Hydrostatic pressure, allowable stress at junction shell/nozzle

[josedipofi]

According to Asme VIII div.2 Tab. 5.6 (ed.2010) the stresses in the shell near nozzle or other opening due to internal pressure are PL,Q anf F.
On the same table on the nozzle within the limits of reinforcement given by paragraph 4.5 the stresses due to internal pressure are general membrane Pm and bending also classified as Pm.
According to figure 5.1 (Stress Categories and Limits of Equivalent Stress) shall be:
Pm<=S
PL<=1.5S
PL+Pb+Q<=Sps
According to 4.1.6.2 (Test condition) we have:
Pm<=0.95Sy
Pm+Pb<=1.43Sy if Pm<=0.67Sy otherwise we have Pm+Pb<=(2.43Sy-1.5Pm) if 0.67Sy<Pm<=0.95Sy.on
At the junction shell-nozzle during hydrostatic test which limit shall I apply?
thank

 

[TGS4]

There are no explicit limits to the stresses that are not general primary membrane when performing an elastic analysis. The stress limits provided in Table 5.3 are considered sufficient in and of themselves. You will notice that the hydrostatic test condition is NOT included in the list of load cases to be evaluated in Table 5.3. There's a reason for that.

Do not mix and match limits from Part 4 and Part 5.

 

[josedipofi]

Thank TGS4,
According to what you are saying once the loads according to Table 5.3 are checked and verified no extra analysis is necessary, even if the test pressure is higher than the one according to ASME that is my case?
Clear that in the code there is not any stress limits (except general primary membrane one) for hydro test, but the supplier required to me to check it because ,what I said, the test pressure is higher that the one according to ASME.

My approach will be:
PL<=1.5(0.95Sy) and
PL+Pb+Q<=Sps
where Sps=3 time the allowable at ambient temperature (PL&Q=local membrane and bending stresses on the connection shell/nozzle)
Do you think this approach is reasonable?
I saw some supplier perform FEA (elastic) and using for hydro test the limits according to part 4,
this was done to evaluate the stress (Pm and Pb) in the tubesheet (between holes) due to pressure only, if I understand well you say that this shall not be done,why?
thank

 

[TGS4]

Such a check is neither required nor advisable. As long as the primary membrane check is performed and passes, I would highly recommend that you don't perform such a check at the hydrostatic condition. Talk your client of it.

 

[prex]

You should check general primary membrane, local primary membrane and primary bending (you have the latter in the tubesheet, but not in the shell to nozzle transition), not secondary stresses. The reason is that secondary stresses cannot cause a failure in a single application of the load.

prex
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[josedipofi]

Prex,
Ok forget secondary stresses but you say to check local membrane stresses PL,
The allowable stress will be?(nozzle/shell transition area)
Thank all

 

[prex]

Well the limit would be 1.5 times the basic allowable.
However, sorry, I have to come back on what I said.
Local membrane, as stated in the code, is in fact a secondary stress (so failure can only occur by strain accumulation over load cycles) and is limited more strictly than other secondaries only to avoid excessive distortion.
So, as the acceptable distortion during hydrotest is otherwise limited by the code, there is no need to check local membranes during test and this is in fact what the code states.
However you can check local membranes with the limit above if you want to insure that no excessive distortion will occur.

prex
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