Stress Corrosion Cracking Tests Research Articles

Evolution from near-neutral to high-pH environments susceptible to stress corrosion cracking: The role of sulfate and bicarbonate

Stress corrosion cracking (SCC) testing was conducted on pipeline steels to investigate the transition from near-neutral to high-pH environments via solution evaporation and concentration. The study clarified the roles of sulfate and bicarbonate in enhancing crack dissolution and their impacts on SCC. In sulfate-absent concentrated solutions, intergranular branching primarily resulted from direct propagation from the crack tip, accompanied by microcrack coalescence. The presence of sulfate effectively halted further growth by inducing crack-tip blunting, thereby reducing the mechanical driving force for crack propagation. This explanation clarifies why regions ideal for SCC exhibit no reported incidents, offering strategies for SCC mitigation.

Preferential intergranular oxidation as a potential degradation mechanism for Alloy X-750 CANDU spacers

Oxidation experiments on Alloy X-750 were performed in reducing CO-CO2 mixtures to assess the possibility of preferential intergranular oxidation (PIO) in relation to CANDU garter-spring spacers. The testing environments simulate hypothetical off-chemistry scenarios, promoting the oxidation of the alloying elements, but not Ni. Surface and cross-section microscopy corroborated by Auger electron spectroscopy confirmed the occurrence of internal and intergranular oxidation in Alloy X-750, accompanied by Ni nodule expulsion to the surface. Results are qualitatively similar to observations in Alloy 600 exposed to 480°C hydrogenated steam, used as an accelerated environment for primary water stress corrosion cracking (PWSCC) testing.

The fitness and corrosion mechanisms of high‐strength steel in corrosive oil–water environment at high temperature

AbstractThis work investigated the mechanical decay mechanism and high‐temperature corrosion mechanism of high‐strength steel via high‐temperature mechanical experiments, and corrosion and stress corrosion cracking tests were performed in simulated working conditions where water, oil, H2S, and CO2 coexist. The results show that the tensile strength and yield strength of high‐strength steel decrease with increasing temperature; the tensile strength and yield strength at 350°C reduce 11.91% and 19.08%, respectively, compared with 25°C. Moreover, the corrosion rate of high‐strength steel gradually increased from 0.0914 mm/a at 150°C to 1.2288 mm/a at 350°C. In addition, the influence of high temperature on the corrosion mechanism was inferred through thermodynamic calculations, and the reason for the presence of Fe3O4 in the corrosion products at 350°C was analyzed. At 350°C, stress corrosion cracking was observed in high‐strength steels when the applied stress reached 90% of the yield strength. Based on the aforementioned studies, the relevant mechanisms related to the decay of mechanical properties, corrosion, and stress corrosion cracking are also proposed.

Stress corrosion cracking behavior of AISI 316L stainless steel treated by surface mechanical grinding

The effects of surface mechanical grinding treatment (SMGT) on stress corrosion cracking (SCC) behavior of machined 316L stainless steel surface were investigated by comparing to those of turned and milled surfaces. The surface stress state, roughness, microstructure, and microhardness induced by the different surface machining processes were tested and analyzed. The SCC tests on the turned, milled and SMGT samples were conducted in boiling MgCl2 solution at 155 ℃, and the crack morphologies were analyzed in detail to establish the relationship between the surface integrities and the resulting SCC behavior. The findings indicated that the SMGT altered the SCC initiation behavior and improved SCC resistance of the turned and milled surfaces of 316L stainless steel, and the surface stress state, microstructure refinement and surface strengthening induced by SMGT contributed to the improvement of the SCC resistance.

Correlation between machining-induced surface alterations and stress corrosion cracking susceptibility of au stenitic stainless steels

Correlation between machined surface alterations and stress corrosion cracking (SCC) susceptibility of austenitic stainless steels is investigated. The machining-induced residual stress, roughness, micro-hardness and dislocation density were characterized and the surface/subsurface cracks were examined after SCC tests in boiling magnesium chloride solution. The results showed SCC crack initiation and early propagation were highly related to the machining-induced alterations. By establishing a quantitative relationship between the surface characteristics and surface crack density, the comprehensive impact of the residual stress, surface roughness as well as the dislocation density on SCC susceptibility is revealed. The predicted crack density is in good agreement with the measured data. As a result, the SCC susceptibility of the machined surface is described by the surface integrity properties.

