Dear all,
I believe someone will reply

1) As per 31.1 in thermal expansion condition allowable stress is more than sustain and occ. case.In thermal exp. the temp. will be considered, so the allowable stress should less than sus. and occ. case.What is the logic.

2) The load input data like W,WW,T,P,D,H and combining of each in different load case, is this method derived for caeser2 calculating purpose or any code describing this.

3) The load combining for sus. is as a cold condition and exp=ope-sus here we are getting subtracting amount .But this force will lesser than operating condition , whatever in the operating condition only will have the max force , but we are not considering in stress check also there is no allowable stress described.what is the reason?

With hope

R.Boopathi

As one answer to 1 and 3:
there is a difference between primary and secundary stresses and both are considered seperately according to B31.1/B31.3/EN13480 and a lot of other piping codes.

on 2: the laod combinations are more or less given in the codes, but not as explicitely that they give formulas. Primary and secundart stresses is what we want to check, so the combinations should be so that they allow us to check stresses seperately.

I hope in your company there will be someone who can and will explain this to you in more detail, cause this is what stress analysis is all about.

1. Thermal stresses are SECONDARY - they are self-limiting because if the pipe yields the stresses relieve. Stresses caused by Weight and Pressure are PRIMARY - if the pipe yields, the load does not relieve. This is elementary stress analysis stuff, if you don't understand it thoroughly you are perhaps in the wrong line of work.

2. Load combinations are at the discretion of the analyst. The B31 Codes require you to calculate sustained loads, but do not explicitly tell you what must be included. Similarly, they require you to calculate a thermal stress range, but you can change the types and locations of supports that you use to control movement to bring the thermal stress range within limits.

3. The Codes are far older than computers. B.C. (before computers), pipe stress analysis was done by hand, usually consisting of one hot and one cold load case. These results were subtracted to determine the thermal stress range. Experience led the Code committees of the day to develop the allowable material stresses and the Code rules essentially in the format used today.

As computers became more widely available, the procedures required by the Codes were already in place so the analysis procedures were revised to continue to use the existing Code rules and materials data. Remember that the Codes, in addition to guidig the behavior of stress analysts, also guide the behavior of fabricators and installers. And, most importantly, they provide a framework for assessing the blame for failures when needed, so they serve as a legal document.

Because the Codes have significant legal standing in the United States, it is virtually impossible for the Code committees to make drastic changes to the Codes, particularly when it comes to changing the way stresses are calculated and interpreted.

I echo corne's hope that you have a senior engineer within your company who can mentor you on this. It's almost impossible, in my opinion, to figure this all out on your own (even with the help of a forum such as this) without getting yourself into trouble.

Thanking you for reply