Corrosion and cracking of weldable 13 wt-% Cr martensitic stainless steels for application in the oil and gas industry

A critical review of the literature has been undertaken to establish the current state of knowledge and understanding of the corrosion and stress corrosion cracking (SCC) of 13 wt-%Cr martensitic stainless steels for applications in the oil and gas industry. Corrosion data for 13%Cr martensitic stainless steels are critically evaluated to establish the conditions in which the various steels are in the active state, pitting or passive state. There is evidence that as welded specimens have poorer pitting resistance at ambient temperatures than at elevated temperatures owing to the formation of an oxidised layer, perhaps depleted in chromium. Data for hydrogen uptake and diffusivity in 13%Cr steels are reviewed. The results suggest that incorporation of Mo in the steel reduces the subsurface hydrogen content when the steel is in the active state, suggesting repressed dissolution kinetics. The data in the literature on SCC of modified 13%Cr steels indicate that increasing the temperature at pH values where pitting is the precursor to cracking decreases the susceptibility to sulphide stress cracking. Whilst a matching weld filler would he expected to be more susceptible to hydrogen embrittlement because of a higher hardness of the weld metal relative to the duplex stainless steel filler, there is limited evidence to suggest that welds with matching fillers are more resistant to cracking than welds with duplex fillers. The heat affected zone of a duplex weld appears to be more susceptible to pitting than for a matching filler. Evidence of intergranular SCC from the root of a girth weld at 110degreesC has been obtained but is eliminated by post-weld heat treatment. Nevertheless, this is an important observation and needs further investigation. CEST/2031 The authors are in the Materials Centre, National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK (aeronwen.griffiths@npl.co.uk). Manuscript received 7 January 2003; accepted 27 January 2003. (C) 2003 IoM Communications Ltd. Published by Money for the Institute of Materials, Minerals and Mining.