High temperature steam line on the pipe rack

[Frankcliu2009]

I am doing pipe stress analysis and pipe support design for a 12" steam line(P=1800PSI and T=1050 F)in the pipe rack. The pipe materials is A335 P91. I added two line stop supports on a 120ft long strait pipe to push pipe expanded to a setting loop. The situation is we have 7000lbs lateral force at 1050 degree, the dispalcement is no more than 3". I plan to use clamp shoe for pipe support. I am wondering if the loading is too high for the line stop design. Can I use low friction slide bearing to reduce the friction loads? What are the reasonable displacements and loads for this 12" steam line? Thanks in advance!

 

[StressGuy]

I'd be more concerned about using a clamp on shoe for an anchor point. Is this going to be a preinsulated shoe?

A 7 kip anchor load doesn't sound unreasonable to me from your description. How much is thermal and how much is friction? I suspect with that short a run you have mostly thermal expansion generated loads. You will definitely need to make your structural group aware of a load of that size so they can brace the location or use a heavier beam.

3" of movement into your loop also doesn't sound unreasonable. Our guidelines are typically to limit the growth into a loop to 6" from each direction to avoid interferences and to control how much expansion is put on the branches that connect to the header.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[DSB123]

Do a search on P91. It's a funny material and has a weld strength reduction factor. It is prone to problems unless it is specified welded and heat treated correctly.

 

[MJCronin]

What are the reasonable displacements and loads for this 12" steam line

This is a high pressure 1050F steam piping line. Why isn't a detailed computerized stress analysis (CAESAR-II)being performed on this line ?

Dispacements and loads will come from the detailed analysis.

Mr. Klein, wouldn't it be more prudent and reasonable to individually run and support this high energy pipe line ? (i.e. not use the pipe rack)

It has been a long time, but as I recall there were maximum piping temperature limitations for rack piping, simply because of the problem of excessive displacements and high loadings imposed up high on the rack. (the high loads caused increased expense for the structure)

Does anyone have any guideline or standard practice on steam lines run on pipe racks ?

MJCronin
Sr. Process Engineer

 

[Frankcliu2009]

I appreciate all the input and replies.

I agree with Mr. Klein's concern on clamp shoe. It isn't pre-insulated shoe. The reason I used clamp shoe becasue P91 field welding is challenge and expensive. Clamp shoe has less residual stress compared with welding shoe. But clamp shoe may slide or twisted by the friction force or guided force. I am gona to use fabricated lug or trunion on the pipe to fix the clamp side. The friction force from CAESAR II calculation is 1500lb in max but guide/line stop force can contribute more. My concern to the total of 7k lateral force not only on the pipe rack steel, and also the pipe support components which is used to limit the movement. I think we may use alloy steel because carbon steel has poor performance at 800F degree.

The reason I want to use low friction bearing plates is to reduce the heat transfer between the shoe and pipe rack steel through lower and uper plates assembly. Another reason is I need to create the pipe slope because this steam line requires 0.005 slop with 1 or 2 in height differrence on supports. Bergen has a claim that the temperature drop through their clamp shoe should be less than 752F which is the highest temperature for their bearing plate design. I have concern on the bearing design with such temperature and movement for my case.

Any suggestions or comments would be great favor for me. Thanks.

Frank

 

[OSIRIS7]

You could weld strips on the pipe at both side of the clamp to prevent it from "slipping".