Anaerobic Adhesives Sealants

Anaerobic Adhesives Sealants are a penetrating one-component liquid plastic which has the property of hardening automatically with little shrinkage in joints between closely fitted metal parts to form a strong heat and oil resistant plastic. The catalytic action of the metal surfaces aided by the absence of air, which acts as stabilizer, causes the liquid to harden and form a tough plastic seal / retainer. The product has excellent chemical resistance but is not recommended for exposure to concentrated acids and alkalies. In general these products are suitable for maximum temperature of 150 deg. C. However some grades can withstand higher temperature. Please refer to manufacturer’s recommendation / technical data sheet for their suitability. Varieties of products are available for different applications and in different grades for an application as under.

Thread Locking

This variety is useful for all types of metallic fasteners to prevent their loosening due to shock and vibration. It can be used instead of conventional locking mechanisms like lock nut, spring washer, nylok nut (nut with nylon insert), tab washer, split pin, etc. The product also seals threads in addition to locking and prevents thread corrosion. Because of this advantage one could avoid seizing, the problem of removal at a later time.

Wicking grade of thread locker is designed for locking pre-assembled fasteners (instrumentation screws, set screws, etc.). This grade is also used to seal porosities and hairline cracks in castings and welds. Due to low viscosity, it has the ability to penetrate into tightened threads, porosities and cracks by capillary action. It hardens in to a tough plastic when confined within metallic surfaces.

Many grades of thread lockers are available for application during assembly. Different grades are made for different locking strengths. Low strength grade is used for low strength metals such as aluminium or brass which could break during disassembly. Very high strength grade is used for heavy duty / permanent application.

Thread Sealing

This variety replaces tapes and pastes used on threaded tube / pipe components. Its application prevents damage caused due to over tightening. Liquid also ensures complete contact between threads for a 100 percent seal. Disassembly can be achieved easily with basic tools.

Fine grade is recommended for fine threaded fittings used in hydraulic and pneumatic installations. Coarse grades are used for coarse metal threads of different sizes. Slow curing grade is recommended where post-assembly adjustment / alignment is required to be carried out.

Gasketing

This variety is used instead of pre-formed gasket for flanges, pumps, gear boxes, etc. It fills all voids and thus reduces the need for a fine surface finish and does not require re-tightening. Various grades are available for different application requirement.

Retaining

This variety is used to retain / bond non-threaded cylindrical metal components like bearing, gear, coupling, etc. Use of this product reduces the need for close tolerances for assembled parts and hold worn / loose fitting parts (it can replace press fits with slip fits). Many grades are available to suit different requirement (like strength, temperature, gap between components).

Method of Application

Clean surfaces with soap, hot water, cleaner / solvent to remove oil, grease, dirt, etc.
Apply primer on inactive surfaces like aluminium, stainless steel, magnesium, zinc, black oxide, cadmium, titanium, etc.
Apply primer on all type of surfaces (active and non active) if work is to be carried out at temperature below 5 degree C.
Apply adhesive sealant to a component and assemble it. During assembly of cylindrical items give slight clockwise and anticlockwise twist to spread the adhesive.
Application of heat accelerates the curing speed.
Anaerobic adhesive sealants are non-toxic. A sop and water wash after handling is sufficient.

Storage

To obtain the normal shelf life of one year the material should be stored between 5 to 28 deg. C in a cool dry location.

Disassembly of Adhesive bonds

Most bonds can be broken apart simply by ordinary tools. Strong bonds can be heated up to 250 deg. C before using mechanical methods.

Note:
Henkel Loctite sales two grades of thread locker, one grade of thread sealant, one grade of gasketing and one grade of retaining based on anaerobic technology in semi-solid stick form. It is easy to apply them for overhead application.

Cyanoacrylate Adhesives

They are single component general purpose adhesives. They are Cyanoacrylate monomers and traces of water on surfaces to be joined initiates polymerization. Water acts as a catalyst in the process. The notable feature of these adhesives is their exceptional speed of cure which is achieved in few seconds. As it polymerizes due to water, relative humidity (RH) in atmosphere is very important. If RH is less than 40 percent, the speed of cure will be slower, and if it is higher than 75 percent, cure will be faster – but with possible reduced bond strength. As curing takes place very fast, special clamps are not required. Only finger pressure is adequate to make strong joints after parts are accurately positioned. They bond variety of materials. Dissimilar parts also can be bonded by them. They are available in different grades based on type of material to be bonded.

Note:
These adhesives are not recommended for bonding silicon rubber, Viton and Teflon.

Method of Application

Clean both surfaces. A solvent wipe with butyl alcohol, MEK or acetone is considered satisfactory for most surfaces. For aluminium, a dichromate acid etch is recommended.
Apply thin layer of adhesive on one of the surfaces to be bonded.
Assemble parts at once ensuring that they are correctly positioned. Apply light contact pressure to prevent movement and minimize the bond gap.
For Skin protection use nitrile gloves and aprons as necessary. Do not use PVC, nylon or cotton.

Caution

Keep away from children.

Skin contact:

Bonds skin in seconds and caution in use is advised. Do not pull bonded skin apart. Soak in warm soapy water. Gently peel apart using a blunt instrument. If lips are bonded, apply warm water to the lips and encourage wetting and pressure from saliva in mouth. Peel or roll lips apart.

Eye contact:

Immediately flush with plenty of water for at least 15 minutes. Get medical attention. If eyelids are bonded closed, release eyelashes with warm water by covering with a wet pad. Do not force eye open. Cyanoacrylate will bond to eye protein and will cause a lachrymatory effect which will help to debond the adhesive. Keep eye covered until debonding is complete, usually within 1-3 days.

Storage

To obtain the normal shelf life of one year the material should be stored upright in a cool dry location at a temperature below 25 deg. C. The time may be extended by storage at temperature approximately between 0 to 5 deg. C. After refrigeration, allow the bonder to reach room temperature prior to application.

For ready reference important Henkel Loctite products are listed below

Material Suppliers

Companies selling anaerobic and cyanoacrylate adhesives in India are as under.

• Hankek Loctite India Pvt. Ltd.- http://www.loctite.com
• Demech Chemical Products Pvt. Ltd.- http://www.demechchemical.com
• Pidilite Industries Ltd.- http://www.pidilite.com

Hankel Loctite had invented anaerobic technology for thread treatment and gasketing in 1950 and they offer good technical support. For more information please visit their website.

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Test Procedures

Gasket Standards

Gasket Selection

Flange and Bolting Information

Installation Procedure

Storage of Gaskets

Useful Information on Joints

Test Procedures

Gaskets are tested to find out their physical properties. Various important ASME and DIN test procedures for testing of gaskets are as under.

Compressibility and Recovery of Gasket Material – ASTM Designation: F36

This method covers determination of the short-time compressibility and recovery at room temperature of sheet gasket materials. Good recovery upon release of load is indicative of torque retention of a gasketed joint. Compressibility and recovery as defined by ASTM are two worthwhile physical property criteria for supplier and purchaser to agree upon as routine tests.

Creep Relaxation of Gasket Material – ASTM Designation: F38 Method B

ASTM F38 provides a means for measuring the amount of creep relaxation of a gasket material at a stated time after a compressive stress has been applied. This method is designed to compare related products under controlled conditions in regard to their ability to maintain a given compressive stress as a function of time. A portion of the torque loss on the bolted flange is a result of creep relaxation. The result of creep relaxation is loss of thickness of a gasket, which causes bolt torque loss, resulting in leakage.

Fluid Resistance of Gasket Materials – ASTM Designation: F146

These methods provide a standardized procedure for measuring the effect of immersion on physical properties of non-metallic gasketing materials in specified fluids under defined conditions of time and temperature. They are not applicable to the testing of vulcanized rubber (they are tested as per D471). This test can be used as a routine test when agreed upon between the supplier and purchaser.

Sealability of Gasket Materials – ASTM Designation: F37

Test methods A and B provide a means of evaluating fluid sealing properties at room temperature. Method A is restricted to liquid measurements and Method B (most common) can be used for both gas and liquid measurements. These test methods are suitable for evaluating the sealing characteristics of a gasket product under differing compression flange loads. Since this physical property is important for proper function of a gasket, it should be used as an acceptance test when test methods are agreed upon between supplier and purchaser. These precise measurements of leakage rates are designed to compare gasketing products under controlled conditions. The leakage measured comes either through the gasket, or between the gasket and the flange faces, or both. In most cases, the leakage measured is a result of leakage through the gasket.

DIN designation 3535 provides a means of measuring leakage of a gas through a gasket. The apparatus used in this method is considerably more versatile than that used in ASTM F37.

Tension of Non-metallic Gasket Materials – ASTM Designation: F152

The Universal Tester is used to determine the tensile strength of non-metallic gasketing products. The types of products covered are those containing various organic fibers, inorganic fibers, flexible graphite, or fluorocarbons as described in F104. F152 is not applicable to the testing of vulcanized rubber (they are tested as per D142). The measurement of tensile strength characterizes various classes and grades of products of a given type. It also aids the purchaser in determining whether the gasketing product approved for a given application is being manufactured to acceptable quality. Tensile strength is not necessarily the most important function of a gasket material. Expanded graphite for example is relatively weak, though it performs very well as a gasket material.

Torque Retention – DIN 52913

This test is designed to determine the torque retention capabilities of gasketing products, when subjected to the compression load and operating temperature as defined by the test procedure. The test consists of applying a predetermined load on the test gasket via a tension screw, then heating the gasket/flange assembly to the desired temperature (there is no internal pressure). The standard test period is either sixteen (16) hours or one hundred (100) hours. At the end of the required time period, the compression load which is left acting on the test gasket is measured. This allows one to calculate the torque retention capabilities of various gasketing products.

Blowout of Gasket Products – (No ASTM Designation)

Gasket manufacturers also carry out blowout resistance test on gaskets at varying pressures and temperatures. Test results are used to provide P (psig or bar) x T (deg. F or deg. C) values for various products.

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Gasket Standards

Various standards are used to specify gasket dimensions and properties as under.

Standards for Gasket Dimensions

Cut Gasket

ASME B 16.21 – for ASME flanges as per ASME B 16.5.
BS EN 12560 Part 1 (formerly BS 7076 Part 1) – for BS flanges as per BS 1560.
BS 3063 – for BS flanges as per BS 10.
BS EN 1514 Part 1 – For DIN flanges as per DIN / EN 1092 (formerly BS 4504).

Spiral Wound Gaskets

ASME B 16.20 – for flanges as per ASME standard.
BS 3381 – for flanges as per BS standard.
BS EN 12560 Part 2 – for DIN / BS type of flanges.

API Ring Joints

ASME B 16.20 – for flanges as per ASME standard.
BS EN 12560 Part 5 – for flanges as per DIN / BS standard.

Corrugated Metallic Type

BS EN 12560 Part 4 – for flanges as per DIN / BS standard

Standards for Gasket Properties

Gaskets are tested for properties and types are specified in accordance with various standards as under.

ASME Standards – F 36, F 37, F 38, F 152, F 146, F 104
BS 7531, BS 2815, BS 1832, BS 125
DIN 3535, DIN 52913, DIN 3754
French standard NFT 48001
IS 2712 (Now BIS, Bureau of Indian Standard)

Depending upon the application, Indian standard IS2712-1998 have specified grades of compressed asbestos fibres (CAF) as follows:

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Gasket Selection

Primarily gasket selection is based upon temperature of media, pressure of media, compatibility of gasket material for the media and application. It is suggested that gasket shall be selected for above parameters in following sequence.

Temperature

In selection processes, the temperature of the fluid at the gasketed joint should be considered first. This will reduce the number of product candidates quickly, especially as temperatures go from 200°F (95°C) to 1000°F (540°C). Gasket shall withstand system temperature without serious impairment of its performance properties. When system operating temperatures approach a particular gasket material’s maximum continuous operating temperature limit, an upgrade to a superior material is suggested. In some situations cryogenic temperatures must also be considered.

Application

The most important information under application is the type of flange (flat face, raised face, tongue and groove, ring joint flange, etc.), flange metallurgy (steel, nonmetallic, glass lined, etc.) and bolts used. The number, size and grade of bolts used in the application determines the load available. The surface area being compressed is calculated from the gasket contact dimensions. The load from the bolts and the contact area of the gasket result in the compressive load available to seal the gasket. Selection of gasket shall also take care of minor misalignment, flange bowing (flange bending), and flange surface imperfections like – waviness, grooves, scoring and finish. Gasket shall have sufficient strength to resist crushing under the applied load, and maintain its integrity when being handled and installed.

Media

Gasket material shall chemically resist the system fluid to prevent serious impairment of its physical properties.

Pressure

Gasket shall be strong enough to resist internal fluid pressure.

Notes:
Maximum temperature and pressure capabilities do not necessarily operate to gather for all gasket thicknesses and it is recommended that pressure and temperature are considered simultaneously using P x T Limit of a gasket for different gasket thicknesses.

For gaskets cut from sheets, always use the thinnest material which the flange arrangement will allow, but thick enough to compensate for unevenness of the flange surfaces, their parallelism, surface finish and rigidity etc. The thinner the gasket, the higher the bolt load which the gasket can withstand, and the less the loss of bolt stress due to relaxation. Also the gasket area will be lower which will be exposed to attack from the internal pressure and aggressive media. In view of this, ensure that the gasket is as thin as possible. As a rule of thumb, gasket performance decreases as material thickness increases.

Caution:
Choosing wrong sealing product can result in propevtydamace C.d -dor7erkkus0ersknandinh1rydmpheP$Sel!ctKon CknsK$erAtioN7 fmr Ga7ket3 ar%: oh4d $Shall n/t contaminAte t,e qyste- fLqidd $ Is$easily"%nd #leC.ly2emm2abNa av$the`tiM% od`rer,aceienv* <-(i>PlaasE$refar V/ gawkeTdmalqfaCturer&#6179s PR/duap Ra*ge"Manw!l -dDaV% SHaetS$fopdval1es kf VemperatW2e,pres7ureh fN5id comr%ti@)liV=, p`x V$Limits%nd kthE6 pjysia%l p6opG6tigw oF$gaskets for their selection.

Important:
Always use a good quality gasket from a reputable supplier, because the cost of a gasket is insignificant when compared to the cost of downtime or safety considerations.

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Flange and Bolting Information

A joint may fail even though the gasket material itself may be correct due to flange, bolting or improper installation.

Flanges

There are limits on the degree of flange surface imperfection that can be sealed successfully with a gasket. Large nicks, dents, or gouges must be avoided, since a gasket cannot properly seal against them. The surface finish of a flange is described as roughness, lay and waviness.

Roughness is read in millionths of an inch as the average of the peaks and valleys measured from a midline of the flange surface. This is expressed either as rms (root mean square) or AA (arithmetic average). The difference between these two methods of reading is so small that they may be used interchangeably.

Lay is the direction of the predominant surface roughness pattern. Example: multidirectional, phonographic spiral serrations, etc.

Waviness is measured in thousandths or fractions of an inch. Basically, it is the departure from overall flatness.

Generally most manufacturers provide recommendations about appropriate flange surface finishes for particular gasket materials. Recommended values of roughness are as under.

Spiral Wound Gaskets: 125-250 rms
Jacketed or Metal Clad Gaskets: 63-80 rms
Solid Metal Gaskets: 63-80 rms

It is recommend that a flange be machined using a 1/16" radius, round nosed tool to have 30-55 serrations per inch in a concentric or spiral pattern.

The lay of the finish should follow the midline of the gasket if possible. Take, for example, concentric circles on a round flange. Every effort should be made to avoid lines across the face, such as linear surface grinding allowing a direct leak path.

Waviness is seldom a problem under normal conditions. There are two areas that must be watched since excessive waviness is very difficult to handle. The first area is glass-lined equipment where the natural flow of the fused glass creates extreme waviness. Often the answer here is to use thick and highly compressible gasket. The second area of concern is warped flanges. If warpage is caused by heat or internal stresses, remachining is generally sufficient. However, warpage due to excessive bolt loads or insufficient flange thickness results in what is generally called bowing. The solution is to redesign for greater flange rigidity. Sometimes backer plates can be added to strengthen the design without having to replace the parts. Another solution would be to add more bolts.

Bolting

For the majority of flange and gasket joints, the fasteners which provide the compressive pressure on the flanges (and through this onto the gasket) are normally bolts or studs in tension.

Fasteners exhibit stress relaxation behaviour dependent upon their material of construction. This will have a marked effect on the load they are able to generate on the flange / gasket assembly under operating conditions. Consequently, when selecting the fasteners to use for a particular application, always consider the temperature variations which the fasteners will experience in service. Recommended values are as under.

Tension loads above the elastic limit will produce some permanent deformation. The fastener will not return to its original length and its effectiveness as a spring clamp will be impaired. In view of this, select fasteners with sufficient yield strength to ensure they are within their elastic limit at the required load.

The tension in the fastener is generated by tightening nuts along the threads of the fastener. The threads therefore play a major role in the clamping operation, and care must be exercised to maintain their integrity. Threads will strip when the axial forces on the fastener exceed the shear strength of the threads.
Threads strip more readily when fastener and nut material are of the equal strength. For optimum safety, use a nut which has a specified proof load 20% greater than the ultimate strength of the fastener. In this way, the fastener will break before the nut threads will strip. A break is easier to detect than a stripped thread.

Flat, hardened washers should always be used with fasteners to reduce significantly the friction between a turning nut and the joint components. This improves the consistency of the torquing operation improving accuracy and reducing the torque required. Use the same material for the washers and that of nuts.

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Installation Procedure

The most common cause of leaky gasketed joints is improper installation procedures. Care shall be taken at all stages given below.

Cutting of Soft Gaskets

First cut / punch bolt holes. Cut the bolt holes slightly larger than the bolts, to ensure proper seating. Never cut out a gasket by hammering material against the flange. Use a good cutter to cut the required shape of the gasket. Ensure that the inside diameter of the gasket is not less than the inside diameter of the process line to minimize obstruction of the process line.

Handling of Gaskets

When working in the field, carry cut gaskets carefully. If you bend the gasket it will be damaged. Always transport large diameter metallic and semi-metallic gaskets to the installation site on its mounting / packing.

Tools Required and Cleaning

Tools will be required to both clean the flange and tension the fasteners.

Clean fasteners with a wire (ideally brass) brush to remove dirt on the threads. After removing old gasket, clean flange surface of all debris using a wire brush (use stainless steel bristles on alloy components) or a brass scraper (a scraper can be made from a sheet of brass, ~5 mm (0.2 in) thick x 50 mm (2 in) wide, which is filed and shaped to a 45° chisel across the width). Using a hammer, lightly tap the scraper into the flange grooves to remove debris.

Flange spreaders may be used to make gap between flanges for cleaning them. Two spreaders are required for a joint. Use mechanical / hydraulic type spreader based on force required to open flanges.

The tensioners will require regular calibration and may include torque wrench, hydraulic or other tensioners. Instruments to measure tension may include a micrometer, or
Ultrasonic equipment.

Visual Inspection

Inspect various components as under.

Fasteners / nuts / washers – after cleaning examine them to assure freedom from defects such as burrs or cracks.
Flange assembly – inspect the flange surfaces for defects, such as radial scores and warping. Ensure that the flange surfaces are sufficiently flat and parallel.
Gasket – check that the correct gasket is available (suitable for the service, size,
thickness). Examine the gasket prior to installation to ensure that it is free from defects.

If any defect is observed, replace defective components with a good alternative.

Lubrication

It is estimated that in the absence of a suitable lubricant, up to 50% of the torque effort may be used to merely overcome friction. Effectively, this would mean that the same torque applied to non-lubricated fasteners on a joint might provide markedly different loads on each one. Therefore, lubrication is essential when torque is used as the control for setting tension in the joint. After cleaning, lubricate fastener threads and all bearing surfaces (underside of bolt heads, nuts, washers) with a quality lubricant such as an oil and graphite mixture. Ensure that lubricant does not contaminate either flange or gasket faces.

Gasket Installation

Carefully insert the new gasket between the flanges to prevent damage to the gasket surfaces and center it. Do not use tape to secure the gasket to the flange. If it is necessary to secure the gasket to the flange, use a light dusting of spray adhesive (e.g. 3M type 77). Do not use jointing compounds or release agents on gasket / flange faces.

Bolt / Stud Tightening Pattern

One of the most difficult jobs is to produce the correct assembly pressure on the gasket, low enough to avoid damaging the gasket, but high enough to prevent a leak in the seal. It is vitally important to control accurately the amount of force applied to any particular flange arrangement. Always use a torque wrench or other controlled-tensioning device for tightening. The sequence in which bolts or studs are tightened has a substantial bearing upon the distribution of the assembly pressure on the gasket. Consequently always torque nuts in a cross bolt tightening pattern. Always run the nuts or bolts down by hand. This gives an indication that the threads are satisfactory (if the nuts will not run down by hand, then there is probably some thread defect – check again and, if necessary, replace defective parts). Now torque the joint using a minimum of 5 torquing passes, using a cross-bolting sequence for each pass, as shown below.

Pass 1 – Tighten nuts loosely by hand in the first instance, according to the cross bolt tightening pattern, then hand-tighten evenly.
Pass 2 – Using a torque wrench, torque to a maximum of 30% of the full torque first time around, according to the cross bolt tightening pattern.
Pass 3 – Torque to a maximum of 60% of the full torque, according to the cross bolt tightening pattern.
Pass 4 – Torque to the full torque, according to the cross bolt tightening pattern.
Pass 5 – Final pass at full torque, in a clockwise direction on adjacent fasteners.

