Define Pressure Vessel

[Bobfromoh]

When does a metal container become a vessel as opposed to it being a pipe. The ASME Code Section VIII was referenced to determine when a container becomes a vessel. The container exceeds the minimum Code volume requirement. The comment was made that since the container was made of all piping components (pipe, pipe caps, fittings, etc) that it should be called a pipe and designed to the piping codes and not the pressure vessel code.

Can anybody shed some light on this question? Is there documentation beyond the Codes that would define a vessel vs piping component?

 

[ctmfab]

Generally, all the following must be met for the component to be designed as a piping component. If ALL these are met it can be designed as a piping component, if not ALL are met it could be designed as a pressure vessel.

1. It can be described by a piping sketch or iso drawing and referenced piping specs.

2. It is not intended for storing or processing fluids. Items such as mixers, tees, headers, metering devices, or other items that are typically recognized as piping components would not be included.

3. Its primary function to transport fluids (gasses included) from one location to another within a system (a piping system).

4. It is not intended to act as an air receiver. OSHA requires that new air receivers be ASME stamped.

5. The item will not be subjected to more frequent test and inspection intervals than the remainder of the attached system.

If these conditions are used, you should have a good arguement to design the component as either a piping component or pressure vessel.

 

[prex]

What you should bear in mind is that the classification of a component has nothing to do with the materials or fittings used to build it: only the intended usage is relevant. There are so many vessels out there (especially heat exchangers) built with pipe fittings...
In a few words a vessel is a component that has some autonomous function (heat exchange, chemical reaction, storage, and so on), whilst a piping is used to connect different points (vessels) and its primary function is normally to transport a fluid from one point to the other. ctmfab gave a quite detailed layout of why a piping should be classified as such: anyway the (vessel and piping) codes are the ultimate authority in the field, and any doubt on classification should be checked against their definitions.

prex

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