pressure vessel vs pressure piping

[Zziggiz]

Does anyone know aclear definition of a pressure vessel vs pressure piping and how to classify if a section of pipework (eg a header) is a pressure vessel or pipe component.

 

[gr2vessels]

The ever green topic:-
ASME VIII Div 1 gives you a good definition of pressure vessels and a clear exclusion of the pipework (refer excerpt below);-
"U-1(c)(2): Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol:
(a) those within the scope of other Sections;
(b) fired process tubular heaters;
(c) pressure containers which are integral parts or components of rotating or reciprocating mechanical devices, such as pumps, compressors, turbines, generators, engines, and hydraulic or pneumatic cylinders where the primary design considerations and/or stresses are derived from the functional requirements of the device;
(d) except as covered in U-1(f), structures whose primary function is the transport of fluids from one location to another within a system of which it is an integral part, that is,piping systems;
(e) piping components, such as pipe, flanges, bolting, gaskets, valves, expansion joints, fittings, and the pressure containing parts of other components, such as strainers and devices which serve such purposes as mixing, separating, snubbing, distributing, and metering or controlling flow, provided that pressure containing parts of such components are generally recognized as piping components or accessories;"

However, the header may be part of the pressure vessel, mainly if it is welded to the vessel;- on the same token, you might want to have the header tested at higher conditions than required by the vessel code, then you classify the header as piping component. The pressure vessel code recognizes the next circular butt weld of a nozzle pipe/neck, after the shell to nozzle neck junction, but after that any item welded to the nozzle neck, like nozzle extension pipe or distribution header or similar is to be treated as piping item. The BPV code also allows you to include in its jurisdiction the header, if you want/need to do so.
I'm sure all this helped only to increase your confusion, but more important is that you can make your own best engineering judgement and classify the header as it would be best engineered and safe. That's the ultimate goal of your classification. Have your best argument to support your classification, be that the cost saving while providing a safe operation for it or safety paramount prevailling over the cost.
cheers,
gr2vessels

 

[zdas04]

I like to look at it from the other side. ASME B31.8 (Section 831.35(d), Special Components Fabricated by Welding) formalizes the topic some by saying (emphasis added)

“Prefabricated units, other than regularly manufactured butt welding fittings, that employ plate and longitudinal seams as contrasted with pipe that has been produced and tested under one of the specifications listed in this Code, shall be designed, constructed and tested under the requirements of the BPV Code.”

B31.8 clearly draws the line at longitudinal welds as opposed to pipe (including ERW and other piping fabricated by the manufacturer from plate to an included specification) and butt weld fittings.

In other words you can make the argument that the line can be drawn at the existence of post-manufacturer longitudinal welds.

David