Stress Corrosion Cracking Failure Research Articles

Electrochemistry Numerical Study of Stress Corrosion Cracking under Near-Neutral Soil Solution

Stress Corrosion Cracking (SCC) is a phenomenon in which cracks develop in certain materials due to a combination of stress and corrosion. This process is commonly observed in low-alloy steels with a ferritic-pearlitic structure, such as X70, which are often used in buried pipeline applications within the oil and gas industry. These materials are particularly susceptible to SCC failure in dilute solutions. To simulate SCC conditions, the Near-neutral simulated soil solution (NS4) has been established as a widely accepted industry standard for conducting crack growth experiments in many laboratories. This paper aims to investigate the role of electrochemistry in SCC under near-neutral soil solution conditions by presenting a numerical study using COMSOL on the effects of applied potential on corrosion rate in near-neutral soil solutions. According to the findings, the electrode thickness, current density, and corrosion rates were mostly affected by an applied potential of -1.2 V. This implies that slight modifications in the applied voltage can greatly influence the corrosion rate of the electrode. This outcome aligns with prior research on the influence of potential on electrode performance and emphasizes the crucial role of precise control of the applied potential in electrochemical systems.

Stress corrosion cracking failure of X80 carbon steel U-bend caused by Desulfovibrio vulgaris biocorrosion

Sulfate reducing bacteria (SRB) are widely present in oil and gas industry, causing pitting corrosion on pipeline steel. Stress corrosion cracking (SCC) often occurs in the presence of mechanical stress before pitting perforation failure, leading to economic losses and even catastrophic accidents. In this study, stress distribution simulation using the finite element method (FEM), corrosion analysis techniques and electrochemical corrosion measurements were employed to investigate the SCC mechanism of X80 pipeline steel caused by Desulfovibrio vulgaris, which is a common SRB strain used in microbiologically influenced corrosion (MIC) studies. It was found that D. vulgaris MIC caused sharp microcracks on an X80 U-bend coupon after only 2 weeks of immersion at 37 °C in the deoxygenated ATCC 1249 culture medium inoculated with D. vulgaris. The X80 U-bend coupon's weight loss-based uniform corrosion rate for the 12 cm2 surface was 60% of that for the unstressed flat square coupon (2.3 mg cm−2 vs. 3.8 mg cm−2). This was likely because the square coupon had wide MIC pits, providing a larger effective surface area for more sessile cells (4.2×108 cells cm−2 on square coupon vs. 2.4×108 cells cm−2 on U-bend coupon) to attach and harvest more electrons. An SCC failure occurred on an X80 U-bend pre-cracked at the outer bottom after a 6-week immersion in the D. vulgaris broth. Apart from MIC damage, this could also be because D. vulgaris metabolism increased the availability hydrogen atoms on the steel surface, and promoted the diffusion of hydrogen atoms into the metal lattice, thus increasing the brittleness of the steel.

Method study on failure probability and uncertainty analysis of stress corrosion cracking in fixed parts of PWR

To estimate the failure probability of stress corrosion cracking (SCC) in the fixed parts of pressurized water reactors (PWR), an approach based on the Paris model was developed and its uncertainty analysis was performed as well. In the study of SCC failure, the uncertainty of fracture toughness was translated into integral form to improve calculation efficiency. Moreover, uncertainty parameters such as crack size and Paris model coefficients were studied in the uncertainty analysis. On this basis, the thermowell of the pressurizer of PWR as an example was analyzed in this study. The Monte Carlo (MC) method and polynomial chaos expansion (PCE) approach were used to calculate the mean value, relative uncertainty, upper limit of tolerance interval of failure probability, and sensitivity coefficient of input parameter to compare the advantages and disadvantages of these methods. According to the results, compared with the other method, 300 sets of sampling with Latin Hypercube sampling (LHS) and Sobol sequences can converge the mean, and 300 sets of sampling with Halton sequence and Hammersley sequence can converge the relative uncertainty. When LHS with the 4th order Wilks' formula and Halton sequence with the 1st order Wilks' formula to compute the upper limit of tolerance interval, the accuracy and cost of the computation can be balanced. According to the results of the sensitivity analysis, crack aspect ratio is the most sensitive parameter. PCE surrogate model can accurately calculate the mean, relative uncertainty, the upper limit of tolerance interval and sensitivity coefficient, thereby reducing the computational cost.

