Page 27 - Design Criteria.qxd

28 ® Welcome to the Next Generation of Sealing Technology
Sizing Parameters for Spiral Wound Gaskets
Regardless of the type of flange facing in use, FLEXITALLIC gaskets must be sized to ensure the spiral wound element is seated
against a flat surface. This is of utmost importance. If a spiral wound element protrudes into the flange bore or extends beyond the
raised face, mechanical damage will occur to the gasket during compression, and ultimately failure will result. In addition, should the
gasket protrude into the flange bore, the windings can possibly enter the process stream with severe damage resulting to other equip-
ment. With recessed flange facings, limiting dimensions of the gasket are established by dimensions of the groove. On flat or raised
face flanges, considerable leeway is available. Note that due to radial growth and clearance requirements, spiral wound gaskets are
normally sized differently than other types of gaskets. The following rules will be generally applicable for limiting dimensions of spi-
ral wound components.
Gasket Confined On Both I.D. & O.D.
This is the type facing encountered in tongue and groove joints, and groove to flat face joints. Standard practice is to allow 1/16" nom-
inal diametrical clearance between the I.D. of the groove and the I.D. of the gasket and 1/16" nominal diametrical clearance between
the O.D. of the gasket and the O.D. of the groove.*
Gasket Confined On the O.D. Only
This is the type of facing encountered with male and female and female to flat face facings. Standard practice is to allow 1/16” nom-
inal diametrical clearance between the O.D. of the gasket and the O.D. of the groove.* If possible, allow a minimum 1/4" diametri-
cal clearance between the I.D. of the seating surface and the I.D. of the gasket.
Gasket Unconfined On Both the I.D. & O.D.
Allow a minimum 1/4" diametrical clearance between the gasket I.D. and the I.D. of the seating surface. The O.D. should be kept as
close as possible to the bolt circle to minimize flange bending moments. If the gasket is used with raised face flanges, allow a mini-
mum 1/4" diametrical clearance between the gasket O.D. and the raised face O.D. and determine the I.D. on the basis of the desired
gasket width.
Important - Please note the above rules establish general limits for sizing FLEXITALLIC gaskets. It is frequently necessary to
adjust dimensions in order to achieve a proper balance between gasket area and bolt area in order to maintain a reasonable compres-
sive force on the gasket and the minimum gasket factor "m". Please refer to section covering ASME Boiler and Pressure Vessel Code.
Metal Guide Rings
When Flexitallic gaskets are required to be equipped with inner and/or outer metal rings, limitations on the minimum widths of the
rings are necessary due to machining limitations and rigidity of the complete assembly. Standard practice is to size outer rings with
the outside diameter equal to the diameter of the bolt circle less the diameter of one bolt for rings up to 60" O.D. Above 60" O.D. rings
are sized to the diameter of the bolt circle less the diameter of one bolt hole. The table below indicates the minimum width for solid
metal rings based on the ring I.D.
Diameter of Ring Minimum Width**
Outer Ring Inner Ring
Up to 10” Inside Diameter 3/8” 1/4”
10” to 24” Inside Diameter 7/16” 3/8”
24” to 50” Inside Diameter 1/2” 3/8”
50” to 70” Inside Diameter 5/8” 1/2”
70” and Larger 3/4” 1/2”
*Note: 1/16" nominal O.D. clearance for gaskets up to 60" O.D.; from 60" O.D. to 80" O.D., allow 5/64"; above 80" O.D allow 3/32" nominal O.D.
clearance.
**Note: Where space is limited and narrower ring widths are necessary, it may be possible to supply inner and outer spacer rings of metal spiral
wound construction. Consult FLEXITALLIC Technical Department for advice.