18 sealing materials contents Hofland ® spiralwound gaskets fig. G2004 properties Hofland ® spiralwound gaskets consist of a V-shaped metal strip spirally wound in combination with a soft, filler material. The metal strip provides outstanding recovery, while the flexible filler guarantees excellent sealing. Due to this combination of materials the Hofland ® spiralwound gasket is suitable for sealing under severely fluctuating temperature and pressure conditions. Depending on the applic ati on th e spir alwo und gas ket can be specified with outer and/or inner rings. • Hofl and ® spiralwound gaskets are suitable for use across a wide gasket stress range. • Hofl and ® spiralwound gaskets can be used to seal fluid pressures up to 250 bar and from cryogenic temperatures up to elevated temperatures of 1000°C. • Because of its sturdy design th e Hofland ® spiralwound gasket is simple to install without being damaged (although extra care should be taken during transportation and installation of large diameter gaskets without inner or outer guide rings). • The outer guide rin g simplifies asse mbly and prevent s blow-out of the gasket. • By combinin g different wi nding mate rials and metal s, the gasket can be tailored to suit a wide variety of operating conditions. • Because of its non-adhesive propertie s the gasket is easy to r emove after service. • The gasket doe s not cause any damage to the flange faces.
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V-shaped metal strip spirally wound incombination with a soft, filler material. The
metal strip provides outstandingrecovery, while the flexible filler
guarantees excellent sealing. Due to thiscombination of materials the Hofland®
spiralwound gasket is suitable for sealingunder severely fluctuating temperature and
pressure conditions. Depending on theapplication the spiralwound gasket can be
specified with outer and/or inner rings.
• Hofland® spiralwound gaskets are suitable for use across a wide gasketstress range.
• Hofland® spiralwound gaskets can be used to seal fluid pressures up to250 bar and from cryogenic temperatures up to elevated temperaturesof 1000°C.
• Because of its sturdy design the Hofland® spiralwound gasket is simpleto install without being damaged (although extra care should be takenduring transportation and installation of large diameter gaskets withoutinner or outer guide rings).
• The outer guide ring simplifies assembly and prevents blow-out of thegasket.
• By combining different winding materials and metals, the gasket canbe tailored to suit a wide variety of operating conditions.
• Because of its non-adhesive properties the gasket is easy to removeafter service.
• The gasket does not cause any damage to the flange faces.
Econosto produces the following types of Hofland® spiralwound gaskets.
This gasket consists of filler and V-shaped metal strip wound in combina-tion. This profile is usually used in male/female and tongue/grooveflanges.
Identical to RF1, but fitted with an inner ring.
This standard spiralwound gasket type consists of a wound componentfitted with an outer centering ring.
Identical to the SG-type, but fitted with an inner ring.
A standard spiralwound gasket (SG-type) with dimensions tailored for usewith Ring-Type-Joint (RTJ) flanges.
This type of gasket consists of a wound component fitted with a narrow,wound centering ring. Centering windings ensure correct centering inflush flanges (e.g. in heat exchangers).
This gasket type is identical to HX-R, but also fitted with an inner ring,rendering this gasket type suitable for mounting in male and femaleflanges.
section 1 | metallic and semi-metallic gaskets • spiralwound 21
contents
profile with a GT-zone:
special profiles
special shapes
type MH
type TC/HH
In the event of a graphite-filled spiralwound possibly causing anundesirable reaction between graphite and the medium to be sealed, orof possible medium contamination, the problem can be solved by using aspiralwound gasket with a GT-zone.
The spiralwound element of a GT-zone gasket consists of outer windingsof non-asbestos or ceramic material with a central winding zone made ofgraphite or PTFE (depending on the operating conditions) to improvegastightness, see illustration.
This results in a spiralwound gasket with the following properties:
• Does not pollute the sealed medium• Excellent gastightness
Combined with the other advantages of a spiralwound gasket, the
spiralwound with GT-zone may be used in a wide range of operatingconditions.
For spiralwound gaskets with straight sides (e.g. for gate valve bonnets)
we recommend that an inner ring be used if the length/width ratio > 2.
Spiralwound gaskets can be produced ina wide variety of shapes, such as ovaland pear-shape, with pass-partition barsand many other types. Generally, thepass-partition bars on spiralwoundgaskets are metal-jacketed bars.
This spiralwound gasket is identical tothe RF1 profile but oval shaped to fitmanholes.
This type of gasket is for hand holes andspecial flange assemblies (tube cap andhand hole covers). They are available ine.g. square, rectangular, oval diamond
and pear shapes.
A drawing specifying the correct dimen-sions is required to manufacture specialshapes.