Effect of ultrasonic impact peening on stress corrosion cracking resistance of austenitic stainless-steel welds for nuclear canister applications

In nuclear applications, the utilization of austenitic-based stainless steel (ASS) components is an ideal material choice for storing spent nuclear fuels in dry storage canisters (DSC). However, due to the chloride rich environments in which they operate, failure in the form of stress corrosion cracking (SCC) frequently occurs. The following study assesses the efficacy of ultrasonic impact peening (UIP) on SCC susceptibility of gas tungsten arc welded (GTAW) stainless steel (SS) components, with an aim to control the SCC failure. The UIP induces residual compressive stresses (RCS) and a severely plastically deformed (SPD) layer containing nanograins on the surface. The superior SCC resistance of UIP'ed specimens is due to the synergistic effect of grain refinement and RCS. The underlying mechanisms for these findings were elucidated based on the modification of microstructural features and mechanical properties. These findings demonstrate that UIP is a potential technique for DSC application to mitigate the SCC susceptibility of ASS weld joints.

Characterisation of stress corrosion durability and time-dependent performance of cable bolts in underground mine environments

Premature failures of cable bolt caused by stress corrosion cracking (SCC) has been more and more often observed with the increasing depth of underground mines. Investigating and predicting this failure are critical in maintaining and accessing the integrity of the reinforcement system. In this study, with application of the designed SCC-AE testing system, the SCC failure processes of cold-drawn cable bolts used in underground reinforcement system was investigated using the acoustic emission (AE) techniques in simulated underground conditions. Damage evolution of the specimens was monitored with AE in real-time. The scanning electron microscopy was adopted to examine the fractographic features of the failed specimen. Through the integrated analysis of specimens’ elongation, the evolution of acoustic activities and fractographic features, three different stages during SCC failure processes were determined including cracks initiation due to the local corrosion, cracks propagation characterised as tear ridges appearance and fast fracture failure evidenced by the shear lips. The parameters of elongations, AE signals in each failure stage were investigated and the SCC propagation rates were determined. As a result, this study confirms the AE technique in combination with the designed testing system can give important insights into the SCC failure as well as the possibilities of real-time SCC monitoring in underground reinforcement systems.

Revealing the effect of heat treatment on stress corrosion cracking behavior of Monel 400 alloy in hydrofluoric acid vapor environment

The effect of heat treatment (HT) on the stress corrosion cracking (SCC) of Monel 400 alloy in hydrofluoric acid (HF) vapor was investigated through cracking crystallographic analysis. The SCC resistance is ordered as 750 °C-HT > AR > 850 °C-HT > 950 °C-HT > 1050 °C-HT, while the SCC failure mechanism is similar which is active dissolution-slip tearing. HT increases grain size and reduces residual strain, and large grains promote both slip and active dissolution, all contributing to higher SCC susceptibility. In addition, residual strain accelerates corrosion degradation, which counteracts the beneficial effect of fine grain on SCC resistance. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations. They can be provided on request.

Dislocation-aided electrochemical behavior of precipitates in stress corrosion cracking of Al–Zn–Mg–Cu alloys

The effects of electrochemical behavior of precipitates and dislocations on the stress corrosion cracking (SCC) of Al–Zn–Mg–Cu alloys were investigated. Fine anodic η (MgZn2) precipitates were readily dissolved, providing continuous channels for intergranular cracking, and coarse cathodic Cu-rich precipitates led to localized pitting attack of the surrounding matrix. This indicates that both precipitates promote intergranular SCC failure. Additionally, SCC resistance was decreased by stress localization owing to the high dislocation density on coarse Cu-rich particles. Our results demonstrate that tailoring the alloying content combined with T6 heat treatment is beneficial for increasing SCC resistance to compensate for the harmful effect of precipitates on SCC.

