High Stress Corrosion Cracking Susceptibility Research Articles

Hydrogen permeation and SCC susceptibility of X70 pipeline steel in CO2-saturated water environment containing acidic impurity

The effect of HNO3 and H2SO4 impurities on hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of X70 steel in CO2-saturated water environment was investigated. Concurrently, a method for characterizing the contribution of corrosion-produced hydrogen to SCC was developed. HNO3 and H2SO4 boost the hydrogen permeation through promoting cathodic hydrogen evolution. The hydrogen embrittlement induced by corrosion-produced hydrogen, together with anodic dissolution, dominates the SCC process of X70 steel. The steel has much higher SCC susceptibility in H2SO4-containing environment than in HNO3-containing environment, which is closely related to the much stronger hydrogen embrittlement effect caused by H2SO4 than HNO3.

Imidazoline behavior as corrosion inhibitor in the electrochemical characterization of SCC behavior of an API X70 steel exposed to brine solution

Abstract The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

Study on corrosion, hydrogen permeation, and stress corrosion cracking behaviours of AISI 4135 steel in the tidal zone

High-strength steels are widely used in marine engineering; however, they suffer from the risks of corrosion, hydrogen permeation, and stress corrosion cracking (SCC) in wet–dry cyclic marine environments. In this study, the corrosion, hydrogen permeation, and SCC behaviours of AISI 4135 steel in the tidal zone were investigated using electrochemical corrosion, electrochemical hydrogen permeation, and slow strain rate tests, respectively, via field exposure. The results showed that the AISI 4135 steel sample placed at the high tide level had high SCC susceptibility because of severe pitting corrosion and hydrogen permeation, whereas the steel samples placed at the middle and low tide levels had low SCC susceptibilities. The dry/wet time ratio was crucial in determining the SCC behaviour and mechanism of the steel in the tidal zone. With increasing time ratio, the SCC mechanism changed from micro-void coalescence control to localised anodic dissolution and hydrogen embrittlement in tandem.

Hydrogen effects on passivation and SCC of 2205 DSS in acidified simulated seawater

In this work, hydrogen effects on passivation and stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) in acidified seawater were investigated. Results show hydrogen deteriorates passive film, accelerates localized anodic dissolution (AD) and causes hydrogen damage, leading to high SCC susceptibility by hydrogen embrittlement (HE) and hydrogen facilitated anodic dissolution (HFAD). SCC initiates in ferrite, and propagates as transgranular-SCC (TGSCC) and intergranular-SCC (IGSCC). When loaded along rolling direction (RD), hydrogen segregating in austenite hardens austenite during SCC propagation; while hydrogen enriching in ferrite causes hydrogen enhanced localized plasticity (HELP) effect for transverse direction (TD) load.

Combined effects of machining-induced residual stress and external load on SCC initiation and early propagation of 316 stainless steel in high temperature high pressure water

Combined effects of machining-induced residual stress and external load on stress corrosion cracking (SCC) initiation and early propagation of 316 stainless steel were explored in high temperature high pressure water environment. Three different external loads were applied to machined specimens with varied residual stresses. The results revealed that the residual stress promoted SCC initiation while the external load further contributed to continuous crack propagation. Additionally, it was found the SCC initiation and early propagation were highly related to biaxial stress state. The biaxial stress state with high SCC susceptibility at 300 °C water environment was obtained.

Stress Corrosion Cracking of 2205 Duplex Stainless Steel with Simulated Welding Microstructures in Simulated Sea Environment at Different Depths

The stress corrosion cracking (SCC) of 2205 duplex stainless steels (DSSs) with different microstructures in simulated sea environments were studied by electrochemical measurements, electron backscattered diffraction and slow strain rate tensile tests. Heat treatments were used to obtain different microstructures. The DSSs were held at 1350 and 850 °C for 30 min and then quenched in the water. The results showed that the DSSs had a higher SCC susceptibility in simulated shallow sea environment than in the simulated deep-sea environment. Electrochemical mechanism of the SCC process was controlled by environment factors (temperature, hydrostatic pressure and dissolved oxygen content). The mechanisms of SCC changed from anodic dissolution in the simulated shallow sea environment to hydrogen embrittlement in the simulated deep-sea environment. Moreover, the quenched DSSs, especially the steel held at 850 °C, were more vulnerable to SCC than as-received steel in the simulated sea environment due to the deterioration of the microstructure.

