, and Australia, has been performed. Transgranular AISCC was proven the reason for failures in the majority of investigated anchors made of Type 304L stainless steel. Intergranular cracking due to sensitization by improper welding or heat treatment was also identified as a critical safety issue for both Types 304 and 316 stainless steel types. Comparison of literature data and climatic data from the failure locations suggests that limited washing of deposits in confined zones together with elevated temperature and low RH generated locally by direct sunshine are the key factors of AISCC initiation and ultimately of anchor failure.

Atmospheric Stress Corrosion Cracking of Stainless Steel Rock Climbing Anchors, Part 2: Laboratory Experiments

Atmospherically-induced stress corrosion cracking (AISCC) in the presence of chloride deposits has been responsible for considerable incidents of rock climbing anchors breaking under minimal loads in seaside locations, putting climbers lives at stake. However, to date, failures due to AISCC have only been documented in anchors made of Type 304/304L and similar, and no rigorously documented failures have been shown to occur to Type 316/316L anchors. In order to support preparation of a new standard classifying anchors according to their corrosion resistance, the influence of environmental parameters such as periodic washing of chloride deposits, electrolyte pH, and type of rock on AISCC initiation and crack growth rate was studied in laboratory conditions by exposing U-bent specimens of stainless steel Types 321, 304, and 316L with MgCl2 deposits in air at 40°C to 50°C and at 35% to 45% relative humidity. The type of rock and electrolyte pH were not critical parameters for AISCC. Alkaline conditions only slightly prolonged stable crack initiation period and decreased the crack growth rate. Periodic washing in sufficiently short intervals was capable of significantly retarding or even arresting AISCC. The crack growth rate in Type 316L stainless steel was 2- to 3-fold slower than in the molybdenum-free Types 304 and 321. These last two effects are quite likely responsible for the lack of failures observed in Type 316/316L. In view of the lifetime expectancy of rock climbing anchors and other safety-relevant members, the crack growth rate was unacceptably high in all studied materials and their installation should be avoided in vulnerable seaside regions.

Stress Corrosion Cracking of Sensitized 304 Stainless Steel Under MgCl2 Droplets

Stainless steels have been widely applied in the building, chemical plants and other industries due to their excellent weldability, superior anticorrosion properties, and so on. However, stainless steels suffer from localized corrosion in chloride-containing environments. Especially, in an atmospheric environments near the seashore, localized corrosion can be initiated easily because a very severe corrosion condition, a thin water-layer containing very high concentration of chloride ions, can be made on stainless steels. Moreover, local corrosion sites such as pits can become initiation sites for crack initiation of stress corrosion cracking (SCC) when the steels are subjected to tensile stress. Therefore, it can be considered that atmospheric SCC is one of the most severe degradations for stainless steels in atmospheric corrosion environments. There are some researches to investigate SCC in the atmospheric corrosion environments with chloride deposits1, 2. This study is aimed at investigating initiation and propagation of stress corrosion cracking of sensitized 304 stainless steel under tensile stress in MgCl2droplets. Austenitic 304 stainless steel sheet of 1 mm in thickness were used as a material. Tensile specimens with a gauge part of L15 mm x W8 mm were cut out from the sheet. The specimens were heated for 90 min at 700 oC and followed by furnace cooling for sensitization. The sensitized specimens were abraded to JIS #1000 grit with SiC papers. Then they were degreased with ethanol in an ultrasonic bath and rinsed with Milli-Q water (18 MWcm). SCC behavior under MgCl2 droplets was investigated by a constant strain tensile test with a horizontal tensile test machine. In the test, a specimen was first elongated to a certain stress value and then kept at a constant strain. After applying the constant strain, 20 mL droplets of 250 mM MgCl2 were placed on the gauge part of the specimen. The gauge part with the droplets was exposed to an environment at 50 OC and ca. 35 RH% for 3 days in a small chamber. During the test, in-situ surface observation was carried out with a digital microscope. After the test, surface of the specimen was observed by SEM-EDX. Fig. 1 shows surface and cross-sectional images of sensitized 304 stainless steel with 8.5% strain under MgCl2droplets. When the droplets are place on the gauge part of the specimen, the droplets evaporate and reach to an equilibrium state with the concentration of 10 M at 35%RH. At this time, the thickness of the solution film of the droplets can be estimated to be 70 mm. Actually pitting corrosion was initiated within 1 h after the droplets were applied. As shown in Fig. 1(a), which is taken at 12 h after a pit is formed in a droplet, some tiny cracks initiate from the edge of the pit. As the test time advances, the cracks propagate in the normal direction to the tensile axis and reach ca. 600 mm after 72 h. During the propagation of the cracks, hydrogen bubbles gushing from the inside of the cracks were observed. Cross-sectional observation in Fig. 1(d) reveals that cracks initiate from the bottom of the pit and propagate in the bulk direction both with transgranular and intergranular cracking modes. In the presentation, crack propagation mechanism of sensitized 304 stainless steel will be discussed.

