Re: [PSUBS-MAILIST] PVHO Question

Shawn,

ASME PVHO-1-1997 "Safety Standard for Pressure Vessels For Human Occupancy" focuses on the nonmetallic viewport fabrication and certification. For certification requirements for the pressure hull, you need to look to one of the engineering classing societies such as the American Bureau of Shipping "Rules for Building and Classing Underwater Vehicles, Systems, and Hyperbaric Facilities". If you want to get your pressure hull certified by ABS, you would fall under the guidance given in chapters on Metallic Pressure Boundary Components and Fabrication. Can pressure hulls other than cylindrical or spherical (e.g., conical) be certified? The rules are well defined for metallic pressure hulls made up of frame stiffened cylindrical sections, elliptic, spherical or tropispherical heads, and conical sections. Equations are given to calculate the maximum external pressure a hull fabricated with any of these components operate at as well as acceptable out-of-roundness tolerances. They have factors of safety that are very conservative. The opening paragraph in the Chapter dealing with metical pressure boundary components says, "Metallic components of pressure boundaries are to comply with this section. Designs based on other recognized standards will be given special consideration." My reading of this is that it is possible to get ABS to certify a pressure hull that is made of components not called out in ABS but it would be a tough job and add significantly to the certification cost. My guess is that at the very least, it would require a full FE analysis of hull, a destructive test of a prototype hull fully instrumented with strain gages along with the normal external hydrostatic proof test in the presence of the ABS Surveyor to pressure of 1.25 times the design depth for two cycles.

Cliff