Exclusion From the Scope of ASME BPVC VIII-1

[Paulettea]

Dear All,

I have some doubts regarding the scope of work in VIII-1. The introduction part of the code says that some classes vessels are not included in the scope of Division 1. Among those excluded is the following:

a vessel for containing water under pressure, including those containing air the compression of which serves only as a cushion, when none of the following limitations are exceeded:
(-1) a design pressure of 300 psi (2 MPa);
(-2) a design temperature of 210°F (99°C);

What is the logic behind this exclusion? To my eyes this class of vessel is very normal and there is nothing special about them.
What happens for this class of vessels if the pressure exceeds 300 psi or the temperature exceeds 210 F? Is it included in the scope of the Division?
What happens for this class of vessels if the vessel contains a liquid other than water? What is so special about water?

Warm Regards

 

[metengr]

Water is considered mostly incompressible in pressure vessel space, and will not pose a significant safety hazard. Think about hydrostatic testing.

 

[mk3223]

Yes, the vessel shall be designed per BPV VIII-1 if the vessel design "exceeds" the conditions of the Code per U-1 (c) (2) (-f). And, if the liquid other than "water", the vessel shall be designed per BPV VIII-1 Code.
IMO, the equipment not needed to follow this Code is because "water" has a minimum danger under the specified conditions.

 

[JStephen]

Most of the non-water products that would be stored under pressure are either flammable or toxic to some extent, so they present more hazard than just water.

Picking what is excluded from the code is going to be a matter of judgment and committee vote, though, not so much a clear technical definition. Those exclusions may have represented concerted lobbying by affected groups or may reflect customary practice prior to the wording of the requirement. You have similar issues with the minimum size and minimum pressure- the hazard associated with failure is less with smaller than 6" size or lower than 15 psi, but it's not a drastic reduction when you cross that line.

Around here, many of the older hydropneumatic tanks in public water systems are non-code vessels. Typically, 2,500-10,000 gallon horizontal tanks designed for 60-100 psi.