M & Y values your questions answered

"What are M & Y Values?" We are frequently asked at Corseal to provide M & Y values for our gaskets so that the customer can design flange joints using the ASME Boiler and Pressure Vessel Code. Occasionally, our sales & technical team are asked to explain how these values are used and how they are determined for our gaskets.  In simple terms, a flange must be designed to create sufficient compression load (usually expressed in stress, as psi) on the gasket contact area to create an initial seal. The gasket must conform to the flange surface (serrations when present) and must be compressed enough to seal off any internal voids or spaces. This stress is basically the "Y" value. The "M" value allows the flange designer to determine the compression load on the gasket required to maintain a seal when the vessel is pressurized. The flange must have sufficient strength and bolting to hold the joint together against the hydro-static end force, and to apply some additional "net stress" on the gasket. The "M" value is used as a multiplier or maintenance factor. The design will be such that the flange and bolting will hold the flanges together under pressure (the hydro-static end force) and exert an additional stress on the gasket of "M" multiplied by the internal pressure. The designer calculates the load required to seat the gasket (related to "Y") and performs a second calculation using the "M" value and the design internal pressure. The flanges are then built based on the larger of the two calculated values.

See below for SPIRAL WOUND & CAMPROFILE GASKETS values.

What are the M and Y values for Kammpro(Camprofile), CMG, CMGT, CMGPTFE, Spiral Wound Gaskets (W, WR, WRI), and WRI-LC?

Gasket Style

M-value

Y-value (PSI)

Kammpro

2.75

3,700

CMG

2.75

3,700

CMGT

2.75

3,700

CMG-PTFE

2.75

2,500

Spiral wound

3

10,000

WRI-LC

3

5,000

What is the yield strength for B7 bolts?

105 KSI

How can torque value be calculated?

T = (S * D * A * R) / 12

Where:

  • T: torque value (ft-lb)
  • S: required bolt stress (PSI)
  • D: bolt diameter (in)
  • A: area at root of thread (square inches)
  • R: friction factor
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