Pipeline deflection and Expansion Joint

[Mechville]

I recently inspected a pipeline suspended under a bridge. The pipeline has anchors and a single-end slip expansion joint at each end (for a total of 2 anchors and 2 expansion joints). On the east side, beyond the anchor, the pipeline 90s down and then 90s back to horizontal perpendicular to the bridge. At the upper 90 elbow of the vertical section the piping has deflected significantly (the perpendicular section is held in place by guided supports), indicating axial thermal expansion along the length of the bridge. The anchor appears to have failed to hold, with pipe shield displaced out the side of the anchor clamps, as well as pipe shields for the rollers and guides along the bridge.

However, the expansion joints do not appear to be compressed and when I viewed it at what would have been near the hottest temperature the pipeline will experience. Is it possible the pipeline expanded, overwhelming the anchor, but the anchor is now holding the pipe in a deflected position?

In any case, my planned recommendation is to remove the vertical portion and replace the expansion joints with properly sized joints or a piping loop (if they'll allow it).

 

[LittleInch]

This needs a few photos and a drawing to be able to comment.

Any anchor that is not welded to the pipeline will fail.

The forces are huge and any clamp type won't be able to handle it.

But we can't see what you can see until you post some photos...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Snickster]

Pictures or sketches would really help.

I think I see what you are talking about. You have a suspended pipe under bridge with anchors at each end between the slip type expansion joint and the first elbow down, but maybe not elbow down on the west side but maybe just goes straight, don't matter.

Seems like the east side there is a noticeable movement of the upper elbow at the joint. If that is the case then it appears that the anchor at that end must have failed since I believe that is the only way that elbow can move like that. I think what happened is that the anchor failed causing the elbow to move due to the pressure thrust, and then pulling the pipe suspended under the bridge with it. In such case even with thermal expansion of the suspended pipe between the slip joints, there may not be any compression as the whole line is put in tension by the thrust force on the elbow, being that the movement due to pressure thrust is much more than thermal expansion of the suspended pipe. This assumes that there are stops on the slip joint that don't allow it to pull apart.

 

[1503-44]

Minimum info.
Pipeline Design Code?
What's the pipeline carrying?
What pipe material spec?
Pipe Diameter?
wall thickness?
Pressure?
What is the distance between anchors?
What is the offset?
What is the pipe operating temperature?
What is the pipe installation temperature?
If it is not welded, what is the construction?

Why was an expansion joint used? That was probably a mistake which should have been handled with added flexibility.

From what you have said already, I would agree that you should probably replace the expn jts with a dog leg or full loop. Use guides if necessary. Remove all anchors.

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

 

[LittleInch]

Reading this again it would seem that your anchors are actually clamped to the outside of the pipe coating? Pipe shield is a strange term which confused me.

Unless you know the unstressed length of a corrugated steel expansion joint you probably wouldn't be able to say if it is compressed or not as the compression length is a falsify small fraction of its length.

It certainly sounds like the anchor has failed and the pipe may be stuck there now or it moves to and fro using the zig zag as its expansion loop.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[nackra]

I have used this fitting on projects:

https://ebaa.com/products/spotlight/FLEX-TEND_Installation/index.php

1503-44 hits critical points