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The Black Art of Gasket Selection


J A HarrisonsDeciding on the correct gasket to use in an application is not always the easiest of decisions. 

 

There are many factors to be considered when choosing a gasket for your pipework or vessel including pressure, temperature and chemical compatibility. The perfect gasket would have the chemical resistance of PTFE, the heat resistance of graphite, the strength of steel, require as little seating stress as a soft rubber and be inexpensive. Unfortunately, the perfect gasket doesn’t exist.

 

A Piping Engineer once described the process of selecting the correct gasket for an application as a ‘Black Art’. This isn’t the case but it is easy to see how it can be perceived to be so. Make the wrong choice and the consequences can be expensive or possibly even fatal.

 

A leaky joint is expensive with the costs running into thousands of pounds each year in lost production, wasted energy, lost product and impact on the environment. Many of the products a gasket has to contain within the pipework or vessel are harmful to the environment or to us so it is essential you choose the correct gasket for your application and that it is installed correctly. The majority of gasket failures are due to human error either in the choice of material or incorrect installation.

 

In most instances there are just five pieces of information required to choose the correct gasket

 

S – Size

T – Temperature

A – Application

M – Media

P – Pressure

 

The gasket supplier needs to know the size to ensure it fits and to select the thinnest gasket possible for your application; the temperature and pressure to ensure the material can withstand both. They need to know the media to ensure that what is going through the pipe or is contained in the vessel won’t attack the gasket material. Finally, it is good to know the application so there is an understanding of what the gasket is required to do.

 

With this knowledge the correct gasket can be selected to minimise operating costs, to avoid environmental pollution and reduce hazards to the general public and your employees.

 

Having selected your gasket all that remains is to fit it correctly.

  1. Ensure the flange or sealing face is clean, in good condition and parallel and that all remains of old gasket materials are removed.
  2. Install the gasket in a dry state, the use of gasket compounds is not recommended. Most modern gaskets are equipped with a non-sticking finish to aid in their removal. Jointing compounds have a detrimental effect on the load bearing and stability characteristics of the material. In some conditions this could lead to failure of the gasket.
  3. Ensure the gasket is the correct size. The gasket must not intrude into the bore of the pipework and should be installed centrally.
  4. Ensure all bolting is free of dirt and ensure the nuts can run freely down the thread before use. Apply a suitable lubricant to the face of the nut and washers, the bolt and to the nut thread to reduce friction when tightening.
  5. Every gasket manufacturer recommends that the bolts are tightened using a controlled method, in most cases this is a correctly calibrated torque wrench. Fit the gasket carefully in position being careful not to damage the gasket faces. When tightening the bolts tighten them in at least 3 passes. Finger tighten the nuts the apply 30%, 60% and 100% of the recommended torque. Always torque nuts in a cross bolt tightening pattern.
  6. If the above steps are followed retightening of the gasket after the joint is assembled should not be necessary. If retightening is considered necessary this should only be carried out at ambient temperature or during the first start-up of the pipeline or plant. Retightening of compressed fibre gaskets at higher operating pressures or prolonged use could lead to failure and possibly blow out.
  7.  For your safety never re-use a gasket.

 

J A Harrison is an independent gasket manufacturer offering a wide range of gasket materials from leading manufacturers. We offer honest, unbiased advice on the best gasket solution for your application.

 

Call our technical team on 0161 832 2282 or email enquiries@jaharrison.co.uk

 

Jamie Hill

Technical Sales Manager

J A Harrison & Co Ltd incorporating Alliance & Heatshield Engineering.





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