Hot isostatic pressing vessel explosion (Grafton, MA)

Tom's longest sustained case in the lecture. 250-ton HIP vessel containing Harley-Davidson cylinder heads and other castings. Broke into 70 pieces averaging 5 tons each at 2 AM. Operator nearly killed by a five-ton fragment that landed on his desk. Tom and John McNichol of Chromalloy were the first two into the pit. Three-circle analysis: (1) transient thermal stresses (vessel designed for steady-state only, no 3D model); (2) bad microstructure (Charpy testing done on a too-small surrogate piece that cooled faster than the 200-ton forging, masking the real properties); (3) hydrogen embrittlement / SCC from Nalco molybdenum oxide water-treatment inhibitors pitting the outer wall ("101 Dalmatians"). Designed as leak-before-break; should have leaked at an 11-inch critical flaw, but actual critical flaw size was 1 inch because each circle compromised the toughness.

One of these vessels blew up by Grafton, the north end of Worcester. It broke the whole thing in brittle fracture into 70 pieces averaging five tons apiece. This was 17 inches thick at the ends, but the center was 10 or 11 inches thick, where the crack started. It sent a 15-ton piece into the supporter. Some of the neighbors in that end of Worcester were not so pleased, but it didn't land on anybody. The guy was operating it at 2 AM. It's a pretty expensive vessel, so we operate them fairly continuously — put in a batch, take out a batch, don't shut it down because it takes 24 hours to heat it up. He was on the night shift, just had to go change the chart paper, was going to come over to the chair, and the thing blew up and landed a five-ton piece crushing his table.