m & y factors in bolted connection design
m & y factors in bolted connection design
(OP)
My understanding of m & y factors of gasket:
1) "Factor m": In order to ensure leak proof flanged joint in operating condition, residual compressive stress in gasket shall be minimum "m" times internal pressure.
2) "Factor y" is interpreted as minimum gasket seating stress required to create an initial seal with essentially no pressure in the vessel.
Question:
If "m" factor take cares of sealing of joint in operating condition, what is the necessity checking sealing at no pressure condition using factor "y"?
1) "Factor m": In order to ensure leak proof flanged joint in operating condition, residual compressive stress in gasket shall be minimum "m" times internal pressure.
2) "Factor y" is interpreted as minimum gasket seating stress required to create an initial seal with essentially no pressure in the vessel.
Question:
If "m" factor take cares of sealing of joint in operating condition, what is the necessity checking sealing at no pressure condition using factor "y"?





RE: m & y factors in bolted connection design
That said, I think you'll find the m&y factors to be of limited use beyond initial design.
Nathan Brink
RE: m & y factors in bolted connection design
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: m & y factors in bolted connection design
RE: m & y factors in bolted connection design
RE: m & y factors in bolted connection design
I would like to elaborate my query with example.
A flanged joint, with spiral wound gasket, is subjected to an internal pressure of 1.5 MPa.
1) While designing for operating condition, if compressive stress in gasket is maintained at "m" times internal pressure (i.e. 4.5 MPa); it won't allow leakage.
In that case, flange will be designed for bolt load corresponds to compressive stress in gasket (i.e. 4.5 MPa) plus hydro-static end load due to internal pressure.
2) While designing for gasket seating condition, minimum seating stress of 69 MPa is required to be considered that to avoid leakage at almost no pressure condition. {which is contradictory with first condition}...
Now the query is,
During operation, joint will be leak proof by maintaining just 4.5 MPa compressive stress on gasket. Then what is the need of considering 69 MPa as min seating stress??
In other words, in this situation, gasket seating condition will govern bolt load & subsequently flange will be over-designed.
RE: m & y factors in bolted connection design
The bolted joint must be designed for both conditions. This is explained fairly well in Apx 2 and elsewhere.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: m & y factors in bolted connection design
You're not designing for a leak free joint at no pressure, you're designing for a minimum seating stress. The gasket actually needs to be deformed to work. That's how it seals, your metal/graphite/Teflon/etc deforms to match the seating surface.
Nathan Brink
RE: m & y factors in bolted connection design
The "m" is the the factor used to work out the very bare minimum you must keep on the gasket while it is in service to retain a seal.
In your example you need a minimum 69MPa effective gasket stress at install, then during service as long as it remains above 4.5MPa the gasket "should" not blow out. (I wouldn't try that...)
That is the very basic m and y theory, which basically works for 75% of cases, everything else you really need to use better calculations... The EN-1591 is the current top of the range, but as you can imagine much more complicated.