I have Worthington steels with galvanize finish. The galvanized tanks are the ones that require a pre-stretch. It has to do with the way the finish affect the flexing of the tank. I had some failed that were really ok. XSScuba contacted the hyrdo facility and straightened them out. Also, the usual method of measuring the % of tank stetch does not apply. There is a number (REE) on the tank instead that used to determine if the tank passed or failed. If the % of stretch method is used a good galv tank will fail usually.