Stress corrosion cracking behavior of super 13Cr tubing in phosphate packer fluid of high pressure high temperature gas well

This paper describes a stress corrosion cracking (SCC) failure case of super 13Cr tubing serviced for six years in a high-pressure, high-temperature (HPHT) gas well. The failure causes and processes were studied by various characterizations and SCC simulation testing. The failure mode of super 13Cr tubing is brittle transgranular fracture, and the dominating role in SCC failure is the synergistic action of KH2PO4 phosphate packer fluid and CO2, leading to corrosion damaged zone, which is a selective corrosion along the martensitic multiscale boundaries. Under tensile stress, cracks developed at the corroded martensitic multiscale boundaries and propagated due to the low structural strength of the corrosion-damaged zone. Due to its compatibility with 13Cr tubing, formate is recommended as an alternate packer fluid for high-pressure, high-temperature (HPHT) gas wells.

Unexpected failure of cast superduplex stainless steel exposed to high chlorides containing water: From failure analysis to corrosion mechanisms settlement

This work deals with the failure analysis of a super duplex valve operating in technical waters with high chlorides content up to 80 °C. A careful fracture surfaces and microstructural characterization was combined with corrosion studies (SKPFM (Scanning Kelvin Probe Force Measurements) and polarization curves) of different valve regions in order to determine the failure mechanism.It was found that the cast material presents a segregated microstructure containing ferritic phases with different PREN (Pitting Resistance Equivalent Number). This strongly affects the corrosion properties of the material, enhancing the susceptibility to localized corrosion and leading to SCC (Stress Corrosion Cracking) failure.

Stress Corrosion Cracking and Copper Alloy Products

Stress corrosion cracking (SCC) is a common cause of structural failure. The simultaneous action of the corrosive environment and tensile stresses creates cracks that have an intercrystalline or transcrys-talline character. These are cracks with a fragile morphology of the fracture surface without signs of plastic deformation in their vicinity. SCC cracks occur in several alloys. This paper focuses on copper alloys in which this type of failure occurs frequently. Examples from practice show cases where the occurrence of SCC violation was related to the conditions of use of components and their production technologies. The paper does not aim to capture all the influences associated with the occurrence of SCC failure of copper alloy products.

Crack Propagation in Pipelines Under Extreme Conditions of Near-Neutral PH SCC

Stress Corrosion Cracking (SCC) process through which cracks occur in a variety of susceptible materials is a result of a combination of residual or applied stresses and corrosion. In oil and gas field, buried pipeline steels are made of low-alloy steels with a ferritic-pearlitic structure, such as X70. In dilute solutions, these materials are prone to SCC failure. The Near-neutral simulated soil solution (NS4) solution is established to imitate SCC conditions and subsequently became the industry requirement for crack growth experiments in the majority of laboratories. The strain-assisted active crack pathways are considered while modelling SCC growth as an oxide film rupture and anodic dissolution process. It’s been hypothesized that increasing the strain concentration can help with dissolution at the film-free crack tip. This research focuses on estimating the SCC crack growth rate under various environmental conditions in oil and gas pipelines using finite element modelling. The simulation is carried out using the J-integral theory in the COMSOL Multiphysics program. Simulations are performed to model the crack growth rate (CGR) using slip anodic dissolution (film rupture) mechanism. The plastic strain gradient is required to compute the SCC CGR (da/dt). Because the plastic strain located at crack tip increases proportionally to the crack length as it propagates, the CGR increases as the stress intensity factor (SIF) increases. The crack growth rates increase when constant loads are applied and as the temperature rises, and elevating the cathodic potential has a minimal influence on the propagation rate of cracks but raises the material yield strength and imparts brittle behavior to it.

