Numerical Simulation of Hydrogen Assisted Cracking in Supermartensitic Stainless Steel Welds

摘要

Replacement of expensive duplex stainless steel and conventional carbon steel by a new generation of supermartensitic stainless steel has been taken into account since the last decade in order to meet the technical- economical challenge for transportation flowlines of unprocessed oil and gas products in offshore technology. Supermartensitic stainless steels can provide appropriate material properties, such as: improved strength-to-weight ratio, enhanced useful corrosion resistance, as well as application at relatively low cost. With decreased carbon content and increased molybdenum content compared to traditional martensitic stainless steel, hydrogen assisted stress corrosion cracking (HASCC) problems have been found during service caused by hydrogen being taken up during service environments by cathodic protection. Hydrogen assisted cold cracking in supermartensitic stainless steel can also occur during fabrication welding with hydrogen picked up during welding, since this steel is relatively crack-susceptible by hydrogen. Therefore, effects of hydrogen assisted cracking (HAC), i.e. HASCC and HACC, on characteristic susceptibility of girth welds of supermartensitic stainless steel pipelines, are studied in the present thesis by numerical modelling, which is developed using an available commercial finite element program.