Hydrogen Embrittlement - Loading Rate Effects in Fracture Mechanics Testing

The fitness for purpose methodology is more and more used in the oil and gas industry to evaluate the significance of pre-existing flaws and material deficiencies with regard to the suitability of continued operation of equipment. In this methodology, traditional fracture mechanics is integrated with expertise in inspection technology, material evaluation, and corrosion damage assessment, stress analysis and the mechanics of materials. Application of the fitness for purpose methodology for equipment operating in hydrogenation environments or in sour service is rather complex, in particular, due to the uncertainty in the reduction of the fracture toughness caused by hydrogen embrittlement. Hydrogen embrittlement is a time-dependent fracture process caused by the absorption and diffusion of atomic hydrogen into the steel, which results in a loss of ductility. An experimental study has been performed to quantify the reduction of fracture toughness of an API 5L grade X56 pipeline steel, and a numerical model has been presented to understand the experimental results.