Failure analysis: Chloride stress corrosion cracking of AISI 316 stainless steel downhole pressure memory gauge cover

The downhole pressure memory gauge cover which is the focal point of this failure case study was hung in the production tubing of a sour gas well at a depth of 3200 m during a multiple rate productivity index test. Approximately 140 h after start up, the tool cover failed. The memory gauge cover experienced repeated premature failures. One failed sample was investigated by chemical and microstructural analytical techniques to find out the failure cause and provide preventive measures. The gauge cover alloy was type AISI 316 stainless steel. During investigation many branched cracks were observed on the external surface of the gauge cover grown from the pits perpendicular to the cylinder axis. The results indicate that pressure memory gauge cover failed due to chloride stress corrosion cracking (CLSCC). Also according to slow strain rate test, it was evident that the best alternative for the downhole pressure memory gauge cover alloy is Nitronic 50 and the second option is 17-4 PH stainless steel.