STRESS-CORROSION CRACKING OF DUPLEX STAINLESS-STEEL WELDMENTS IN SOURCONDITIONS

Duplex stainless steels are widely used in the oil and gas production industry for a variety of applications. The stress corrosion cracking (SCC) behavior of wrought material is reasonably well understood, and usage limitations are placed upon these alloys in NACE MR0175 for sour service. However, the SCC behavior of weldments is not as well unders tood, limiting use of welded material in H2S-containing environments. The SCC resistance of duplex stainless is influenced by their microstr ucture and chemical composition. An investigation of the SCC behavior of welded 22% Cr and 25% Cr alloys in a simulated oilfield environment has been conducted. Mechanized orbital TIG was used to butt weld 168 mm OD tubes. The shielding gas contained nitrogen additions of up to 7 % (UNS S327620) and 10% (UNS S31803). Slow strain rate testing (SSRT) was conducted on cross-weld specimens in sodium chloride solutions ove rpressured with varying partial pressures of H2S and CO2. Nitrogen upt ake from the shielding gas has detrimental effect on SCC resistance of duplex stainless steel weldments. While this effect is only modest, i t is in direct contrast to the beneficial effect it has on pitting cor rosion resistance.