Selection of marine gasket (GASKET)
1. Preface In the ship system, the connection between pipes and pipes, pipes and equipment, pipes and accessories requires a large number of gaskets . The correctness of the gasket selection will affect the seal at the connection, and thus affect the function of the entire system. To select the appropriate gasket, you need to know the characteristics of the sealed medium, as well as the pressure, temperature and standards of the connecting flange of the system.
2 Classification of marine gaskets There are many types of marine gaskets, usually divided into three categories according to material and structure:
a. Non-metallic gaskets: rubber ( Dingqing rubber , silicone rubber , fluoroelastomer ), polytetrafluoroethylene , non-asbestos (aramid oil-resistant rubber, fiber-reinforced rubber), cloth rubber and other gaskets
b. metal gaskets : copper , copper corrugated, carbon steel, stainless steel and other gaskets
c. Combination gaskets: metal composite, metal winding and other gaskets
C At present, seal gaskets with non-asbestos fiber as reinforcement material and rubber as elastic matrix are usually called non-asbestos rubber fiber gaskets, or asbestos-free gaskets. In addition, no gasket can fully meet different usage requirements, so the main performance should be selected to meet the requirements of the sealing gasket under this working condition, that is, to meet the main usage requirements; on the other hand, the concentrated gaskets are often suitable for the same use occasion. At this time, in addition to comparing the necessary technical performance indicators, cost factors should also be considered. 1. Things to note when selecting gaskets: Wooden Asbestos is a highly carcinogenic substance recognized by the wood, so when selecting, it is prohibited to use asbestos and its products to correctly select sealing gaskets. The correct selection of sealing gaskets is the key to ensuring that the equipment and the pipelines are leak-free. The gaskets should be reasonably selected according to the physical properties, pressure, temperature, equipment size, operating conditions, and length of continuous operation cycle of the medium. When choosing a gasket, you should fully consider:
1. It has good elasticity and recovery properties, can adapt to pressure changes and temperature fluctuations,
2. It has appropriate softness and can fit well with the contact surface
3. It does not contaminate the medium
4. It has sufficient toughness, and does not cause damage due to pressure and fastening force
5. It does not harden at low temperatures, and the shrinkage is small. 06. Good processing performance, easy installation and compression
7. Non-bonding sealing surface, easy disassembly
8. Cheap price and long service life
. In the use of gaskets, the pressure and temperature are mutually restricted. As the temperature increases, after the equipment is running for a period of time, the gasket material softens, creeps , stress relaxation, the mechanical strength will also decrease, and the sealing pressure will decrease. 2. Characteristics of gaskets Industrial rubber board Natural rubber is suitable for water, seawater, air, inert gas, alkali, salt aqueous solutions and other media, but is not resistant to mineral oil and non-polar solvent . The long-term use temperature does not exceed 90ºC, and has excellent low temperature performance and can be used above -60ºC. Dingqing rubber is suitable for petroleum products, such as petroleum, lubricating oil, fuel oil, etc., with a long-term use temperature of 120ºC. If it can withstand 150ºC in hot oil,
neoprene is suitable for seawater, weak acid, weak alkali, and salt solutions. It has excellent oxygen and ozone oxidation performance and is second only to Dingqing rubber. Due to other rubbers used together, the long-term use temperature is below 90ºC, the maximum service temperature does not exceed 130ºC, and the low temperature is -30~-50ºC.
There are multiple varieties of fluoroelastomer, which has good acid resistance, oxidation resistance, oil and solvent resistance. It can be used in almost all acid media memory for some oils and solvents, and the long-term use temperature is less than 200ºC.
Polytetrafluoroethylene is prone to cold flow and creep under pressure and high temperature, so it is generally used for collateral, Chinese, strong corrosion and media that do not allow contamination, such as strong acids, strong alkalis, halogens, drugs, etc. The safe use temperature is 150ºC, the pressure is below 1Mpa, and the strength of filling polytetrafluoroethylene is slightly higher, but the use temperature does not exceed 200ºC, and the corrosion resistance is reduced. In addition, polytetrafluoroethylene has good low temperature resistance.
Due to the increase in temperature, the material creeps, causing the sealing pressure to drop significantly. Even if the temperature does not rise, the compression force on the sealing surface will decrease over time, resulting in a relaxed pressure. This phenomenon will occur in various gaskets, but the polytetrafluoroethylene gaskets are more serious.The friction coefficient of polytetrafluoroethylene is small, and the gasket is easy to slide outward when pre-tightened, so it is best to use concave and convex flange sides. When using a flat flange, the outer diameter of the gasket can be contacted with the bolts to prevent the gasket from slipping.
Metal wrapping pad utilizes the heat resistance, elasticity and strength of metal and the softness of non-metals, so it has good sealing performance. According to the characteristics of the gasket, during the construction of the ship, the gaskets usually selected by the ship are provided by 
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