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Expansion joints, as a kind of elastic compensation element, have the advantages of reliable work, good performance, compact structure and so on, and have been widely used in the fields of chemical industry, construction, water supply, drainage, petroleum, light and heavy industry, refrigeration, sanitation, plumbing, fire-fighting, electric power and other basic engineering fields, which play an important role in people's life.

   The function of expansion joints:

   Piping systems can expand or contract thermally due to temperature changes in two different states: shutdown and startup. If these expansions or contractions are not compensated (eliminated), it will cause serious damage to the system, so that the system cannot work properly. Expansion joints are used to absorb thermal expansion or cold contraction.

    Expansion joints are classified Metal Expansion Joints and Non-metallic expansion joints according to the material。

    Metal expansion joints: Metal expansion joints are usually made of metal materials, such as carbon steel and stainless steel. They have high strength and stiffness and can withstand high pressure and temperature, so they are widely used in harsh environments such as high temperature, high pressure, corrosive media, etc. Metal. The construction of metal expansion joints usually includes components such as bellows, flanges and end pipes, which are connected by welding or bolting.

    Non-metallic expansion joints：Non-metallic expansion joints are usually made of non-metallic materials, such as rubber, polyurethane, PTFE and so on. They have good flexibility and toughness, can withstand large displacement and bending deformation, so in the equipment needs a larger expansion and contraction space or require a better sealing performance of the occasion to be applied.

    Metal expansion joints and non-metal expansion joints have the following differences:

    1、Different compensation functions：Under the condition of the same external dimensions, the compensation function of non-metallic expansion joints is much larger than that of metallic expansion joints. Especially for the compensation function of transverse displacement, the compensation function of non-metallic expansion joints is almost one order of magnitude larger than that of metal expansion joints.

    2、Differences of compensating resistances：Expansion joints are like elastomers that resist forces after being shrunk or stretched, and metallic expansion joints resist much more than non-metallic ones. This resistance is too great for the system and can break the surrounding equipment.

    3、High temperature and corrosion resistance is different：The material of non-metallic expansion joint not only has good high temperature resistance, but also has acid and alkali resistance. Ordinary carbon structural steel in the 600 ℃ environment its yield limit is equal to zero, the temperature is higher will be oxidised skin. Carbon steel expansion joints are easy to crack in the working process, stainless steel expansion joints in the low temperature environment, low leakage point corrosion will occur, and its cost is also considerable.

    4、Different thermal insulation and energy saving performance：The structure of non-metallic expansion joints has thermal insulation properties in itself. Metal expansion joints, on the other hand, do not have this condition, and in order to keep the heat in, in the outer layer of metal expansion joints, also covered with a layer of insulation.

    5、Different maintenance and replacement intervals：Non-metallic expansion joints require no maintenance during their normal life cycle; non-metallic expansion joints are much easier to replace than metallic expansion joints.

    6、Differences in service life：The service life of expansion joints is closely related to the environmental conditions. Non-metallic expansion joints have better abrasion and corrosion resistance, relatively speaking, under the same conditions, the life of non-metallic expansion joints will be longer than the life of metal expansion joints.

    7、Differences in operating pressure：Thanks to their flexible design and the special materials they are made of, non-metallic expansion joints can withstand higher working pressures.

    8、Different mediums of use：Metallic expansion joints are suitable for liquids, gases and powders. Non-metallic expansion joints can be both gases and liquids.

    Expansion joints as an important piping component, in a variety of industrial piping systems play an important role in understanding the principles and applications of expansion joints to help better select and use expansion joints. Improve the stability and safety of piping system. At the same time, the correct maintenance and repair is to ensure that the expansion joint long-term stable operation of the key.