pressure balance plug valve|Can you tell the material of these valves?
01 Jan

pressure balance plug valve|Can you tell the material of these valves?

Many valves can adapt to a variety of working conditions, but if the valve material is unreasonably selected, the performance and service life of the valve will be greatly reduced. First of all, choose according to the scope of use of various valve materials, in order to make it play the best performance.

Material of valve body, bonnet and disc
The valve body, bonnet and disc are the main parts of the valve, which directly bear the pressure of the medium. The materials used must meet the requirements of "valve pressure and temperature grade".
The commonly used materials are as follows:
grey cast iron
Gray cast iron is suitable for water, steam, air, gas, oil and other media with a nominal pressure of PN≤1.0MPa and a temperature of -10℃~200℃.

Malleable cast iron
It is suitable for water, steam, air and oil medium with nominal pressure PN≤2.5MPa and temperature -30~300℃.

Ductile iron
It is suitable for water, steam, air, oil and other media with PN≤4.0MPa and temperature of -30~350℃.

Acid-resistant high-silicon ductile iron
It is suitable for corrosive media with nominal pressure PN≤0.25MPa and temperature lower than 120℃.

Carbon steel
It is suitable for water, steam, air, hydrogen, ammonia, nitrogen and petroleum products with a nominal pressure of PN≤32.0MPa and a temperature of -30~425℃.

Copper alloy
It is suitable for water, sea water, oxygen, air, oil and other media with PN≤2.5MPa, and steam media with a temperature of -40~250℃.

High temperature copper
It is suitable for steam and petroleum products with nominal pressure PN≤17.0MPA and temperature≤570℃.

Low temperature steel
It is suitable for media with nominal pressure PN≤6.4Mpa, temperature≥—196℃ ethylene, propylene, liquid natural gas, liquid nitrogen and so on.

Stainless acid-resistant steel
It is suitable for nitric acid, acetic acid and other media with nominal pressure PN≤6.4Mpa and temperature≤200℃.

Sealing surface material
The sealing surface is the most critical working surface of the valve, and the quality of the sealing surface is related to the service life of the valve. Generally, the sealing surface material should consider factors such as corrosion resistance, scratch resistance, erosion resistance, and oxidation resistance.

Soft material
Rubber (including nitrile rubber, fluorine rubber, etc.)
Plastics (PTFE, nylon, etc.)

Hard sealing material
Copper alloy (for low pressure valves)
Chrome stainless steel (used for ordinary high and medium pressure valves)
Stellite alloy (used for high temperature and high pressure valves and strong corrosion valves)
Nickel-based alloy (for corrosive media)

Stem material
During the opening and closing of the valve, the valve stem bears the forces of tension, compression and torsion, and is in direct contact with the medium. At the same time, there is relative frictional movement with the packing.
Therefore, the valve stem material must ensure sufficient strength and impact toughness at the specified temperature, a certain degree of corrosion resistance and scratch resistance, and good manufacturability.
Carbon steel
When used in water and steam medium with low pressure and medium temperature not exceeding 300℃, A5 ordinary carbon steel is generally used.
When used in water and steam medium with medium pressure and medium temperature not exceeding 450℃, 35 high-quality carbon steel is generally used.

alloy steel
40Cr (chrome steel) is generally used when it is used for medium pressure and high pressure, and the medium temperature does not exceed 450 ℃ in water, steam, petroleum and other media.
38CrMoALA nitriding steel can be used when it is used in water, steam and other media with high pressure and medium temperature not exceeding 540℃.
25Cr2MoVA chromium molybdenum vanadium steel is generally used when used in high pressure steam medium with medium temperature not exceeding 570℃.

Stainless acid-resistant steel
It is used for non-corrosive and weakly corrosive media with medium pressure and high pressure, and the medium temperature does not exceed 450°C. 1Cr13, 2Cr13, 3Cr13 chromium stainless steel can be selected.
When used in corrosive media, stainless acid-resistant steel such as Cr17Ni2, 1Cr18Ni9Ti, Cr18Ni12Mo2Ti, Cr18Ni12Mo3Ti, and PH15-7Mo precipitation hardening steel can be selected.

Heat-resistant steel
When used for high-temperature valves whose medium temperature does not exceed 600℃, 4Cr10Si2Mo martensitic heat-resistant steel and 4Cr14Ni14W2Mo austenitic heat-resistant steel can be selected.

Stem nut material
The stem nut directly bears the axial force of the stem during the opening and closing of the valve, so it must have a certain strength.
At the same time, it and the valve stem are threaded transmission, which requires a small friction coefficient, no rust and avoid seizure.
Copper alloy
Copper alloy has a small coefficient of friction and does not rust, and it is one of the commonly used materials at present.
For low pressure valves with Pg<1.6Mpa, ZHMn58-2-2 cast brass can be used.
For Pg16-6.4Mpa medium pressure valve, ZQAL9-4 Wuxi bronze can be used.
For high pressure valves, ZHAL66-6-3-2 cast brass can be used.

steel
When working conditions do not allow the use of copper alloys, high-quality carbon steels such as 35 and 40 can be selected, and stainless acid-resistant steels such as 2Cr13, 1Cr18Ni9, and Cr17Ni2 can be used.
Working conditions are not allowed to refer to the following situations.
For electric valves, stem nuts with melon clutches require heat treatment to obtain high hardness or surface hardness.
The working medium is corrosive to copper. When selecting steel stem nuts, pay special attention to the phenomenon of thread seizure.

Filler material
On the valve, the packing is used to fill the space of the packing chamber of the valve cover to prevent the medium from leaking through the valve stem and the space of the packing chamber of the valve cover.
Soft filler
Plant-based fillers are cheaper and are often used in low-pressure valves below 100°C.
Mineral packing can be used for valves at 450-500°C.
The temperature of the packing medium of rubber O-rings is generally limited to below 60°C.
The packing on the high temperature and high pressure valve is also compacted with pure asbestos and flake graphite powder.

Hard filler
Strings woven from plant matter, namely hemp, flax, cotton, jute, etc., or minerals, namely asbestos fiber, or asbestos fiber woven with metal wire inside and coated with graphite powder, etc., and there are also pressed molded fillers, And the newly developed flexible graphite filler materials in recent years.