The SCC Behavior of E690 Welded Joint in Thin Electrolyte Film Containing Sulfur Dioxide

E690 steel, as a newly-developed high strength steel in recent years, is of great potential to be widely used in offshore platforms in the near future. Since the stress corrosion cracking (SCC) susceptibility of high strength steel increases sharply with the strength, E690 may experience risks of stress corrosion cracking (SCC) and therefore catastrophic failures when used in marine environment, especially in polluted marine atmosphere containing SO2. In general, the welded joints have lower mechanical strength compared to the majority of the steel structure and are considered more vulnerable to corrosion and stress corrosion cracking. In this study, slow strain rate tests (SSRT) and electrochemical measurements, combined with metallographic analysis and micro-hardness tests, were employed to investigate the behavior and mechanism of SCC in the E690 welded joint. The metallographic observation revealed at least three different microstructure types in the heat affected zone (HAZ) of E690 welded joint, including coarse grained heat affected zone (CGHAZ), fine grained heat affected zone (FGHAZ) and intercritical heat affected zone (ICHAZ). CGHAZ exhibited the highest micro-hardness. FGHAZ showed a little lower micro-hardness than base metal (BM). And the micro-hardness of ICHAZ was equal to or even lower than that of BM. The results showed that the E690 welded joint had a very high SCC susceptibility in thin electrolyte film containing sulfur dioxide. From the fracture morphologies, distinct characteristics of brittle fracture were observed. The plasticity index in SO2 atmosphere was significantly decreased compared to that in air, showing the loss percentage of elongation and area reduction up to 30.0 % and 36.9 %, respectively. After etching, the morphology of the cross-section indicated that ICHAZ of the welded joint was the most susceptible location to SCC due to its more negative potential and higher corrosion current density from the electrochemical measurements. Fracture morphology showed that stress corrosion cracks were more likely to initiate and extend along the interface of martensite-austenite (M-A) island and adjacent ferrite.

Local chemistry–electrochemistry and stress corrosion susceptibility of X80 steel below disbonded coating in acidic soil environment under cathodic protection

In this study, local chemical and electrochemical states underneath disbonded coatings were investigated using a simulated system. Moreover, the stress corrosion cracking (SCC) susceptibility of X80 steel at different positions was evaluated. Results demonstrated that the microenvironment underneath the disbonded coating changed considerably under cathodic protection (CP). The dissolved oxygen content dropped quickly and transformed into anaerobic state immediately. The pH at the bottom of disbonded coating evolved into an acidity of ~5, accompanied by a remarkable concentration of Cl−, which were probably responsible for the severe corrosion and high SCC susceptibility at the crevice bottom. By contrast, the middle part of the disbonded coating had low SCC susceptibility because of effective CP and weak hydrogen evolution.

The effect of grain boundary structure on the intergranular degradation behavior of solution annealed alloy 690 in high temperature, hydrogenated water

The environmental degradation of four different types of grain boundaries were investigated on alloy 690 following slow strain rate tensile tests in 360°C hydrogenated water. Random high angle boundaries (RHABs) support fast Cr diffusion that promotes the formation of a continuous surface oxide film and grain boundary migration. Surprisingly, coherent twin boundaries (CTBs) are susceptible to intergranular oxidation and do not exhibit Cr diffusion or grain boundary migration. When CTBs are changed to transformed twin boundaries (TTBs) by cold work, they behave like RHABs. Finally, incoherent twin boundaries (ITBs) undergo intergranular oxidation with limited Cr depletion but no boundary migration beyond the oxide. The Cr diffusivity along grain boundary in this alloy is directly related to the density of coincident site in the grain boundary plane and determines the morphology of oxide formed near the grain boundary. CTBs are still highly resistant to stress corrosion cracking (SCC) due to the semi-coherent interface between the intergranular chromia and grain matrix. In contrast, the intergranular oxides formed along RHABs inherit highly-disordered boundary structure from the original grain boundaries and show much higher SCC susceptibility. The grain boundary structure dependence of SCC resistance should be understood from its effects on solute diffusivity, structure of intergranular oxide and the local stress-strain state.