Prediction Model for Atmospheric Stress Corrosion Cracking of Stainless Steel

The analyses present the result whereby the initiation lifetime of atmospheric stress corrosion cracking, ASCC is 1.1 years under the following conditions of repair-welded joints: surface residual stress in the axial direction of the welded joints of 362 MPa, residual stress in the thickness of 200 MPa, degree of sensitization, Ra, of 20%, and density of adhesion salt of 0.1 g/m2 [NaCl]. According to the relationship of da/dt-K, it is considered likely that the cracks initiated would penetrate the thickness of 20 mm within 7.6 years or so.

湿潤大気応力腐食割れ予測モデル

ステンレス鋼製溶接構造物を海洋性湿潤大気環境下で使用すると，溶接による鋭敏化が起きていれば湿潤大気応力腐食割れ (Atmospheric Stress Corrosion Cracking, ASCC) を起こすことがある．本報では，ASCCの発生と進展過程をモデル化した．補修溶接を施した溶接継手の軸方向の表面側の残留応力を362 MPa，板厚内部の残留応力を200 MPa，鋭敏化度を20％，付着塩分量を0.1 g/m2[NaCl]とした時のASCC発生寿命は1.1年で，き裂進展速度の応力拡大係数依存性から約7.6年で20 mmの板厚を貫通する可能性がある．

Non-destructive testing of materials subject to atmospheric stress corrosion cracking

In-service inspection revealed atmospheric stress corrosion cracking (ASCC) on 304L stainless steel piping. The method requiring inspection qualification was a surface method, namely penetrant testing (PT), as physical dimensions of the smallest flaw requiring detection by PT was ill defined for both pitting and cracking defects. Qualification was considered in terms of flaw volume together with absolute flaw linear dimensions. Inspection qualification would, therefore, determine the adequacy of the applied technique by both physical reasoning and by empirical measurement to determine the largest flaw that could escape detection.

Initiation and Propagation of Stress Corrosion Cracking of Stainless Steel Canister for Concrete Cask Storage of Spent Nuclear Fuel

Abstract Resistance to atmospheric stress corrosion cracking (SCC) and crevice corrosion was examined for various candidate canister materials in the spent fuel dry storage condition using concrete casks. A constant load SCC test was conducted on the candidate materials in air after deposition of simulated sea salt particles on the specimen gauge section. UNS S31260 and UNS S31254, highly corrosion-resistant stainless steels (SS), did not fail for more than 46,000 h at 353 K with relative humidity of 35%, although UNS S30403 and UNS S31603 SS failed around 500 h by SCC. Crack growth measurement was done to explain this result. Cracking on S31603 propagated around 3 × 10−10 m/s at K values larger than 10 MPa·m0.5 at 353 K with RH = 35%. S31260 SS showed a crack growth rate of 4 × 10−13 m/s at the same condition. Crevice corrosion potentials of S31260 and S31254 SS became larger than 0.9 V vs. saturated calomel electrode (SCE) in synthetic seawater at temperatures below 298 K, while those of S30403 and S316...

Marine Atmospheric SCC of Unsensitized Stainless Steel Rock Climbing Protection

A failure investigation into the root cause of fixed austenitic stainless steel climbing anchor hardware in tropical marine climates has been presented. The incident 316L climbing anchor was fixed in a seaside limestone cliff in southern Thailand and underwent transgranular chloride stress corrosion cracking (TGSCC) after 10 years of service. Since stainless steel does not normally undergo stress corrosion cracking (SCC) at ambient temperatures, the conditions known to promote ambient temperature TGSCC of austenitic stainless steel are reviewed. A mechanism that may give rise to TGSCC in limestone climbing anchors in warm marine environments is postulated.

Atmospheric Stress Corrosion Cracking (ASCC) Susceptibility of Stainless Alloys for Metallic Containers

ABSTRACTMetallic canisters placed in concrete casks and containing spent nuclear fuel elements, will be exposed to a moist oceanic atmosphere while the decay heat generated in the fuel elements cools for more than fifty years. Thus, the surface environment of the metallic canisters will be wet and covered with chloride compounds. The canisters may suffer atmospheric stress corrosion cracking. Therefore, corrosion tests for some potential alloys were conducted in an aqueous bittern solution, containing 22% enriched chloride compounds simulating the expected surface conditions of the canisters, to aid in selecting appropriate alloys based on corrosion resistance. The results suggest that the corrosion resistance of ordinary stainless steels, such as SUS304 and SUS316, is not high enough to avoid ASCC (atmospheric stress corrosion cracking) in the environment. Thus, a higher-grade stainless steel, namely, NSSC270 (20Cr-18Ni-6Mo-0.2N-Low C)or SUS836L (23.5Cr-25Ni-5.5Mo-0.2N-Low C, equivalent to AL-6XN) has been selected for this application.

