ASME 31.8 Chap VIII allowable stress in OPE case

Hi I got this link for new topic.

pls answer genuine doubt raised during analysis of pipeline.

I am using material A790 UNS 32750 material

SMYS is 551 MPA

Deaerated is 446 MPA as per DNV OS F101

Hence entered Sy cell 446
and Fac 0.72

load case modeled is Ope L1= W+D1+T1+P1

As per Asme 31.8 all stress for ope is S,

ans Se is SMYS*T*Fac


hence in stress summary in output

I should get 446
or

446*.72= 321.12 Mpa


But I got 356 Mpa

How is this possible pls explain at earliest.


Regards,
Suhas
______________________

Would this thread http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=50919 help you?

I quote from there:
"B31.8 VIII has three Code equations and three allowables, whereas the output report only has room for one Code stress and one allowable. So CAESAR II determines the ratio from all three pairs, and puts the governing (highest ratio) values of Code stress and allowable in the report. The allowable shown in the report could correspond to the hoop stress, the longitudinal stress, or the combined (equivalent) stress."

I suspect 356MPa is reported there because it is the allowable for the case with the highest ratio as value of Code stress/ allowable Stress.

Thanks. A lot
If I understood correctly.

Allowable stress factor is .72 or 0.8 or .9 based on maximum stress ratio for hoop, longi or combined stress for perticular nodal point in stress model.
But does caesar model gives type of stress as longitudanal if all stresss fac selected .8
Pls reply

"CAESAR II determines the ratio from all three pairs, and puts the governing (highest ratio) values of Code stress and allowable in the report."

The calculation is made for all three cases, the listed (shown) case is only one and it is selected based on highest ratio Code Stress/ Allowable Stress of three.

I hope this answers to your question.

Thanks I checked its matching for caesar model under my review currently.

One more doubt, I do not have yield stress values for -35 deg cel.

Can you provide the value.

Currently I am copiying yield values for amb temp in mateial database.

But thats not right.

correct?

Depending on material in discussion, you may take yield stress values for -35 deg as for ambient temp, providing that metal has enough toughness- a characteristic that permits a metal to absorb energy by undergoing plastic deformation rather than fracturing in the presence of high stress concentrations (cracks or notches) under low temperatures.

While ductility is measured as deformation occurring in a tension test of a uniaxially loaded smooth specimen, toughness is commonly measured in terms of the energy absorbed in breaking, under impact loading, a specimen that is notched.

See for example B31.3 "Lower Temperature Limits, Listed Materials" under "Material" chapter.

How did you apply the derating factor T ? Didnt you notice something?