The Effect of Grain Boundary Structure on the Intergranular Degradation Behavior of Solution Annealed Alloy 690 in Simulated Pressurized Water Reactor Primary Environment

The environmental degradation of four different types of grain boundaries were investigated on alloy 690 following slow strain rate tensile tests in 360 oC hydrogenated water. Random high angle boundaries (RHABs) support fast Cr diffusion that promotes the formation of a compact surface oxide film and grain boundary migration. Surprisingly, coherent twin boundaries (CTBs) are susceptible to intergranular oxidation and do not exhibit Cr diffusion or grain boundary migration. When CTBs are changed to transformed twin boundaries (TTBs) by cold work, they behave like RHABs. Finally, incoherent twin boundaries (ITBs) undergo intergranular oxidation with limited Cr depletion but no boundary migration beyond the oxide. The Cr diffusivity along grain boundary in this alloy is directly related to the density of coincident site in the grain boundary plane and determines the morphology of oxide formed near the grain boundary. CTBs are still highly resistant to stress corrosion cracking (SCC) due to the semi-coherent interface between the intergranular chromia and grain matrix. In contrast, the intergranular oxides formed along RHABs inherit highly-disordered boundary structure from the original grain boundaries and show much higher SCC susceptibility. The grain boundary structure dependence of SCC resistance should be understood from its effects on solute diffusivity, structure of intergranular oxide and the local stress-strain state.

Environmentally assisted cracking of forged 316LN stainless steel and its weld in high temperature water

The corrosion fatigue (CF) and stress corrosion cracking (SCC) crack growth rates (CGRs) of type 316LN SS and its welds that are used for pressurized water reactor primary water components were evaluated. Effects on CGRs of loading condition, water chemistry and metallurgical microstructure were studied. Experimental results indicated that stress intensity factor K, loading ratio, and frequency control the CGRs of materials along with corrosion potential, chloride, and pH also significantly influencing the cracking behavior. Similar CGRs under various conditions were observed in the base metal and its weld, with low SCC susceptibility in hydrogenated water, but high SCC susceptibility in oxygenated water. The weld metal showed lower SCC CGRs than base metal in oxygenated high purity water but shifted to higher values after adding ppb levels of chloride because of the presence of δ-ferrite in the weld.

Stress corrosion cracking behaviors of RE-containing ME21 magnesium alloy processed by equal-channel angular pressing

A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equal-channel angular pressing to obtain fine-grained microstructure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks' solution at the strain rate of 1 × 10−6 s−1. All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks' solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks' solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.

Morphology and stress evolution during the initial stages of intergranular corrosion of X70 steel

Pipeline steels are vulnerable to stress corrosion cracking (SCC) during intergranular corrosion (IGC) at potentials of active dissolution in moderately alkaline carbonate-bicarbonate solutions. Morphology evolution accompanying IGC has not been fully described, despite the relevance of the corrosion geometry to crack initiation. The present article reports a characterization of concurrent morphology and mechanical stress development during the initial stages of IGC of X70 steel in sodium bicarbonate solution, in the potential range of high SCC susceptibility. Morphology was revealed by scanning electron microscope examination of cross sections through the IGC layer, and stress evolution was monitored by curvature interferometry. At potentials in the range of SCC susceptibility, IGC creates triangular wedges of porous corrosion product centered at grain boundary triple junctions. The wedge shape indicates a higher corrosion rate at the grain boundary compared to the grain surfaces. Compressive stress is generated during IGC due to internal oxidation on grain surfaces forming a thin compact corrosion product layer. Polarization at a potential below the SCC range resulted in selective grain dissolution with no internal corrosion product or compressive stress increase. Silicon solute atoms are selectively oxidized into the compact grain boundary corrosion product film.

