To find optimum manufacturing processes and resulting microstructures of high strength linepipes used in sour environments, the nature of hydrogen induced cracking of high strength steels of grades up to API-X70 equivalent was examined. Furthermore, microstructure and strength dependency of occurrence of HIC were also investigated. HICs were observed at approximately 3 mm to 5 mm apart from external surfaces of steel plates. Occurrence of this type of HICs were predominant in higher strength steels equivalent to grades X65 and X70. Strength dependency of occurrence of the HICs near the external surfaces was observed. There was the maximum strength without HIC and this strength changed by varying microstructures. Uniform and polygonal microstructures obtained by raising rolling finishing temperatures and applying Accelerated Cooling process showed good HIC resistance. Up to the X65 grade pipes can be produced by this uniform microstrueture. This could be one possible microstructure for the higher grade linepipes, such as X70 and X80 for sour environments.
Microstructure and strength dependence of occurrence of HIC in linepipe steels
Veränderung von Mikrostruktur und Festigkeitsverhalten von Rohrleitungsstählen beim Auftreten von Wasserstoffversprödung
Mechanical Working and Steel Processing Conference, 38 ; 38 ; 535-541
1997
7 Seiten, 11 Bilder, 2 Tabellen, 10 Quellen
Conference paper
English
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