Supermartensitic stainless steels (SMSS) have high strength and good resistance to corrosion in produced fluids containing CO2 and are cheaper than other competing corrosion resistant alloys. Hence, they are attractive flowline materials and they have been successfully used in a number of offshore applications. Nevertheless, service failures have occurred and two failure mechanisms in particular have caused difficulties at welds: (i) hydrogen embnttlement/ hydrogen induced stress cracking resulting from hydrogen picked-up under cathodic protection and (ii) intergranular stress corrosion cracking (IGSCC). When developing welding procedures for supermartensitic stainless steel flowlines, efforts should be made to minimise the risk of hydrogen induced stress cracking due to hydrogen pick-up from cathodic protection and intergranular stress corrosion cracking of the HAZ in hot, acidic fluids. Wherever possible, welds in supermartensitic steel should not be exposed to cathodic protection at around -1000 to -1100 mVSCE particularly where dynamic plastic strain may be experienced in service. Where this is not possible, the occurrence of weld flaws should be minimised and efforts made to limit the stress concentrating effect of the weld toe. This paper presents experimental data on each of these two failure phenomena and gives details of the currently available ways of avoiding these problems, highlighting where further information is required. The current work and other published studies indicate that brief induction postweld heat treatment (PWHT) at about 650C for 5 minutes will remove sensitivity to intergranular stress corrosion cracking of the HAZ. Further work is required to establish the required control of the PWHT process to ensure a consistent beneficial effect but, based on the current work, an allowable temperature range of 620-660C is suggested.
Use of supermartensitic stainless steel pipe for offshore flowline applications
Einsatz eines supermartensitischen Stahlrohrs für Off-Shore Flowline-Anwendungen
2006
8 Seiten, 7 Bilder, 5 Tabellen, 11 Quellen
Conference paper
English
Welding consumables for supermartensitic stainless steels
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