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What is a gasket?

2024-01-10

A gasket is a material made of paper, rubber or copper that is placed between two flat surfaces to strengthen the seal. It is a sealing element placed between the static sealing surfaces to prevent fluid leakage.

A gasket is a mechanical seal between two objects. It is usually used to prevent leakage from pressure, corrosion, and natural expansion and contraction of the pipeline between the two objects. Since machined surfaces are never perfect, irregularities can be filled in using shims. Gaskets are typically made from sheet materials such as paper, rubber, silicone, metal, cork, felt, neoprene, nitrile, fiberglass, or plastic polymers (such as Teflon).

Gasket-Sealing Gasket Installation Requirements:

① The sealing surfaces of the gasket and flange should be clean, and there should be no scratches, spots or other defects that affect the sealing performance of the connection.

② The outer diameter of the sealing gasket should be smaller than the outside of the flange sealing surface, and the inner diameter of the sealing gasket should be slightly larger than the inner diameter of the pipe. The difference between the two inner diameters is generally 2 times the thickness of the sealing gasket to ensure that after compression, the inner diameter of the sealing gasket The edge shall not extend into the container or pipe, so as not to interfere with the flow of fluid in the container or pipe.

③ The pretightening force of the sealing gasket should not exceed the design requirements to prevent the sealing gasket from being over-compressed and losing its rebound ability.

④ When tightening the gasket, it is best to use a torque wrench. For large bolts and high-strength bolts, it is best to use hydraulic tighteners. The tightening torque should be calculated based on the given sealing gasket compression, and the oil pressure of the hydraulic tightener should also be determined through calculation.

⑤ When installing the sealing gasket, tighten the nuts in sequence. But it should not be tightened once to reach the design value. Generally, it should be cycled at least 2 to 3 times so that the stress of the sealing gasket is evenly distributed.

⑥ For pressure vessels and pipelines with flammable and explosive media, safety tools should be used when replacing sealing gaskets to avoid sparks from the tools colliding with flanges or bolts, resulting in fire or explosion accidents.

⑦ If there is leakage in the pipeline, it must be depressurized before replacing or adjusting and installing the sealing gasket. Operation under pressure is strictly prohibited.

Gasket application scope:

The choice of gasket material mainly depends on the following three factors: temperature, pressure, and medium.

1. Metal gasket material

① Carbon steel:

It is recommended that the maximum operating temperature does not exceed 538°C, especially when the medium is oxidizing. High-quality thin carbon steel plates are also not suitable for use in equipment that manufactures inorganic acids, neutral or acidic salt solutions. If carbon steel is subjected to excessive stress, the accident rate of equipment used in hot water conditions will be very high. Carbon steel gaskets are commonly used in high concentration acids and many alkaline solutions. Brinell hardness is about 120.

② 304

Stainless steel 18-8 (chromium 18-20%, nickel 8-10%), the recommended maximum working temperature does not exceed 760°C. In the temperature range of -196~538℃, stress corrosion and grain boundary corrosion are prone to occur. Brinell hardness is about 160.

③ 304L

The carbon content of stainless steel does not exceed 0.03%. The recommended maximum operating temperature does not exceed 760°C. Corrosion resistance is similar to 304 stainless steel. The low carbon content reduces the precipitation of carbon from the crystal lattice, and its grain boundary corrosion resistance is higher than that of 304 stainless steel. Brinell hardness is about 140.

④ 316

Stainless steel 18-12 (18% chromium, 12% nickel), about 2% molybdenum is added to 304 stainless steel. When the temperature increases, its strength and corrosion resistance improve. When the temperature increases, it has higher creep resistance than other ordinary stainless steels. The recommended maximum operating temperature does not exceed 760°C. Brinell hardness is about 160.

⑤ 316L

It is recommended that the maximum continuous working temperature of stainless steel does not exceed 760℃~815℃. The carbon content does not exceed that of 316 stainless steel, which has better resistance to stress and grain boundary corrosion. Brinell hardness is about 140.

⑥ 20 alloy 45% iron, 24% nickel, 20% chromium and a small amount of molybdenum and copper. It is recommended that the maximum operating temperature does not exceed 760℃~815℃. Especially suitable for manufacturing equipment resistant to sulfuric acid corrosion, with a Brinell hardness of about 160.

2. Non-metallic gasket materials

① Natural rubber NR has good corrosion resistance to weak acids and alkalis, salts and chloride solutions, but poor corrosion resistance to oil and solvents, and is not recommended for use in ozone media. Recommended operating temperature -57℃~93℃.

② Chloroprene rubber CR Chloroprene rubber is a kind of synthetic rubber that is suitable for corrosion resistance to moderately corrosive acid, alkali and salt solutions. Good corrosion resistance to commercial oils and fuels. However, its corrosion resistance is poor in strongly oxidizing acids, aromatic hydrocarbons and chlorinated hydrocarbons. Recommended operating temperature -51℃~121℃.

③ Cyanide butadiene rubber NBR is a synthetic rubber that has good corrosion resistance to oil, solvents, aromatic hydrocarbons, alkaline hydrocarbons, oil and natural gas in a wide temperature range. Good corrosion resistance to hydroxides, salts and nearly neutral acids. However, its corrosion resistance is poor in strongly oxidizing media, chlorinated hydrocarbons, ketones and lipids. The recommended operating temperature is 51℃~121℃.

④ PTFE combines the advantages of most plastic gasket materials, including temperature resistance from -95°C to 232°C. In addition to free fluorine and alkali metals, it has excellent corrosion resistance to chemicals, solvents, hydroxides and acids. PTFE material can be filled with glass, its purpose is to reduce the cold flow and creep properties of PTFE.

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