Flat gaskets: what they are, what they are used for and materials catalog

In the complex world of industrial piping and fittings, flat gaskets play an essential role in ensuring the static tightness of flanged joints. Would you like to know what a flat gasket is and what it is used for? At Epidor Seals and Rubber Technology we have prepared a training video on flat gaskets, where we will explore the fundamental concepts related to this sealing material, from its function to the materials used, and we will highlight the importance of understanding the regulations and measurements for its correct selection.

The layout of a pipeline is rarely straight; in fact, almost never. The various sections that make up this layout can be welded together or bolted together. In the latter case, the ends of the section to be joined end in a piece called a flange, which consists of a collar with a ring and holes for the fastening bolts. Flanges are also used to install filters, valves, flow meters or other accessories in pipelines.

The flange, the hardware (nuts, washers and bolts) and the sealing gasket constitute the flanged joint. The flange allows the connection with the fastening bolts and the sealing gasket prevents leakage of the fluid flowing through the pipe.

Flat gaskets solve static sealing problems in flanged joints of pipes or other fittings such as valves, elbows, tees, etc. Unlike dynamic sealing, there can be no relative movement between the sealing gasket and the flanges. Hence its classification as a static sealing solution.

The function of flat gaskets in pipelines and flanged joints

A flat gasket is a vital component in the flanged joint which, together with the flange, the fastener forms what is known as a “flat gasket".“Sealing Triangle”. Three elements that share responsibility in the event of an escape.

Flat gaskets solve sealing problems in flanged joints, providing an effective barrier to prevent fluid leakage in pipes and fittings such as valves, elbows and tees. Unlike dynamic sealing, where there is relative movement between the gasket and flanges, static sealing focuses on preventing any leakage without such movement.

While it is true that, when a leak is detected in a pipeline, it is common to attribute the responsibility to the gasket, the reality is more complex, since both the flange faces and the hardware also play a crucial role and, therefore, may be the cause of the leak.

Flat gasket materials and manufacturing process

The diversity of materials used in the manufacture of flat gaskets is extensive and we will choose one gasket material or another depending on the service conditions, such as temperature and pressure (also chemical resistance to the process fluid). From elastomers to nickel alloys, titanium or stainless steels, each flat gasket material serves a specific purpose. For example, expanded PTFE may be recommended over elastomers because of its superior chemical resistance.

Most flat gaskets are produced by cutting the raw material on cutting tables (except for metallic and semi-metallic gaskets). The process of producing gaskets on a cutting table involves immobilizing a sheet of material (typically 1,500 by 1,500 mm square) under vacuum and using a software-controlled cutting head to shape the gasket according to the CAD drawing.

Flat gasket materials catalog

If you wish to download the flat gasket materials catalog, If you are a member of a group, you should know the types of materials and groups that you can find:

• Materials based on compressed fibers.
• Restructured PTFE materials, virgin PTFE and expanded PTFE.
• Materials for making graphite gaskets and other materials for high temperature services.
• Most common materials, such as elastomers: food grade elastomers and sponge elastomers with the option of an adhesive side.

For all materials, information is provided on working temperatures, whether they have certifications and thicknesses in stock.

Flange gasket standards and dimensions

The wide variety of flanges requires specific standards to establish measurements according to size, type and material, so it is important to know that there are also standards for gaskets, depending on the flanges on which they are installed.

In fact, certain countries have developed their own standards, which means that a flange gasket standardized according to DIN will not be compatible with a flange of the same size that is standardized as ASME, BS, GOST or JIS.

Why it is essential to follow the same standards for the flange and the flat gasket

The surface of a flange can have two different configurations: it can be completely flat or it can have a shoulder that delimits an inner contour specifically designed to accommodate the gasket. In the first scenario, the flange is classified as «raised face» (RF type), and it is common for the gasket to have no holes and to be positioned between the bolts. On the other hand, when the flange surface is flat, it is common that the gasket covers the entire flange, including the bolt area, and therefore has the corresponding holes. This configuration is common when soft gasket materials are used and low pressures are encountered. In the case where the gasket has holes, it is referred to as a FF-type gasket.

Metric flanges, identified by their nominal diameter (DN) in millimeters, are associated with the pressure class PN in bar. In contrast, imperial flanges, whose nominal pipe size (TNT) is expressed in inches, are linked to the pressure class in psi, commonly known as «pounds» and represented by the pad symbol (#). It is crucial not to mix these parameters to avoid confusion. For example, specifying DN 100 and # 300 is incorrect, as it implies an improper combination of measurements.

Thus, when a gasket follows a specific flange standard, it is imperative to provide detailed information to avoid misunderstandings. This includes indicating the cutting standard, its size, the pressure class of the pipe and the need to cut holes for hardware.

In the case of non-standardized joints with holes, it is essential to specify measurements such as inside and outside diameters, the number of holes, their location with respect to the center (primitive diameter) and the angles in case they are not equidistant with respect to one of the axes.

Finally, if the gasket is not standardized and lacks bores, the necessary information is reduced to the indication of its inner and outer diameters. It should be noted that the thickness of the gasket becomes irrelevant in the cut-to-length manufacturing process, the choice of thickness being the sole responsibility of the user.

When do I know if a flat gasket needs to be replaced?

When replacing an existing gasket, it is essential to inquire about the reason behind the replacement and investigate any previous problems with the old gasket. Selecting the right material is crucial, and asking the right questions becomes even more important to avoid future complications.

Conclusion

In summary, flat gaskets play a critical role in ensuring the integrity of flanged joints in industrial piping systems. Understanding their function, available materials, regulations and associated measures is essential to ensure optimum performance. At Epidor Seals and Rubber Technology, We are committed to providing valuable information to help you make informed decisions on your engineering projects. Explore our flat gaskets and flanges catalog and discover from the design to the application of these gaskets.