Effects of load waveforms on stress corrosion behavior of pipeline steel

The effects of different load waveforms on stress corrosion cracking (SCC) of X70 pipeline steel were studied by means of fluctuating slow strain rate tensile test (F-SSRT). The results show that the SCC sensitivity of F-SSRT specimens with square wave loading is weak, and the fracture is straight; the SCC sensitivity of F-SSRT specimens with superimposed triangular wave loading is in the middle, and the fracture edge is serrated; The F-SSRT specimens with superimposed sine wave loading own the strongest SCC sensitivity, and the fracture is an oblique section fracture extending along the 45° direction. Different superimposed loads with different waveforms result in different SCC test results including different fracture morphology and change rules, which are caused by the change of the direction and magnitude of the applied force of the superimposed load, not only attributing to the different superimposed load energy.

Reducing stress corrosion cracking susceptibility of high-strength aluminum alloy and its fastener by a novel electromagnetic shocking treatment

A novel electromagnetic shocking treatment (EST) is put forward to reduce the stress corrosion cracking (SCC) susceptibility of high-strength aluminum alloys and its fasteners by selectively modifying grain boundary (GB) microstructure. The effect of EST on the microstructure, mechanical properties and SCC susceptibility of T73-Al7075 alloy and its high-lock nuts has been investigated. Mechanical properties, electrochemical performance and constant strain SCC test have been carried out for T73-Al7075 alloy, microhardness test and SCC test under wet-dry cyclic condition have been carried out for its high-lock nuts, as well as microstructure characterizations via SEM, EBSD and TEM have been carried out for T73-Al7075 alloy. Comparing to the received sample, the strength of EST sample basically keep consistent while the elongation increases slightly, besides, the electrical conductivity and electrochemical corrosion performance improves. The SCC susceptibility of T73-Al7075 alloy and its high-lock nuts have been reduced after EST. Microstructure characterization shows that the grain morphology and matrix intragranular precipitate distribution of the EST sample keep almost the same as those of the received sample, which is consistent with the almost unchanged mechanical properties of alloy sample. However, EST induces the transformation of grain boundary precipitates (GBPs) and the formation of stripy/wavy GB as observed experimentally, which indicates that EST promotes nonlinear GB wetting or pre-melting and even grain bridging. The phase transformation and GB complexion transition induced by EST are main factors attributing to the obvious improvement of SCC resistance of T73-Al7075 alloy and its high-lock nuts. It can be deduced that anodic dissolution cracking will be relieved because of the dissolution and coarsening of GBPs. Hydrogen induced cracking and crack propagation can be relieved with the occurrence of grain bridging. They are both beneficial to improve SCC resistance of Al7075 alloys. This work provides a novel EST method to targetedly embellish GB microstructure, optimize GB complexion and connectivity, and then enhance the service performance of solid alloys and even finished parts.

Corrosion-Resistant Stainless-Steel Strands for Prestressed Bridge Piles in Marine Atmospheric Environments

This study demonstrated that stranded highly cold-worked 2205 stainless steel (SCW2205) exhibits superior corrosion resistance when compared to stranded cold-worked AISI 1080 (ASTM A416) steel and cold-worked modified austenitic stainless steel 201, making it a viable candidate for prestressing applications with extended service life. Laboratory and field testing were performed. The material microstructure was characterized using scanning electron microscopy/energy dispersive x-ray spectroscopy, transmission electron microscopy, and x-ray diffraction. Then, laboratory corrosion testing, including linear sweep voltammetry, pitting resistance exposure, and four-point bend stress corrosion cracking (SCC) testing, was performed under different conditions. These conditions included concrete pore solution saturated with chlorides, direct exposure to artificial seawater, various concentrations of NaCl and MgCl2, representative inland salt deposition conditions, and oxidizing conditions with high chloride concentrations. The laboratory studies were augmented with field testing (259 d), comprised of four-point bend SCC, U-bend SCC testing (ASTM G30), and atmospheric contaminant measurements. The pitting resistance results, corrosion morphology, stable pit safe range, SCC results in the lab and in the field, and hydrogen embrittlement (HE) testing by slow strain rate testing (SSRT) under cathodic polarization as a diagnostic showed that SCW2205 outperformed the other steels tested, in the case of marine atmospheric corrosive conditions. SCC in SCW2205 was characterized by a selective localized anodic dissolution of the ferrite matrix and environmentally assisted cracking in the austenite phase. However, SCC was only found in SCW2205 at or above 65°C. SSRTs confirmed susceptibility to hydrogen uptake and a hydrogen-assisted mechanism of HE given sufficient hydrogen. It is speculated that hydrogen uptake in pits or crevice sites might be a route to hydrogen absorption worth exploring further since the absence of cathodic polarization in application precludes hydrogen production and uptake.

