The selection of material for the three-pass stopper shall be based on specific working conditions. The commonly used materials for valve body and housing (if there is a separate casing structure) can be summarized as follows:
1.Valve body material Stainless Steel Series
304 Stainless Steel: suitable for conventional industrial environment and weakly corrosive media (e.g. water, oil, room temperature solution), low cost, corrosion resistance to meet basic requirements.
316L Stainless Steel: contains molybdenum, has excellent acid, alkali and salt fog resistance, and is suitable for highly corrosive environments (e.g. seawater, acidic oil, pharmaceuticals) and areas with high cleanliness requirements (e.g. food, pharmaceuticals). Its surface electrolytic polishing accuracy is up to Ra ≤ 0.2 μm (high-end models), meeting FDA and cGMP standards.
Fluorinated stainless steel steel: Apply a layer of teflon or polyaniline to the stainless steel body. It can withstand almost all highly corrosive media (except molten alkali metals and fluorine gas) and is suitable for the transport of concentrated acids and alkalis (e.g. in chemical reaction vessels).
Carbon steel Series
ASTM A216 WCB carbon steel: Suitable for low pressure non-corrosive situations (e.g. tap water, compressed air), low cost but low corrosion resistance. Contact with corrosive agents should be avoided.
Alloy Steel Series
Under high temperature and high pressure conditions (e.g. steam, hot oil), abrasion resistance and high temperature resistance are improved by welding hard materials such as tungsten chromium and cobalt alloys, but the choice depends on the specific composition of the medium.
II. Tubing (if there is a separate tube structure)
Same as the valve body
In most designs, piping may be part of the internal structure of the valve body. The material is the same as the valve body (e.g. 304/316L stainless steel), ensuring that the thermal expansion coefficient matches, avoiding distortion or leakage due to temperature differences.
Special material tubing
Fluorine-coated tubing: If a separate tubing structure is required and the medium is a highly corrosive liquid, fluoride plating (PTFE/PFA) may be used and incorporated into the stainless steel valve body to balance corrosion resistance and structural strength.
Carbon steel tubing: In the case of low pressure without corrosion, carbon steel tubing may be used to reduce costs, but the corrosion of the medium must be ensured.
III. Core principles of Material Selection
Corrosion Resistance: Materials are selected according to the composition of the medium (e.g. pH, chlorine content) such as 316L stainless steel resistant to seawater corrosion and fluorine-lined materials resistant to concentrated acids and alkalis.
Temperature resistance: For high temperature conditions (e.g. steam), metal seals (stainless steel to stainless steel) should be selected, with a temperature resistance of up to 300°C, and soft seal materials (e.g. PTFE) with a maximum temperature resistance of 260°C.
Hygiene Standards: Food and pharmaceutical industries should use 316L stainless steel + PTFE/silicone rubber seals with a a surface polishing accuracy ≤ 0.4 micron, in accordance with FDA, EU 10/2011 standards.
