Extended laboratory testing of type 316 compression fittings for sour service

Compression fittings are widely used in pressure and vacuum systems in a number of industries including chemical processing, nuclear power and oil and gas production. Previous tests showed type 316 stainless compression fittings can crack when exposed to NACE TM0177 solution at elevated temperatures for 30 days. Following up this finding, one-month, three-month and twelve month tests have been conducted on type 316 compression fittings and instrumentation tubing in order to assess their suitability for sour service. Loops were constructed, containing a total of over three hundred fittings from four manufacturers and filled with sour fluids comprising high chloride content solutions. They were pressurized to 50 bara (5MPa) with CO{sub 2} and H{sub 2}S partial pressures in the range 0--0.8 bara (8 kPa) and maintained at temperatures in the range 60--120 C. The tests showed that, even in mildly sour conditions, at elevated service temperatures cracking can occur and that the threshold H{sub 2}S partial pressure decreases with increasing temperature.