rtv gasket factors

[Tmoose]

ASME pressure vessel Section VIII Div 1 - the various flange calculations include "m" and "y" factors based on gasket material.
For low durometer elastomers (<75 A)the minimum design seating stress can be zero, but "m" is zero only for self energizing types like 0-rings and gaskets with V sections oriented to respond to pressure.

This site has a more understandable description of the meaning and use of the m and y factors, although it claims .5 is typical “m” for rubber, but unlike ASME does not list any as low as 0.

http://www.boltscience.com/pages/gasket.htm

Xiameter (Dow Corning) tech support is still struggling to dig up an answer re: "m" factor.

This is the part I really need clarified, since I believe the factors don't give credit for the adhesion that takes place with formed in place RTV if components are assembled before the RTV forms a skin.

"Seals and Sealing handbook" by Flitney and Brown (viewable thru Google books) says "RTV gaskets seal by adhesion, not compression....."


Does anyone know of guidelines or standards that may more fully consider use of RTV ?

thanks

Dan T

 

[Compositepro]

I agree that an RTV gasket relies on adhesion for sealing. That also makes it somewhat unreliable. Loss of adhesion will result in a leak. RTV does, however, tend to swell when exposed to fluids.

 

[MikeHalloran]

I don't think it's as simple as just adhesion.

Yes, RTV sticks like crazy, especially when you don't want it to, but successful gland designs almost always include a cavity, like on o-ring cavity, where the cured sealant forms a true packing that resists extrusion by resisting deformation.

I was really enthusiastic about the stuff until I figured out that a loose goober extruded during seating will eventually find its way to an engine's oil pump, where it clogs the relief valve and causes overpressure failure of the filter gasket on a cold start (by actual distortion of the filter flange, not simple extrusion of the gasket). The sound of five quarts of oil leaving the engine is fairly distinctive once you've heard it.


Mike Halloran
Pembroke Pines, FL, USA