A new design criterion based on pressure testing of torispherical heads
- Lehigh Univ., Bethlehem, PA (United States). Dept. of Mechanical Engineering and Mechanics
- Praxair, Inc., Tonawanda, NY (United States). Research and Development Dept.
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. Plastic limit pressures for the two heads were calculated at 190 and 240 psi, respectively. 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. For Vessel 2, no indication of any sign of failure was observed until it burst at a pressure of 1,080 psi by a ductile fracture along the longitudinal weld of the shell. The main conclusion is that there is a problem in the application of the double elastic slope collapse criterion to torispherical heads. It was determined that when using this criterion a collapse pressure signaling excessive deformation cannot be determined with any certainty. Furthermore, the test data do not show anything at any of the calculated collapse pressures that suggests excessive deformation. Thus, the collapse pressures for torispherical heads cannot be confirmed by test. This leads to the inconsistency that if the collapse load is divided by a safety factor, say 1.5, to obtain an allowable pressure, the actual safety margin of the design is not known and may not be 1.5. For a material with sufficient ductility, the use of an estimated burst pressure appears preferable. A design criterion based on the membrane stress at the crown of a torispherical head reaching the ultimate tensile strength is proposed, which is simple, can be supported by theoretical arguments, and is shown to be conservative by current test results as well as by those of two previous test programs.
- OSTI ID:
- 477281
- Journal Information:
- Bulletin - Welding Research Council, Journal Issue: 414; Other Information: PBD: Aug 1996
- Country of Publication:
- United States
- Language:
- English
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