Shanghai Hongguan Special Alloy Flanges are used in various industrial fields such as petrochemicals, power and heat engineering, municipal water supply and drainage, biomedicine, and marine shipbuilding. Flanges serve as the core detachable connectors for pipelines and process equipment, and play a key role in sealing, pressure bearing, docking disassembly, and equipment maintenance. They are also one of the accessories with a high failure rate in industrial pipeline systems. Many enterprise selection personnel often encounter problems such as flange cracking, seal leakage, medium corrosion failure, low-temperature brittle fracture, etc. The core reason is that the flange adaptation equipment is selected incorrectly and the material selection for working conditions is not up to standard. This article combines the national standard GB, chemical HG, and American standard ASME industry general standards to comprehensively sort out commonly used flange adaptation equipment, subdivide temperature, pressure, and medium three working conditions, and organize the most comprehensive flange material selection specifications to assist engineering procurement, process design, and operation and maintenance personnel in accurate selection.

1、 What industrial equipment are flanges mainly used for? Summary of applicable scenarios across the entire industry

The flange relies on bolt fastening and gasket sealing structure, which is suitable for all industrial equipment that requires detachable docking, segmented maintenance, and external pipeline connection. It covers all scenarios of general civil, heavy industry and chemical, and special high-risk. The equipment classification is as follows:

1. Pipeline conveying equipment (maximum flange usage scenario)

Various types of process transportation pipelines, municipal water supply and heating pipelines, natural gas long-distance pipelines, oil and gas gathering pipelines, refrigerant liquid nitrogen transportation pipelines, plant circulating water pipelines, pipeline segmented docking, branch pipe diversion, and pipeline cut-off positions are all equipped with flat welding and butt welding flanges for connection, which are indispensable connectors for pipeline systems.

2. Fluid power equipment

Centrifugal pumps, multi-stage pumps, oil pumps, corrosion-resistant chemical pumps, Roots blowers, centrifugal compressors, air compressors, and booster inlet and outlet ports are all equipped with customized flange docking pipelines to meet the pressure requirements of fluid inlet and outlet. Low pressure multi-purpose plate flat welding flanges and high-pressure medium specific butt welding flanges are used.

3. Valve self-control equipment

Gate valves, globe valves, butterfly valves, ball valves, check valves, regulating valves, safety valves, flame arresters and other pipeline self-control valves, with integrated forged flanges at both ends of the valve body, suitable for pipeline docking. High grade sealing surface flanges are preferred for valves with flammable and explosive media.

4. Pressure bearing heat exchanger equipment

Industrial boilers, boiler steam drums, tube heat exchangers, plate heat exchangers, reactors, distillation towers, storage tanks, high-pressure reactors, pressure vessels, buffer tanks, equipment manholes, pipe openings, external interfaces, head positions, dedicated pressure vessel flanges, with a pressure rating much higher than that of ordinary pipeline flanges.

5. Specialized supporting equipment for segmented industries

-Power industry: turbine cooling system, power plant main steam pipeline, waste heat recovery equipment, complete sets of desulfurization and denitrification equipment

-Marine shipbuilding industry: ship ballast water system, ship fuel pipeline, offshore platform anti-corrosion pipeline, coastal water intake equipment

-Food and pharmaceutical industry: sterile fermentation tanks, purified water equipment, ingredient pipelines, sterilization units, exclusive sanitary flanges

-Water treatment industry: clean water pump station, reverse osmosis equipment, dosing and anti-corrosion unit, complete set of sewage aeration equipment

2、 Core basis for selecting industrial flanges: Three major working conditions determine the flange material

There are many types of flange materials on the market, and there is no universal flange. The core principle of industry selection is the trinity selection of design temperature, nominal pressure, and medium properties. Temperature determines toughness, pressure determines wall thickness strength, and medium determines corrosion resistance. The material requirements are classified according to working conditions and adapted to on-site construction and drawing design standards.

