Sustained Load Case Failure

Hi

I need some help regarding statics analysis of piping on Caesar II. The problem I am facing is that the piping loop satisfies the Operating Load Case (W+T+P+F) but shows overstressed nodes in Sustained Load Case (W+F+P).

The question is why a piping loop satisfies Operating case including parameter of T but fails in Sustained Case?

Waiting for early replies

Thanks

not enough supports as for other comments well I will hold them in reserve for now at least

Hello Zahid,

I would be interested in knowing what your acceptance criteria are for saying "satisfies the Operating Load Case (W+T+P+F)". What Code are you using?

Regards, John.

To a stress engineer, your question is akin to wondering why the hole is on the inside of the pipe.

Take a step back and read carefully the code document you are trying to satisfy with Caesar

superpiper.. your directness is atypical of a member of the EU.. well said but atypical... go read some of the PED for punishment!

Hello Zahid,

Please do not let us discourage you. Please give us some additional details to help us better understand your question.

Regards, John.

Directness not intended, just being light hearted.
Although i did work with a stress engineer who once thought a pipe shoe ran the whole length (including bends) of the pipe.

As for reading PED.
No way dude, i have a life to live, i go blind after about 10 mins of reading stuff like that!!!

B31.3 has adopted certain wants and desires out of the PED in order to obtain ISO-ization.... I found it to be a rather lengthy tome but it had a few gems in it....

Wonder if Zahid has his problem taken care of?

Another thing that could be a factor in a sustained overstress is very high pressure... the long axis pressure stresses are usually a small percentage but I have seen them drive the design towards added supports.....

Zahid,

Charge everything to the process of learning. Sometimes it could hurt. I remember two nights I was not able to sleep when I made a mistake and finally brought it out to the Proj. Mgr. At least I did not keep the problem. Anyway on your problem, I also experienced an unreasonable figure in pipe support load due to a figure so high in pipe insulation density which I punch myself in error. Sometimes when your hand is too fast you could type-in node number in 2 even 4 digets before the input page fully open that could go to pipe density field. Always check the spreadsheet as it always easy. Check if the supports are getting unreasonably high figures and maybe that is the problem.

Regards,

good point.... Ive seen slips like that affect pipe density, and fluid density as well... plot the deflection of the SUS case...

I typod a number in one time so high it was approaching the density of neutron star material!!!!

............would that be miraculum or unobtanium mein gelehrter Großvater?

I concur. Most of my surprises have been due to my slow witted fingers having chance encounters with the keyboard.

unobtainium will be weightless, have no thermal growth, be twice as strong as P91 for fatiuge as well as sustained loads, and be creep resistant to 3500F, and cost no more than carbon steel....

so my mistake was neutron star matter of sorts!

Zahid Alamgir

Are you there? Speak to us oh fellow piping engineer.

Regards, John.

Zahid,belonging to this part of the world maybe I can understand your problem better.
I presume that you have specs (from your consultant) where the pipe is already designed for pressure. so that's not a concern.Now if you are using B31.3 it does not check stresses for allowable case (prior to 2004 edition).So how are you comparing operating case stresses?Are you using the 2004 edition.
Most probably there is some problem woth supports or wrong densities.Again wrong densities will make your system fail all along it's length (almost all nodes if not all).If your system if failing at certain nodes then please provide supports near that point.
I feel you are from an operating plant.Are you really required to do stress analysis yourself.Otherwise why don't you throw this to your detailed engineering contractor.I always wanted to be on client's side for that reason.
Another thing don't get discouraged form some hard hitting replies.These are the people we have to learn from.
Thanks Mr Breen for not only sending good replies but also the encouragement to young engineers.I remember three years back I was in tough situation and I could convince my client only after showing your reply to them.
Regards

NO NO NO!

The piping system still must pass the B31.3 codes requirements for Sustained Load stresses the operating case per appendix P does not negate this fundamental and important consideration.

If a line goes over the Sh value at any of the various temperatures and conditions it will experience, anyhere in the world due to sustained loads it is overstressed plain and simple.

My apologies if I didn't made it clear. what i wanted to say was that Caesar 4.5 does not check code allowables for operating case.It checks for sustained case and expansion case only.
Regards

version 5.0 will allow as an option, users to check the operating load stresses in accordance with appendix P

Verify the span between support or change the type of support of loop.

Best regards

Well my mentors, it seems we have blown our chance to assist our colleague's learning process by our mindless glibness!! Zahid came here looking for help and was likely put off by the "typical witty banter" that he was subjected to. We should try to be a lot more sensitive to people's feelings. These are sincere people asking sincere questions. Yes, I have read the "I am not gonna help people who...(insert your list here)... but for those who feel that way I would suggest picking and choosing the questions that you weigh in on. If you don't like the question, ignore it and move along to the next question. I would suggest that we all started by asking uninformed questions about (really) fundamental engineering issues (if we could find somewhere to ask these questions). Or, perhaps more likely, we stood around shuffling our feet until someone else screwed up the courage to ask "the dumb question". I think it is likely that there are many times more people lurking on this discussion board, not asking their questions because of the way the mentors sometimes treat such questions. Some of us are forgetting where WE came from. Other "Kings" of the art seem to be protecting their throne by saying "off with their head" when the pretenders to the throne dare to approach. Maybe it is time for each of us to ask ourselves what drives us to post answers on dicsussion boards.

There is no "Piping Stress Analysis 101" into which people can enroll so maybe forums like this are where these people must start - THIS is where people take their uninformed questions. The books that we suggest here are expensive, sometimes out of reach and they cannot answer all the questions. This is one of the few places where people can "do their homework". I would suggest that in any endeavor, NO good is ever done by ridicule. It is NOT NECESSARY to make an effort to humble people who are already humble.

Now that I have that off my chest, I wonder if Zahid's model is simply seeing a case of lifting off the supports? Zahid if you are still out there, give us another chance and provide more details about your question.

Regards, John.

And does it? I haven't been able to find
(Thanks Richard!).

BTW, the online documentation doesn't seem to have
a "search" capability.

=Shannon

Never mind, found it, I'm guessing I just
had to ask the question in public and look
foolish (grin). Right where I thought it should
be too

-Shannon