A gasket is a mechanical seal that fills the gap between two or more joining surfaces, usually to avoid leakage when under strain from or onto the joined objects. Gaskets require mating surfaces that are “less than optimal” on machine parts where defects can be filled in. Inadequate or excessive gasket tension is a common concern because of the variety of heat exchanger models. Gaskets which are too large will create inadequate tension. The solution to this issue is to shorten the gasket, contributing to improved seating friction and improved sealing. Most seating stress-poor heat exchangers can only be repaired by looking at the dimensions and measuring the tension. With excessive gasket stress you may have too much bolt load leading to harm of the graphite sealing feature. In this case, the best choice is to the width of the bolts and maybe even to change the bolting material to one that has more width at a lower yield.
In a flange assembly the gasket is a main factor. As stated in Heat Exchangers ‘Mechanical Architecture, the flanges are made up of three sub-components. Under bolting up and working conditions the dynamic relationship between these sub-components decides the flange’s effective operation. However, some leaking happens through the gasket, and it is for this reason that it attracts the most coverage. A wide range of gasket materials and types are used, most of them compliant with national requirements defining consistency and measurements.
Types of gaskets
Rubber. The first material used was natural rubber; now, synthetic rubbers are commonly available in many grades.
Fiber jointing compressed asbestos. This became the most commonly used material for low pressure operation, but substitutes are now being pursued as manufacturers and operators are seeking to limit their use of asbestos.
Compressed synthetic fiber jointing. This current collection of gasket products uses Kevlar, a Du Pont registered trademark, and glass fiber with elastomeric binders, and is an attempt to substitute CAF.
Graphite foil. The content consists of approximately 100 per cent laminated graphite to allow it handling and power of service to a metal heart.
Metal jacketed asbestos. A will swap gasket, because it can be fitted to multipack heads with integrated move partition bars. It shows the asbestos millboard core which is covered by a metal jacket and can be produced from a variety of materials.
Spiral wound. These gaskets are made of stainless steel or high alloy sheet metal, with a non-metallic filler wrapped in a cone. This can be made in a broad range of materials and are suitable for high integrity gaskets. It indicates a gasket with the addition of strong rings to allow stress stoppage and position stoppage on the bolts. The internal ring can be fitted with partition bars.
Solid metal joints. They are available in a variety of parts, e.g., rectangular or octagonal, or as patented versions used for high pressure applications. The surface finish of the flange is critical to obtaining leak-free gasket. The finish should be selected to match the particular gasket used, and if necessary the gasket manufacturer involved. One of the most popular endings is a “gramophone” stop.
The gasket is set in a facing flange. A completely enclosed facing has machined steps inside and outside the gasket to provide maximum blowout or extrusion position and protection. This facing has the highest integrity, it often uses partial or unconfined facings for lower pressure / integrity.
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