Loss of resilience and interface contact
Re-use of gasket The re-use of gaskets is not recommended
Metal gaskets work hardened
Where possible metal gaskets such as copper should be annealed prior to use. When they can give further useful service.
Material deteriorates rapidly
Material incompatibility with contained fluid / temperature
Check manufacturer’s material recommendations and select a material or gasket type capable of withstanding the conditions Gasket extrudes from
faces
Too high a seating stress See recommendations under design faults
Excessive use of jointing compounds
Unless specified by gasket manufacturer the use of compounds and pastes is not
recommended.
Incorrect dimensions Design or manufacturing errors
Gasket should always have clean cut edges with the bore slightly larger than that of the vessel or pipe
8.0 Troubleshooting Leaking Joints.
Gasket badly corroded select replacement material with improved Gasket Extruded
Excessively
select replacement material with better cold flow
Properties, select replacement material with better load Fig no 14
carrying capacity - i.e., more dense.
Gasket Grossly Crushed Select replacement material with better load carrying capacity, provide means to prevent crushing the gasket by use of a stop ring or re-design of flanges.
Gasket mechanically damaged due to overhang of raised face or flange bore.
Revise gasket dimensions to insure gaskets are proper size.
Make certain gaskets are properly centered in joint.
No apparent gasket compression achieved
Select softer gasket material. Select thicker gasket material.
Reduce gasket area to allow higher unit seating loads.
Gasket Substantially thinner O.D than I.D.
Indicative of excessive “flange rotation” or bending. Alter gasket dimensions to move gasket reaction closer to bolts to minimize bending movement. Provide stiffness to flange by means of back-up rings. Select soft gasket material to lower required seating stresses. Reduce gasket area to lower seating stresses.
Gasket unevenly compressed around circumference
Improper bolting up procedures followed. Make certain proper sequential bolt up procedures are followed.
Gasket thickness varies periodically around
Indicative of “ flange bridging” between bolts or warped flanges. Provide reinforcing rings for flanges to better distribute bolt load. Select gasket material with lower
circumference. seating stress. Provide additional bolts if possible to obtain better load distribution. If flanges are warped remachined or uses softer material.
9.0 SEALING LAYER MATERIALS AND SEALING STRESSES
The following table gives information regarding different types of materials offered as sealing layer materials. Also given is recommended seating stress for reliable sealing purpose.
Fig no 15
Temp.
te -200 550 250 Good Aggressive
Media 20 90 400
PTFE -200 250 100 Good Aggressive
Media 20 90 400
CAF -150 450 100 Modera
te Liquids 65 161 400
Silver -200 750 250 Good Aggressive
Media 125 240 450
9.1 CORE THICKNESS
When a is replacing an existing gasket (eg. spiral wound gasket), It is recommended that 4mm thick core shall be used to prevent unnecessary stresses on existing pipelines.
For new systems, it is recommend to use 5mm thick cores. This value should be taken into account of the design stage.
Pipe system Core thickness Seated Thickness (Core + 2 sealing layers)
Existing New
4mm 5mm
5.0mm to 5.2mm 6.0mm to 6.2mm
9.2 Gaskets consist of a metal core
(Generally Stainless Steel) with concentric grooves on either side with sealing materials. The sealing layers (depending on the service duty) can be Graphite, PTFE (Teflon), CAF or Metal (e.g. Aluminum or Silver). Gaskets used without sealing layers to provide an excellent seal but there is a risk of flange surface damage.
o The very wide seating stress range (minimum to maximum stress) of the gasket makes it:
§ Highly suitable for varying temperature and pressures.
§ Less sensitive to assembly faults (inaccurate bolt tensioning).
§ Suitable for light and heavily constructed flanges.
o Dependent on layer material gaskets are resistant to temperatures up to 1000 o C
Resistant to media pressures up to 250 bar.
The additional benefits are:
o When assembled the layer thickness of the sealing material is extremely small (0.5mm) thus reducing leaks, reject rates and environment pollution.
o The gasket will not damage the flange surface and can be easily removed.
o Reduces maintenance costs
o Emergency sealing of damaged flanges by using 1mm thick sealing layers until the flange can be re-worked.
o Flange face protection. Gaskets will not damage the flange faces even at extreme seating load.
o Excellent performance when subject to fluctuating temperatures and pressures.
o Direct replacement for existing gaskets. No special flange finish is necessary.
o Eco-friendly by significant reducing leakage into the atmosphere.
1.0 Do’s & Don’ts 10.1 Do’s
1. Apply additional torque to improve compression on gasket, which avoids leakages.
2. Bolts should be tightened in sequence i.e. diametrically opposite and gradually increasing load on each bolt alternately to distribute uniform load on gasket.
3. Once plant reaches operating temperature all gaskets are “followed-up” to restore compression.
4. Ensure threads sufficiently long to allow nuts to make contact with metal faces, which gives uniform compression.
5. Check manufacturer’s material recommendations and select a gasket, which is capable of withstanding the conditions.
6. Use better load carrying capacity material.
10.2 Don’ts
1. The re-use of gaskets is not recommended.
2. Do not select the under size gaskets which will protrude into the flow path of the fluid and could create turbulence.
3. Do not use of pastes or compounds unless specified by manufacturer, which reduces the friction between the gasket, and thereby load bearing properties.
5. Do not grease the gasket, as it is incompressible.
11.0 Standards
There are variety of standards that govern dimensions, tolerances and fabrication of gaskets. The more common international standards are:
11.1 Materials British
BS 1832 – Specification for oil resistant compressed asbestos fiber jointing.
BS 2815 – Specification for compressed asbestos fiber jointing.
Grade A – For water, inert gases, inert liquids or steam up to 64 bar and 510°c
Grade B – For water, inert gases, inert liquids or steam up to 16 bar and 230°c
German
DIN 3754 – Specification for various compressed asbestos fiber grades.
American
ASTM F104 – Classification system for non- – metallic gasket materials.
11.2 Dimensions
British
BS 3063 – Dimensions of gaskets for pipe flanges to BS 10, BS 1770 and BS 2035.
BS 4865 – Dimensions of gaskets for pipe flanges to BS 4505, BS 4622 and BS4722.
Part 1 – Dimensions of non- - metallic gaskets for pressures up to 64 bar.
Part 2 – Dimensions of metallic spiral wound gaskets for pressures 10 to 250 bar.
BS 3381 – Design material and dimensions of metallic spiral wound gaskets for use with flanges to BS 1560.
American
ASME B16.20 – Dimensions of metallic gaskets for pipe flanges, ring joint, spiral wound and jacketed
ASME B16.21 – Dimensions of non-metallic flat gaskets for pipe flanges API 601 – Metallic gasket for piping.