SPIRAL WOUND GASKET
A Spiral wound gasket for flanges feature a metal sealing element filled with graphite, PTFE, ceramic fibers and, non-asbestos fibers (fillers). For this reason, spiral wound gaskets are classified as “semi-metallic” gaskets.
The metal component of the spiral wound gasket provides strength to the seal, whereas the fillers enhance the gasket’s conformability and resilience. Inner and outer rings can be added to the core sealing element to facilitate the installation and enhance the pressure rating. Spiral wound gaskets with graphite fillers are the most commonly sold type.
Flexitallic USA introduced spiral wound gaskets in the petrochemical industry back in 1912 to cope with an increasing demand for leak-proof seals in applications with higher and higher (and fluctuating) temperatures and pressures. Other reputable spiral wound gasket manufacturers are Garlock and Lamons.
Indeed, a spiral wound gasket is designed to withstand, better than other types of flange gaskets, the mechanical stress generated by high temperature and pressure applications. Spiral wound gasket application range, therefore, from oil and gas to power generation.
The diameter of a spiral wound gasket may range between a few mm up to 5.000 mm, and the spiral wound gasket thicknesses range from 3.2, 4.5, 6.4, to 7.2 mm.
A Spiral wound gasket may be ordered in different shapes, such as oblong, rectangular, oval, pear and diamond.
ASME B16.20 is the spiral wound gasket specification.
The round type is, of course, the standard shape for the raised face (RF), male-and-female (M&F), and tongue-and-groove flanges (T&G) for petrochemical applications.
SPIRAL WOUND GASKET TYPES
A few different types of spiral wound gaskets exist, depending on:
- the number of rings (outer and inner)
- the materials of the inner and the outer ring of the gasket
- Type 00: Spiral Wound Gasket without rings: they are used for tongue and groove, male and female flanges.
- Type 01: Spiral Wound Gasket with inner ring: they are used for male and female or special flange types.
- Type 10: Spiral Wound Gasket with outer ring: they are used for raised face flanges.
- Type 101: Spiral Wound Gasket with inner and outer rings: they are used for raised face flanges.
- Special Section: Spiral Wound Gasket with special rings: they are used for special flanges and special usage.
Each manufacturer, of course, has specific codes to designate the different spiral wound gasket types, but the typical designs are recurring regardless of the producer.
The image shows how the different spiral wound gasket types used for flanged joints in piping applications:
SPIRAL WOUND GASKET MATERIALS
Spiral Winding Materials
The sealing element of a spiral wound gasket is produced by interleaving plies of alternating metal winding strip combined with a filler material. The formed metal strip in the key sealing element of this type of semi-metallic gasket.
The most common winding materials are:
- SS 304L
- SS 316L
- SS 321
- Nickel alloys
Filler materials are used to enhance the conformability and the resilience of a spiral wound gasket. The most used filler material is graphite, however, other filler materials may be used depending on the application:
- Ceramic fibers
Inner and Outer Rings Materials
The inner and the outer rings of a spiral wound gasket may be the same material of the winding core or a different one.
Solid inner rings are required by the ASME B16.20 specification for flanges with pressure rating 900# NPS 24 and larger, 1500# NPS 12 and larger, pressure class 2500#, NPS 4 and larger.
The inner ring improves the pressure rating of the spiral wound gasket, as it provides additional compression to the flanged joint and provides a heat and corrosion barrier protecting the gasket windings and the flanges from erosion.
|Spiral Wound Gasket Material|
|TEMPERATURE RANGE in C°||VOLUMETRIC MASS [G/CM3]|
|Soft Iron (Armco)||–||1.1003||–||–||90 – 100||-60||500||7.85|
|Steel (LCS)||RSt.37.2||1.0038||–||–||100 – 130||-40||500||7.85|
|Stainless Steel 304||X5CrNi 18||1.4301||304||304S15/16/31||130 – 180||-250||550||7,9|
|Stainless Steel 304 L||X2CrNi 189||1.4306||304L||304S11||130 – 190||-250||550||7,9|
|Stainless Steel 309||X15CrNiMo 2012||1.4828||309||309S24||130 – 190||-100||1000||7,9|
|Stainless Steel 316||X5CrNiMo 1810||1.4401||316||316S31/33||130 – 180||-100||550||7,9|
|Stainless Steel 316 L||X2CrNiMo 1810||1.4404||316L||316S11/13||130 – 190||-100||550||7,9|
|Stainless Steel 316 Ti||X10CrNiMoTi 1810||1.4571||316Ti||320S31||130 – 190||-100||550||7,8|
|Stainless Steel 321||X10CrNiTi 189||1.4541||321||321S12/49/87||130 – 190||-250||550||7,9|
|Stainless Steel 347||X10CrNiNb 189||1.4550||347||347S31||130 – 190||-250||550||7,9|
|Nickel 200||Ni 99.2||2,4066||NO2200||3072-76 NA11||90 – 120||-250||600||8,9|
|Monel 400||NiCu 30 Fe||2.4360||NO4400||3072-76 NA13||110 – 150||-125||600||8,8|
|Inconel 600||NiCr 15 Fe||2.4816||NO6600||3072-76 NA14||120 – 180||-100||950||8,4|
|Incoloy 800||X10NiCrAITi 3220||1.4876||NO8800||3072-76 NA15||140 – 220||-100||850||8,4|
|Incoloy 825||NiCR 21 Mo||2.4858||NO8825||3072-76 NA 16||120 – 180||-100||450||8,14|
|Hastelloy B2||NMo 28||2.4617||N10665||–||170 – 230||-200||450||9,2|
|Hastelloy C276||‘NiMo 16Cr15W||2.4819||N10276||–||170 – 230||-200||450||8.9|
|Titanium||Ti 99,8||3.7025||–||–||110 – 140||-250||500||4,5|
SPIRAL WOUND GASKET COLORS
Spiral wound gaskets made with different windings and filler materials are easy to spot, as each combination is designated by the application of color codes (the main color designates the winding materials, the stripes indicate the type of filler):
- Metallic winding materials: the metallic winding material is designated by a solid color identification around the outside edge of the centering, as shown in the image below
- Non-metallic filler color coding: the gasket filler materials are designated by a number of stripes placed at equal distances around the edge of the centering ring
Color Codes for Winding Materials
|Metallic Winding Material for Spiral Wound Gasket||Abbreviated Winding|
|Carbon steel ||CRS||Silver|
|304 SS ||304||Yellow|
|304 L SS ||304 L||No color|
|309 SS ||309||No color|
|316 L SS ||316 L||Green|
|347 SS ||347||Blue|
|321 SS ||321||Turquoise|
|Monel 400 ||MON||Orange|
|Nickel 200 ||NI||Red|
|Hastelloy B ||HAST B||Brown|
|Hastelloy C ||HAST C||Beige|
Color Codes for Filler Materials
|Polytetrafluoroethylene ||PTFE||White stripe|
|Mica-graphite ||Manufacturer’s designation||Pink stripe|
|Flexible graphite ||F.G.||Gray stripe|
|Ceramic ||CER||Light green stripe|
|Inconel 600 ||Inconel 600||Gold|
|Inconel 625 ||Inconel 625||Gold|
|Incoloy 800 ||Incoloy 800 H / HT||White|
|Incoloy 825 ||Incoloy 825||White|
SPIRAL WOUND GASKET MARKING
The illustration shows the typical marking of spiral wound gaskets:
SPIRAL WOUND GASKETS DIMENSIONS