Stress at nozzle. WRC107

[scalabres]

Hi all,

I'm with a pipe line (16'', CS) that serves steam to three vessels. I have done the stress analysis and everything is OK. But if I do a WRC107 analysis at the nozzles of the vessels, problems arise:

I have four hypothesis,

1. The three vessels operating, and so all hot.
2, 3 and 4. Two operating and one off.

In the first case, I have no problems in the nozzles, but in the other ones the test fails (only in one vessel). In the Vessel Stress Summation at Reinforcing Pad Edge, not in the Vessel Stress Summation at Nozzle Junction. And only in the Pm+Pl+Q sumation, not in the other ones. I have taken into consideration sustained, expansion and occasional loads.


The question is if I should reconsider the whole design of the line, making again the stress analysis and again studying the nozzle or if I can handle with this "failed" on the WRC107 test, taken into account that it only appears in these conditions.

In the case that I can't pass over the test, which methods do you know to relax the stress at nozzles in vessels?

Advanced thanks

 

[DSB123]

scalabres,
In your pipe stress analysis have you input the vessel branches as fixed anchor points? If so, then if you include the shell flexibilities into the analysis this will reduce the resultant local loads onto the vessels and may be enough to achieve acceptablity of the loads when you perform the local load calc.

 

[codeeng]

Assuming these are ASME vessels then first check your allowable stress. It used to be 3S (3Sm) but has now increased to 2Sy if Sy < 0.7 UTS. If it still fails then provide some flexibility as DSB123 suggests. The easiest way to do this is run an FEA like NozzlePro.

 

[scalabres]

Thanks for your answers, DSB123 and codeeng. I have solutioned the problem with your help.