Gasket failure in compression
Gasket failure in compression
(OP)
When a flange is subjected to only external loads (bending moment) without any internal pressure, half of the gasket will be subjected to more compresssive force/pressure than the other half. ASME code convert the bending moment into effective pressure and apply all over the ring. However in reality part of the gasket will be subjected to more compressive force/pressure than the rest of the gasket part. Shouldn't we have to check the gasket for bearing failure due to this compressive force when there is only external forces(bending moments) applied on the flange as this case will occure in installtion condition. Could you please anyone clarify or tell me if there is any method available to check this gasket failure mode. Thanks





RE: Gasket failure in compression
However I suppose that local lack of seal/failure can be an issue.
Hope it helps.
Stefano
RE: Gasket failure in compression
RE: Gasket failure in compression
Use spiral wounds with inner & outer rings, no problem.
You can overcompress sheet gaskets for sure, but I don't know of any commom calculations.
Regards,
Mike
RE: Gasket failure in compression
You can calculate bearing stress from the bending moment( similar to the way calculate bearing stress at the skirt base ring or concrete due to wind or seismic), you can also calculate bearing stress due to preloading. Add together now you get the total compressive bearing stress. Then call gasket supplier what is the maximum compressive stress. Do note that gasket is not in elastic mode when bolting for service, that means it can take big compressive load.
RE: Gasket failure in compression
I would second SnTMan's suggestion - with spiral wound gaskets use inner and outer rings. These rings can handle significant additional compressive stresses.
RE: Gasket failure in compression
There are several WRC Bulletins and PVRC projects that have looked at the effect of external bending moments on bolted flanges. Also, many ASME PVP (Pressure Vessels & Piping) research papers on this topic.
RE: Gasket failure in compression
The gasket is supposedly evenly compressed on assembly, prior to pressure or external loads. As the load moment is introduced, (and I will exclude ANSI 150# flanges), the bolting away from the direction of moment will see increased stresses and the gasket at that point may be subjected to reduced compression if the the bolts are elastically deformed by some percentage. On the other side, a spiral wound gasket with both Inner and Outer metal rings, or with an exteranl only ring, will be subjected to gasket compression equivalent to the bolt elongation/decrease in compression to the opposite side. Having said all of that, in most ANSI/ASME flange designs, the bolt loading is normally in the range of 50-70% of the bolt yield strength (see Appendix S of ASME Sec. VIII), and is normally sufficient to offset flange rotation due to external bending moments.
Rick
RE: Gasket failure in compression