Hydrogen Assisted Stress Corrosion Cracking Research Articles

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.

SCC susceptibility of solution-annealed 316L SS in hydrogenated hot water below 288 °C

Stress corrosion cracking (SCC) susceptibility of solution-annealed 316L stainless steel was evaluated by slow strain rate test in oxygenated, deaerated and hydrogenated water below 288 °C. At 288 °C, no SCC was found in the specimens tested in oxygenated water, while in hydrogenated water, SCC occurred irrespective of dissolved-hydrogen (DH) content in the late stage of deformation where cold-working was followed by necking. The SCC susceptibility diminishes as temperature decreased from 288 °C to RT, which was accompanied by a reduction of oxide film thickness. At 220 °C, SCC occurred at the highest DH content only, which suggests a combined effect of DH content and test temperature on the SCC susceptibility. The combined effect can be explained by anodic reaction rate, hydrogen diffusion rate and hydrogen trapping ability. The SCC susceptibility appeared to increase with DH content, which was reasonably explained by suppression of the protective oxide film formation on specimen surface and increasing hydrogen content in the specimen. Based on an SCC model that hydrogen reduces cohesive force in austenitic stainless steel lattice, the SCC behavior can be interpreted in terms of hydrogen-assisted SCC (HASCC) where corrosion-induced hydrogen production, suppression of the formation of protective oxide film caused by hydrogen, work-hardening, and hydrogen-induced reduction of cohesive force of the lattice atoms are necessary.

Modeling the Effects of Dissolved Hydrogen, Temperature, pH, and Global Stress on Stress Corrosion Cracking of a Cr-Ni Model Alloy in High-Temperature Water

As an extension of recently presented stress corrosion cracking (SCC) models for pure nickel and iron in high-temperature water, the anodic path, hydrogen-assisted stress corrosion cracking of a model Cr-Ni alloy is presented, utilizing Alloy 600 (UNS 06600) mechanical properties. With the local anodic path corrosion as the crack initiation phase, the respective oxides precipitate while the crack tip solution acidify and establish local hydrogen ion reduction conditions. Depending on the applied global stress, local plastic straining then provides an active crack tip surface that transfers atomic hydrogen to the plastic zone ahead of the crack tip. Hydrogen-assisted crack propagation is then controlled by the calculated local hydrogen ion reduction charge and the plastic strain distribution ahead of the crack tip. The results show that for global stress levels close to the yield stress and at constant dissolved oxygen contents, the increasing dissolved hydrogen contents provide peak crack growth rates at ...

Identification of corrosion mechanisms by univariate and multivariate statistical analysis during long term acoustic emission monitoring on a pre-stressed concrete beam

Acoustic Emission (AE) technique was used to monitor Hydrogen Assisted Stress Corrosion Cracking (HASCC) activated by using ammonium thiocyanate solution during a long term laboratory corrosion test on a pre-stressed concrete beam using post-tensioned steel strands. By univariate analysis, three stages of damage mechanisms were identified: activation, propagation and rupture. We therefore proposed a combination of principal component analysis and self organising maps algorithms as a new procedure to identify the progression of different damage mechanisms during time until final failure. Initiation, propagation and critical rupture phases were clearly identified and associated to specific features of the AE events.

Hydrogen-assisted stress corrosion cracking simulation using the stress-modified fracture strain model

This paper proposes a numerical method to simulate hydrogen-assisted stress corrosion cracking, via coupled diffusion elastic-plastic finite element damage analyses based on phenomenological stress-modified fracture strain model. For validation, simulated results using the proposed method are compared with published experimental data of FeE 690T compact tension tests under air and hydrogen condition with various constant load-line displacement rates. The simulated results agree well with experimental data.

Investigation of hydrogen assisted cracking of a high strength steel using circumferentially notched tensile test

Abstract The novel circumferentially notched tensile (CNT) test technique is used for the first time for an investigation of hydrogen assisted stress corrosion cracking. Effect of hydrogen on the fracture strength of high strength steel AS-4340 is examined in neutral 3.5% NaCl solution at room temperature and under hydrogen supply from within the material and/or external environment. A progressive drop in the stress intensity factor at the fracture was observed as a result of: (a) increasing span of hydrogen pre-charging (hence increasing internal hydrogen) and (b) decreasing rate of loading (hence increasing external supply of hydrogen). The measured critical stress intensity factors corresponding to varying degrees of supply of internal hydrogen are consistent with the computed hydrogen concentrations ahead of the crack tip. The experimentally determined threshold for hydrogen embrittlement in the regime of slower loading rates are consistent with the published data. The results presented here establish the usefulness of the CNT test technique for the investigation of HASCC in high strength steel over a wider range of loading rate.

Modelling of mode-I stable crack growth under hydrogen assisted stress corrosion cracking

The paper presents a new strategy based on combined analytical and finite element (FE) solution to hydrogen assisted stress corrosion crack growth. The diffusion process is solved analytically through both one-and two-dimensional modelling. These solutions are adopted with two-dimensional FE based cohesive zone model of crack extension study. The results fit well with published experimental data and show improvement over the predictions by full FE approach. The new solution approach helps to reduce time required for simulation/computation. The study has produced a relationship between concentration dependent reduction in cohesive strength and plastic strain rate.