The gasket is identical to RF1, but fittedwith an outer winding. Centering isachieved by positioning the winding over
two bolts opposite each other (seeillustration).
type WL
type HE
type HE-SG
type HS/SG-IR
type SP-N2
In order to manufacture the above gaskets, we require a drawingspecifying the exact dimensions and position of the bars.
Fitted with pass-partition bars for use onheat exchangers and vessels, this gaskettype is otherwise identical to the RF1profile. Metal-jacketed bars generally havea thinner design than that of spiralwoundgasket components.
The bars are usually fixed throughmicroplasm welding or silver soldering.The welding method is chosen dependingon the gasket material.
Fitted with an outer centering ring, theHE-SG is otherwise identical to the HE
profile.
Fitted with an outer centering ring and aninner ring, the HS/SG-IR is otherwiseidentical to the HE profile.
The SP-N2 is a highly specialized typeof gasket, consisting of a Hofland®
camprofile gasket and a Hofland® spiral-wound gasket separated by a perforatedintermediate ring. The sealing layers onthe camprofile and the filler of the spiral-
wound gasket are made of identicalmaterial. The perforated intermediate ringis flushed with inert gas (such asnitrogen).
This design enables the operator tomeasure any leakage, making the gasketsuitable for use in critical applicationswhere a high degree of gastightness andoperational reliability is required.
section 1 | metallic and semi-metallic gaskets • spiralwound 23
contents
profile selection
advantages of the centering ring:
advantages of the inner ring:
The illustrations on the rightrepresent standard Hofland®
spiralwound gasket shapes forvessel and heat exchanger
flanges.
The spiralwound gasket centering ring offers the following advantages:
• Optimum gasket positioning between the bolts.• Protection of the sealing element.• Additional security against gasket blow-out.• Acts as a compression limiter preventing overloading and
overcompression of the spiralwound element.• Prevents radial flow of soft fillers, such as PTFE.
For these reasons the use of spiralwound gaskets with outercentering rings is generally recommended.
Gaskets provided with an inner ring offer the following advantages:
• Prevents radial flow of soft fillers, such as PTFE.
• Reduces turbulence, minimizing flow resistance and crevice corrosion.• Acts as an additional heat shield when the spiralwound gasket is
subjected to high temperatures.
Inner and outer rings are particularly recommended for use on Hofland®
spiralwound gaskets exceeding class 600 lbs, but specifically recom-mended for high temperatures and pressures to optimize reliable sealingperformance.For special flanges (male-female, tongue and groove, etc.) the type ofspiralwound gasket selected will depend on the flange geometry,operating conditions and bolt specifications. Econosto specialists will bepleased to assist you where necessary.
section 1 | metallic and semi-metallic gaskets • spiralwound 25
contents
filler selection
filler material:
PTFE:
non-asbestos:
Ceramica®:
graphite:
The table below may be used to select the correct filler. It should bepointed out that graphite will be the optimum filler in most cases. Onlywhere graphite could cause media pollution, or is not chemically resis-tant, should the use of another type of filler material be recommended. Insuch cases, an alternative solution might be to use a gasket with GT-zone.See page 21.
Graphite is a universally applicable, high-quality, non-asbestos materialwith the following properties:
• Very good chemical resistance• Resistant to high (fluctuating) temperatures and pressures• Resistant to ageing• Excellent gastightness
PTFE (Teflon®) is a high quality synthetic material with the followingproperties:
• Excellent chemical resistance• Resistant to temperatures up to 250°C
• Resistant to ageing• Excellent gastightness
Non-asbestos is a non-asbestos sealing material consisting of syntheticfibre, with nitrile rubberbinder and mineral fillers.
Ceramica® is an aluminium silicate suitable for applications at highoperating temperatures. The material is characterized by poorgastightness and is therefore frequently used in combination withgraphite.
diameter, the spiral-wound gasket isavailable in a varietyof thicknesses. Thetable below specifiesthe thicknesses andthe recommendedoptimum thicknessafter fitting.
The spiralwound gasket is usually produced with a thickness of 4.5 mm.However, in some cases a different thickness may be selected to obtaineffective sealing.
The table below specifies gasket thickness for certain applications.
t1
[mm]
d
[mm]
bmax
[mm]
t2
[mm]
thickness after assembling
[mm]
7.2 100 - 3600 33 5 5.3 - 5.6
6.4 200 - 1600 30 4 4.7 - 4.9
1601 - 3000 28
4.5 16 - 630 35 3.2(1) 3.2 - 3.4
631 - 1600 30
1601 - 3000 25
3.2 16 - 630 25 2 2.3 - 2.5
631 - 1500 20
2.5 10 - 200 8 1.5 1.8 - 2.0
(1) Standard spiralwound gasket. In case materials other than carbon steel are used: