Flange / bolt / gasket system overview

Flange / gasket arrangements

- common systems
- flange surface finish
- fasteners
- nuts
- washers
- live-loading
- flange protection systems

Gasket selection

- material selection
- gasket types
- thickness selection
- cutting soft gaskets
- gasket and gasket material storage
- handling of gaskets and gasket materials
- reuse of gaskets / fasteners

Assembly procedures

- tools required
- cleaning
- visual inspection
- lubrication
- gasket installation and centralisation
- calculation of torque
- bolt / stud tightening pattern
- tagging
- re-tightening

Disassembly procedures - release compounds

Key recommendations

Guidelines to minimise joint failure

- failure due to the fastener
- failure due to the gasket
- failure due to the flange
- minimising the chances of joint failure

Health and safety aspects of gasket materials

The new document has been prepared in collaboration with the Fluid Sealing Association of the USA and emphasises the global nature of the sealing challenges faced by users:

- increasing legislative and financial requirements to reduce emissions
- new sealing technologies
- new sealing materials often requiring more careful selection, handling and installation to ensure safe and reliable performance

It is hoped that the document will be taken up by interested organisations to form the basis of maintenance operative training schemes.

As an example of the valuable guidance provided, a list of Key Recommendations made in the document follows:

The integrity of the seal depends upon:

• selection of correct components appropriate for the application
• careful preparation, cleaning, installation and assembly
• correct bolt tightening and loading

Flange / gasket arrangements:

• selection of the proper gasket material is important with regard to the flange finish
• never use fewer bolts than the number designed for the flange

When selecting fasteners (bolts or studs):

• select fasteners with sufficient yield strength to ensure they are within their elastic limit at the

• select bolts / studs with the same modulus of elasticity
• ensure there is no corrosion of the fasteners
• do not reuse fasteners

When selecting nuts:

• select nuts with a proof load 20% greater than the ultimate tensile strength of the fasteners

Washers:

• always use washers
• use the same material for the washers and the nuts

Gasket selection:

• 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

Thickness selection:

• ensure the gasket is as thin as possible

Cutting of soft gaskets:

• use a good cutter
• never try to cut out a gasket by hammering material against the flange
• ensure the gasket is the correct size
• cut the bolt holes slightly larger than the bolt shaft diameter
• ensure that the inside diameter of the gasket is not less than the inside diameter of the process line

Storage of gaskets and gasket materials:

• store in a cool, dry place, away from direct sunlight, water, oil and chemicals
• store sheet materials flat
• avoid hanging gaskets. Store gaskets flat. Large diameter spiral wound gaskets should be stored in

• gaskets should be kept clean and free from mechanical damage (ideally, store in sealed poly bags)

Handling of gaskets and gasket materials:

• carry gaskets carefully, ideally with some form of protective cover
• do not bend or buckle
• do not damage the surface
• for large diameter metallic and semi-metallic gaskets, always transport the gasket on its mounting

to the installation site

Reuse of gaskets / fasteners:

• do not reuse gaskets or fasteners

Assembly procedures, visual inspection:

• replace defective components with a good alternative. If in doubt, seek advice

Lubrication:

• lubricate fastener threads and all bearing surfaces (underside of bolt heads, nuts, washers)
• use only specified or approved lubricants
• apply the lubricant in a consistent manner as a thin, uniform coating
• ensure lubricant does not contaminate either flange or gasket faces
• avoid contamination of the lubricant by storing in a closed container. After use, store in a "clean" area

Gasket installation and centralisation:

• carefully insert the new gasket between the flanges to prevent damage to the gasket surfaces
• for larger diameter spiral wound gaskets, seat the gasket in its mounting on the flange, remove the securing straps, then slide the gasket from its mounting onto the flange using an appropriate number of persons to avoid damage to the gasket
• ensure the gasket is central in the flange
• do not use tape to secure the gasket to the flange. If necessary, use a light dusting of spray adhesive
• do not use jointing compounds or releasing agents
• line up the joint components and examine them to ensure that an acceptable fit has been obtained
• take care when bringing the flanges together, to ensure that the gasket is not pinched or otherwise damaged

Bolt tightening pattern:

• always use a torque wrench or other controlled-tensioning device (recently calibrated)
• always torque bolts or nuts in a cross bolt tightening pattern

Tighten up using a minimum of 5 passes:

• Pass 1 - tighten bolts loosely by hand in the first instance, according to the cross bolting 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-bolting pattern. Check that the flange is bearing uniformly on the gasket
• Pass 3 - torque to a maximum of 60% of the full torque, according to the cross bolting pattern
• Pass 4 - torque to the full torque, according to the cross bolting pattern
• Pass 5 - final pass at full torque, in a clockwise direction on adjacent fasteners

Re-tightening:

• do not re-torque an elastomer-based asbestos-free gasket after it has been exposed to elevated temperatures

Disassembly procedures, release compounds:

• do not use jointing compounds

• use soft gasket materials which have an anti-stick coating applied by the manufacturer

Some language versions of this document are available for free download and complimentary hard copies are usually available from Flange Gaskets Division Member Companies.

Alternatively, hard copies are available from the ESA (inclusive of postage) at € 25

or equivalent local currency :           

The document is complementary to the Glossary of Sealing Terms which was published by the ESA in November 1997 (ESA Publication No. 008/97). As a special introductory offer, a copy of the Glossary and the Guidelines is available together at € 40 (or equivalent local currency) for the pair: