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The stress corrosion cracking (SCC) behaviors of X100 pipeline steels with different heat-treated microstructures in carbonate/bicarbonate solution at various potentials were investigated in this study. Several analyses were performed using electrochemical measurements, slow strain rate tensile (SSRT) tests, scanning electron microscopy (SEM), and electron back-scattered diffraction (EBSD). The results showed that the SCC susceptibilities of heat-treated microstructures increase as the cathodic potential shifts from −850 to −1200 mVvsSCE. At a weak cathodic potential, the different microstructures show clear SCC sensitivity, showing that hydrogen cannot be ignored in this circumstance when the alkaline environment is not considered seriously. At a mild cathodic potential, hydrogen sensitivity controls SCC behavior, but at a larger negative potential, both electrochemical effect and hydrogen sensitivity influence SCC behavior. The SCC cracks propagate along the high angle grain boundary (HAGB) at open circuit potential (OCP) and as the applied potential is adjusted negatively, the cracks would either follow low angle grain boundary (LAGB), HAGB or random orientation propagation paths. The synergistic influence of dislocation, grain boundary, grain size, martensite/austenite (M/A) island, and carbide controls the SCC process of the X100 pipeline. SCC susceptibility was shown to be high in microstructures with coarse grain and high dislocation density, whereas grain boundaries such as the martensite/austenite (M/A) island and carbide offer sites for SCC initiation.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) with different microstructure in simulated deep-sea environments was studied through microstructure characterization, electrochemical measurements, hydrogen determination and slow strain rate tensile (SSRT) tests. Hydrogen degrades corrosion and SCC resistance by penetrating into matrix, weakening passive film and accelerating anodic dissolution (AD). Therefore, SCC is controlled by hydrogen embrittlement (HE) and hydrogen-facilitated anodic dissolution (HFAD). Microstructure has a great impact on SCC, and quenched DSSs are more SCC susceptible due to coarser grains, unbalanced partition of two constitutional phases, brittle precipitates and higher defect density. • Assessing SCC of 2205 duplex stainless steel with weld microstructure in simulated deep sea. • SCC is dominated by HE and HFAD. • Clarifying why simulated weld microstructure are more SCC susceptible. [ABSTRACT FROM AUTHOR]

• The hydrogen plays an important role in high-pH SCC under cathodic potentials. • Under cathodic potentials, cracks propagate along the low residual strain path. • FIB is used to research the microstructure of crack. Stress corrosion cracking (SCC) of X100 grade pipeline steel was researched in carbonate/bicarbonate solutions by using slow strain rate tensile (SSRT) tests, electrochemical testing, X-ray photoelectron spectroscopy (XPS), electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), the focused ion beam (FIB) lift-out technique and transmission electron microscopy (TEM). It is found that the X100 pipeline steel has low SCC sensitivity at the open circuit potential (OCP) and has high susceptible to SCC owing to the combined effect of anodic dissolution (AD) and hydrogen embrittlement (HE) at the applied cathodic potentials in carbonate/ bicarbonate solutions. At applied cathodic potentials less than about −950 mV, the SCC processes of X100 steel are dependent on AD and HE, while at more negative applied potentials, HE plays a more dominant role. The detailed SCC mechanism was studied by advanced detection methods. The results show that cracks propagated along the interface with low residual strain at various cathodic potentials, indicating that the low residual path is more active for both the anodic reaction and dislocation emission, and the high residual strain area may act as the cathodic zone. This phenomenon will be helpful to the design of high-SCC-resistant high-strength pipeline steel. [ABSTRACT FROM AUTHOR]

• Under the action of Cl-, sulfide and stress, cracks initiate on the inner wall of the tube and expand to the outer wall, which is the main cause of failure. • Intergranular corrosion, pitting corrosion and sulfide stress corrosion cracking are found on the failed tube. • The relationship between corrosion products and microcrack characteristics of the failed Cr-containing tube is carefully analyzed. • Cl element is largely enriched on both sides of the crack at the rust/matrix interface. With the development of oil and gas resources, the service condition of tube steel becomes more and more severe in oilfields, leading to a large number of corrosion failure cases in actual production. The systematic analysis of the failed parts can help to find failure reasons and propose protection methods. In this paper, the failure analysis of a high-strength tube fractured in a real oilfield was carried out by inspecting the basic properties and corrosion characteristics of the steel. SEM, EDS and XRD were used to analyze the chemical compositions of the products on the surface and around the crack tip. Results indicated that the failure of the tubing steel was due to the stress corrosion cracking under the effects of Cl-, sulfide and stress. Intergranular and pitting corrosion characteristics were also discovered on the failed tube. Microcracks started on the inner wall and propagated to the outer wall. Cl- largely aggregated at both sides of the crack tip, providing a driving force for crack propagation. [ABSTRACT FROM AUTHOR]