Electrochemical characterization and stress corrosion cracking of E690 high strength steel in wet-dry cyclic marine environments

In this work, stress corrosion cracking (SCC) in E690 high-strength steel was investigated in simulated wet-dry cyclic marine environments using electrochemical techniques, constant load SCC examinations, morphology characterization via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). It was found that E690 steel exhibited high SCC susceptibility in wet-dry cyclic offshore environments. The SCC follows a combined mechanism of anodic dissolution and hydrogen embrittlement, which nucleate in pits beneath the rust layer and tend to propagate along bainite slices in a transgranular fashion. Cracks grow with a low propagation rate during the early stage and expand with a far faster rate when the crack size exceeds a critical value. Both the electrochemical and SCC behavior of the E690 steel in wet-dry cyclic environments were influenced by the rust layer. The rust scale causes enrichment of chloride in the sublayer and localized acidification. This synergistic effect is responsible for the mechanism and properties of SCC in this material.

Microstructure, Residual Strain and Stress Corrosion Cracking Behavior in 316L Heat-Affected Zone

Austenitic stainless steels are usually chosen to make many components of nuclear power plants (NPPs). However, their microstructure in the heat-affected zone (HAZ) will change during the welding process. Some failures of the weld joints, mainly stress corrosion cracking (SCC), have been found to be located in the HAZ. In this research, the microstructure, micro-hardness, residual strain and SCC behavior at different locations of the 316L HAZ cut from a safe-end dissimilar metal weld joint were studied. However, traditional optical microscope observation could not find any microstructural difference between the HAZ and the base metal, higher residual strain and micro-hardness, and higher fraction of random high-angle grain boundaries were found in the HAZ than in the base metal when studied by using electron back-scattering diffraction scanning and micro-hardness test. What’s more, the residual strain, the micro-hardness and the fraction of random grain boundaries decreased, while the fraction of coincidence site lattice grain boundaries increased with increasing the distance from the fusion boundary in 316L HAZ. Creviced bent beam test was applied to evaluate the SCC susceptibility at different locations of 316L HAZ and base metal. It was found that the HAZ had higher SCC susceptibility than the base metal and SCC resistance increased when increasing the distance from the fusion boundary in 316L HAZ.

Stress corrosion cracking behaviour of 316L stainless steel exposed to CO2–H2S–Cl− environments in the absence and presence of methyldiethanolamine (MDEA)

Stress corrosion cracking (SCC) behaviour of 316L stainless steel in CO2–H2S–Cl− environments with and without methyldiethanolamine (MDEA) was investigated by slow strain rate testing and scanning electron microscopy (SEM). The results show that elongation ratio, reduction in area ratio (RAR) and time to failure ratio (TTFR) of 316L stainless steel were low in CO2–H2S–Cl− environments. The corresponding fractography exhibited flat brittle fracture with quasi-cleavage pattern, indicative of high SCC susceptibility. Hydrogen penetration and corrosion pits could be responsible for the high SCC susceptibility of 316L stainless steel in this condition. For the CO2–H2S–Cl− environments in the presence of MDEA, 316L stainless steel possessed high ER, RAR and TTFR (nearly 100%). High SCC resistance of 316L stainless steel could be associated with MDEA induced removal of H2S/CO2 and absorption on the steel surface.

