Large Bore Pipe W/O Saddles/Shoes 1

[StressGuy]

I'm struggling to find some references on how to approach this particular problem - at what point does a pipe need to be on a shoe/saddle support due to the local stresses at the support location?

For larger lines, I'm used to them being on a saddle for insulation and/or because they need to be sloped for draining. From that, I've used variations of the Zick analysis and various saddle design tools to check the horn stresses and such. That's all well charted territory.

In this case, I've got a vapor line, uninsulated, and unsloped. So, all the normal triggers that would put this line on shoes aren't in play.

So now I'm having to approach this from a pure structural integrity standpoint. It's intuitively obvious that there is some threshold where a liquid filled pipe is going to need the reinforcement of a support saddle to keep it from ovalizing. Every horizontal pressure vessel already does it. Finding a mathematical basis to determine that threshold is proving difficult.

Does anyone have any reference papers that address this topic? I'll happily run calcs or built a spreadsheet to do an evaluation. Even some kind of general guideline, like a D/t ratio that has some industry agreement would help.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[HTURKAK]

Regarding design info. pls look AWWA MANUAL MI 11 Steel Pipe-A Guide for Design and Installation (Section 7).

You may look also Process Industry Practice PIP PNC00001 Pipe Support Criteria for ASME B31.3
Metallic Piping.

PIP PNC00001 '5.12 Pipe Supports for Large OD Pipe (Greater than NPS 24)
5.12.1 Saddle reinforcement or wear pads shall be used at the point of support bearing to handle the weight load and to protect abrasion....'

 

[XL83NL]

Hi Edward, I'm quite sure you're more experienced in this matter than me (I have very little experience with this area in piping design), but have you checked Peng & Peng's book on Pipe Stress Engineering, and the info provided in there related to this matter? If you don't own a copy of the book, I can recommend this book to you as being one of the very (if not the) best books on pipe stress engineering that's out there.

(PS: they have over the years also provided some excellent technical articles on there website, hyperlinked above)

Huub

 

[1503-44]

Unless your pipe walls are too thin, D/t >100 ?, you probably won't find a structural/stress/integrity realated issue to having no shoes. As you say, they are there to make building the pipe centerline location to proper elevation, protect insulation and to make thermal sliding movement to release thermal stresses a bit easier. If you have an integrity-stress related problem, having shoes or not is unlikely to make any difference. I.E. If shear strength of the pipe wall is a problem due to load reaction of the support on the pipe, you need more pipe wall thickness. There is only one other criteria I can think of. It is often very convenient, if not legally required by CFR 49 for pipelines in the US, to be able to adequately visually inspect the region of the pipe in the vicinity of a support for corrosion. That is not easy if you have to lift the pipe up to see what's going on there. We used to put an adjustible pipe support chair (with seating/leveling bolts) that could be removed to enable ease of inspection in these areas.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[KevinNZ]

For our steam and hot water pipes we check local loads at pipe shoes with FEA. We find that from about DN500 up the pipe does need a well designed shoe. But all our pipes have shoes for insulation anyway.

Pipe shoes also mitigate vibration wearing a hole in the wall at the support contact point.

 

[StressGuy]

I wanted to give a follow up - I finally found some useful information. The book "Pipe Stress Engineering" by the Pengs (father and son) has a section in it on pipe supports and specifically addresses the topic of bare pipe on a support. It has derived some equations to facilitate an analysis and even has a table based on it with recommendations for pad, saddle, and full encirclement stiffening rings for different sizes and wall thicknesses.

In my case, if I could guarantee the line I have would never see liquid (and we'd have to do an alternative to a hydrotest), I could have gotten away with a repad. However, after grilling my process folks some more, they did indicate there are scenarios where the line can get mostly full of liquid. So, that pushed it over into the "gotta have shoes" category.

The book is a useful reference that I've actually had in my collection for a while, I just hadn't realized it covered the topic in such detail.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.