Hydrostatic pressure, allowable stress at junction shell/nozzle
Hydrostatic pressure, allowable stress at junction shell/nozzle
(OP)
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
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





RE: Hydrostatic pressure, allowable stress at junction shell/nozzle
Do not mix and match limits from Part 4 and Part 5.
RE: Hydrostatic pressure, allowable stress at junction shell/nozzle
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
RE: Hydrostatic pressure, allowable stress at junction shell/nozzle
RE: Hydrostatic pressure, allowable stress at junction shell/nozzle
prex
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RE: Hydrostatic pressure, allowable stress at junction shell/nozzle
Ok forget secondary stresses but you say to check local membrane stresses PL,
The allowable stress will be?(nozzle/shell transition area)
Thank all
RE: Hydrostatic pressure, allowable stress at junction shell/nozzle
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
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads