As per ASME Sec VIII Div-1 UG-22 f " The loadings to be considered in designing a vessel shall include test pressure and coincident static head acting during the test."

My query is " Whether the nozzle reinforcement shall be checked in hydro case also".

(Let us consider a case, where, Allowable hydrotest pressure is 0.9 of yield and yield stress for Shell material is 260 MPa & for Nozzle it is 240MPa,)

In PV elite we can check all the components with MAWP and MAPnc

Checking in MAPnc case will ensure that nozzle reinforcement is ok with code allowable at cold condition.

But the allowable in case of hydro is 0.9 of yield and in case of MAPnc it is code allowable and Increase in pressure in case of hydro is 1.3*stress ratio at ambient to design.

Hence, the increase in pressure and allowable stress in both the cases are not proportionate.

So, the required thickness for shell and nozzle will be different in hydro and MAPnc case.

Hello sommath

PV Elite and CodeCalc do not do a special calculation for nozzles during the hydrotest. The principle is that all stresses for the major pressure envelope are raised by a factor of 1.3 for the hydrotest, and in our experience, the nozzle and its reinforcment will not be overstressed during the hydrotest. The most critical components are shells and heads.

Even if the hydrotest is based upon 90% of yield, the nozzle is unlikely to be overstressed. We have not heard of this happening from our many users.

However, it you would like to check the nozzles for the hydrotest, you can pick the most critical nozzle or nozzles, overwrite the design stress at ambient temperature to 1.3S or 90%yield, and run the programme. Just look at the design case, not the hydrotest case.

Hi somnath

The nozzle reinforcement need not be checked for hydrotest case. However, some EPC's request this to be checked as a contractual requirement.

So, first design the vessel in PVElite as per the design condition. You should get the MAWP, MAEWP, and hydrotest pressure.

"Save As" this file with another name.
In this file, enter "user define" the MAWP, MAEWP, and hydrotest pressure that you got in the design condition calculation. Also, change the design temperature as ambient. For all the materials change the allowable stress (ambient, operating, & hydrotest)to 1.3S or 90% yield of respective material.

Somnath,

I have a question for you,

But, if you ensure that the nozzles are stronger than the main shell/heads in the operating condition and in the new and cold condition, then how can it control in the hydrotest condition.

Hey guys,

We have a case where a customer is performing a "design verification" of some vessels we previously shipped, and verifying our PVElite designs with an alternate vessel design program. They say some of our nozzles are overstressed in the hydro test case, when a vertical field hydro case is considered. After some investigating, the Brand X program is calculating the nozzle stress at hydro using a method published in ASME PVP Vol. 399.

Scott Mayeux makes a good point that vessels and nozzles should be designed for the design case, not the hydro case. I think we can convince this customer that the check is not required. But I wanted to point out that 1) customers are sometimes asking for it, and 2) the Brand X program does make this check, and 3) that nozzles can be overstressed in the hydro case only using this method.

Keep up the good work,

Bill Huffman, P.E.
Chief Engineer
Ward Tank & Heat Exchanger Corp.