HP Steam 30" lifting off

HI,

Now im doing stress analysis for 30" line with design temperature of 400 deg C, steam is de hydrated by water injection to 300 Deg C. design pressure is 47 bar. In Caesar result line is not lifting where in site line is lifting by 45mm in supports A,B,C,D and Q,R,S,T when the pressure is 36 bar and temperature is 400 deg on inlet side 286 on outlet side. Can any one guide me how to move forward in this case. regards
samuel samuel.stephen@woodgroup.com

Dear Samuel,

It is my personal experince share with you.

Normally, High pressure steam piping has always very high pressure and temperature. While analysis, even though supports are not lifting and take full loads of piping, please use at your selected Guide locations - Hold Down Guides, means the normal guide + rest locations use "Y" Restraint in C2 Model, instead of "+Y" and normally in each contractor Support STD, there are Hold Down Guide Supports are always available.

AS you had said, no supports lifting, if there is no support lifting, there shall be no impact on Civil loads. But by using the HOLD DOWN GUIDE "Y" In CAESAR, it will help at SITE, the piping vertical expansion will be restricted by such supports.

Lines where Steam Out case or Nitrogen purging lines, this also can help you.

Please check as I had share my experience, it may help you.

Regards
SND

Dear SND,

Thanks for your suggestion, let me check and revert back.

regards
samuel

Hi stephen

When I have been to my first site survey, I was suprised that piping had acted almost as c2 result. So I suspect there is something wrong in the piping system.

You need to check your c2 input first, check you input all the condition correctly.
And then, check the site if it has been installed as drawing. Sometimes construction crew can make mistake while installing supports.

Also, I assume the system has a desuperheater. If so, the line condition can be vary by this equipment, also there could be lots of requirement demended by vendor. You need to check that with mechanical guy.

After investigating, everything is set accordingly, you can restrict system as SND said by using hold down support or guide, stopper.

It is all my opinion and you should talk with your LE first.

Hi MK,
Thanks, line is De-Superheated. caesar II input is correct. i discussed the issue with operations guys and process awiating for there suggestions and input.

Samuel

Hi Samuel,

Thermal bowing is suspected as the locations of lift-off supports are near water injection and are at the lowest level. If condensate stagnates at the bottom of piping during operation or piping is not sufficiently drained before start-up, thermal bowing may occur resulting in bending piping upward.

There are several reasons for this kind of behavior of the site piping:

1. The piping model does not reflect the site condition, or visa versa.
2. The piping model is not correct to reflect the actual scenario. This requires an expert pipe stress engineer to verify.
3. The piping model weights of valves are different than the actual weights. Use the correct weights in the model.
4. The densities used in the pipe model are not correct. Check model.
5. If the model is absolutely correct the spring rates of hangers might be higher than the model requires. Check model and the installed hanger rates.

This diameter pipe and pressures require heavy valves, and I would expect they were supposed to be supported on both sides. The model does not show this on some valves. This may be manipulating the expected behavior of the piping.

Dear Parky,

thanks for your suggestion. i had checked with thermal bowing effect. Assuming a temperature difference of 55 deg c. It resemble the site condition. I have asked process to check the reason for condensate. is there is any other way to avoid the lifting off.

Dear Ibrahim,

Thanks for your suggestion.

regards
samuel