Hi all,

I have got some technical practice documents
of very well known company in oil and gas field.

Where, i got one doubtful techniques..like..
For "Steam out case" ...

" steamout temperature must be considered for
flexibility purposes only when in excess of design.
Allowable stress may be increased by a factor of 1.33
and allowable forces by a factor of 2.0 because of
short time loading. Refer to ANSI B31.3."

I have made a detail search regarding this,
but not getting satisfactory explanation.
Only in section 302.3.6 I able to get this...

"...use of 1.33 times the basic allowable stress
provided in Table A-1, the allowable stress for
occasional loads of short duration...."

My doubt is that is it pactrical or justified
to use 1.33 factor on basic allowable stress for
steam out case?

i need your help..
Thanks in advance
S Koley

your doubts are correct I disagree with the direction you have been given this is not the intent of the code IMHO...

at best you might be able to use f=1.2 under certain circumstances.... or do a proper fatigue evaluation (very painful)

Many engineering company's working practices are not fully complient with the code. They do it based on their experience and at their own risk.

The problem in your case is the specification refers B31.3 for their own theory which is non code complient. So think twice before doing something based on some other companies specifications. Comply with code or your project specifications. Priority may be (1) Safety Requirements/regulations (2) Statuatoty/regulatory/local reuirements (3) Project Specifications (4) Company Specifications.

Do we need to consider steam-out for our stress calculation keeping the line in cold condition?

Some folks say only run steam out when T(steam)> T(design) but remember that during steam out the pipe is empty and may lift-off supports etc. if the line is normally liquid filled.

So Bob we no need to worry about lift-off supports and our concern is only to check nozzle loads.

The posible severe condition are stated in the contract. You can verify all condition which as we knew the maximum govern's.

Maniam

No. You need to also ensure the pipng meets the Code stress allowables during the steamout event in additon to any equipment allowables.

IMHO,

I treat steam-outs as a operating case and stress acordingly
I would be wary of any significant gain by trying to achieve complience with a occational case.


Quote "So Bob we no need to worry about lift-off supports and our concern is only to check nozzle loads."

thats a worrying statement, one should always be wary of supports lifting off, and closing ones eyes to other potential problems in the design is not best practice

Lifting supports are always considered by stress check and the nearby supports which are overloaded. We are always wary about lift-off supports
My concern is when we do a calculation with line is under cold condition and equipment is done for steam-out condition. Assume the calculation with a tower line in which the column steam out temp is 150 deg c and the line is under cold conditon and because of it by default the support starts lifting off due to differential displacements. Kindly can you suggest me how cautiously you will handle this lift-off supports and how do you make this support to rest on steel during steam out condition.