WRC107 in Codecalc 2

[alanw7272]

Hi,

I notice in Codecalc WRC107 they have now included a 'stress summations' box in which the software shows resultant vessel stress and a 'passed' or 'failed' result. This is great as in a glance the engineer can see whether the vessel stress is acceptable, or can they?

I do not think these results (stress summations) include for secondary membrane and bending stresses which are also shown in the results as per previous Codecalc releases. From my understanding these membrane and bending stresses are limited to 1.5S (ASME VIII Div.2) and I have seen many results where Codecalc shows the vessel stress to be acceptable but these stresses seem too high.

I appreciate how the loads are produced is a factor and so for this question I assumed that loads are both thermally and mechanically produced.

Please review and let me know some thoughts. Thanks

 

[LSThill]

alanw7272 (Mechanical) and Team Members:

FE-107

http://www.paulin.com

In general WRC 107 comparisons to FE/Pipe results are excellent when thin shells are analyzed and when the model is within the accepted parameters of WRC 107. Nozzles in the centers of heads are evaluated most accurately. Most WRC 107 programs give the stress intensity at four points around the nozzle on both the inside and outside of the geometry. This stress is usually compared to 3Sm and is caused by all operating loads on the nozzle. The resulting stresses from a WRC 107 run of this type should be compared to the Pl+Pb+Q stresses from the finite element calculation. Note that Pl stresses evaluated in accordance with ASME Section VIII Division 2 are membrane stresses. These are the average stresses through the thickness and do not include the bending stress component at the junction. (See ASME Section VIII Division 2 Appendix 4 Table 4-120.1.)




WRC 297 comparisons in the vessel or header tend to be good but become overly conservative when the high stress moves into the branch when the t/T ratio becomes less than 1.0. This result is certainly demonstrated in the finite element calculation.




WRC 107 tends to be somewhat less conservative than finite element results, but that WRC 107 results parallel FE calculations through d/D ranges of 0.1 to 0.8, where the WRC and Finite element curves cross, the WRC 107 results becoming much more conservative beyond this range. (When the approach used outside of WRC curve parameters is “last curve value.”)




The following list summarizes areas where WRC 107 and WRC 297 are considered weak, or where further concern should be displayed:




a) d/D > 0.5

b) t/T < 1.0

c) Pad reinforced nozzles

d) Hillsides or laterals

e) Area replacement rules for pressure are barely satisfied and large D/T.

f) Temperatures are approaching the creep regime.

g) Cycles are greater than 5000.

h) Design and operating conditions are approximately the same.

i) The load consists of high-pressure stresses and high loads.

j) The Piping attached to the nozzle is long, flexible, and somewhat unrestrained.



L S THILL

 

[alanw7272]

Thanks for your reply L S THILL.

Forgetting FEA for the time being and focussing on WRC107, I understand from your reply that you only check the final stress results (Pl+Pb+Q) regardless of the imposed loads being sustained or expansion related?
From reading Appendix 4 of ASME VIII Div.2 I would think to check local membrane and bending to 1.5Sm, especially going on the generally accepted assumption that piping loads are produced from both mechanical and thermal loads.

On another note, I appreciate the limitations of WRC107 but many fabricators do not have access to FEA tools and thus rely on these calculations. Do you envisage a time when WRC107 will no longer be accepted?

Thanks

 

[DSB123]

alanw7272,
You are correct ALL of the Code limits must be met.