The Technology Limitations of the Application of PTFE Liner

Every year, in China, the corrosion of equipment of petroleum, chemicals, pharmaceuticals, pesticides, dyes and other industrial areas  cause  about 400 billion yuan of economic losses and 15 million tons of steel losses.

However, in the reinforced of polyethylene (PE), polypropylene (PP) and polyolefin (PO), poly vinyl fluoride fluoride - six propylene copolymer (F46), soluble polytetrafluoroethylene (PFA), poly three vinyl chloride fluoride (F3), polyvinylidene fluoride (F2 two) for chemical equipment corrosion lining,  there are some limitations: First, the use of temperature is low (less than 120 degrees, more than 100 degrees), easy to cause the lining material become soft and melting, which resulting in sealing  leakage. Second, in the process of corrosive acid, alkali and other media, lining get damaged by corrosion easily . The third is the impact of liquid media become wear and tear, resulting in sealing leakage. Fourth , for complex structure, equipment liner’s molding is difficult. It can get  deformed and delaminated.

Although  PTFE has the best chemical stability and a wide range of temperature resistance, which can stand long-term working temperature from -250 to 260 degree . It shows high corrosion resistance in corrosive acid, alkali, salt, strong oxidant, strong reducing agent, organic solvents and other corrosive medium (except molten alkali metal and element fluorine), is an ideal material of chemical anticorrosion equipment lining, and is much better than other non-metallic materials on corrosion resistance , better than stainless steel, titanium and advanced alloys. It is applied in chemical industries, petruoleum and chemical equipment and accessories. However, the coefficient of thermal expansion of polytetrafluoroethylene material is very high (77 * 10-6~100 * 10-6 DEG C), which is about 10 times that of metallic materials (stainless steel 16.4 * 10-6/ C, carbon steel 11 * 10-6/ DEG C). Moreover, the cold flow property of PTFE (creep) and the defects existing in the PTFE liner molding technology, can not completely make PTFE liner and chemical equipment metal joint tightly. Therefore, there are also limitations in its practical application:

One is in the process of chemical equipment using. The heating and cooling cause the temperature change, resulting in the metal shell and liner non uniform expansion and contraction. Especially under the condition of negative pressure operation, PTFE liner has many defects such as deformation, bulging, wrinkling and delamination, collapse and flattening.

The other is when the lining is flanging and shaped, because there exists stress difference,  flanging and fracture can happen easily, which will result in leakage and corrosion.