It is still unclear how environmentally assisted cracking, especially sulfide stress cracking (SSC), is caused by corrosion and fracture behavior. In this study, a new in situ technique for an SSC visualization challenge was established and applied for the visualization of microcrack propagation resulting from a single pitting on the steel surface of 13% Cr martensitic stainless steel during four-point bending SSC tests and discussed by combining ex situ x-ray computed tomography (XCT) and electron backscatter diffraction (EBSD). The dynamic behavior of microcracks was visualized successfully, and the microbubbles behavior with the corrosion reaction was also captured. Regarding the relationship between internal structure and microstructure for cracking, it was found that a cavity was formed in the interior of prior to the cracks seen on the surface by XCT, and cracks by EBSD were propagated along prior austenite grain boundaries. On the basis of in situ observations and complementary ex situ analyses, the actual situation of crack on the steel surface was revealed and discussed with both corrosion and fracture over time. This approach provides an opportunity to clarify the SSC occurrence process based on actual SSC tests and contributes to the determination of phenomenological criteria. Furthermore, by combining this in situ technique with commonly known electrochemical measurements such as polarization curves, open-circuit potentials, and electrochemical impedance spectroscopy, it is possible to directly discuss various electrochemical data corresponding to corrosion and fracture behavior, including dissolution and gas evolution.

The localized corrosion behavior of Type 304L stainless steel (UNS S30400), Alloy 625 (UNS N06625), and three experimental NiCoCrMo multiprincipal element alloys (MPEA), exposed to methanol/lithium chloride solutions with different water contents, is examined in this paper. Cyclic potentiodynamic polarization tests indicated that water increased the pitting and repassivation potentials and the critical temperature at which localized corrosion occurred in chloride solutions. The effect of water on repassivation potential in methanol-chloride solution depended on the chloride concentration and alloy content. At lower chloride concentration and higher alloy content, water had a greater inhibiting effect on repassivation potential, suggesting a competitive reaction between chloride and water on the metal surface in the pit. The localized corrosion resistance of the MPEAs followed the same trend as that of commercial stainless steels and Ni-base alloys in terms of the effect of alloying elements. The implications of these results on the mechanisms of localized corrosion are discussed.

Ordinary Portland cement (OPC) is the main hydraulic construction material, the fabrication of which is an important source of carbon dioxide. Presently, alternative binders are attracting a lot of interest as a way to minimize their environmental impact. Calcium sulfoaluminate cements (CSAs) show massive potential for emissions reduction and possess unique properties. Nevertheless, there is an essential knowledge gap concerning the durability of CSA structures in terms of reinforcement corrosion. This work studies the corrosion behavior of plain carbon steel in media of fixed and variable composition that simulate the liquid phase of fresh CSA-based materials at different stages of binder hydration. The findings of electrochemical and nonelectrochemical techniques suggest that sulfate-induced corrosion of mild steel starts at early stages of hydration in pure CSA and in blended CSA-OPC binders. Once initiated, corrosion of reinforcement would continue regardless of favorable conditions found in the hydrated state in both systems, even though short-term repassivation was observed. In addition, the origin and possible solutions to tackle the corrosion problem are discussed.

Mechanical polishing (MP), electropolishing (EP), and magnetoelectropolishing (MEP) were applied on 308L stainless steel (SS) weld cladding. The surface characteristics after surface treatment and the oxides after immersion in the primary water of a pressurized water reactor were studied. XPS results showed that the passive film of surface-treated MEP 308L SS had higher Cr/(Ni+Fe) than MP and EP 308L SS, and reported surface-treated MEP 316L SS. Transmission electron microscopy results showed that duplex-layer oxide films consisted of Fe-rich spinel outer crystals and Cr-rich inner layers were formed on all surface-treated 308L SS cladding after immersion. The inner oxide layers on austenite were Cr-rich spinel dominant oxides and much thicker than the chromia-dominant oxides on ferrite. MEP decreased the inner oxide layer thickness on austenite of oxidized 308L SS. The oxidation resistance of the ferrite matrix with higher Cr content was not obviously impacted by surface treatment. A higher Cr/(Ni+Fe) in the preformed passive film on the austenite was mainly responsible for the better oxidation resistance of MEP 308L SS cladding. The improvement of oxidation resistance by MEP on dual-phase 308L SS cladding was different from that on single-phase 316L SS, suggesting that a local heterogeneous passive film on surface-treated MEP 308L SS was more likely degraded to a duplex-layer oxide film compared to the single-layer one on MEP 316L SS.