After the five basic torquing passes are completed, it may be beneficial to repeat pass 5 until no further rotation of the nut is observed. The final tightening must be uniform, with each bolt pulling the same load.

Hydraulic tensioners are often used to preload fasteners. In this method when the tensioner load is applied, the nut is run down against the joint (finger tight). The hydraulic pressure is then released and the tensioner removed.

Another way to tighten large bolts is to insert a heating rod in a hole drilled down through the centre of the bolt. As it heats up, the bolt expands length wise, and the nut can be run down against the joint (finger tight). The heater is now removed, and as the bolt cools, it shrinks, so developing tension.

Re-tightening

For the majority of materials in the flange system (including gaskets, fasteners, nuts, washers), relaxation sets in after a fairly short time. For soft gasket materials, one of the major factors is usually the creep relaxation of the gasket. These effects are accentuated at elevated temperatures. Due to this the compressive load on the gasket is reduced, increasing the possibility of a leak. Consequently, some engineers recommend that fasteners should be re-tightened (to the rated torque) 24 hours after the initial assembly. Re-tightening shall always be carried out at ambient temperature. However, this is an area of conflicting views!

Elastomer-based CAF gasket materials continue to cure in service, especially on start up as the operating temperature is reached. Once fully cured, gasket materials may become embrittled and liable to cracking under excessive load, and this is especially the case with elastomer-based asbestos-free materials. As it is impossible to predict the time for embrittlement, always consult the manufacturer for advice about re-tightening. As a general rule do not re-torque an elastomer-based asbestos-free gasket after it has been exposed to elevated temperatures.

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Storage of Gaskets

Although many gasket materials can be used safely after storage for many years, ageing will have a distinct effect on the performance of certain types of gasket materials. Primarily, this is a concern with materials which are bonded with elastomers. They in general should not be used after about 5 years from the date of manufacture. If required, they shall be used only after careful inspection. Materials with elastomeric binders will inevitably deteriorate over time, and even more quickly at higher ambient temperatures. Degradation is also catalysed by intense sunlight. Since graphite and PTFE materials contain no binders, sheets and gaskets of these materials have a virtually indefinite shelf life. In general,

• During storage gaskets should not be subjected to extreme heat or humidity – store in a cool, dry place, away from direct sunlight, water, oil and chemicals.
• Store sheet materials flat.
• Avoid hanging gaskets – they may distort. Store soft gaskets flat. Large diameter spiral wound gaskets should be retained on their mounting board.
• Gaskets should be kept clean and free from mechanical damage (for maximum protection, store in sealed poly bags).

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Useful Information on Joints

In this section other useful information related with a joint is given.

Flange Insulation Sets

Flange insulation sets are installed in pipeline systems to isolate the flow of electrical current. For example – in order to ensure efficient operation of cathodic protection systems for stainless steel pipelines, it is necessary to divide the pipelines into manageable lengths. The installation of flange insulation set at flanged joint ensures effective sealing and isolation from electric current. Different types of sets are available for different types of flanges.

Flange insulation sets comprise the following components which ensure that full electrical isolation is achieved.

• Central insulating gasket which is fitted between the flanges.
• Insulating sleeve per flange bolt.
• Insulating washers per flange bolt.
• Metal backup washers per flange bolt.

The components are manufactured from insulating materials with high compressive strength and good stability

Direct Tension Indicators

Direct tension indicators provide the means to measure bolt tension (bolt load). They are manufactured as per ASTMF959 and F959M. They are generally used with structural fasteners. The Direct Tension Indicator (DTI) is a specially hardened washer with protrusions on one face. The DTI is placed under the bolt head or nut, and the protrusions create a gap. As the bolt is tensioned, the clamping force flattens the protrusions, reducing the gap.

DTI's stay on the job, providing permanent visual and measurable proof that the bolt is correctly tensioned to specification. Gap corresponds to bolt load verified by a test certificate traceable to NIST.

Reuse of a Gasket

A gasket’s function is to conform to flange high and low spots when compressed, and its ability to reseal decreases after it is compressed. Gaskets which contain rubber and which have experienced elevated temperatures will be even less likely to reseal. In view of this, it is recommended not to reuse a gasket. Even if the gasket appears to be okay, it is not worthwhile. The cost of a new gasket is minuscule compared to the cost of down time caused by a leak or blowout and the considerations of safety and environmental protection.

Joining of Gasket Sections

For making a large gasket, it is recommended to make a dovetailed joint instead of beveled joint.

Spacers in Flanges

Some installations require a very thick gasket to fill a large gap between flanges. It is recommended not to stack numerous gaskets in the same flange. Tests have shown that a better way to fill a 1/2" gap, for example, is to install a 1/16" gasket on each side of a 3/8" thick incompressible spacer ring. Ideally, the spacer ring shall be consistent with piping metallurgy, serrated, and cut to the same dimensions as the gasket. Higher minimum torque is recommended when using this type of arrangement.

Hydrostatic Testing Precautions

If hydrostatic tests are to be performed at pressures higher than those for which the flange was rated, higher bolt pressures must be applied in order to get a satisfactory seal under the test conditions.

For this, use high-strength alloy bolts (ASTM B 193 Grade B7 is suggested) during the tests. They may be removed upon test completion. Higher stress values required to seat the gasket during hydrostatic tests at higher than flange rated pressures may cause the standard bolts to be stressed beyond their yield points.

Upon completion of hydrostatic testing, relieve all bolt stress by 50% of the allowable stress.

Begin replacing the high-strength alloy bolts (suggested for test conditions) one by one with the standard bolts while maintaining stress on the gasket.

After replacing all the bolts, follow the tightening procedure recommended in the bolting sequence diagrams.

Troubleshooting Leaking Joints

One of the best methods for determining the cause of joint leakage is the careful examination of the gasket where the leakage occurred. 

Common Wrong Practices

• Reuse of old gasket (due to non availability of new gasket).
• Procurement of material by generic name with out specification (for example, neoprene sheet).
• Improper storage – Storage of gasket sheets in vertical rolls.
• Cleaning of flanges by chisel / hack saw blades (leading to flange damage).
• Cutting of gasket by hammering against flange / use of chisel instead of sharp cutter.
• Use of many gaskets to fill large gap between flanges.
• Use of one thickness and one type of gasket for all plant application.
• Application of grease on gasket / flange faces.
• Application of tape / thread to hold gasket in position.
• Use of ordinary fasteners instead of high tensile fastener (due to loss / damage to old fasteners).
• Use of dirty / rusted fasteners with out lubrication.
• Improper sequence of bolt tightening.

