The Oil & Gas Industry has had a long history with 17-4PH precipitation hardening stainless steel that has been marked by successful applications and numerous field failures. The results of an investigation into why and where the alloy has worked successfully and unsuccessfully are presented. A summary of a literature search of test data is presented with the results of laboratory tests exploring the boundaries of application. The lack of conservatism with our current wording of NACE MR0175 / ISO 15156 is discussed with recommended changes to this standard that permit limited use while avoiding many of the misapplications.