Stress corrosion cracking of duplex stainless steel weldments in sour conditions

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 understood, limiting use of welded material in H{sub 2}S-containing environments. The SCC resistance of duplex stainless steels is influenced by their microstructure 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 S32760) and 10% (UNS S31803). Slow strain rate testing (SSRT) was conducted on cross-weld specimens in sodium chloride solutions overpressured with varying partial pressures of H{sub 2}S and CO{sub 2}. Nitrogen uptake from the shielding gas has a detrimental effect on SCC resistance of duplex stainless steel weldments. While this effect is only modest, it is in direct contrast to the beneficial effect it has on pitting corrosion resistance.