Low carbon type 12Cr line pipes with high corrosion resistance in the C02 and H2S environment have been developed, and they have come to be widely used in field applications of flow line and gathering line. Conventionally, duplex stainless steel and super duplex stainless steel welding consumables, have been applied for girth welding of these materials. In these cases, their undermatching weld joint has been pointed out. The ordinary matching type gas metal arc welding (GMAW) consumables have the inevitable problem of poor toughness. That is owing to the elevation of oxygen content in weld metal by invasion from active gases added to the shielding gas. GMA welding in the pure inert shielding gas has been investigated applying new matching type consumables. The girth welding trial of 12Cr line pipe with the pure inert gas was finalized with the satisfactory result. The microstructure of weld metal shows a martensitic structure, and overmatching was confirmed. No weld crack was observed by lowering carbon and nitrogen of the welding consumable. The toughness of weld metal reveals over 100J in Charpy V-notch impact test at-40°C. The corrosion resistance of matching welded joint was same as base metal. The matching welded joint shows good SSC resistance and hydrogen embrittlement resistance.
Keywords: martensitic stainless steel, matching welding consumables, C02 corrosion, sulfide stress cracking, pitting, heat affected zone, cathodic protection, hydrogen embrittlement, gas metal arc welding (GMAW), gas metal arc (GMA), toughness