Failure Analysis of the Crack and Leakage of a Crude Oil Pipeline under CO2-Steam Flooding

This paper presents the failure analysis of the crack and leakage accident of a crude oil pipeline under CO2-steam flooding in the western oilfield of China. To analyze the failure behavior and cause, different testing, including nondestructive testing, chemical composition analysis, tensile property testing, metallographic analysis, and microanalysis of fracture and chloride stress corrosion cracking (SCC) testing, are applied in the present study. The obtained results showed that the pipeline under the insulation layer of high humidity, high oxygen content, and high Cl− environment occurred pit corrosion, and the stress concentration area at the bottom of the corrosion pit sprouted cracks. Besides, it is demonstrated that the cracks were much branched, mostly through the crystal, and the fracture showed brittle, which is consistent with the typical characteristics of chloride SCC. Meanwhile, the insufficient Ni content of the pipeline material promoted the process of chloride SCC, and the high-temperature working conditions also aggravated the rate of chloride SCC. In addition, efficient precautions were provided to avoid fracture.

Experimental and numerical analysis of mechanical fields on cross-shaped specimens for stress corrosion cracking of cold-worked austenitic stainless steels exposed to primary environment

A stress corrosion cracking (SCC) test was performed on a cold-worked austenitic stainless steel in simulated primary water, using a cross-shaped specimen permitting sequential loading. Crack density and location were investigated by scanning electron microscopy after the SCC test. To analyse the mechanical fields in the cracking areas, finite element simulations of the whole mechanical loading were conducted, involving both strain-path and temperature changes. Combined isotropic-kinematic hardening was used as constitutive equation and identified with tensile tests performed at room temperature and at 340 °C. Partial validation of the model was obtained by comparison of numerical strain fields with experimental measurements obtained by digital image correlation performed on a representative “ex-situ” test in air. Variations of the strain and stress fields during this test were discussed in relation with the cracking network observed at the end of the SCC test.

Development of sustainable novel Mg-Ca-Sc alloys with exceptional corrosion resistance

Mg-based alloys have been widely researched for biomaterial and structural applications as they fulfill several prerequisites, such as lightweight, high specific strength, and good biocompatibility, which are highly desirable. However, a long-standing obstacle to the widespread use of magnesium is its low corrosion resistance and increased cost upon increasing alloying content to enhance corrosion resistance. In this study, we report the effect of the simultaneous addition of rare-earth element (Sc) and non-rare earth element (Ca) maintaining low alloying content (∼ 1 wt%) on the mechanical, tribological, and corrosion behavior of Mg. The novel as-cast Mg-0.6Ca-0.5Sc alloy exhibited excellent corrosion resistance with a corrosion rate ∼ 40 % lower than the conventional as-cast WE43 alloy and ∼ 88 % lower than AZ31 alloy. A finer grain size and strong basal texture were achieved through thermomechanical processing, further enhancing the corrosion resistance of the as-cast novel alloys by ∼ 45 %. Stress corrosion cracking and wear testing in physiological saline solution were also conducted to study the combined effect of stress and corrosive electrolyte. The tensile and compression behavior remained practically the same upon adding Sc. However, the addition of 0.5 wt% Sc reduced the yield asymmetry by ∼ 10 % in as-cast and ∼ 5 % in recrystallized conditions. Furthermore, Mg-0.6Ca-0.5Sc alloy exhibited significant strength (∼ 175 %) and ductility (∼ 67 %) improvement under tensile testing in a physiological saline solution environment compared to Mg-0.6Ca alloy. The developed novel Mg-0.6Ca-0.5Sc ternary alloy exhibited enhanced resistance to corrosion, stress corrosion cracking, and wear relative to the Mg-0.6Ca binary alloy.

Effect of retrogression and reaging (RRA) on pitting and stress corrosion cracking (SCC) resistance of stir zone of high strength AA7075-T651 alloy joined by friction stir welding

The main purpose of this study is to investigate the influence of retrogression and re-aging post weld heat treatment (RRA-PWHT) on potentiodynamic corrosion (PC) and stress corrosion cracking resistance (SCC) of stir zone (SZ) of AA7075-T651 alloy butt joints developed using friction stir welding (FSW). FSW was employed to overcome the problems in fusion welding of AA7075-T651 alloy such as solidification cracking, heat affected zone (HAZ) softening, grain coarsening, dissolution of strengthening precipitates and inferior mechanical performance. The SZ of joints were subjected to potentiodynamic corrosion test in 3.56 wt% NaCl solution. The circumferential notch tensile (CNT) specimens were subjected to SCC test at various conditions of axial stress level in 3.56 wt% NaCl solution. The microstructural features of butt joints SZ were characterized using optical (OM), scanning electron (SEM) and transmission electron microscope (TEM). The results disclosed that RRA-PWHT joints exhibited greater PC and SCC resistance compared to as-welded joints. The threshold stress level for the failure of CNT specimens of parent metal, as-welded joints and RRA-PWHT joints was 242 MPa, 175 MPa and 198 MPa, respectively. The threshold stress level of RRA-PWHT joints and as-welded joints is 81.81% and 72.31% of parent metal threshold stress level. It is correlated to increase in vol% and coarsening of grain boundary precipitates with enrichment of copper at the grain boundaries.

