Laboratory Method for Simulating Hydrogen Assisted Degradation of Gas Pipeline Steels

Integrity of natural gas transmission systems is of great importance for energy and environmental security. Deterioration occurs in gas transit pipelines due to operational conditions and action of corrosion and hydrogenating media and leads to changes in microstructure and mechanical properties of pipeline steels, which influences on pipeline performance. Hydrogenation of metal during corrosion process together with working stresses facilitates a development of in-bulk damaging at nano- and microscales. Reducing brittle fracture resistance of pipeline steels under operation increases significantly a failure risk of gas pipelines, associated with in-bulk material degradation. Therefore hydrogen assisted degradation of pipelines steels under operation calls for effective methods for in-laboratory accelerated degradation. The present study is devoted to the development of the procedure of laboratory simulation of in-service degradation of pipeline steels. The role of hydrogen in degradation of pipeline steels was analysed. The procedure of accelerated degradation of pipeline steels under the combined action of axial loading and hydrogen charging was developed and induced in the laboratory. The procedure was consisted in consistently subjecting of specimens to electrolytic hydrogen charging, to an axial loading up and to an artificial aging. Pipeline steels in the different states (as-received, post-operated, aged and after in-laboratory degradation) were investigated. The tensile mechanical behaviour of steels and impact toughness were experimentally studied. It was definitely concluded that the applied procedure caused the changes in the metal mechanical properties at the same level compared to the properties degradation due to operation. The developed procedure enables, on a laboratory scale, simulating of pipeline steel degradation during long-term operation under simultaneous action of hydrogenation and working loading, and it makes possible to predict the mechanical behaviour of pipeline steels during service.