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The pipeline steels which are used for transportation of natural gas and crude oil suffer from hydrogen damage at their internal as well as external surfaces. The internal surfaces of pipelines are generally affected due to hydrogen induced cracking and the external surfaces due to the soil environmental conditions which cause stress corrosion cracking. In the present investigation, the electrochemical corrosion behavior of X70 pipeline steel was studied in sour environment and near neutral soil environment. To assess the mechanism of hydrogen damage in steel, electrochemical hydrogen charging and permeation techniques were used to characterize the hydrogen distribution, trapping and its diffusion in X70 pipeline steel. It has been found that corrosion behavior of pipeline steel in the sour environment is higher than the near neutral soil solution. From the hydrogen permeation study it is established that the hydrogen permeation rate increases with the square root of the charging current density, and the increase of hydrogen flux is directly proportional to the subsurface hydrogen concentration.

Fatigue lives at high peak stresses for peak-aged (T6) and overaged (T73) 7075 aluminum alloy were compared in the uncorroded and precorroded (pitted) states. Absolute fatigue lives of T73 samples were much higher than that of T6 in the virgin as well as precorroded condition, but the normalized life of T73 was less than that of T6, indicating an intrinsic crack initiation resistance in the former, borne out by fractography, which showed that fatigue cracks almost always initiated at pits for T73 but not for T6. The various crack initiation methodologies observed and the effect of pitting on fatigue lives in the two aging conditions are discussed.

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Pitting corrosion of two tempers (T6 and T73) of 7075 Aluminium alloy were quantified by digital image processing. The effect of pitting corrosion on fatigue life in 7075 Aluminium alloy in two aging conditions was studied. Pitting was found to be slightly more severe for T6 tempers compared to T73 tempers for different time of exposures. The fatigue lives of two tempers of 7075 Aluminium alloy at high peak stresses were compared in the uncorroded and pre-corroded (pitted) states. Absolute fatigue lives of T73 samples were much higher than that of T6 in the uncorroded as well as pre-corroded condition. The various crack initiation methodologies observed through fractographic analysis is discussed.