HI

I AM MR SHUKLA , I AM LEAD ENGINEERING MANAGER FOR ONE OF THE COMBINED CYCLE POWER PLANT

I WANTED TO KNOW FROM ALL OF YOUR EXPERTISE ENGINEERS ABOUT CONSIDERING LOAD CASES FOR STRESS RELAXATION FOR IP STEAM PIPING IN ORDER TO EXTRACT EFFECT OF RELAXATION ON RESTRAINT FORCES-MOMENTS

HISTORY OF THE ISSUE IS THAT REQUEST HAS BEEN MADE BY OUR CUSTOMER IN GERMANY AND WE ARE NOT SURE HOW TO DEAL WITH THIS REQUEST

I don't think you should expect to get a competent answer to this request without payment. I suggest that you put together a request for quotation and issue it to reputable engineering firms.

You may well have to issue this in two phases - first, define the requirements carefully, then get the answers.

Hi Shukla

You may use hot elastic modulus of elasticity in lieu of cold elastic modulus to get nozzle & support loads.
You will get lesser force & moment due to the same.
You may have to check expansion stress for cold elastic modulus as per code requirement.
So you may set two load case with Ec & Eh1.
Go to "load case options" then change elastic modulus by drop menu.
For relaxation , I don't know how much useful it will be, anyway you have to design your piping system for worse case.

Regards

Habib

Shr,

I suspect that Mr. Shukla's reference to stress relaxation is with regard to local yielding of high temperature pipe and consequent reduction in restraint reactions in the hot state. This is commonly known as self springing since the reduction in hot load then appears as a cold load. It has nothing to do with use of hot modulus in a stress calc.

Hi MoverZ

Yes your point is correct, I think Mr. Shukla is trying to get relax force & moment on support & load based on self springing.

But my point is even if we got lesser value by self springing effect still we need to design piping system by normal stress analysis maximum load. So it will not help much.

By the way can we make caesar setting to get that kind of load. I understand we have to set time also for the same.

Regards

Habib

I do not want to involve in the discussion with stress relaxation, however, if your client is asking for that, the conditions of the supports are more questionable depending on the age of the plant. Condition of constant and variable spring hangers need to be checked for the remaining life of the plant. Some cases you need to replace some or all of them to suit your requirements.

Please forgive me if I am wrong, but, I guess your client or yourselves are trying not to take responsibility of the existing plant piping.

If the relaxation of the piping is only concern for the nozzle forces, Craig is right. you need to find a consultant that specialised on this issue.

If I were you I would model everything in the existing piping with the proper supports (replaced or existing supports checked for adequacy) and nozzles, if required I would change the routing. Getting involve with the stress relaxation issue may become an endless project for you. Perhaps, your client is trying to explain that with different wording.

Regards,

Ibrahim Demir