Acknowledgements:

Article titled Gaskets – Materials and Types and this article are written based on information from websites of Fluid Sealing Association, European Sealing Association, James Walker Moorflex Limited and Garlock Sealing Technologies. For more information please refer to their websites. Their site addresses are as under.

http://www.fluidsealing.com
http://www.europeansealing.com
http://www.jameswalker.biz
http://www.garlock.com

Site addresses of Indian gasket manufacturers are as under.

http://www.hindcompo.com
http://www.champion-india.com
http://www.jaygaskets.com
http://www.goodrichgasket.com

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Gasket

A gasket is a compressible material, or a combination of materials, which when clamped between two stationary members prevents the passage of the fluid across these members. To prevent passage of fluid, the gasket must be able to flow into (and fill) any irregularities in the mating surfaces being sealed, while at the same time be sufficiently resilient to resist extrusion and creep under operating conditions. The seal is effected by the action of force upon the gasket surface (usually by bolts), which compresses the gasket, causing it to flow into any surface imperfections.

Gasket Materials

Wide varieties of materials are used in the manufacture of gaskets. This section is aimed at providing a brief overview of the common materials. For simplicity they are divided into 4 parts.

• Elastomeric materials
• Fibrous materials
• Other materials
• Metallic materials

Elastomeric Materials

They are the “entry level” to sheet sealing products. More commonly, they act as the binder when compounded with various fibres and fillers. They are made in various composition (hence performance) and are available in specification grade and commercial quality.

Butyl Rubber (IIR, also known as isobutylene,isoprene)

An elastomer offering good resistance to ozone and gas permeation. Suitable for mild acids, alkalis and esters, but little resistance to oils and fuels.
BS 3227 Grades B60, B70.

Chlorosulphonated Polyethylene

An elastomer with excellent chemical resistance against acids and alkalis. Good oil resistance. Outstanding fire protection properties.

Ethylene Propylenediene (EPDM)

Elastomer which offers good resistance to ozone, steam, strong acids and alkalis, but is not suitable for solvents and aromatic hydrocarbons.
BS 6014 Grades EP60S, EP70S, EP80S.

Fluoroelastomer

A fluorinated hydrocarbon which offers excellent resistance to acids, aliphatic hydrocarbons, oils and many corrosive applications. Not suitable for amines, esters, ketones or steam.

Natural Rubber (NR)

Excellent for recovery properties. Good resistance to most inorganic salts, mild acids and alkalis. Not recommended for oils and solvents, or where exposure to ozone, oxygen or sunlight is prominent.
BS 1154 Grades Z40, Z50, Z60, Z70, Z80

Neoprene (Chloroprene, CR)

Excellent resistance to oils, ozone and weathering. Suitable for moderate acids, alkalis, salt solutions, petroleum, solvents, oils and fuels. It is not recommended for strong acids or hydrocarbons.
BS 2752 Grades C40, C50, C60, C70, C80

Nitrile (NBR)

Improved chemical resistance and temperature capabilities over neoprene. Good resistance to hydrocarbons and oils. Not suitable for chlorinated hydrocarbons, esters, ketones and strong oxidizing agents.
BS 2751 Grades BA40, BA50, BA60, BA70, BA80, BA90
BS 6996 Grades BO60, BO80

Silicone

Excellent temperature properties, and unaffected by ozone and sunlight. Not suitable for many hydrocarbons and steam.

Styrene Butadiene (SBR)

Suitable for use with weak organic acids and moderate chemicals. Not suitable for strong acids, most hydrocarbons or ozone.

Fibrous Materials

Aramid

Aromatic amide fibre, offering high strength and stability, with medium temperature suitability. Raw fibres can fibrillate.

Asbestos

Since the 1890’s, the most common material used for sealing flanges, because of its ability to seal effectively over a broad range of service conditions. Now increasingly replaced by asbestos-free substitutes (mandatory in many locations).

‘Asbestos’ is the term applied collectively to various classes of fibrous minerals used in the industry characterized by their resistance to heat, strength and flexibility of their fibres. Chrysotile (white) asbestos is by far the most important variety. It is a hydrated silicate of magnesium. It may also contain small traces of aluminium and iron, and dependent on the quantities of these traces the colour of chrysotile asbestos in the crude rock form varies from pure white to greyish-green. Individual chrysotile asbestos fibres are silky and very flexible with a diameter smaller than that of any synthetic fibre.

Asbestos is incombustible and is a poor conductor of heat. It is unaffected by temperatures up to approximately 450 deg. C, when it begins to lose its chemically combined ‘water of crystallisation’; this process is completed at about 700 deg. C, but the residue which remains fibrous, does not fuse until temperatures of 1450-1500 deg. C are reached.

Asbestos is inert and is not toxic to touch, smell or ingestion. Asbestos fibre is not a health hazard unless its dust becomes airborne and such dust is continuously inhaled in large amounts over a prolonged period. Chrysotile fibres are the least harmful of all varieties of asbestos due to their curvi-linear nature. International Labor Organization (ILO) has recommended not to use Crocidolite (blue asbestos) variety of asbestos fibres, which is the most harmful due to its needle like structure.

Carbon Fibre

High thermal conductivity ensures rapid heat dissipation and allows high temperature capability (except in oxidizing atmospheres). It has wide chemical resistance and may be used in the pH range 0 – 14. It is not suitable for oxidizing environments.

Cellulose

Natural fibre, suitable for low temperature and medium pressure applications. Raw fibres can fibrillate.

Glass

Inorganic complex of metal silicates. It offers good strength and moderate chemical resistance. Suitable for medium to high temperature applications. The fibres do not fibrillate.

Man Made Mineral Fibre (MMMF)

Also referred to as “mineral wool”. Inorganic fibres consisting of metal silicates, with a wide range of diameters. Suitable for medium to high temperature applications. Fibres do not fibrillate.

Other Materials

Flexible Graphite

Following processing into its exfoliated form, the material is essentially pure graphite, typically over 95% elemental carbon. The material has a wide chemical resistance. It is suitable for exceptionally wide temperature range from up to 400 deg. C in oxidizing environments and under certain circumstances, to 2500° deg. C in inert conditions. It has excellent resistance to stress relaxation, even at elevated temperatures.

Mica (Vermiculite)

Naturally occurring, complex aluminium silicates, characterized by laminar morphology and near-perfect basal cleavage. The structure possesses a high degree of flexibility, elasticity and toughness. Excellent thermal stability and chemical resistance.

Cork

It compresses readily with negligible lateral flow, recovers speedily, and is relatively inert. It lacks flexibility and mechanical strength.

PTFE

Extremely wide chemical resistance (PTFE is attacked only by molten alkali metals and fluorine gas), with excellent anti-stick and dielectric properties. Material has high compressibility, which allows it to conform well to flange surface irregularities. Easy to handle. Low permeability. Extremely low coefficient of friction. Susceptible to degradation by radiation. It can be prone to relaxation and creep

Metallic Materials

Various metallic materials used for making gasket are:  Carbon steel, 316, 316L, 304, 304L, 321, 347, 410, Titanium, Alloy 600, Alloy 625, Alloy 800, Alloy 825, Alloy 200, Alloy 400, Alloy B2, Alloy C276, Alloy 20, Alloy x-750, Aluminium and Copper.

Standard Classification for Non-metallic Gasket Materials

ASTM Designation F104 provides a means for specifying or describing pertinent properties of commercial non-metallic gasket materials. Materials composed of asbestos, cork, cellulose, and other nonasbestos materials in combination with various binders or fillers are included.
Materials normally classified as rubber compounds are covered in Method D2000.

