The most accepted authority in the design and construction of pressure vessels is the ASME Code. The existence of economical and safe pressure vessels is due primarily to the guidance of the ASME Code. Although the Code provides excellent guidance many an inspector has unintentionally burdened a vessel shop with non-existent Code requirements or misinterpretations of rules that add unnecessary costs with no benefit. Having said that, we always say that there are two parts to any Code question-- the Code part and the practical part. The Code will allow construction details which may be fine for a light duty application but on the other hand could be totally inappropriate for a heavy duty industrial application. To just buy a vessel "with a Code Stamp" can be a big mistake. This is very apparent in Division 2 or PVHO-1 vessels which are so complicated that these codes require that the  buyer retain a knowledgeable professional engineer to prepare a "User Design Specifications" (UDS) to insure that the finished vessel is appropriate for the intended use. Bartlett Engineering is qualified to provide a User Design Specification (UDS) for Division 2 or PVHO-1 vessels.