Material selection of ultra-low temperature valve: valve body: ferritic stainless steel can be selected when the temperature is higher than - 100 ℃, austenitic stainless steel can be selected when the temperature is lower than - 100 ℃, and copper alloy or aluminum alloy can be selected for low pressure and small caliber valves. Valve rod: It is made of austenitic stainless acid resistant steel, and needs to be properly heat treated to improve the tensile strength. At the same time, it must be plated with hard chromium (coating thickness 0.04~0.06mm), or nitrided to improve the surface hardness. Gasket: when the service temperature is higher than - 196 ℃ and the maximum service pressure at low temperature is 3MPa, the asbestos rubber plate made of long fiber from asbestos can be used; When the service temperature is higher than - 196 ℃ and the maximum service pressure at low temperature is 5MPa, stainless steel with asbestos spiral wound gasket, stainless steel with PTFE spiral wound gasket or stainless steel with expanded graphite spiral wound gasket can be used. Fastener: when the temperature is higher than - 100 ℃, the bolt material shall be alloy steel such as Ni, Cr Mo, etc., which shall be subject to appropriate heat treatment to prevent thread bite; When the temperature is lower than - 100 ℃, the bolt material can be austenitic stainless steel. The nut is generally made of Mo steel or Ni steel, and the thread gauge is coated with a disulfide key.

Technical plan
According to the application request of non-metallic compensator, we put forward the corresponding technical plan.
Considering that the flue environment of FGD project is bad, the medium contains various acidic substances, such as SO2, SO3, HCl and HF, which are highly corrosive to nonmetals. At the same time, there is a certain amount of fly ash and scouring. In addition, considering the temperature, pressure and product size, we have made the following plans in terms of material selection and structural design.