Types of Gaskets

Depending on construction, gaskets can be classified into three main types:

• Soft (non-metallic)
• Semi-metallic
• Metallic

The mechanical characteristics and performance capabilities of these categories will vary extensively depending on the type of gasket selected and the materials from which it is manufactured.

Soft Gaskets (non-metallic)

Often they are composite sheet materials, suitable for a wide range of general and corrosive chemical applications. Generally they are limited to low to medium pressure applications. They are available either in sheet form or as gaskets cut accurately to any reasonable shape and size.
Types include: Elastomers, compressed asbestos fibre (“CAF”), asbestos-free (non-asbestos) compressed fibre materials, graphite, PTFE, cork, mica, etc.

Elastomer (Rubber) Sheet Gaskets

Elastomers are incompressible, extensible, highly impermeable and elastic.

Incompressible—can be deformed, but can never be reduced in volume.
Extensible—can be assembled over a projection or shoulder and snap tightly within a groove.
Highly impermeable—can serve as a tight barrier against the passage of gases or liquids.
Elastic—little flange pressure required to effect intimate contact with gasket, allowing it to move with the flange surfaces, always maintaining a seal.

Elastomer gaskets are used for relatively low pressure applications as at high seating stresses a rubber gasket may extrude from between the flanges. They are available in a wide range of specification (premium) grades for industrial and military requirements as well as “commercial” grades for general purpose applications.

Neoprene sheets are widely used as gasket material.

For ready reference physical properties of premium grade (ASTM) rubber gaskets made by Garlock are reproduced below.

Material	EPDM	Neoprene	Neoprene	Neoprene	Nitrile	SBR	Fluoro-elastomer (Type A)	Fluoro-elastomer (Type A)	Fluoro-elastomer Blend
Style	8314	7986	7797	9064	9122	22	9518	9520	9780
Hardness (Shore A) ± 5	60	60	80	60	60	75	75	75	65-75
Tensile strength, min. (ASTM D412), psi (N/mm2)	1,000 (7)	2,000 (14)	1,500 (10)	2,400 (17)	2,000 (14)	700 (5)	1000 (7)	1,000 (7)	1200 (8)
Elongation, min., %	300	350	125	790	500	150	175	180	175
Compression set, ASTM Method B (ASTM D395) 25% deflection, maximum %	22 hrs @158°F (70°C) 25	70 hrs @212°F (100°C) 35	70 hrs @212°F (100°C) 75	-	22 hrs @212°F (100°C) 20	22 hrs @158°F (70°C) 40	-	22 hrs @350°F (175°C) 50	-
Temperature range, °F (°C)	-40°F (-40°C) to +300°F(+150°C)	-20°F (-29°C) to +250°F(+121°C)	-20°F (-29°C) to +250°F(+121°C)	-20°F (-29°C) to +250°F(+121°C)	-20°F (-29°C) to +250°F(+121°C)	-10°F (-23°C) to +200°F(+93°C)	-15°F (-26°C) to +400°F(+204°C)	-15°F (-26°C) to +400°F(+204°C)	-15°F (-26°C) to +400°F(+204°C)
Pressure, max., psig (bar)	250 (17)	250 (17)	250 (17)	250 (17)	250 (17)	250 (17)	250 (17)	250 (17)	250 (17)
P x T max., psi x °F (bar x °C)	30,000 (900)	20,000 (600)	20,000 (600)	20,000 (600)	20,000 (600)	20,000 (600)	30,000 (900)	30,000 (900)	30,000 (900)

Typical physical properties of Commercial grade Neoprene (made by James Walker brand number 264 C) is as under.

Hardness, IRHD: 55 to 70
Density, Mg/m3: 1.4 ±0.2
Tensile strength, MPa: 5
Elongation at break, %: 200
Operating temperature range: –20 deg. C to +100 deg. C.

Insertion Sheets

Elastomer sheet is called insertion sheet when it is reinforced by a cloth / fabric to give it additional strength and resistance to spread under compression.

Kalrez® Perfluoroelastomer FFKM by DuPont

This high performance elastomeric material made by DuPont combines the resilience and sealing ability of rubber with almost universal chemical resistance and temperature capabilities up to 316° C. Various grades of Kalrez® are available for critical and/or high purity sealing applications.

Compressed Asbestos Fibre (“CAF”) Sheets

Historically, compressed asbestos fibre sheet material has been the material of choice for “soft” gasket materials. It is regarded as easy to use and very tolerant of abuse, for which it is recognized as very “forgiving”. The material is used to seal almost all common applications, and usually gave reasonable performance. Jointing sheets are manufactured by calendering process in which the mixture of asbestos fibre, filler and binder is compressed between two rollers under load. The overall characteristics are influenced by asbestos quality and the nature of binder (usually elastomer). Tensile strength of the material depends on length of asbestos fibre and chemical properties are decided by type of binder. They are available either in sheet form or as gaskets cut accurately to any reasonable shape and size.

Compressed Asbestos-free (non-asbestos) Fibre Sheets

More recently, with the tendency away from the use of asbestos fibres, a new generation of non asbestos fibre jointing material substitutes has been developed by the sealing industry. The sheets are made by calendaring process typically using carbon, glass and aramid or a mixture of these fibres. Overall, these new materials can outperform their asbestos equivalent, but are usually less forgiving and handling of these materials require more care. The maximum temperature capabilities are however slightly reduced compared to asbestos. For a given material, the maximum temperature limit also reduces with increasing thickness. In view of this wherever possible use the thinnest gasket.

Graphite Sheets

Graphite sheets contain more than 95% pure exfoliated graphite. An Ultra High Purity (99.8%) grade is available for nuclear industry applications. More care is required in handling and storage of these sheets as they get easily damaged.

PTFE Sheets

PTFE is generally used because of its outstanding chemical resistance. As it can be prone to relaxation and creep, filled grades are often employed to overcome some of these effects. Fillers are also used to improve wear resistance and thermal conductivity. Glass fibre, graphite, molybdenum disulphide, bronze, etc. are used as filler materials. They are widely used for food and pharmaceutical service.

Tape / Cord Expanded PTFE (also known as joint sealant)

Usually on a spool or roll, this high compression material is very flexible and is available with adhesive on one side to aid installation. The material can be rolled out onto the flange mating surface, cut off, overlapped and compressed between the flanges. It is often referred to as “form in place”, an ideal do-it-yourself gasket material for easy field installation. Generally used for less severe pressures and temperatures, especially where flanges are lightly loaded or of relatively flimsy construction.

Cork / Corkelastomer Sheets

Elastomer-bonded cork sheets are generally used as cork lacks flexibility and mechanical strength. They are mainly used on low pressure duties such as oil covers (transformers) and applications where the available bolting is relatively low (on glass, porcelain, etc.). Their expanded nature is also found beneficial in inhibiting the transmission of noise and machinery vibration and are used for air ducts in air conditioning. Many grades are available for covering applications in electrical (high voltage switchgear), marine, aerospace (aircraft fueling equipment), automobile and mechanical engineering.

Semi-metallic Gaskets

They are composite gaskets consisting of both metallic and non-metallic materials. The metal generally provides the strength and resilience to the gasket. They are suitable for both low and high temperature and pressure applications.
Common types are: Kammprofile, metal eyelet, metal jacketed, metal reinforced soft gaskets (tanged graphite, wire reinforced compressed asbestos fibre materials, etc.), corrugated metallic and spiral wound gaskets.

