Abstract
This paper summarizes a series of the authors’ research in the field of assessing the operational degradation of oil and gas transit pipeline steels. Both mechanical and electrochemical properties of steels are deteriorated after operation, as is their resistance to environmentally-assisted cracking. The characteristics of resistance to brittle fracture and stress corrosion cracking decrease most intensively, which is associated with a development of in-bulk dissipated microdamages of the material. The most sensitive indicators of changes in the material’s state caused by degradation are impact toughness and fracture toughness by the J-integral method. The degradation degree of pipeline steels can also be evaluated nondestructively based on in-service changes in their polarization resistance and potential of the fracture surface. Attention is drawn to hydrogenation of a pipe wall from inside as a result of the electrochemical interaction of pipe metal with condensed moisture, which facilitates operational degradation of steel due to the combined action of operating stresses and hydrogen. The development of microdamages along steel texture was evidenced metallographically as a trend to the selective etching of boundaries between adjacent bands of ferrite and pearlite and fractographically by revealing brittle fracture elements on the fracture surfaces, namely delamination and cleavage, indicating the sites of cohesion weakening between ferrite and pearlite bands. The state of the X52 steel in its initial state and after use for 30 years was assessed based on the numerical simulation method.
Highlights
The main pipelines for the transportation of hydrocarbons, typically made of carbon steels, are long-term operated objects subjected to the action of corrosive environments.their technical state should be periodically assessed
Since fracture typically occurs through the weakest places in the material, the fracture surface of the specimens after the Charpy testing should be enriched with carbon compounds the mechanical properties sensitive to operational degradation [22,24]
14 of 19Since fracture typically occurs through the weakest places in the material, the fracture surface of the specimens after the Charpy testing should be enriched with carbon compounds
Summary
The main pipelines for the transportation of hydrocarbons, typically made of carbon steels, are long-term operated objects subjected to the action of corrosive environments. The present paper aims to summarize the investigation results in various aspects of the operational degradation of pipe steels of gas mains, mainly performed in the frame of the NATO project G5055 [23,24,25] and under the scientific cooperation between the Karpenko Physico-Mechanical Institute of the NAS of Ukraine and Kielce University of Technology of Poland [26] For these purposes, a number of existing mechanical, physical, and electrochemical methods suitable to degradation assessment have been used, and some new ones have been elaborated to evaluate the current state of operated metal
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
