Expansion stress for transient temperature

Dear all
We are dealing a 10” line with normal operating temperature 250 deg C and there is one transient temperature of -50 deg C.
We are checking expansion stress range from
1) 21 deg to 250 deg C &
2) 21deg to -50 deg C
Do we really require to add both the stress to get total stress range i.e . from -50 deg C to 250 deg C.
Off course if we do that will be very safe play. But whether it is mandatory to do the same.

Hi Shr,

It would be enough to evaluate the two stress range. because -50 to 250degC stress range is not attainable...

Regards!

I disagree with Bom.

The very definition of stress RANGE would be from -50 to +250 degC., as required by ASME B31.3 for instance.

Capturing this in a Caesar II stress analysis is a simple matter of proper load case selection and combination.

Hi Bom,

if Both the temperature(from -50deg c to 250 deg c) happends in a single cycle, it is better to consider the complete stress range( ie sum of exp range from max temp to ambient and minimum temp to ambient).And indiviudal stress range also will be checked( max to ambient/ min to amb)seperately.

Apart from that I have a clarification.This case( ie from -50 to 250) will not happend regularly( it means that like normal cycle). Hence , Can we take the stress range factor "f" as the maximum of 1.2(refer ASME B31.3 page 16 FIG 302.3.5.)?So that the total stress range will be checked with SA=1.2(1.25Sc+.25Sh)

The coade does not say about this, it seems.

I request any one can explore this clarification.

regards

Sha..

evaluation of the stress range as B31 mandate "It shall be the total displacement strain". Both of the two evaluation will be incorrect(1 and 2)or without meaning..

Sa the stress range must be evaluated read the code before asking questions on the forum or do a search with "Stress Range" as the stress term

Shr,

See B31.3 para. 319.2.3 for the Sa.

There seems to be an assumption by some that the range of a thermal strain cycle must be direct. That is not true.
Even if the pipe "rests" at ambient temperature for a while the total strain range (in this example) is based on the change between 250 to -50. Even if -50 is held for only a short time, the pipe "sees" that strain. (It's like when you dent your car fender, the applied strain is of short duration but the dent remain.)
Yes, C2 only runs from ambient to operating. It's up to the user to build the maximum range (here, either by subtracting the two expansion ranges cases or by running a new case of Operating 1 - Operating 2; of course linear models can be simpler)
And sha (indirectly) brings in the matter of cummulative damage. But even if you hit -50 only a few times, the N you use to set f may increase. You are supposed to convert the N from ambient to 250 (and all other ranges) to an added N for the -50 to 250 case. See eqn. (1d) in B31.3.

yep theres a code interp somewhere I sent in to both committees...they in effect said that whether its at temp for 5 seconds or 5 hrs or 5 years its all the same....

See B31.3 Interpretations 8 & 9, for March 29, 2006 Meeting, file numbers 06-379 & 06-387 respectively.

Thanks for filing those John.

- Ken A. Nisly-Nagele

John,

I wish I had that Code Interpretation handy to show some Project Managers.

This was lately given by Sir John Luf.. http://cstools.asme.org/csconnect/pdf/CommitteeFiles/21681.pdf

Regards!