The microstructures and electrochemical pitting behaviors of AA2024 in successive spark plasma sintering, solid solution treatment (SST), and aging treatment (AT) states were investigated. The effect of intermetallic compounds (IMCs) on corrosion behaviors of AA2024 was analyzed. It was observed that the number and size of IMCs decreased after SST, and increased again after subsequent AT. The as-SST sample showed the best pitting resistance. Corrosion morphologies analysis indicated that pits initiated at the periphery of IMCs, both the big and small particles might be the nucleation sites of pits. For the sintered AA2024, after immersion in 3.5 wt% NaCl solution for 30 min, the critical size for IMCs causing pits is 0.107 μm2. For the IMCs bigger than this size, whether pits initiate around them during immersion depended on the potential difference of these particles with the matrix.

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.

The influence of iron contamination on a stainless steel surface was evaluated based on a novel rust deposition procedure. The main variables that control the corrosion process and the influence of iron contamination on localized corrosion resistance of austenitic and super duplex stainless steel were investigated. Cyclic potentiodynamic polarization tests and environmental exposure with different rust surface contamination degrees were performed. Potentiodynamic polarization curves showed that iron contamination deteriorated the local corrosion resistance of both stainless steels. Environmental salt-spray exposure results indicated that the alloy resistance to rust contamination increased with the materials’ pitting resistance equivalent. Likewise, the extent of localized corrosion decreased with the rust contamination degree. These findings suggested that preferential corrosion from rust contamination was associated with the occluded solution chemistry. Environmentally friendly cleaning methods, including chemical treatments and laser cleaning, were evaluated as alternatives to hazardous pickling based on hydrofluoric-nitric acid. Last, practical recommendations for rust contamination of stainless steel are addressed.

This work investigates the oxidation of austenitic stainless steel 316 at temperatures close to the critical point of water: subcritical water at 330°C and 27 MPa, the transition between subcritical and supercritical water at 374°C and 27 MPa, and supercritical water (SCW) at 380°C and 27 MPa. The surfaces of the samples were characterized using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy before and after exposure. Magnetite (Fe3O4) was found to be present on all surfaces of all samples. The samples exposed to subcritical water also showed the presence of a nickel-iron chromium mixed spinel Ni(Fe2-xCrx)O4. The oxide morphology was observed to vary based on exposure temperature; an increased nucleation and growth rate, and an increased generation of Fe2+ was observed on samples exposed to the transition region and SCW.

The effects of environments in altering the atomic strain distribution in AA 7004 while subjected to slow strain rate testing to environmentally assisted cracking are investigated. Two different temper conditions—one where predominantly G.P. zones are present and the other with predominantly η′/η precipitates were chosen for the present study. Three different test environments—glycerol (Gly), 3.5 wt% NaCl (OCP), and 3.5 wt% NaCl with 100 mV cathodic charging vs. open-circuit potential (CP) were used. Under the above environmental conditions, the alloy aged at 140°C for 24 h, containing predominantly G.P. zones, showed the existence of the tensile nonshear components of the strain. On the other hand, the alloy aged at 140°C for 48 h, containing predominantly η′/η precipitates, showed only one of the two nonshear strain components that were tensile in nature, with a simultaneous reduction in the shear component of strain. The work highlights that the effects of the environment on the deformation behavior of the alloy are evident by way of alterations in strain distribution at the atomic level, which could possibly explain the increase in dynamic recovery for the microstructure containing primarily the G.P. zones, and the decrease in dynamic recovery for microstructures consisting predominantly of η′/η precipitates.

Top of the line corrosion (TLC) is a serious concern in wet gas transportation pipelines operating in a stratified flow regime. Extensive research on TLC has been conducted in hydrocarbon-free environments while, in production environments, condensable hydrocarbons are always present. When water and hydrocarbons co-condense, the condensate comprises two immiscible liquids which have different wettability and corrosivity. In this study, the co-condensation process was investigated using a borescope for visual observation and a set of conductivity probes for quantification of water-wetted area. The corrosion behavior of carbon steel under water-only condensation and water/hydrocarbon co-condensation scenarios was evaluated with weight loss measurements and surface analytical techniques (scanning electron microscopy, energy dispersive spectroscopy, and 3D profilometry). The results showed that water and hydrocarbon condensation processes interacted with each other. Even though the rate of hydrocarbon condensation was much greater than that of water, the hydrophilicity of the steel surface always ensured that it would be mainly wetted by water. However, the presence of n-heptane interfered with the water droplet coalescence and segregated water into smaller droplets which affected the water chemistry. This resulted in a potentially higher pH and iron ion concentration in the water droplet as compared to a water-only scenario. The corrosion rate consequently decreased and was found to be less dependent on the water condensation rate in the co-condensation scenario, as compared to a pure water system.