Pre-stressing Expansion Loops During Construction

[Mechville]

I have designed an aboveground pipeline with an expansion loop to account for thermal expansion from ambient temperature. The client has requested information on prestressing the piping/loop based on the temperature at the time of construction. I'm generally aware that this is possible from previous conversations with engineers and construction teams, but I cannot find any guidance to provide to the client. Can someone point me in the right direction? Is it as simple as installing a bit more or less length on the straight piping spans, using a linear relationship between my expected length of expansion as a function of temperature?

E.g. if I've calculated 10 inches of expansion for a 100 degree temperature range, do they install 1 more or less inch of piping for every 10 degrees off the median temperature?

 

[akpipelineengr]

We commonly cold spring North Slope pipelines. Install temps of -20F are common, so most operators specify cold spring to account for the steel contraction from 60F. Codes don't permit any credit to be taken in the design of the expansion loops, but it is a best practice.

 

[1503-44]

As a matter of practical interest, could you please explain exactly how you do that? D9 method, or do you have some other techniques?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[akpipelineengr]

For smaller lines and shorter cold spring lengths, a choker and come-along or two might get the job done. Otherwise I think the D9 sideboom method is standard.

 

[1503-44]

So you are talking bending prestress. I was wondering about axial stress. That can get to be a bigger job than what several D9s can do for any decent size pipe and, if cold, you have to compress it, then there's buckling worries too.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Mechville]

Thanks everyone for the input! It sounds like it is largely a means and methods issue with no particular industry standard solution.

Also now I know about the D9 technique!