The operation of autoclave vessels at elevated temperature and pressure is common across a variety of industries. Many of the older operating vessels were fabricated from multiple forgings by welding. Austenitic stainless steels are the material of choice for many of these vessels, and precautions to prevent sensitization in the weld heat affected zone may not have been implemented during construction, which can increase susceptibility to environmental cracking conditions. Recently a vessel developed a through wall leak during the operating cycle. Three complimentary vessels at the same facility were inspected resulting in one additional vessel not returning to service and two with similar flaws. A multi-disciplinary approach was used to evaluate the failure, perform a fitness for service determination, and nondestructive examinations to monitor the flaw growth and validate the fitness for service inputs. The overall approach is discussed.