STRESS CORROSION BEHAVIORS OF E690 HIGH-STRENGTH STEEL IN SO2-POLLUTED MARINE ATMOSPHERE

With the development of industry, the atmosphere in many cities along the coastal lines such as Qingdao in China has been polluted with SO2, and has been changed to coastal-industrial atmosphere with the coexistence of SO2 and Cl-. The corrosion and stress corrosion cracking (SCC) behavior and mechanism of steel in this environment is different from that in the coastal atmosphere containing only Cl- or the industrial atmosphere containing only SO2. Previous study have indicated that SO2 in the marine atmosphere can greatly promote the stress corrosion cracking of high-strength steel due to acidification of thin electrolyte layer and reproduction of H+ through FeSO4. E690 steel, as a newly-developed high strength steel, is very promising to be widely used in offshore platform in the near future for its excellent performance. However, there is few research about its SCC behavfor in marine atmosphere, especially in SO2-polluted atmosphere. Therefore, it's of great importance to investigate the SCC behavior and mechanism of E690 steel in this environment. In this work, U-bend specimen corrosion test under dry/wet cyclic condition, electrochemical measurements, crack morphology observation and rust layer analysis, were conducted to investigate the effect of SO2 on SCC behavior of E690 steel in simulated SO2-polluted marine atmosphere. The results indicated that E690 steel has a high SCC susceptibility in SO2-polluted marine atmosphere with a combined mechanism of anodic dissolution (AD) and hydrogen embrittlement (HE). SO2 in the atmosphere can facilitate the densification of inner rust layer by promoting the formation of alpha-FeOOH and enrichment of Ni and Cr in the inner rust layer, leading to the concentration of Cl- under the rust layer, which may result in the initiation and propagation of SCC cracks significantly and therefore enhance the SCC susceptibility.

The effect of hydrogen on stress corrosion behavior of X65 steel welded joint in simulated deep sea environment

In order to investigate stress corrosion cracking (SCC) of X65 pipeline steel and its welded joint area in deep sea environment. The simulated methods were used to obtain the welded joint of hardening and softening tissue in heat affected zone (HAZ) by annealing at 1300°C for 10min and then, normalized in air and quenched in water respectively; the other was to get 1000m depths of marine environment. The effect of hydrogen on SCC behavior of X65 pipeline steel in simulated deep sea environment was analyzed by a combination of hydrogen-charging, slow stain rate test (SSRT), scanning electron microscope (SEM) and electrochemistry. Results demonstrated that with the increasing of charging current density, Fracture of as-received appeared brittle characteristics and normalized and quenched steel generated micro cracks, Hydrogen-charging will enhance the SCC susceptibility of the steel in simulated deep sea environment. The corrosion potential of X65 steels was low in deep sea environment with hydrogen evolution reaction and showed some SCC sensitivity in deep sea environment. Heat treatment altered the microstructure of the steel, resulting in a change of SCC susceptibility. In particular, the quenched steel with a bainite micro-structure which had a higher SCC susceptibility than as-received and normalized steel in deep sea environment.

Comparative study of the SCC behavior of E690 steel and simulated HAZ microstructures in a SO2-polluted marine atmosphere

Simulated microstructures of the typical CGHAZ, FGHAZ, and ICHAZ of an E690 welded joint were prepared with heat treatment at peak temperatures of 1300, 850, and 750°C, respectively. Slow strain rate tensile (SSRT) tests were implemented to investigate the stress corrosion cracking (SCC) behavior of E690 steel and the simulated HAZ microstructures in a SO2-polluted marine atmosphere. Results revealed that E690 steel and its simulated HAZ microstructures all had a high SCC susceptibility in the simulated SO2-polluted marine atmosphere with a combined mechanism of AD and HE. The SCC susceptibility gradually increased in the following order: BM, CGHAZ, FGHAZ, and ICHAZ. The cracking mode of BM and CGHAZ was transgranular, whereas that of FGHAZ and ICHAZ was intergranular. The lower SCC susceptibility of BM and CGHAZ was probably due to the impeding effect of lath bainitic grain boundaries on SCC propagation, whereas the higher SCC susceptibility of FGHAZ and ICHAZ was attributed to the facilitating effect of M-A islands on crack initiation and propagation.

Stress corrosion cracking of E690 steel as a welded joint in a simulated marine atmosphere containing sulphur dioxide

Stress corrosion cracking (SCC) behavior and mechanism of E690 welded joint in simulated marine atmosphere containing SO2 were investigated using SSRT method and electrochemical measurements. Results showed that it had very high SCC susceptibility in this environment with a combined mechanism of anodic dissolution and hydrogen embrittlement (HE). The intercritical heat affected zone in the welded joint was the most vulnerable location to SCC because this zone has less strength, more negative potential, and higher corrosion current density. The M-A constituents had a detrimental effect on SCC behavior in the synergetic effect of stress concentration, micro-galvanic corrosion, and HE.