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Gasketted plate heat exchangers (PHEs) still account for a majority of the compact heat exchangers currently in use in UK industry.

That is probably why so many companies have sprung up offering gasket replacement services in competition with the OEMs.

With fewer overheads, many offer gaskets at lower prices.

Unfortunately, buying on price alone is probably not the best option, since an inferior gasket can look so much like the genuine article that it is difficult to tell them apart.

A genuine gasket from a major OEM like Alfa Laval has a polymer content of at least 50 per cent.

A cheaper copy, on the other hand, may contain as little as 20 per cent polymer.

Fillers and softeners are used to provide volume and make the inferior copy look as much like the original as possible.

Superficially, the two gaskets look identical.

It’s only in use that the differences become obvious.

Simply formulating the right gasket compound takes experience and a thorough understanding of sealing science.

Achieving the right rubber mixture can involve choosing say five to 15 different substances from around 1,700 different grades of polymer, vulcanising chemicals and processing materials.

The working environment, the service temperature and pressure, the actual nature of the duty and the inter-reaction between the gasket material and the PHE plates all have to be considered before the final combination of materials is made.

For instance, while Fluorcarbon elastomers are generally compatible with an oil contaminated mixture of glycol and water, the addition of just 100ppm of an amine type corrosion inhibitor picture causes the fluorocarbon polymer to dehydrofluorinate and leads to gasket failure.

It is essential to take into account every potential chemical reaction and evaluate and understand its possible effects on the gasket material.

The ideal gasket working environment is a steady-state operation involving no pressure or temperature fluctuations, conditions that are rarely found in most processes.

Temperature and pressure changes, caused by shutdowns for product changes or cleaning, can affect the gasket material and shorten service life.

Sudden extreme deterioration of the elastomer can lead to catastrophic failure.

The interaction between the plate and gasket materials also has to be considered.

Stainless steel and nickel alloys react badly with chlorine and chloride ions.

It makes sense to avoid using them with something like chlorophene rubber that could, under the right circumstances, release chloride ions.

The same is true of other gasket materials such as resin-cured compounds, poor quality graphite and compressed fibre materials, which can create localised corrosion, including stress corrosion cracking.

More exotic materials such as titanium, tantalum, niobium, zirconium and their alloys are also very susceptible to fluorine and fluoride ions.

Some fluorine might be released during the vulcanisation stage; more can be released as a result of polymer reaction to temperature extremes or the presence of phenols, alcohols, amines or ammonia.

Irrespective of its origin, the presence of fluorine traces can lead to localised corrosion including stress corrosion cracking.

Rubber expands with heat and this natural property is what makes it so difficult to produce an accurate copy of an existing gasket simply by measuring it.

If the original gasket has swollen during service due to physical or chemical reactions, any copy will be inexact and its sealing performance, both short and long term, could be severely compromised.

There is a lot to take in to consideration when selecting the right PHE gasket.

Unfortunately, the real difference sometimes only becomes apparent in service as the cheaper gasket ages and loses its sealing efficiency.

If that happens, any initial savings made on gasket cost could look rather feeble when set against the value of product losses.

Alfa Laval's operations are based on leading global positions in the three key technologies of heat transfer, separation and fluid handling. Continuous product development is essential to strengthen competitiveness. About 2.7 per cent of total sales are invested annually in research and development, resulting in 25–30 new product launches a year.

Alfa Laval's products are sold in approximately 100 countries, 50 of which have their own sales organisations. The company has 20 large production units (12 in Europe, six in Asia and two in the US) and 70 service centres.

The customer's peace of mind depends on having the right service setup. For Alfa Laval, service is a total concept that covers everything from supplying the smallest spare part to being a lifetime performance partner. Alfa Laval has a global network with more than 200 skilled service specialists, a broad range of competitive service solutions, unique expertise based on more than 120 years in business and service centres in hundreds of locations in more than 50 countries.

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