Common materials and usage conditions of valve seals
Commonly used materials and their usage conditions are as follows:
Synthetic rubber
The comprehensive properties of synthetic rubber such as oil resistance, temperature resistance, and corrosion resistance are better than those of natural rubber. Generally, the operating temperature of synthetic rubber is t ≤ 150°C, and that of natural rubber t ≤ 60°C. The rubber is used for sealing of stop valves, gate valves, diaphragm valves, butterfly valves, check valves, pinch valves and other valves with a nominal pressure PN ≤ 1MPa.
Nylon
Nylon has the characteristics of small friction coefficient and good corrosion resistance. Nylon is mostly used in ball valves, stop valves, etc. with a temperature t ≤ 90°C and a nominal pressure PN ≤ 32MPa.
Polytetrafluoroethylene
PTFE is mostly used in stop valves, gate valves, ball valves, etc. with a temperature t ≤ 232°C and a nominal pressure PN ≤ 6.4MPa.
Cast iron
Cast iron is used for gate valves, globe valves, plug valves, etc. with temperature t ≤ 100°C, nominal pressure PN ≤ 1.6MPa, gas and oil.
Babbitt alloy
Babbitt alloy is used for ammonia stop valves with temperature t -70~150℃ and nominal pressure PN ≤ 2.5MPa.
Copper alloy
Commonly used copper alloy materials include 6-6-3 tin bronze and 58-2-2 manganese brass. Copper alloy has good wear resistance and is suitable for water and steam with temperature t ≤ 200°C and nominal pressure PN ≤ 1.6MPa. It is often used in gate valves, globe valves, check valves, plug valves, etc.
Chromium stainless steel
Commonly used grades of chromium stainless steel include 2Cr13 and 3Cr13, which have good corrosion resistance after quenching and tempering treatment. It is commonly used in valves for media such as water, steam and petroleum with a temperature t ≤ 450°C and a nominal pressure PN ≤ 32MPa.
Chromium nickel titanium stainless steel
The commonly used grade of chromium-nickel-titanium stainless steel is 1Cr18Ni9ti, which has good corrosion resistance, erosion resistance and heat resistance. It is suitable for steam, nitric acid and other media with a temperature t ≤ 600℃ and a nominal pressure PN ≤ 6.4MPa, and is used for stop valves, ball valves, etc.
What are the causes of static sealing surface damage?
The sealing pair does not produce relative movement but is in a relatively static state, which is called a static seal, and the surface of the seal is called a static sealing surface.
The reasons for damage to the static sealing surface are summarized as follows:
① The surface roughness of the static sealing surface is relatively high, mainly due to long use time, media erosion, and poor maintenance.
② There are obvious indentations on the static sealing surface, which is mainly caused by the hardness of the gasket being selected to be too high or the gasket being mixed with sand, welding flash, etc.
③ There are scratches and scratches on the static sealing surface, which are mainly caused by violations of operating procedures and improper force during disassembly and cleaning.
④ The static sealing surface is severely corroded, mainly caused by corrosion of the medium and improper selection of valves.
⑤ There are obvious grooves on the static sealing surface, which is mainly the result of medium erosion due to failure to repair the static sealing surface in time after leakage occurred.
⑥ Deformation of the static sealing surface is mainly caused by insufficient stiffness, excessive connection force, and thermal creep at high temperatures.
⑦ There are leak holes on the static sealing surface, which are mainly caused by defects such as wrinkles, pores, and ballast caused by poor manufacturing quality.
⑧ Cracks on the static sealing surface are mainly caused by unreasonable design, poor manufacturing quality, improper installation or operation, and long-term exposure to alternating loads.
Damage to the static sealing surface is one of the main causes of valve leakage and should be taken seriously.
