What is the minimum size of a pressure vessel that requires ASME code certification? Citation of the code number or section would be useful. Thank you.
It must be pretty small. Some use piping codes for small capacity storage.
Section VIII Division I
U-1(i)(vessels having an inside diameter, width, height, or cross section diagonal not exceeding 6 in. (152 mm), with no limitation on length of vessel or pressure;
U-1(j)(3) 1.5 cu ft (0.04 m3) in volume and 600 psi (4.1 MPa) design pressure.
Just because it's not an ASME VIII pressure vessel doesn't mean you have no need to design and fabricate the thing in question with reference to SOME code...
If it's relieved below 15 psig, it's "non code"- unless some other code applies (ie. big storage tanks). Owner's choice.
Higher than 15 psig but below ASME VIII's scope? It's a piece of B31.3 pipe.
I've noticed they sell little air compressors that have two small tanks instead of one bigger tank. The only reason I can think of to do so is to get below this code minimum.
There are vessels, miniature vessels, and fittings. In another life, I worked with a heat exchanger manufacturer. The smallest standard models were about the size of a lunchbox thermos. These little heat exchangers were required to be registered as fittings. Even if you build with pipe & fittings, these components will have to meet pressure piping code standards, in addition to code compliant assembly methods.
