Hello,

We have a condensate line (10" STD, T=120°C, P=100 kPa)whose line stopper has been removed due to the slug force (maybe at startup). The entire line has moved about 15" southwards (slug force is southwards). Many of the supports were moved out of the guides.
The client wants us to check the piping condition before they reposition the system back to its original position while hot. I have done several runs:
1. Model as-designed piping

2. Model as-built piping (missing base stopper on as-built)

3. Remove stopper, apply arbitrary slug force to produce displacement equal to field measured displacement. Check code stresses, also check ope+occ stresses if system has yielded. Luckily the system's operating stresses are below Sy.

4. Apply arbitrary forces axial & lateral enough to bring back the displaced system to its original position. (Simulating the process of repositioning the piping system). I treated these forces as occ combined it with sus and I checked it against 1.33Sh. Is this correct ? (following the logic of the B31.3 code,although I am dealing with an existing system)

5. Model system with recommended restraints (same as as-designed)

Also, I am planning to:
1. Design stopper properly to resist slug force.
2. Make a procedure for the repositioning work and monitor the actual repositioning work.
3. Monitor field construction of as-designed piping system (making sure that stoppers are placed where they should be)

Am I missing something ?
Please advise especially on the correct repositioning process.

Thanks,

If you or your customer wants to know what is the stress level now and/or after repositioning I do not think you get an accurate answer by calculation. I would do:
- good visual inspection of the line now
- NDT of any suspect area, replace as required
- check line for internal erosion, especially bends
- check inside surface for micro cracks (thermal shock)
- if the line has compensators ask some expert to check them
- design line with correct supporting
- reposition the line by cutting it up to release unknown stresses

If the customer wants to position the line while it is hot I would give very long disclaimer or would not agree to sign off.

Thanks Mr. Jouko,

Could you give me some references on how to check a hot line for internal erosion and for micro cracks ? Also, there are no compensators.

Thanks again.

Those would be done when the line is cut. In theory using high temperature probes you can do something using ultrasonic testing during operation but accuracy may not be there.

API 579 provides important informations on Fitness for Service..

In my opinion look for any spool got twisted as you say it has moved by 15", if that is the case change the spool and reanalyse in fully corroded case and check how much corrossion you can allow in the analysis and also check for hoop and axial stresses. Provide the line stop and make the structure rigid enough to take the slug force if any and the existing line can be used. I did experienced similar case and followed the similar procedure as written above. I did ask the operation guy to investigate for corrossion and report back to engineering.

Thanks everyone for sharing your thoughts.
Hopefully someone would share his experience regarding hot line repositioning.

Regards,