Hello members.
I was going through the technical paper written by charles Becht & David W Diehl.
There are some points for which i would like to get clarification.
1)How does the new rule address non linear effects such as piping liftoff
if it addresses it so is there a case for checking Hot sustained in case of piping lift off.
2) Operating loads will be reduced as we are using hot modulus of elasticty so are we becoming more liberal n case of loads ?
3) Effect of gaps are considered in operating stress cases How ?

These are my basic doubts Please answer my questions if your time permits.

Hi Ramnathan

1) To understand in simple way, operating stress = sustain stress + expansion stress
So if operating stress is safe there is no need to worry about sustain stress or expansion stress. Operating stress will understand the case when a support lift up same as operating load.
So if we use appendix P to check operating stress all possible code stress failure will be taken care off.
If we do not use appendix P Caesar will calculate stress as sustain stress & expansion stress separately. While calculating sustain stress Caesar will consider no temperature in line so it will calculate stress considering all support are sitting.
If in operating case some support lift that will not be taken care of by normal sustain stress calculation. So separate hot sustain calculation is required in that case.

2) calculation using Ec is good because we will have some extra safety margin within the calculation. But Eh may be used because at particular temperature that is practical value of elastic modulus.
3) Explanation same as point 1.

SHR has it wrong.

Appendix P has no check for collapse loads. Stress due to sustained loads (SL) must remain below the code-defined limit of Sh.

Appendix P simplifies the Eqn (1b) allowable stress for expansion range by removing the calculated value SL. Why is it simpler? Because sometimes we have trouble determining what SL is. As Ramanathan points out, liftoff would alter the SL calculation. Which SL to use in (1b)?
But why is SL in (1b) anyway? It's a check for ratcheting. With that check removed, one must now complete this evaluation by also taking a look at the operating stress - something that until now was not a Code check.

On Ram's 2)... I wouldn't call it more liberal, I'd call it more accurate. But don't use these reduced loads to calculate expansion stress range. The code is clear in specifying the reference modulus (70F) for stress range calculations.

3) CAESAR II iterates until all nonlinear restraints are satisfied. If the pipe does not move enough to close the gap, that restraint is excluded from that load case solution. If the pipe moves to close the gap, that stiffness is included in the stiffness matrix (and moved to close the gap) for the structural analysis.

Thanks Dave
Yes SL must be less than SH.
That means even if will check operating stress we must check hot sustain stress in lift off case ?

Hi shr,

Can you further explain about the operating stress you had addressed?
As mentioned by Sir Dave Operating Stress has no code check , so there is no point of comparing it from sustain stress. Or to make it simple, we cant say our system pass without any refference.. Right?

B31.3 says you must consider/evaluate:
1) stress due to sustained loads
2) stress due to strain (expansion stress) range
3) stress due to sustained loads and stress due to occasional loads

Appendix P offers an alternative to evaluating the expansion stress range. This alternative is a little more complicated - calculation-wise - but that's what the PC's good at.

Hi again
When we are using Appendix P do we need to check for hot sustained when Piping liftoffs How will we take acall please explain

The software knows that the support has lifted off, so the nonlinear support routines "turn off" the support for load cases where this occurs. When it then uses the hot load case in an algebraic calculation of the thermal stress range, the phenomenon is accounted for in the calculation (Sh - Sc), so there is no need to have a cow about the subject.

As Dave Diehl notes above, using Appendix P is more work than simply using the basic Code rules. Since few of us have over-generous stress analysis budgets, why do things you don't have to?

Really, we get this question repeatedly. Many of you must stop treating output from a software program as a holy book to be accepted without question. Instead, it is a calculation to be evaluated by an engineer using common sense and occasional hand calculations to verify what the calculation says is going on. Once you have reached that mind-set, you will have become a much better pipe stress analyst.

We are not treating anything as holy
In my current project client has instructed us to use appendix p calculations also.I have done analysis using both cases. We are checking Hot sustained also when we see liftoffs My doubt is whether we are becoming overly conservative by checking hot sustained when we are using appendix P.

Appendix P is an alternative set of rules for evaluating expansion stress range. You are still obligated to satisfy base Code rules for stress due to sustained loads. If you worry about "hot sustained", Appx. P does not relieve that concern.

As a humble suggestion to you all, i insist you people to go thru the
training manual of Caeser II(c2TR - tarting from 6-18 to 6-20); this will clarify all of your concern(related to Hot Sustained, sustained etc; giving consideration to almost every school of thoughts).

Satisfying the Code recommended check for the Sustained Stress & also for the Stress at Operating condition(as per Appendix P, is as good as the previous recommendations of the Code(i.e, the Sustained & Exp. stress range).

Only thing is that, here, the term SL is expected to have added to the Liberal case of Exp. stress Range(Eq.1(b)of Para 302.3.5(d)), and instead the whole of the Computed Stress developed for the Operating case is equated with this.

The benefit is that you need bother about switching between the Liberal & non-Liberal case.