Root cause analysis of the failure of the steam generator orifice assembly of a test reactor

Radiographic examination performed based on the increase in flow through one of the steam generators (SG) indicated the physical separation of orifice assembly from the orifice holder. Subsequently, this failed orifice assembly was cut from the feed water inlet header of the SG Module and subjected to further investigation. Both metallurgical and mechanics based post-failure investigations were performed. The failure of orifice assembly is attributed to stress corrosion cracking (SCC). Scanning electron microscopic (SEM) observation of the fractured surface showed an inter-granular mode of SCC failure. SCC occurred due to the residual tensile stresses developed due to the geometrical constraint against the thermal shrinkage during welding.A minimum gap of 160 µm at the top mating portion of the orifice assembly before the welding could have absorbed the thermal shrinkage to prevent the existence of sustained residual stresses and thereby SCC failure. Austenitic stainless steels are highly susceptible to SCC under the combined action of tensile stress and favourable environmental conditions. Under the favourable situation to SCC, cracks propagate slowly without any noticeable deformation until the stresses in the remaining ligament of metal exceed the fracture strength. Based on the insights gained from the root cause analysis, the design of the orifice assembly has been revised to mitigate a similar kind of failure in future.

Polystyrene/TiO2 nanocomposite coating for strength and toughness enhancement of aluminum alloy 2024–T3 in accelerated stress corrosion cracking

The polystyrene/TiO2 nanocomposite coating is evaluated for reducing the susceptibility of aluminum alloy AA2024-T3 to stress corrosion cracking (SCC). The as-synthesized titania nanoparticles of aspect ratio (AR) 1, 2, and 4 are individually loaded at 25 wt% to the acetone-dissolved polystyrene (PS) to make the nanocomposites. Coated compact tension specimens are tested under accelerated SCC testing that combines the constant displacement rate equivalent to 10−7 s−1 and 3.5 wt% NaCl solution dripped at the crack tip. The load and crack-mouth opening displacement of each specimen are recorded and analyzed to determine the indices to the mechanical ductility, strength, toughness, and fracture toughness. The PS/TiO2 AR1 coated specimens exhibit the least SCC susceptibility, with a relatively high fracture toughness of 55 MPa-m1/2 and more than 60 h of lifetime without apparent cracking under the SCC testing. Intriguingly, the PS-coated specimens perform similarly well. The results are explained by an SCC failure mechanism that considers the complex interaction among the agglomerated nanoparticles, polystyrene matrix, and the substrate in various aspects. The mechanism suggests that the nanocomposite coating with a higher yield strength and less permeability performs better. The highly loaded nanoparticles such as 25 wt% used herein make the nanocomposite only more marginally yieldable than polystyrene, but undesirably introduce morphological and electrochemical defects that count against the SCC susceptibility improvement.

Preventing failure of the anchoring system in underground coal mines

Cable bolts are commonly used as anchoring element in many underground mines. Reports on the premature failure of cable bolts in underground coal mines due to stress corrosion cracking (SCC) have been increasing in the past two decades. The previous studies found that the diffusion of atomic hydrogen into steel causes the SCC in cable bolts, which is known as hydrogen-induced stress corrosion cracking (HISCC). While the research on the mechanism of the HISCC in underground mines needs to be continued, it is essential to develop prevention measures to avoid such a failure. In this study, a variety of prevention measures that claim to prevent corrosion of steel were examined. Specifically, barrier coating, i.e., polymer, epoxy coating, as well as the sacrificial coating, i.e., hot-dip galvanising, methods were tested. Testing specimens were made by inserting loading pins between locked cable bolt king wires (coated) to simulate the in-situ stress condition. Cable bolt specimens were then fully immersed into a hydrogen sulphide solution to determine their resistance against HISCC. The test results showed that all the coatings had delayed the failure in varying degrees, but very few have significantly extended the time to fracturing. The polymer and epoxy coatings have become breached during the testing, and the failure occurred shortly after. The galvanised coating was dissolved in the testing solution and again allowed access of the solution to the steel surface, and subsequently resulted in failure. This indicates that these coatings can be potentially applied to prevent SCC failure; however, their impacts on the performance of bolts, such as their bonding with grout and bolt, still need to be considered.

