pipeline design question - overbend/underbend 3

[AKRIDER1978]

Hello,

I'm reviewing an old pipeline drawing that references an overbend and underbend location on the line. Basically it's an offset in the line where the pipeline elevation changes to go under a road crossing. The drawing specifies the elevation change and the distance between the bends. I'm developing a repair sleeve to go over the bend area and need to know if bend locations (overbend/underbend) are typically laid out using the centerline of the pipe/bend or are these location points taken from the start/end of the bend arc. It would seem to make the most sense to reference these locations at the centerline in the same manner that a normal pipe offset is laid out on a non-pipeline drawing (isometric, ortho, etc.).

I appreciate any advice from the pipeline design/engineering experts on this forum.

Thanks!

-AK

 

[racookpe1978]

I strongly suspect that - regardless of the theory of over-bend/underbend, and (almost) regardless of what was drawn on the grade crossing, and regardless of what what specified in the top level contract words, the field did not install and fabricate the bend according to any 3D model or piece of paper you may find.

To repair a bend, you'll probably have to go there, remove the fill, and find a way to ray-trace laser-scan model it to custom fabricate a cover plate. Or get a good welder and a lot of filler metal.

 

[pmover]

good post r...1978, i know that is correct.

AKRIDER,
ever hear of clock springs?

https://www.clockspring.com/

 

[AKRIDER1978]

Thanks for the information! I agree that reality is often different from what was planned. The reason I ask is more from a design perspective of what the original design intent was. I assume overbends/underbends are typically shown on design drawings based on pipeline centerlines but I just wanted to see if anyone knows what the industry standard is. This specific line was built with induction bends having specific angles for the overbends/underbends so an exact angle was determined and a bend fabricated long before the line was ever installed. This being the case, I want to know what the designer intended. I know a distance between the bends and the elevation change. If I knew exactly where they were taking their measurements from, I would know what bend angle was needed to accomplish the change. Thankfully, I'll be able to verify this location prior to the repair. I was just asking to get an expert opinion on the intent of the design and what the pipeline design community typically does in these cases. Thanks again!
-AK

 

[LittleInch]

You would normally create a specific drawing with cross section. Top of pipe is fairly common as it can be easily measured and laid out in the field.

If you can't see it you can't measure it.

Making something beforehand is big risk.

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