Corrosion resistance of common valve materials_ Teflon

Polytetrafluoroethylene (Teflon or PTFE), commonly known as “plastic king”, is a polymer compound made of polytetrafluoroethylene by polymerization

butterfly valve

Except for molten alkali metal, PTFE is hardly corroded by any chemical reagent. For example, when it is boiled in concentrated sulfuric acid, nitric acid, hydrochloric acid or even aqua regia, its weight and properties remain unchanged, and it is almost insoluble in all solvents, only slightly soluble in total alkanes (about 0.1g/100g) above 300 ℃. Polytetrafluoroethylene is non hygroscopic, non combustible, extremely stable to oxygen and ultraviolet, so it has excellent weather resistance.

Polytetrafluoroethylene (PTFE) is widely used as the material of valve seat, which is used in all kinds of working conditions requiring acid-base resistance and corrosion resistance. Polytetrafluoroethylene is wound on a rubber ring and fixed in the groove of the separate valve body. After the valve is opened, its rubber core will produce resilience, so that polytetrafluoroethylene can slowly return to the required position, so that it can be cut off tightly in the next closing. This structure can seal 720 psi (50 bar) differential pressure after opening 100000 times.

The rubber O-ring is isolated from the fluid in the pipeline. The seal can automatically compensate for wear and thermal changes. An offset valve plate with cam function reduces torque and seal wear.

Other structures include a PTFE “sliding seal” which is placed on top of an elastic rubber O-ring. This structure has successfully operated up to 1500 psi (103 bar) differential pressure. The valve seat clamped between the valve body and ring is fixed by the pipeline flange. Combined with glass fiber filled PTFE seat with lip and sealing function, it allows thousands of bubbles to close tightly. For smaller diameter valves, this material is used, and the operating temperature range is – 320 ℃ ° To 500 ° F. The differential pressure is 720 psi. Special dry lubricated metal seats operate up to 700 ° F。 The eccentric disc and offset shaft structure make the disc lift away from the seat within a few degrees of initial rotation, which eliminates the unbalanced load and thus prolongs the service life of the seat. This form of valve has a 30 inch diameter range.

 

 


Post time: Jun-24-2021

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