Effect of Testing Conditions, Gauge, and Temper on Stress Corrosion Cracking of AA7xxx Aluminum Aerospace Plate Alloys

The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describes a brittle intergranular cracking phenomenon in 7xxx aluminum alloys and recommends testing conditions. These testing conditions are severe compared with expectations regarding, temperature, humidity, and stress in aerostructures. In this study, strong increases in time to failure of smooth specimens tested in humid air were observed when reducing either temperature or stress to levels closer to what is representative of in-service conditions. The cracking morphologies after testing in hot, humid air were identical to those described in the literature for in-service occurrences of stress corrosion cracking (SCC), including the observation of crack arrest markings consistent with a mechanism of alternate local corrosion and crack propagation by hydrogen embrittlement. The differences between such fracture surfaces and those observed in the industry standard SCC screening test, which uses a chloride-containing solution to accelerate initiation and propagation, can be attributed to the pitting of the crack surface in a chloride-containing solution in the wake of the propagating crack. The performances of 7xxx-T7 aluminum plates SCC testing in either hot, humid air or a chloride-containing aqueous solution have been compared as a function of thickness, over-aging treatment, and composition. There is a strong effect of plate thickness in both tests, with substantial decreases in initiation time and lifetime for thinner plates. The effect of plate gauge is such that “legacy” materials (such as 7010-T7651, 7050-T7651, and 7050-T7451) passing the SIB 2018-04R2 test at high thicknesses, fail at lower gauges, yet have been flying for nearly 50 y. An increase in SCC performance with increased overaging is observed in both tests. As a consequence, comparisons of SCC performance of alloy compositions should be made wherever possible at identical plate thickness and for aging treatments that result in comparable strengths. When this is done, high Zn concentration 7449-T76++ (7449-T7651 with additional aging) shows a slightly worse strength-SCC balance than 7010-T7651 and 7050-T7651. The observed trends in SCC performance in the two tests are consistent, suggesting that similar repeated initiation and propagation mechanisms are responsible for cracking in humid air and in aqueous NaCl environments.

Effects of Multi-Pass Turning on Stress Corrosion Cracking of AISI 304 Austenitic Stainless Steel

Austenitic stainless steels are extensively used in mechanical engineering. The machined surface integrity has an essential influence on the stress corrosion cracking (SCC) performance of stainless steels. In this paper, the effects of multi-pass turning on the SCC susceptibility of AISI 304 austenitic stainless steel were investigated by correlating the SCC crack density to the machining-induced surface characteristics in terms of roughness, micro-hardness, and residual stress. In the multi-pass turning, the surface roughness and residual stress were the least after the double pass turning, and the surface micro-hardness was the maximum after the triple-pass turning. The SCC susceptibility was evaluated after SCC tests in boiling MgCl2 solution. The results showed that the weakest SCC sensitivity was observed in double-pass turning 304 stainless steel, while the most susceptible SCC was found in triple-pass turning. Compared with the double-pass turning, the increase in SCC sensitivity of triple-pass turning was attributed to the larger roughness, higher micro-hardness and greater residual tensile stresses.

A Comparative Study of the Corrosion Behavior of 30CrMnSiNi2A in Artificial Seawater and Salt Spray Environments

In this work, the corrosion behavior of 30CrMnSiNi2A in a simulated marine environment was studied. The electrochemical behavior was studied by changing the temperature and pH of the solution environment. Detailed information about the rust layer was obtained by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The stress corrosion cracking (SCC) behavior of the steel in artificial seawater was studied through a slow strain rate tensile test (SSRT). The experimental results showed that the corrosion products were mainly composed of α-FeOOH, γ-FeOOH, and Fe3O4, while the content of Fe3O4 in the rust layer formed in the salt spray environment was much higher. The steel in the salt spray test showed a much higher corrosion rate than that observed when it underwent a full-immersion test. The decrease in the pH value mainly accelerated the cathodic reaction, and the temperature simultaneously promoted anodic dissolution and cathodic reductions. The decrease in the elongation during SCC test was minimal, while the index for the reduction-in-area showed a slight SCC susceptibility in the seawater environment, suggesting that anodic dissolution is the dominant mechanism of SCC degradation.

