Dear friends,

Can anybody elaborate the definition of restrained and unrestrained piping base on B31.8?
for example a line on pipe rack which has a loop with semi anchor is restrained or unrestrained piping?

Please give other examples.

I have studied B31.3 833 but it is a bit vague for me.

Why are you using B31.8 for pipe on a rack? See, for example, 802.1 (d).

What is a semi anchor? Is that like semi pregnant?

We would prefer you to give an example. Then we might be able to help you.

I think Reza refer semi anchor as (Rest+Axial stop) support between two expansion loop in pipe rack.
Generally we put (rest+guide +axial stop) support in most of the cases to isolate a system in lieu of putting a physical anchor support to avoid excessive force & moment on the support location unless otherwise system is very critical one.
Some times rest +axial stop support also use to isolate stress system ( If guide at that location creates problem )in that case we add 2-3 more support as reference in both the stress calculation to get fairly good enough boundary condition .
Rest +Axial support we called as semi anchor / Partial anchor.

Pipeline Codes include formulas for the net longitudinal compressive stress that must be applied only for "totally restrained lines", which means "zero longitudinal strain". This stress status is characteristic to pipeline buried, far away from pig traps.

By contrast, "unrestrained lines" means "those portions of the piping without substantial axial restraint". You have to understand they are not "totally restrained" or "partially restrained"-(buried, the soil exerts substantial axial restraint, but they are not fully restrained).

You can see that "restrained" doesn’t refer to the existence of a singular axial stop, anchor or "semi-anchor" (?!) on the above ground lines.

In this approach you can consider "fully above ground" as "unrestrained lines". And the term "soil restrained" (or simply buried) instead of "restrained".


Best regards

Where have these terms 'semi anchor' and 'partial anchor' come from ?

An anchor is a restraint which restricts translations and rotations in all three planes. Anything else is not an anchor at all.

A restraint is just that. Something that fixes one or more degrees of freedom.

Why invent daft, meaningless expressions, when plain English will do nicely ?

shr:

Yes, that was exactly my point. B31.8 does not have a clear definition of how to classify pipe in racks BECAUSE B31.8 IS NOT SUPPOSED TO BE USED FOR PIPING IN RACKS. There are a few exceptions to this, i.e. at in-line compressor stations, but even then it is our practice to use B31.3 for the piping adjacent to the compressor because of the vibration / fatigue issues.

I had the dubious privilege some years back of working with a client's engineer on a long line in a rack that operated at about 275 F (135 C). He wanted to use B31.4 for that line because it had higher allowable stresses listed for the carbon steel material. I kept trying to convince him that B31.4 had a temperature limit (below 275 F) and in any case was not intended for fatigue loading applications, with no result. Fortunately, I convinced his project manager, and the project manager eventually threw him off the job because he had become too much of a hindrance to getting it done.

Thanks CraigB
For sharing your experience. Yes we must avoid violating code rule even some individual from Client's side is asking for that.

Just to add one new term.
Some body call the support as directional anchor or sliding anchor.
http://www.flexhose.com/terminology.htm#Directional%20Anchor

I don't see the relevance of quoting stuff from a bellows vendor concerning use of English. A 'sliding anchor' is quite clearly a contradiction in terms.

Oh, but wait a moment .... when my boat bumped another one at the beach, that was due to a sliding anchor .... or maybe it was a not anchored anchor.