Hi All,

I am doing a stress analsyis for a 6" pipe with 36" expansion in total. My understanding is that there is only one expansion loop required as long as the pipe won't interfere with other pipe and the loop leg is long enough. Am I right? Is there a limit the pipe can expand?

Thanks,

I recommend that you divide the total run into six segments with anchors between each segment.
Each segment will have an expansion loop.
Each segment will take 6" of total expansion.
The total expansion in each segment will be divided to 3" on the upstream of the loop and 3" on the downstream side of the loop.
Guides will be required (for each upstream portion and downstream portion) at about the 2/3 point from each anchor to the loop.

For simply determine the expansion loop bend length (L2) using "nomograph to determine loop size" based on nominal pipe size (D) and expansion to be absorbed dL = Lo*alpah*dT.

After that maybe the size is to big due to the big value of expansion to be absorbed. If this the case you can divided L0 by L01, L02,..., L0n as suggested by Jop so then now you may have the proper size.

If you pass the exp stress without loop, you still need to check the load on support especially at the both end if this too huge for structure. The loop reduces this load.

Thanks Jop & Samsul.

The loop leg is about 18m to absorb the 18" expansion on each side. It passed exp stress. I thought we don't have to change it because

1. It passed exp stress.
2. There is enought room for the loop. It will be installed in an open space area.
3. It won't interefere with other piping. There is enough space between the piping.
4. Our client has standard long pipe support so it won't fall off the beam.

Am I right?

"Am I right?" No!

1. Just because it passed stress does not mean that it is good design.
2.Enough room and open space is not a good argument. It may be okay today but five years from now it may be an obstruction to an important plant addition.
3. Won't interfere with other piping is a hope but may not be a valid excuse for bad design. A loop that big with that much expansion will do what it wants to do.
4. A long "Shoe" pipe support is required but has no real bearing on the issue.

I have the nomograph in front of me right now. Using pencil and the ruler for OD 6" and dL = 36" I draw the straight line to match bend length L2 = 90 ft = 27. 4 m (approximation).

But as suggested by Jop you can generate 2 exp. loop for example with size L2 = 13.7...etc, then you have two closed system separated by three anchor point (assume straight line here).



yes I agree, check if the displacement report convinces you that your pipe doesn't fall from the support/beam. There is a documented accident regards to this mistake by not checking Diplc. report or may be no stress analysis done for such line.

I would be concered with the 18m loop leg squirming. How are you guiding these loop legs to ensure that they move the way you intend them to. I'm not sure of your layout or if it is on a pipe rack but you generally can have a lower cost design if you can constrain the loop in the piperack so additional supports and piles are not required. Just remember that code compliance does not neccesarily mean good design.

If you can convince yourself, your supervisor and your client that one large loop is the best design you are the engineer and have to stand by you work but I would look at several other layouts that may be "better" design or more cost and space effective.

18" expansion in my experience would be something. You must consult your senior piping engineer for your design param., There are several limitation in the design of the loop but depending on its location or porpose.

Your company has its limitation set for good engineering design. Most common limitation are economical acnhor location and horizontal deflection. For your case check your anchor load for the effect of friction. And as mention above if your system has shoe for 18" displacement, i cant think of what will happen or what it look like..

and please dont forget to put a guide!


Regards,

Sorry, 18m is the lenght of H. So the total loop is 45m (2H+W). The line is like aboveground transmission line. Acturally our client already have loops like this size in field. It is running good so far. They have 36" long pipe shoe (The first time for me to see such a long pipe shoe also!).

We now will go with two loops because we cannot have one straingt line according to the land survey.

Thanks everybody for all your input.

The line slipped off the structure which was designed without taking care of large thermal movement, support, and reaction.