A gasket is a mechanical seal that fills the space between two or more mating surfaces with the goal of preventing leakage from or into the joined objects while under compression. Gaskets allow for less-than-perfect mating surfaces on machine parts, and they can fill irregularities and increase the likelihood of sealability, especially in high-pressure applications and flanges that have a high differential temperature range. In the oil and gas industry and other heavy industries, there are many different types of gaskets used, including standard ANSI/ASME pipe flanges and gaskets used in heat exchangers.

The gasket stress is crucial when it comes to gasket assembly, not the bolt load. To illustrate this, consider the analogy of the chip in chips and queso, which is the vehicle that gets the queso to the mouth. The bolt is the vehicle that gets the gasket stress correct.

The eight most common types of gaskets used in oil and gas are envelope gaskets, flat metal gaskets, non-asbestos sheet material gaskets, ring type joint gaskets, kammprofile gaskets, spiral wound gaskets with an inner ring, spiral wound gaskets without an inner ring, and solid metal gaskets.

Envelope gaskets, which can be either double jacketed or have PTFE on the outside of a stainless steel metal core, do not have a lot of compression or recovery and do not hold up to radial sheer. Flat metal gaskets usually have a stainless steel core without any filler material and are used in low criticality applications. Non-asbestos sheet material gaskets, which can be elastomeric or graphite, are typically used with low pressure and low temperature, but they can be used in flanges where chemical resistance is needed.

Ring type joint gaskets, which come in oval or octagonal shapes and are also called RTJ gaskets or ring joint gaskets, were traditionally found in high-pressure and high-temperature applications, but they are now being phased out in favor of spiral wound gaskets with inner rings. Kammprofile gaskets are commonly found in heat exchangers and are made of a stainless steel metal core with a flexible graphite filler material. Spiral wound gaskets with an inner ring are the best metal gaskets for all pressure ratings of pipe flanges, and they are also great for heat exchangers. The filler material for these gaskets is typically flexible graphite, but an elastomeric filler material such as PTFE can be used if chemical resistance is needed.

In conclusion, gaskets play an important role in sealing machine parts with less-than-perfect mating surfaces. Different types of gaskets are used in various applications, with each type offering its unique advantages and limitations. It is essential to consider gasket stress during assembly to ensure optimal performance.