HYDROSTATIC TEST ATMOSFERIC VESSEL 1

[GabrieleB]

Is possible to apply ASME VIII Div.1 to an atmosferic vessel? In any case is correct to require an hydrostatic test for this type of vessel? Which pressure I have to specify for hypothetical hydrostatic test? Thanks in advance for your answer.

 

[vesselfab]

I thought we were specified to 15 psig minimum design pressure which would yield a minimum of 20 psig test.

 

[jte]

Gabriele-

Yes, you can apply an ASME Section VIII stamp to a vessel designed for atmospheric (i.e. 0 psi gage) pressure. Yes, Div. 1 lists vessels having an internal or external pressure not exceeding 15 psi as an excemption to the scope in U-1(c)(2)(h). This sometimes confuses people who haven’t read the second half of U-1(c)(2) in which it is stated that …however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol.

If you have a vessel with a 0 psi design pressure, then the thickness will be governed by hydrostatic pressure or structural considerations (dead and live loads, wind, seismic…) or minimum thicknesses (see UG-16(b)). Keep in mind that you have to add CA to that minimum. So you will have some thicknesses to work with. At this point you can calculate the actual MAWP.

As an owner/user, I would say that if the calculated MAWP is over 15 psi, consider setting the MAWP at 14 psi and not applying the U stamp just to avoid the 15 psi point which can have legal/regulatory implications and it can buy some flexibility if the vessel is considered for different service in the future. However, if your customer wants a U stamp, you can apply it even if the MAWP is zero psi. I suppose it may be possible, though not likely, to have just enough hydrostatic head in just the right vessel to have zero psi at the top and be at max stress at the bottom. Calculate the hydrotest pressure accordingly. Again, from an owner/user perspective, I’d say use the MAP as the hydrotest basis rather than MAWP.

On the other hand, I could see that a fabricator might want to use a lower value than the calculated MAWP since the design requirement is zero pressure… But that approach makes me question the fabricator’s willingness to provide added value to the customer (at little to no extra cost) – and their faith in their own capability to fabricate a vessel which will pass a relatively low pressure hydrotest.

jt

 

[chicopee]

Atmosferic vessel, must be an italian vessel, not a US vessel,so our US rules don't apply.