Snubber below silencer in open discharge PSV - is it right ?

Snubber below silencer in open discharge PSV - is it right ?

In open discharge psv, after PSV pops up fully, force time history in the last open leg is steady which can not be withstood by a hydraulic snubber.

Moreover, at PSV inlet and outlet sections are small enough to withstand any bending moment arising out of yielding of snubber in steady load.

ASME B31.1 App-II 5.7.2 has shown a note of caution in repeated, not-so-transient load appearing in open PSV discharge.

I do not think snubber a right choice in open discharge PSV outlet below silencer; what our forum members think ?

reg,
sam

It's a common configuration - whether a snubber or a rigid support. This is the standard API 520 configuration... for local vents.

If it's a local vent, the transient effects are typically ignored and flow is assumed to be instantaneous.

If it's a remote vent, the transient effect is proportional to the lengths of piping runs between the silencer and relief valve. Loads at the silencer should take into account pressure losses in the piping, but if you want to be conservative, you don't have to.

You might have misunderstood me! This is not a standard API 520 configuration.

Piping Snubber is not a common hardware as a open discharge PSV outlet support, rigid support is, if it is taken from same header from which PSV inlet is coming up!

But, special snubber with bypass eliminated can hold PSV thrust force for prolonged duration. Bergen Snubber & Restraint catalogue claims it.

reg,
sam

A standalone snubber should not resist thermal loads, unless it's allowed to "bottom out," at which point it's a rigid support with the gap, probably with similar capacity of the dynamic snubbing aspect.

I can imagine there being a market for combined snubber springs in tight quarters, much like for an automobile suspension, but I'm not aware of any on the market.

Might you upload the reference?

http://www.pipesupports.com/sites/default/files/PS-snubbers-catalogue-METRIC.pdf

In the above doc, page 6/126 bottom, special hydraulic snubber with bypass eliminated to hold PSV thrust force for prolonged duration has been discussed.

It is risky to volunteer using such a device on a safety valve in a real plant. It will require manual bypassing of snubber before steam piping cools down; otherwise, safety valve neck may break.

reg,
sam

Then it seems like they propose a snubber that's allowed to "bottom out" hydraulically (not mechanically) that you could estimate as a bi-linear restraint.

Is it common? I don't think so. Is it be safe? If it's engineered and maintained.