Kammprofile

Kammprofile gaskets consist of a metal core with concentric serrated grooves on each side and the addition of a soft layer of sealing material bonded to each face. Selection of the metallic core material and sealing layer materials is dependent on the service duty. The serrated metallic core is very effective for sealing in applications where high temperatures, high pressures and fluctuating conditions exist. It can be used without sealing layers, but there is a risk of flange damage. The sealing layers protect the flange surfaces from damage and also offer excellent sealing properties when supported by the serrated metallic core. These gaskets can seal pressures up to 250 bar and withstand temperatures up to 1000 deg. C. The serrated metallic core can be re-used, subject to inspection after cleaning and re-layering.

Metal Eyelet

In these gaskets a metal bead (usually stainless steel) is put around the inner periphery of gaskets cut from sheet material to protect the gasket’s internal diameter. The gaskets can be produced using a wide variety of compressed asbestos fibre and compressed non-asbestos fibre materials. However they are more commonly used with expanded graphite. The region beneath the bead receives greater compression due to the thickness of the metal and thus is more highly stressed than the rest of the joint. This additional compression is more easily achieved with graphite than with other materials. Other advantages of this construction are as under.

• Anti blow-out giving extra safety.
• Provides extra strength to the gasket, making it easier to handle and assemble.
• Non contamination of the medium from the gasket material, for example – graphite.
• Prevents erosion at high velocities.

Metal Jacketed

These gaskets are specially designed and widely used for heat exchangers, autoclaves, columns, pressure vessels, valve bonnets, etc. The gaskets are manufactured from a soft, pliable filler core surrounded by a metal jacket, chemically and thermally resistant to the working conditions. Metal jacket may totally or partially enclose the filler. Metals such as soft iron, carbon steel and stainless steel are used in annealed condition to encase a soft filler material, usually non-asbestos millboard. Alternative fillers include expanded graphite, PTFE, compressed non-asbestos fibre and ceramic fibre.

Metal Reinforced Soft Gaskets

When gasket width has to be narrow as in cylinder heads and exhaust manifold on internal combustion engines, compressed asbestos fibre (“CAF”) sheets and compressed asbestos-free (non-asbestos) fibre sheets are reinforced with mesh wire gauge to resist the blow out. Sheet jointing of pure exfoliated graphite are reinforced with a central layer of 0.1mm thick tanged stainless steel to give them extra strength for easy of handling and fitting. In these gaskets the graphite is compressed onto the perforated metal sheet to give a secure mechanical lock without adhesive. Extra strength to such sheets is also given by bonding a central layer of stainless steel or nickel foils.

Corrugated Metallic

Corrugated metallic gaskets have a corrugated metal core (normally stainless steel), with expanded graphite facings. They are used for standard pipeline duties, and heat exchangers.

Spiral Wound Gaskets

Spiral wound gaskets are manufactured from V-shaped metal strips, spirally wound with an inlay of soft filler material between each turn. They form a very effective seal when compressed between two flanges. A V-shaped crown centered in the metal strip acts as a spring, giving gaskets greater resiliency under varying conditions. Filler and metal strip material can be changed to accommodate different chemical compatibility requirements. When spiral winding only (containing preformed metal and soft filler material) is used as a gasket, inner and outer diameters of winding are reinforced with several plies of metal without filler to give them greater stability. A spiral wound gasket may include a centering ring, an inner ring or both. The outer centering ring centers the gasket within the flange and acts as a compression limiter. The inner ring provides additional radial strength. The inner ring also reduces flange erosion and protects the sealing element. These gaskets are widely used in refineries, chemical processing plants, power generation, and a variety of valve and specialty applications.

Spiral wound gaskets may be used in place of solid metal oval or octagonal API ring joint gaskets when their gasket groove is badly worn out.

The spiral wound gasket industry is currently adapting to a change in the specification covering spiral wound gaskets. Previously API 601, the new specification is ASME B16.20. These specifications are very similar.

Gasket identification markings required by ASME B16.20 are as under.
.

These gaskets are generally used for higher temperatures and pressures. A variety of metals are available for the winding strip as well as for the support rings for different temperature application as under.

Material	Minimum		Maximum		Abbreviation
	°F	°C	°F	°C
304 Stainless Steel	-320	-195	1,400	760	304
316L Stainless Steel	-150	-100	1,400	760	316L
317L Stainless Steel	-150	-100	1,400	760	317L
321 Stainless Steel	-320	-195	1,400	760	321
347 Stainless Steel	-320	-195	1,700	925	347
Carbon Steel	-40	-40	1,000	540	CRS
20Cb-3 (Alloy 20)	-300	-185	1,400	760	A-20
HASTELLOY® B 2	-300	-185	2,000	1,090	HAST B
HASTELLOY® C 276	-300	-185	2,000	1,090	HAST C
INCOLOY® 800	-150	-100	1,600	870	IN 800
INCOLOY® 825	-150	-100	1,600	870	IN 825
INCONEL® 600	-150	-100	2,000	1,090	INC 600
INCONEL® 625	-150	-100	2,000	1,090	INC 625
INCONEL® X750	-150	-100	2,000	1,090	INX
MONEL® 400	-200	-130	1,500	820	MON
Nickel 200	-320	-195	1,400	760	NI
Titanium	-320	-195	2,000	1,090	TI

Material used for filler strips are as under.

Note:
Garlock makes spiral wound gaskets by Controlled Density process – Computerized manufacturing process which ensures that optimum filler density is constant across gasket winding for consistent compression and superior sealability. In such gaskets, high tightness level is achieved with minimal compressive load, for longer-lasting seal.

Metallic Gaskets

They can be fabricated from a single metal or a combination of metallic materials in a variety of shapes and sizes. They are suitable for high temperature and pressure applications. Higher loads are required to seat these gaskets. Common types are: Ring type joints, lens rings, and welded gaskets.

Ring Type Gasket

The solid metal gasket provides an excellent mechanical joint and has almost universal acceptance in the oil, petroleum and chemical processing industries where high mechanical and thermal performance is required. The Type R oval configuration is the original ring joint design and was followed by the Type R octagonal which offered more specific sealing contact areas. Details of these joints are given in ASME B 16.20 and API 6A standards. The gaskets sit in a recess in the flange face having 23° angled walls. The RX joints are an unequal bevel octagonal ring, and are considered to be a pressure energized or pressure-assisted seal. The BX is also octagonal, though shorter in profile and designed to go into a recess that becomes metal-to-metal when the flanges are tightened. These are used on very high pressure flanges up to 20,000 p.s.i. rating. Gasket metal should be selected to suit the service conditions and should have hardness lower than the flange metal.

Lens Rings

They are widely used in high pressure applications and are resistant to overstressing. They are manufactured in accordance with DIN 2696 PN 64 to 400 and DN 10 to 300.

Weld Ring Gaskets

They are suitable for critical applications where a leak-proof joint is essential. Sealing is achieved by welding the two gasket halves together.

Note:
Many varieties of gasket are made by different manufacturers. Only basic types are covered here (for example, varieties of metal jacketed gaskets are – single jacketed open type, single jacketed with outside edge open, single jacketed with inside edge open, single jacketed totally enclosed, double jacketed, corrugated double jacketed, corrugated double jacketed with metal filler, etc.). For more information, please refer to manufacturer’s Product Range Manuals.