Improved corrosion resistance of Ni-base Alloy 600 welded joint by laser shock peening

Stress corrosion cracking (SCC) of welded joint is one of the salient problems influencing the safety of nuclear power structure. In this work, laser shock peening (LSP) was introduced to enhance the corrosion resistance of Ni-base Alloy 600 welded joint. The corrosion behavior was evaluated by electrochemical corrosion and SCC tests, and its anti-corrosion mechanism was analyzed in terms of the residual stress and microstructure evolution. The results indicate that LSP treatment could significantly reduce the electrochemical corrosion rate and SCC sensibility of the weldments by 81 % and 14 %, respectively. The enhanced corrosion resistance of the welded joint was attributed to the compressive residual stress and high-density dislocation tangles induced by LSP. The maximum compressive residual stress of ~460 MPa in weld zone could be obtained with the laser power of 25 J. The microstructure evolution of LSP for weld zone and base metal is dominated by the dislocation activities.

Methods of corrosion testing used for development and commercial exploitation of new shipbuilding steels and alloys. Review. Part II. Corrosion cracking and field marine tests

The review describes methods of stress corrosion cracking (SCС) tests that implement various conditions for samples loading: at a constant static load or deformation, at a constant or increasing load of samples with a previously grown fatigue crack, with a slow strain rate. Such tests shall be carried out to determine the resistance of shipbuilding materials to be used in loaded ship structures in contact with seawater. Brief descriptions of the mechanism of stress corrosion cracking of steels and alloys are given. The necessity to carry out bench tests of steels and their welded joints, as well as models simulating individual units and elements of structures, is indicated. At this stage, conditions are ensured as close to operating conditions as possible due to exposure in various climatic zones of the world’s oceans (variations in temperature, chloride concentration, amount of dissolved oxygen, degree of biofouling, and their simultaneous impact). It is shown that during verification field tests (final stage) new materials promising for operation in marine conditions pass the final evaluation of corrosion resistance in the form of elements of ship structures and systems in the conditions of ship operation.

Mechanisms of Mitigating Chloride-Induced Stress Corrosion Cracking of Austenitic Steels by Laser Shock Peening

This study investigates the effect of laser shock peening (LSP) on the chloride-induced stress corrosion cracking (SCC) of 304 austenitic steels. LSP can induce a high compressive residual stress to a depth of 700 µm and plastic deformation structures of dislocations, deformation twins, and stacking faults. Constant-load SCC tests in MgCl2 solution suggested that LSP can retard the crack initiation and slow the crack growth. LSP-treated subsurface layers experience ductile fracture while the central regions exhibit intergranular SCC. The LSP-induced deformation structures may impede dislocation slips, while the LSP-induced compressive residual stress can lessen the stress intensity factor of crack tips and decrease the local stress for film rupture.

Crack branching behavior and amorphous film formation mechanism during SCC expanding test for multi-layers weld metal of NiCrMoV steels

Multi-layer weld metal of NiCrMoV steels used in nuclear rotor was adopted to perform stress corrosion cracking (SCC) test at 180 ℃, which indicated the crack growth rate in 3.5% NaCl solution was lower than that in pure water. The results obtained from high resolution transmission electron microscopy (HRTEM) analysis revealed that the combined effect of crack branching behavior and amorphous film made contributions to the slower crack growth rate. The aggressive Cl− ions invaded grain in multi-directions that was promoted by dislocation motion, facilitating the main crack to bifurcate. Besides, nanocrystals also enhanced branching behavior by deflecting the crack growth path. An amorphous film forming in crack evolved from the disorder of atom arrangement produced by dislocation accumulation and grew stably with the supplement of carbon atom generated in selective corrosion. The complete amorphous film was absent connected path for migration of aggressive anions, thus weakened the driving force for crack propagation and improved resistance to localized corrosion attack.

SCC behaviour of laser and hybrid laser welded stainless steel weld joints

In this study, stress corrosion cracking (SCC) resistance was evaluated for type 316LN stainless steel weld joints fabricated by advanced welding techniques such as Laser, Hybrid Laser – Tungsten inert gas (HLT) and Hybrid Laser – Metal inert gas (HLM) welding. 316 LN stainless steel base metal exhibited significantly better resistance to SCC. The solidification mode, secondary dendritic arm spacing (SDAS) and tensile residual stress distribution in the weld metal was found to strongly influence SCC resistance of 316LN stainless steel weld joints. The weld joint processed by HLM process exhibited the highest time to failure during SCC testing and hence better SCC resistance due to primary ferritic mode of solidification, finer SDAS and lower width of tensile residual stress distribution.