Dear Friends,

We have a steam pipeline running long distance.....We are getting around 900 mm of displacements near the loop bends. System is well within the allowables for expansion stresses. We are using ASME B31.3 & material is API5LX60/65/70/80

The concern is:
1. With such high displacement values, whether this piping will come back to its original position after first shut down?...
2. If this line could not come back to its original position then will there be any kind of pre-stresses/residual strsses in the pipeline & will it cause any problem in the behaviour of piping if the line is re-commisioned second time....

Your valuable thoughts may help us to take care of more considerations.

Thanks for your time.

I'm not an expert and below is just what I know

Thermal expansion stress is a 'secondary stress', which is not a collapsing load. It means only single affect of thermal stress will not cause severe(or direct) damage to the system.

Because of self-limiting, your piping system can endure small local yielding or minor distortion caused by thermal displacement. Find stress range of secondary stress and see its behaviour, it does have pre-stresses/residual strsses you mentioned but it'll be ok until the stress reach two times of Sy(yield strength) of material.

Piping will be contracted to original position when the system cools down with small local yieldings or plastic strains.
Unless your pipe slide off the supports when it expanded, and after cool down it can't get its original position. It could cause serious problem.

If the calculating expansion is too excessive, add more loops or use springs(guess its on the field, so spring might not be usuable) to absorb expansion.


To get more detail, please refer this thread http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=230

This displacement is almost 1 meter near the loop, and this will require very big loop and very long shoe. How about your directional anchor loads? How did you balance the frictional load at this anchor? Why not use multiple smaller loops instead?

Hey guys...thanks for your valuable thoughts.....Anyhow since the pressure drop & possibility of slug are major concerns, the client is against increasing number of loops.

An issue with that much thermal expansion is that the actual piping system (especially around the loop) won't behave in the field as it does in the Caesar simulation. You will get bigger friction imbalances than Caesar is likely to generate and could therefore get much higher stresses around the loop.

Also, long straight runs are normally a bigger concern with regard to slugging (compared with having additional loops) as it often takes a certain length of straight run before the wave of liquid reaches the top of the pipe.

Thanks MattR