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The selection of flange materials requires comprehensive consideration of a number of factors, the following are some of the main selection criteria:
Working medium: different mediums have different corrosion and compatibility requirements for flange materials. For example, when conveying seawater, salt water and other corrosive media, materials with good corrosion resistance should be selected, such as copper-nickel alloy, stainless steel, etc.; for pipelines conveying food, pharmaceuticals and other media, it is necessary to select materials that meet the hygiene standards, such as 316L stainless steel, in order to ensure that the medium is not contaminated.
Working temperature: according to the temperature of the medium in the pipeline to choose the appropriate material. High-temperature environment requires materials with good thermal stability and high-temperature strength, such as chromium-molybdenum alloy steel, nickel-based alloys, etc., which can be used for high-temperature steam piping, etc.; low-temperature environment requires the material to have a good low-temperature toughness, such as cryogenic steel, austenitic stainless steel, etc., in order to prevent the flange from brittle fracture at low temperatures.
Working Pressure: Piping systems with higher pressure need to choose materials with high strength to withstand the pressure. For example, carbon steel flanges are generally suitable for low and medium pressure pipelines, while in high pressure pipeline systems, alloy steel or stainless steel flanges may need to be selected to ensure the safety and sealing of the flanges under high pressure.
Corrosion resistance: In addition to considering the corrosiveness of the medium, it is also necessary to consider the corrosive influence of environmental factors on the flange. In humid environment or places with corrosive gases such as acid and alkali, materials with good atmospheric corrosion resistance should be selected. Such as industrial pipelines in coastal areas, because the air contains salt, stainless steel flanges are more resistant to corrosion than carbon steel flanges.
Mechanical properties: the material should have sufficient strength, toughness, hardness and other mechanical properties to meet the installation, operation and maintenance requirements of the piping system. High-strength materials can withstand greater external forces and pressures, while materials with good toughness can avoid fracture under shock or vibration conditions. For example, in some piping systems with vibration, it is necessary to choose stainless steel or alloy steel flanges with good toughness.
Processing performance: the processing performance of the material directly affects the manufacturing process and cost of the flange. Materials that are easy to process can reduce processing difficulty and cost, and improve production efficiency. For example, the processing performance of carbon steel is good, easy to forge, welding and machining, while some high-strength alloy steel or nickel-based alloys are more difficult to process, requiring special processing technology and equipment.
Economy: under the premise of meeting the use requirements, the cost of materials is also an important consideration. The price of different materials varies greatly, such as the price of stainless steel flanges is generally higher than that of carbon steel flanges, while the price of nickel-based alloy flanges is even higher. Therefore, it is necessary to choose the appropriate material according to the budget and actual needs of the project, and try to reduce the cost under the premise of ensuring quality and safety.
Standards and norms: The selection of flange materials also needs to comply with relevant standards and norms requirements, such as national standards, industry standards and international standards. For example, in the petrochemical industry, it is usually necessary to follow ASME, API and other standards to select flange materials to ensure that the quality and performance of the flange meet the industry requirements.
Connection method: Different flange connection methods have different material requirements. For example, socket weld flanges are suitable for small-diameter pipelines, which require high weldability of materials; while butt-welding flanges are suitable for high-pressure and high-temperature pipelines, which require materials with good welding performance and strength. Therefore, it is necessary to choose the appropriate material according to the specific connection method.
Service life: Considering the expected service life of the pipeline system, choose the material that can maintain stable performance within the specified time. For some important pipelines in long-term operation, such as the piping system of nuclear power plants, it is necessary to choose high-performance, corrosion-resistant and aging-resistant materials to ensure the safety and reliability of the flanges in the process of long-term use.