Stress corrosion cracking of rockbolts: An in-situ testing approach

Premature failure of rockbolts due to stress corrosion cracking (SCC) is an unresolved global issue in underground structures, particularly underground mines. To date, SCC of rockbolts has been produced in laboratory-based studies under laboratory conditions, however no attempt to produce SCC in-situ in actual underground coal mine conditions has previously been made. In this study, an innovative testing methodology was used in which a rockbolt coupon was developed with multiple stressed sections. The test coupon could be placed in-situ within a borehole in an underground mine, exposing it to the borehole environment, the surrounding rock strata and the groundwater. In-situ coupons were made from both 1355 and HSAC840 grade rockbolt steels and installed within a typical rockbolted horizon where known SCC failure of rockbolts had occurred. SCC occurred in the 1355 grade in-situ coupons, but not in the HSAC840 grade ones despite service failures of HSAC840 rockbolts having occurred in the same underground mine. The difference in behaviour of the HSAC840 coupons and in-service rockbolts is most likely due to different stress regimes acting on the coupons and the rockbolts. Localised corrosion was observed on both steels although analysis of the groundwater indicated that it had low corrosivity. Microbiological analysis showed that a range of bacteria known to be involved in corrosion were present on the rockbolt coupons and in the underground environment. This suggested that the occurrence of localised corrosion and SCC in low corrosivity groundwater could be due to the presence of microbial organisms, in particular, sulphate reducing bacteria. The results of this study provide detailed insights into the SCC of rockbolts in the underground environment. The method developed here can be used to study other reinforcement elements and stressed settings for stress corrosion cracking.

Probing the stress corrosion cracking resistance of laser beam welded AISI 316LN austenitic stainless steel

The stress corrosion cracking (SCC) resistance of the laser beam welded (LBW) AISI 316LN austenitic stainless steel (SS) was assessed and compared to the base metal (BM). The weld joint was produced using a 2.5 kW laser power source at 1500 mm/min welding speed. Microstructural characterization of the base metal and weld joint were done by the following techniques: (i) Optical Microscopy (OM), (ii) Scanning Electron Microscopy (SEM) and (iii) Transmission Electron Microscopy (TEM). The primary mechanical properties such as strength, toughness and hardness of the welded joint were evaluated and compared with the base metal. Stress Corrosion Cracking (SCC) assessment was done in boiling 45 wt% MgCl2 solution at constant load condition as per American Society for Testing and Materials (ASTM) standard G36-94. From the SCC experiment data, steady-state elongation rate ([Formula: see text]), transition time ([Formula: see text]) and time to failure ([Formula: see text]) were found and generalized equations to predict the time to failure of the base metal and LBW joint were successfully derived. The passive film rupture mechanism majorly influenced the SCC failure for 316LN and welded joint. The formation of the discontinuous δ-ferrite network, residual stress and nitrogen pore nucleation at the fusion zone of the LBW joint deteriorated the SCC resistance. The metallographic and fractographic studies revealed brittle transgranular SCC failure of the base metal as well as the LBW joint in all the stress conditions.

A failure case of P110 steel tubing in CO2 flooding well

Purpose This paper aims to analyze a failure case of a P110 tube in a CO2 flooding well. Design/methodology/approach The chemical composition, microstructure and mechanical properties of the failed P110 tubing steel were tested, and met the API Spec 5CT standard. The fractures were investigated by scanning electron microscopy and energy dispersive spectroscopy. Findings Fracture was induced by stress corrosion cracking (SCC) and that the stress concentration caused by the mechanical damage played an important role in the failure. The failure case is a SCC failure affected by mechanical damage and galvanic corrosion. Originality/value The effect of the infiltration of groundwater was studied in the failure case. The stress concentration caused by the mechanical damage played an important role in the failure.

