WRC 414:1996

$34.45

A New Design Criterion Based on Pressure Testing of Torispherical Heads

Published By	Publication Date	Number of Pages
WRC	1996	71

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Description

Two vessels with torispherical heads were pressurized to destruction at the Praxair Tonawanda facility on September 12-13, 1994. The objective was to determine pressures at which observable or measurable indications of failure could be detected. Both vessels had a diameter of 60 inches, were made of SA516-70 steel, and their test heads had a nominal crown radius-to-diameter ratios of 1.0 and 6% knuckles. The head of Vessel 1 had a measured diameter-to-thickness ratio of D/t = 238 and that of Vessel 2 had D/t = 185. According to Section VIII, maximum allowable working pressure (MAWP) by Division 1 for Vessel 1 was 85 psi when using actual (measured) dimensions and Code's allowable stress; for Vessel 2 it was 110 psi. By Division 2, the MAWPs were 70 and 96 psi, respectively. Plastic limit pressures for the two heads were calculated at 190 and 240 psi, respectively. Crown displacement and strain data were obtained up to 350 psi for Vessel 1 and 450 psi for Vessel 2. For Vessel 1, the only observable action was a slow formation of some waviness of the knuckle profile at approximately 600 psi. It lost pressure at 700 psi when a crack developed at a nozzle weld at the bottom of the shell. After-test examination revealed approximately 22 smooth, small-amplitude waves (buckles) around the circumference of the middle of the knuckle. For Vessel 2, no indication of any sign of failure was observed until it burst at a pressure of 1080 psi by a ductile fracture along the longitudinal weld of the shell. After-test examination revealed no measurable waviness of the knuckle.

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