Effects of Shielding with Various Hydrogen-Argon Mixtures on Supermartensitic Stainless Steel TIG Welds

Abstract A number of common defects in stainless steel welding result from the presence of hydrogen in the weld. The service life of the stainless steel joints is further significantly dependent on the presence of hydrogen in the respective environment and the susceptibility of various weld microstructures to hydrogen degradation. As a relatively new materials generation, supermartensitic stainless steels (SMSS) are increasingly applied to substitute more expensive alloys, particularly in the oil and gas industries. As a result of their martensitic microstructure these alloys are prone to hydrogen assisted cracking (HAC). The resistance of SMSS to hydrogen assisted stress corrosion cracking (HASCC) during sour service has been extensively studied, predominantly for industrial purposes. Studies are primarily conducted with parent materials based on standard test procedures. The principal hydrogen behavior in welded SMSS microstructures has been less investigated. The central objectives of the study are to determine the hydrogen interactions with the microstructure of a Gas Tungsten Arc (GTA) welded SMSS and hydrogen trapping mechanisms. The interactions of hydrogen with various Tungsten Inert Gas (TIG) welded SMSS microstructures are investigated by means of X-ray diffraction (XRD) and optic (OM) and electronic microscopy (SEM). A number of methods have been employed for the estimation of the quantities of absorbed hydrogen. Hydrogen interaction with structural defects and the characteristics of hydrogen desorption have been studied by means of thermal desorption spectroscopy (TDS), and hydrogen content measurements (LECO analyses). The effects of the respective microstructure on hydrogen absorption and desorption behavior are discussed in detail.

Failure analysis of a 300M steel pressure vessel

A failure analysis was made in a 300M steel pressure vessel which has failed during hydrotest. The rupture occurred suddenly at a pressure level lower than what has been expected for the proof pressure. According to the results of various examinations it was concluded that hydrogen assisted stress corrosion cracking was the mechanism responsible for the failure. The root causes of this failure have been identified, serving as base for the modification of testing procedures in similar components.

Simulation of hydrogen assisted stress corrosion cracking using the cohesive model

This paper investigates the effect of hydrogen diffusion on stable crack propagation by using numerical finite element simulations based on the cohesive model. The model with its two common parameters, cohesive strength, T 0, and critical separation, δ 0, and its two additional parameters for stress corrosion cracking, the effective diffusivity, D eff, and a material parameter, α, which represents the reduction of the cohesive strength, is described. This model is then employed to predict the stable crack propagation in C( T) specimens made from a high strength structural steel which were tested under hydrogen charging conditions in rising displacement tests using various deformation rates. It is shown that, in general, the prediction of stable crack propagation is promising, but may be further improved by the use of a more sophisticated diffusion equation. Finally, the influence of variations of the effective diffusivity and the cohesive strength reduction on the thus simulated crack growth resistance curves is studied.

Hydrogen-enhanced stress-corrosion cracking of aluminum alloys

We present the results of the investigation of Al-Zn-Mg and Al-Zn-Cu-Mg alloys in NaCl solutions at low strain rates. The contribution of hydrogen to the process of stress-corrosion cracking is analyzed by taking into account the influence of the admixtures of arsenic trioxide and residual hydrogen (remaining after the processes of release and cathodic polarization) on the susceptibility of metals to this kind of cracking. A mechanism of hydrogen-assisted stress-corrosion cracking taking into account the time dependence of the microstructure of grain boundaries, concentration of hydrogen, and its distribution is suggested on the basis of the concept of critical concentration of hydrogen.

Development and Applications of Titanium Alloy SP-700 with High Formability

Abstract A new β-rich α + β titanium alloy, SP-700, was designed to improve hot workability and mechanical properties over Ti-6A1-4V alloy. The chemical composition of the alloy is Ti-4.5A1-3V-2Mo-2Fe, and particularly enhanced properties include superplasticity, hardenability, and fatigue strength. Owing to its extremely fine microstructure and low β-transus temperature, SP-700 is superplastically formable at temperatures below 1073 K without significant increase in flow stress. More advantageously, diffusion bonding is also accomplished around this temperature. The low temperature SPF/DB process not only saves die material life and process costs, but also reduces alloy degradation from exposure at elevated temperatures, e.g., grain growth and oxidation. Isothermal and conventional hot forging are also performed better with SP-700 than ordinary titanium alloys like Ti6A1-4V. The alloy is heat treatable and one of its many mechanical properties is that high strength over 1200 MPa is attained in solution treatment and aging condition. The advantage to this is that the moderately stable β phase tolerates air cooling for solution treatment. Thermal distortion in work pieces, which would be caused by rapid cooling, is consequently avoided. In addition, the alloy is cold workable in such cases as rolling and blanking, when annealed around 1073 K. Furthermore, fatigue life and resistance to hydrogen-assisted stress corrosion cracking are improved due to reduced aluminum content. The superior properties of SP-700 over conventional titanium alloys make new applications possible in non-aerospace fields including sporting goods, hand tools, and wrist watches. Golf drivers, with club heads made of SP-700, are sold commercially. Crampons, a new product of SP-700, withstand cold blanking and bending which reduces production costs and extends life. Due to its high forgeability, SP-700 is expected to extend its application to the production of steam turbine blades. Details of practical applications have been demonstrated together with advantages of properties and fabrication for the blades.

Activation pH and susceptibility to hydrogen assisted stress corrosion cracking of martensitic stainless steels in sulphate solutions

The investigation of two different high strength stainless steels by the slow strain-rate technique has shown the existence of critical pH values (activation pH) for stress corrosion cracking in sulphate-containing media which depend on the steel composition. The slow strain-rate test indicates a sharp decrease of specimen ductility at the activation pH the value of which can also be determined by independent electrochemical methods.