Hi,

I am currently unsure whether to "turn on" the Bourdon Effect when calculating valve forces. I have a valve in-between very long straight sections of buried pipe (i.e. 2 to 3 times the virtual anchor length). However, I find that when I turn on Bourdon effects, there is a significant increase (up to 40%) on the axial forces acting on the valve.

My questions are:

i) Why does the Bourdon Effect make such a large difference (even on straight lengths?) - I am aware that Bourdon effect is the rotation of a non-circular cross section under pressure.
ii) Is this an accurate representation of the "real" forces acting on the valve?
iii) I've seen a lot of discussion relating to the use of Bourdon effect, i.e. Bourdon effects are necessary whenever pressure displacements are "significant", Is this true for straight pipelines too?

Thanks,

Jaidev

The term 'Bourdon effect' as you rightly note is specifically to do with the behavior of a non-circular, curved section of tube (in a gauge) or for instance pipe (elbow). In addition it is taken out of context and used to describe pressure elongation. I guess that this is the source of your axial forces. Caesar allows you to choose none, axial effects (translation) or translation and rotation. Rotation applies to non-circular bends such as pulled sections. There have been many posts on this issue.

There's 2 type of bourdon effect for straight pipe
1) pressure thrust forces on end caps of pipeline. As I think Caesar II assume all free pipe ends have caps, but it's not true for equipment nozzles
2) pressure thrust forces on all nodes with change of direction (bends, tee e.t.c)
3) shortening the pipe because of an increase in the diameter under pressure (Lame's equation)

I will not attempt to answer the question as it relates to software application; however, I think there are some practical considerations of in-line buried valve thrust and movement that may be helpful to understand. As indeed one responder mentioned a Bourdon tube is a device that employs a closed end, curved tube. However, I believe generically in the pipeline field Bourdon effect is often referring e.g. to the deformation effects from lengthening of essentially straight welded or restrained joint pipeline segments etc. in response to otherwise unbalanced pressure thrusts (on thrust foci such as bends, tees, bulkheads etc., that for whatever reasons are not externally buttressed or restrained). I suspect this effect and others are not necessarily well-known/understood in the pipeline field, though even as little children virtually all of us see these pronounced lengthening effects when entertainers blow up little cylindrical latex balloons into much bigger, longer cylinders (e.g. to make/tie balloon “poodles” etc.) Perhaps one reason for this lack of identification in the pipeline field is that with common, extremely high long-term moduli and tensile/compressive strength piping materials like steel and ductile iron (and not extreme pressures), Bourdon deformation of pipeline segments is normally very slight. Another reason that Bourdon effects may be little noticed (at least in the case of a buried in-line valves with traditional pipeline materials), is that e.g. pressure thrust on a closed valve disk is also often at least counteracted/balanced by significant columnar strength of the downstream piping (braced to some extent laterally by the soil), and not just axial tension in restrained upstream piping.
I suspect on the other hand much more pronounced Bourdon deformation effects may dictate much more consideration e.g. with some plastic/viscoelastic pipeline materials (due to in some cases to VERY low at least long-term moduli etc., even hundreds of times lower than that of steel!). Another potential practical issue as it relates to a closed in-line valves and also Bourdon effects is that some manufacturers of plastic, rubber-gasketed systems like pvc pipes are very vocal in their warnings concerning “over-belling” of this type of piping (that I believe has been blamed for, or as a factor in, many field pipe-splitting failures). When Bourdon effects are appropriately determined at least in some in-line valve situations, one may find that at least some over-belling of the downstream piping may be sort of hard to avoid! Of course also, pronounced lengthening of pressure piping segments adjacent unblocked bends might at some point also exert significant bending stresses at the bend locations.