Vessel for Hydrotest over MAWP

[jm2024]

Hello all.

I have designed two electric immersion heaters per Appendix 41 of Section VIII div I. Design pressure is 2500 psi at 700°F. Hydrotest pressure per UG-99(b) is 5372psi. The customer was hoping for us to use one of their vessels in order to hydrotest the heaters. Their vessel's MAWP is 2660psi at 700°F. The vessel cannot be taken above the stamped MAWP, correct? I have run calcs for the vessel that show it will not fail at the 5372psi. However, since it's stamped for 2660psi, nothing will allow us to go beyond that, right? We would need to re-rate in order to use it?

Thanks for any input.

 

[goutam_freelance]

Asper VIII-1 clause UG-98, each MAWP has a coincident temperature. Also, the MAWP can be specified for more than one temperature condition.

So, if the Inspector certifies the MAWP at room temperature(after calculation) in addition to the existing MAWP at operating temperature, then if the new MAWP is equal to or more than 5372 psi, then it will be possible to subject the vessel to 5372 psi.

But in principle, your statement is correct; additional certification will be needed.

 

[jt1234]

Your focal point is the hydrotesting, not the MAWP. That means you shall ask customer what is the hydrotest pressure for the vessel. If it is below 5372 psi, you shall not use that vessel to do hydrotest unless you want to redesign your heater to lower the test pressure to match vessel's.
If this is a new vessel and has not been hydrotested, you shall ask vessel fabricator to agree upon using higher test pressure to match 5372 psi, not you to run the calc saying to your customer it will not fail. Doing that you will be liable for any thing goes wrong.

 

[GD2]

OP,
You are confused. Customer's vessel with 2660psi at 700°F will have a higher hydrotest pressure. The heater Design pressure is 2500 psi at 700°F.
Where is the issue?
Hydrotest pressure of the vessel will be= 1.3 MAWP x LSR

.

 

[LittleInch]

The nameplate doesn't say that and more importantly the test pressure is test pressure, not MAWP. The item providing the pressure should not exceed MAWP when testing the second item. It looks to me that even if the main vessel had indeed been tested above 5372, you can then effectively re-hydro test the first vessel whilst actually hydrotesting the heater elements. That's the whole purpose of MAWP. The working pressure of the vessel is exactly that when testing the heater elements.

Test pressures should be a once in a lifetime event otherwise they become the MAWP.

I've seen this before when testing piping to say 1.5 times the design pressure of a class 600 system ( say approx 150 bar), the test manifold can't be class 600 (DP 102 bar), but needs to be made from class 900 flanges ( 150 bar) or maybe even class 1500 ( 225 bar) as the test pressure is its working pressure / design pressure which you should not be exceeding.

Does that make sense?

 

[jt1234]

"Test pressures should be a once in a lifetime event otherwise they become the MAWP.": Not correct and not making sense.

 

[LittleInch]

Why? You build a vessel and calculate a MAWP. You then test it to some multiple of that MAWP (typically 1.3 x MAWP).

So let's take numbers. MAWP is 2500 psi at ambient temp. So test pressure is 3250 psi @ 15C

Just because it withstood that pressure for a test does not mean you can use the vessel above its MAWP (2500). That's my point which maybe I wasn't clear about.

For the OP I read this as saying he needs 5372 psi @ 60F. Unless his vessel is listed with an MAWP of > 5372 @ 60F, then he can t just use it by saying it won't "fail". That's not how pressure vessel design and operation works.

 

[Trestala]

Their vessel's MAWP is 2660psi at 700°F.

What is the vessel's MAP (not MAWP) though at 60°F? (uncorroded and ambient temperature).