Stress corrosion cracking fracture mechanism of cold-drawn high-carbon cable bolts

Premature failures of cable bolts due to stress corrosion cracking (SCC) in underground reinforcement systems are universal issues with limited practical countermeasures at present. To determine the SCC fracture mechanism which is an essential step to develop the potential solutions, the environment conditions leading to SCC failures were examined using four-point bend tests. Fractographic features of both serviced-failed and laboratory-failed cable bolts were investigated and compared. It was identified that the fracture surfaces of cable wires were characterised by step-shape fracture mode. The highly-oriented wavy lamellae microstructures of cable wires, produced during cold-drawn manufacturing process, have significant effects on the direction and path of crack propagation. Hydrogen-assisted SCC was suggested as the dominant fracture mechanism in cable bolt failures. SCC only occurred in the environmental conditions that promoted the diffusion of hydrogen diffusion into the cable wires, and crack growth rates were determined by the hydrogen diffusion rates. This study provided fundamental knowledge on fracture mechanism of cable bolts which can be applied to further study in identifying potential countermeasures against the SCC of cold-drawn high-carbon cable bolts.

Stress Corrosion Cracking of AZ91 + xCe Alloy Using Proof Ring Test in ASTM D1384 and NaCl-K2CrO4 Solutions

The effect of cerium addition on AZ91 magnesium alloy and its influence on stress corrosion cracking (SCC) were studied using constant load proof ring testing NaCl-K2CrO4 and ASTM D1384 solutions at 70 and 80% of yield stress, respectively. The investigation revealed that the optimum grain refinement of desired phases occurred with 0.5% addition of cerium. The addition levels of cerium above 1.5 wt.% to AZ91 alloy resulted in premature failures due to poor SCC resistance in both solutions (K2CrO4 and ASTM D1384 solutions). The microstructural studies of the experimental alloys were characterized by using optical and scanning electron microscopy. The elemental compositions of cerium-added AZ91 magnesium alloys were studied by energy-dispersive spectroscopy. The results indicate that the mode of SCC failure was found to be transgranular in nature along with secondary cracks containing cleavages which resulted from the hydrogen embrittlement and anodic dissolution phenomena. The AZ91 alloy with 0.5 wt.% cerium exhibits better mechanical properties and high stress corrosion resistance.

Stress Corrosion Cracking Behavior of Tungsten Inert Gas Welded Age-Hardenable AA6061 Alloy

The effects of two temper conditions (T4 and T6 heat treatments) upon the stress corrosion cracking (SCC) of AA6061 plates have been investigated in this work. AA6061 alloys were double-side-welded by the tungsten inert gas (TIG) welding method. SCC behavior of both the as-welded and as-received alloys was reported. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine the precipitate structure of the thermal-altered zones and the base metal (BM), and also the hardness variations were examined using microhardness testing (Vickers hardness). The small-size precipitate structures in the T6 tempered alloy and the coarser precipitate structures in the T4 tempered alloy were found by microstructural investigations. As a result, T4 temper heat treatment of this alloy considerably reduced its susceptibility to stress corrosion cracks due to relatively coarse and more separate precipitate morphology. In welded specimens, SCC failure occurred in the area between the heat-affected zone (HAZ) and the base metal. Stress corrosion resistance in the fusion zone was strong in both temper conditions. The aim of this work was to obtain the effects of heat treatment and welding on SCC behavior of the age-hardenable aluminum alloy. The authors conclude that a deep insight into the SCC resistance of AA6061 alloy indicates the precipitate particle distributions and they are the key point for AA6061 alloy joints in chloride solution.