Acknowledgement:

Information and pictures from websites of Garlock and James Walker are used in this article. For more information please refer their websites.

Compression packing consists of a number of rings which are inserted into the annular space (stuffing box) between the rotating or reciprocating member and the body of the equipment or valve. By tightening a follower against the top or outboard ring, pressure is transmitted to the packing set, expanding the rings radially against the side of the stuffing box and the reciprocating or rotating member, effecting a seal. Compression packings are relatively easy to install and maintain.

In this article information is give on purpose for control of fluid loss, packing materials and construction, material selection, equipment condition and installation instructions.

Purpose for control of fluid loss

• To minimize pollution in environment.
• Plant esthetics (clean shop).
• Survivability of the fluid handling equipment itself.
• Minimize product loss.
• Human safety.

Packing materials and construction

Compression packings are made in a variety of shapes, sizes and constructions, from a wide range of materials. They are made from aramid, asbestos, carbon / graphite filament, fiberglass, flexible graphite, PTFE, synthetic fibers, etc. For more information on packing material please refer article on Gaskets – Material and Types.

The following describes the most commonly used constructions.

Braid-Over-Braid

Round braiding machines braid tubular jackets using yarns, rovings, ribbons and various other materials, either alone or in combination. Size is obtained by braiding jackets one over the other (braid-over-braid). They are relatively dense and are recommended for high pressure, slow-speed applications such as valve stems.

Braid-Over-Core

Finished product is produced by round braiding one or more jackets over a core.

Square Braid

Yarns, rovings, ribbons and other various materials, either alone or in combination, are processed on equipment where strands pass over and under strands running in the same direction. The packing is usually soft and can carry a large percentage of lubricant. Square braided packings are easy on equipment and are generally used for high-speed rotary service at relatively low pressure. The packing’s softness makes it ideal for old or worn equipment.

LATTICE BRAID®

Yarns, rovings, ribbons and other forms of various materials, either alone or in combination, are processed on equipment where the strands crisscross from the surface diagonally through the body of the packing. Each strand is strongly locked by other strands to form a solid integral structure that cannot easily ravel or come apart in service. LATTICE BRAID® packings are suitable for applications on both reciprocating and centrifugal pumps, valves, etc.

Die-Formed

Many compression packing materials are supplied in a pre-compressed ring form, which provides controlled density and size.

Mandrel Cut

Rings formed by wrapping braided stock of the required cross section on a mandrel or shaft with a diameter equal to the desired I.D.

Graphite Tape

Flexible graphite tape (ribbon) is manufactured by exfoliating (expanding) and then compressing natural graphite flakes to a specific density. Graphite has almost universal chemical inertness and is naturally lubricious, compactible and resilient, as well as nuclear radiation resistant.

Material selection

Packing manufacturers make packing for vide variety of application and are sold under their style number / brand names. Information on these products is available in their product catalogue. Selection of packing material shall be carried out based on the operating condition of the equipment. Six parameters of the equipment shall be considered for packing selection. The acronym “STAMPS” is commonly used to designate these parameters.

S = Size — cross section
T = Temperature — of media being sealed
A = Application — type of equipment (i.e., pumps, valves, reciprocating, rotating, etc.)
M = Media — material being sealed
P = Pressure — of media being sealed
S = Speed — shaft speed in fpm (pumps only)

Equipment condition

Condition of equipment is critical for the success of a packing. Following is recommended for valves and pumps.

Valves

Longitudinal scores on the valve stem are not to exceed 1/32″ depth and/or a depth-to-width ratio greater than 1.00.
Stem finish shall be less than 32 (micro inches) AARH.
Stuffing box finish is recommended to be 125 (micro inches) AARH.
Valve stem warpage / runout must be checked and shall not exceed following:

Pumps

Runout: TIR (Total Indicator Runout) not to exceed 0.005″.
Longitudinal scores: Should not be present on pump shaft or sleeve.
Shaft / Sleeve finish: 16 to 32 (micro inches) AARH
Stuffing Box Bore finish: 125 (micro inches) AARH
Stuffing box depth = (5.5 to 7.5) x packing cross section (CS)

Note:

• The bottom of the gland follower should be flat.
• Only small clearance (few thou) shall be there between stem / shaft and stuffing box bottom. If clearance is more, use bottom ring (junk ring) to prevent extruding the packing when it is compressed.
• If stuffing box bottom is beveled, it is recommended to use a system-compatible braided packing ring before installing selected packing.
• Burrs shall not be there on the stem and/or stuffing box bore walls.

Installation instructions

Remove all old packing from the stuffing box. Clean box and stem / shaft thoroughly and examine for wear and scoring. Replace stem / shaft if wear is excessive.

Use packing extractors to remove old packing rings. They have a long flexible shank to gain access to glands in difficult positions. The corkscrew tips are designed to embed firmly in all types of packing, including badly worn and hardened products. A T-handle provides good grip for both screw action and the efficient removal of packing.

Measure and record stem / shaft diameter, stuffing box bore and box depth. To determine the correct packing size, measure the diameter of the stem / shaft (inside the stuffing box area if possible), and the diameter of the stuffing box bore. Subtract the I.D. measurement from the O.D. measurement, and divide the difference by two. This is the required cross-sectional size.

Always cut the packing into individual rings. Never wind the packing into a coil in the stuffing box. Rings should be cut with a butt joint. Cut rings by using a spare stem / shaft, a mandrel with the same diameter as the stem or a packing cutter.

Hold the packing tightly on the mandrel, but do not stretch excessively. Cut the ring and insert it into the stuffing box, making certain that it fits the packing space properly. Alternatively packing rings may be cut using packing ring cutter (cutting jig).

Install one ring at a time in the stuffing box. Make sure it is clean, and has not picked up any dirt in handling. Seat each ring firmly, making sure it is fully seated before the next ring is installed. A tamping tool may be used for this. Joints of successive rings should be staggered and kept at least 90 degree apart. While installing packing rings in pumps, lubricate the I.D. of each ring lightly. When enough rings have been individually seated so that the nose of the gland follower will reach them, bring down the gland follower and apply load with the gland bolts as under.

Load application in valves

After the last ring is installed, bring down the gland follower and apply 25% to 35% compression to the entire packing set. Tighten gland bolts evenly. During tightening, turn the valve stem back and forth to determine easy of turning.

Load application in pumps

After the last ring is installed, bring the follower down on the packing and finger-tighten the gland nuts. Do not jam the packing by excessive gland loading. Start pump, and tighten the bolts until leakage is decreased to a tolerable minimum and the pump is running cool. Tighten the gland nuts one flat at a time. Make sure gland bolts are tightened evenly. Stopping leakage entirely at this point will cause the packing to burn up.

Note for pumps:
If a lantern ring is provided, make sure the lantern ring is installed under the pipe tap hole.

Internet site address of some compression packing manufacturers

http://www.garlock.com
http://www.jameswalker.biz
http://www.inmarco.com
http://www.champion-india.com

Acknowledgement:

This article is written based on technical information from Garlock Sealing Technologies. For more information please refer to their website – http://www.garlock.com