A SCHEDULE 40 SEAMED STAINLESS STEEL PIPE NIPPLE WAS USED IN PLACE OF A SCHEDULE 80 SEAMLESS 3/16"" STAINLESS NIPPLE. THE SCHEDULE 40 NIPPLE BURST UNDER THE 10K PRESSURE USED IN THE HYDROBLAST SYSTEM. OPERATOR OF THE HIGH PRESSURE TOOL THOUGHT NIPPLE WAS SCHEDULE 80.