Atmospheric stress corrosion cracking of a superplastic 7475 aluminum alloy

The influence of different heat treatments upon the atmospheric stress corrosion cracking (SCC) of fine-grained 7475 Al-alloy plates has been investigated. The small size of the matrix precipitates and grain-boundary precipitates (GBPs) was found to be the main cause of atmospheric SCC suscepti-bility. Increasing the size of the matrix precipitates and GBPs by increasing the degree of aging could improve the atmospheric SCC resistance. The size of the matrix precipitates was the major factor affecting the atmospheric SCC resistance when GBPs were larger than a critical size that could nucleate hydrogen bubbles. However, if the size of the GBPs was smaller than this critical size, the improvement of atmospheric SCC resistance due to grain refinement, resulting from a more homo-geneous slip mode, could not be obtained because hydrogen embrittlement became serious. By meas-uring the electrical conductivity, the influence of matrix precipitates, but not that of GBPs, on SCC susceptibility could be obtained. Retrogression and reaging (RRA) treatment could effectively im-prove the atmospheric SCC resistance of T6 temper because RRA temper could produce larger sizes of both the matrix precipitates and GBPs than could T6 tempered condition.

ステンレス鋼管の大気腐食割れ

ステンレス鋼管の大気腐食割れ

室温におけるステンレス鋼の大気腐食割れに及ぼす湿度および塩化物の種類の影響

室温におけるステンレス鋼の大気腐食割れに及ぼす湿度および塩化物の種類の影響

ステンレス鋼の大気腐食割れに及ぼす湿度の影響

In order to evaluate the effect of environmental parameters on atmospheric stress corrosion cracking (SCC) of SUS 304 and 316L stainless steels, SCC tests were carried out in laboratory air controlled temperature and relative humidity (RH) environment by using U-bend specimens with the deposition of 0.5N chloride solution (NaCl, MgCl2, CaCl2, ZnCl2) and synthetic sea water droplets.SCC susceptibilities of steels strongly depend on RH and the maximum susceptibility was observed at the inherent relative humidity (RHmax) for each chloride. The values of RHmax were about 60, 30, 20 and 10% for NaCl, MgCl2, CaCl2 and ZnCl2 solutions respectively, corresponding to their vapor pressure of saturated solution (Psat), and hence, where the specimen surface is covered with a thin saturated chloride solution layer. In case of synthetic sea water, RHmax was almost same as that of MgCl2, suggesting that SCC susceptibility was affected by the salt with lowest Psat even in minor solute composition.The critical values of relative humidity (RHcrit) below which no-SCC was observed were some what lower than RHmax, where the solution dried up. Above RHmax, the SCC susceptibilities decreased with increasing RH, due to the dilution of the chloride solutions.

On the Atmospheric Stress Corrosion Cracking of Low-Alloy High Strength Steels and Stainless Steels

Experiments were conducted extending for three years in which low alloy high strength steels and stainless steels were exposed under static load to various types of atmospher i. e. in air in the industrial, in the marine and in the rural district.The results of the three years' exposure test showed no cracking either in the welded or in the non-welded specimens of low alloy high strength steels. Neither the non-welded specimens of stainless steels showed any cracking. Pitting and intergranular corrosion occurred, however, in the heat-affected zone of the welded stainless steels i. e. SUS 50 (13% Cr) and SUS 24 (18% Cr).

Stress Corrosion of Steels For Aircraft and Missiles

Abstract Atmospheric stress corrosion tests have been conducted on alloy and stainless steels intended for use in high-speed aircraft and missiles. The results of these tests showed that very high strength alloys hardened by heat-treatment, like many nonferrous alloys used in conventional aircraft, are under certain conditions susceptible to atmospheric stress corrosion cracking. Tempering at temperatures of 1100 F and above confers resistance to stress corrosion. Also, the test results indicated that austenitic stainless steels hardened to very high strength levels by cold working are not susceptible. Protective coatings that are anodic to steel appear to be very effective in preventing stress corrosion. A correlation between the specimen tests presented in this paper and service performance has not been established. The test results should be regarded as a guide to effective utilization of steels in aircraft and missile applications, but they should not be regarded as a direct indication of expected ser...