Most of the pressure or storage vessels in service in the United States will have been designed and constructed in accordance with one of the following two pressure vessel design codes: The ASME Code, or Section VIII of the ASME (American Society of Mechanical Engineers) "Boiler and Pressure Vessel Code." The API Standard 620 or the American Petroleum Institute Code which provides rules for lower pressure vessels not covered by the ASME Code. http://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_3.html http://www.hghouston.com/pvessel.html [Broken] The design, fabrication and use of pressure vessels is a serious matter given that failure can have serious consequences (death or injury) to people in the vicinity of failed PV's. If one is designing and building a PV with the intent to use it, one must adhere to the above two codes, whichever is appropriate. Power boilers are a common application: http://engineers.ihs.com/collections/asme/bpvc-2007.htm It might be worthwhile to have a dedicated thread on BPV's, or perhaps just PV's.