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a b s t r a c tMeasurement of near-surface stress generated by metallic corrosion can reveal defects and material property changes relevant to structural degradation by stress corrosion cracking. In this study, stress and topography evolution were characterized during alkaline corrosion of high-purity aluminum. In situ stress measurements revealed tensile increases of the force per width (stress integrated over depth) that scale directly with the sample yield stress. Spectral analysis of the uniform dimpled surface pattern produced by corrosion showed that transient changes of its characteristic wavelength track closely with the force per width. Together, the stress and topography measurements imply that corrosion creates a plastically deformed metal layer. Tensile stress is attributed to the lattice contraction associated with metal vacancies introduced during dissolution. In agreement with this hypothesis, a vacancy diffusion model successfully predicted the time dependence and magnitude of the force response, as well as the observed scaling relation between plastic layer thickness and pattern wavelength. The driving force for vacancy formation is thought to arise from high hydrogen and low aluminum chemical potentials near the corroding surface, the latter imposed by the high dissolution potential relative to the equilibrium potential of aluminum.

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The girth weld tensile properties of API X80 grade high-frequency electric resistance welded (HFW) steel pipe for surface casing with the chemical composition of 0.05C–1.6Mn–0.06Nb (mass %) and the diameter of 558.8 mm and wall thickness of 25.4 mm were investigated by simulated postweld heat-treatment (PWHT). The tensile specimens taken from girth butt welded pipe were heat-treated under the conditions of 625 °C × 2 h and 675 °C × 2 h in an air furnace in order to simulate PWHT of casing products. The result of the girth weld tensile test of the heat-treated specimens showed that yield strength and tensile strength decreased very little and these properties sufficiently satisfied the API X80 specification. The change in strength due to heat treatment was discussed based on microscopic observation of the submicrostructures of the base metal by the electron back-scattered diffraction (EBSD) technique, transmission electron microscopy, X-ray diffraction (XRD), and the extraction residue precipitate classification method. The authors concluded that the fine NbC with a diameter of 12–18 nm, which precipitated during the heat treatment, prevented the decrease of strength due to the slight grain growth and dislocation recovery associated with PWHT. Additionally, the effect of PWHT conditions was evaluated by using small-scale laboratory specimens obtained from the base metal. Tensile properties were summarized as a function of the tempering parameter. As a result, strength remained almost constant at the tempering parameter equivalent to the PWHT conditions of 625 °C × 16 h.