High pressure working condition
The high pressure valve can be of different types:
- A valve whose absolute pressure is lower than 1 atmosphere is called a vacuum valve
- Pressure ≤ 1.6MPa is called low pressure valve
- The pressure of 2.5～6.4MPa is called medium pressure valve
- The pressure of 10.0～80.0MPa is called high pressure valve
- Pressure ≥100.0MPa is called ultra-high pressure valve
There are 2 working conditions for high-pressure valves:
1. The medium is at room temperature but the pressure is very high
, such as valves for oil production and water injection in oil field
2. The medium is in a high temperature state and the pressure is also high, such as the main steam system valves used in thermal power plants.
Although, these two types are also “high pressure valves”, the design criteria and material selection are different. The former only considers strength and stiffness, while the latter should also consider the strength and creep of materials at high temperatures.
High pressure valve materials
Pressure-bearing parts and pressure-controlling parts
are divided, according to their functions in the whole valve, into:
1. Pressure-bearing parts: refer to parts designed to withstand pipeline media (pressure), such as valve bodies, valve covers, packing glands, valve stems, gaskets, and bolts
2. Pressure-controlling parts: refer to parts used to block or allow the flow of media, such as closing parts, valve seats, etc.
The shell includes the valve body, valve cover and other parts, which directly bear the pressure of the medium and are the pressure-bearing parts of the valve. The material must have the required mechanical properties and chemical composition under the specified medium, temperature and pressure. The cold and hot processing manufacturability.
Valve stem material
The valve stem is one of the pressure-bearing parts of the valve. During the opening and closing process of the valve, it is subjected to tensile, compressive, shearing and torsional forces, and is in direct contact with the medium. The rod material must ensure sufficient strength and impact toughness under the specified medium, temperature and pressure, and must have the required corrosion resistance and scratch resistance, as well as good manufacturability.
The sealing surface is the key part of the valve. The material used for the sealing surface should be corrosion-resistant, erosion-resistant, scratch-resistant, have sufficient extrusion strength (specific pressure), and have sufficient oxidation resistance and thermal fatigue resistance at high temperatures. It is also required to have a linear expansion coefficient similar to that of the base material, and to have good processing and welding manufacturability. For the sealing surface of high pressure valves, cemented carbide is usually used.
Material of pressure-bearing fasteners
The pressure-bearing fasteners mainly refer to the middle flange connecting bolts and nuts, which directly bear the pressure of the medium on the valve and play a major role in preventing the leakage of the medium. strength and impact toughness.
Referring to the provisions of GB150.2-2011, JB/T 5300-2008, ASME B16.34 and other standards, the commonly used fastener materials for high-pressure valves are:
1. Alloy steel
Chinese standard: GB/T 3077 30CrMoA, 35CrMoA, 40Cr, 25Cr2MoVA, 25Cr2Mo1VA;
American Standards: ASTM A193-B16, ASTM A194.
2. Stainless steel
Chinese standard: GB/T 1220, 2007 2Cr13, 0Cr18Ni9, 0Cr18Ni10Ti, 0Cr17Ni12Mo2, 1Cr17Ni2, 1Cr18Ni9, 1Cr18Ni9Ti;
American Standards: ASTM A193, B8, B8M, ASTM A194, 8, 8M.
Packing and gasket materials
The packing and gasket for the valve are all packing to prevent the leakage of the medium. The packing is used to fill the space between the packing chamber and the valve stem to prevent the medium from leaking through the space between the valve stem and the packing chamber. The gasket is used to fill the two joint surfaces (such as the sealing surface between the valve body and the valve cover) to prevent the leakage of the medium from the joint surface.
Therefore, the requirements for packing materials
are corrosion resistance, good sealing performance and small friction coefficient. The requirements for gasket materials are corrosion resistance, certain elasticity and plasticity and sufficient strength at working temperature.
Xinhui high pressure valve
The high-pressure valves produced by Xinhui Valve Group are designed and manufactured in strict accordance with the standards, with excellent performance and reliable sealing. The products are widely used in pipelines of various working conditions such as petroleum, chemical, pharmaceutical, and electric power industries.
We have been dedicating for years to the world of industrial valves, to companies that produce valves and actuators for industry, in particular in the oil sector, both for the extraction and refining of hydrocarbons and for transport via land or submarine oil pipelines, still in the sector of chemical and petrochemical plants.