（1） Divided by operating temperature: material requirements for flanges under high and low temperature conditions

Temperature is the top priority for flange selection, with low temperature anti brittle fracture and high temperature creep resistance. It is strictly prohibited to mix high and low temperature conditions with ordinary carbon steel

1. Low temperature conditions (medium temperature<-20 ℃): Suitable for LNG liquefied natural gas, liquid ammonia, liquid nitrogen, and refrigerant low-temperature storage tank pipelines. Recommended materials: A350 LF2 low-temperature carbon steel, 304 stainless steel, 316L stainless steel, aviation aluminum alloy; Working condition requirements: Excellent low-temperature impact toughness, Q235 and ordinary A105 carbon steel are prohibited from use to avoid direct cracking at low temperatures.

2. Normal temperature condition (medium temperature -20 ℃~200 ℃): Suitable for general civilian conditions such as tap water, normal temperature air, ordinary oil products, and normal temperature inert gases. Recommended materials: Low pressure economical Q235 carbon steel, industrial general A105 forged carbon steel; Suitable for pressure PN10-PN16 and Class150 low-pressure systems, with the highest cost-effectiveness.

3. Medium high temperature conditions (medium temperature 200 ℃~450 ℃): Suitable for saturated steam, heat transfer oil, high-temperature circulating water, and medium temperature process media in the factory area. Recommended materials: 15CrMo chromium molybdenum steel, F11 heat-resistant alloy steel, 321 heat-resistant stainless steel; Requirements for working conditions: high temperature strength stability, resistance to high temperature oxidation, and resistance to deformation and creep, suitable for Class300-Class600 medium voltage systems.

4. Ultra high temperature conditions (medium temperature>450 ℃): Suitable for high temperature pipelines of power plant main steam, hydrocracking units, and industrial kilns. Recommended materials: F22, F91 high chromium molybdenum heat-resistant steel, 310S high temperature resistant stainless steel, nickel based alloy; Suitable for high-pressure and high-temperature coupled harsh working conditions, long-term high temperature resistance without deformation, and hydrogen corrosion resistance.

（2） Classification by pressure rating: material requirements for flanges under high and low pressure conditions

The higher the pressure, the higher the requirements for flange forging density and material purity. For high pressure, forging materials must be selected to prevent plate rolling of flanges

1. Low pressure operating conditions (PN ≤ 10/Class150): municipal water supply and drainage, ventilation and dust removal, atmospheric pressure water storage equipment. Material: Q235 plate carbon steel, ordinary A105 carbon steel, matched with plate flat welding flange can meet the needs of use.

2. Medium pressure operating conditions (PN16~40/Class300~600): docking of chemical conventional process pipelines, plant steam pipeline networks, and oil pump units. Material: forged A105 carbon steel, 15CrMo heat-resistant steel, 304/316 stainless steel, standard with neck welding flange, stronger sealing stability.

3. High pressure conditions (PN ≥ 64/Class900 and above): chemical high-pressure reactors, hydrogenation units, and high-pressure oil pipelines in oil fields. Material: F22 alloy steel, F91 heat-resistant steel, 2205 duplex steel, Hastelloy alloy. The flange adopts RTJ sealing style with ring connection surface, and the pressure sealing performance is fully stretched.

（3） Classified by corrosiveness of the medium: Requirements for flange materials for special media such as acid, alkali, and salt

Corrosion of the medium is the main cause of flange perforation leakage, and it is necessary to upgrade the anti-corrosion materials for chloride ions, acid and alkali, and hydrogen sulfide media

1. Non corrosive clean media: water, steam, dry air, inert gas. Preferred A105 carbon steel, with low cost and mechanical performance standards, is the preferred material for industrial use.

2. Weak corrosive media: coastal freshwater, mild weak acid, food processing media. Preferred 304 food grade stainless steel, with mirror polished flange end faces to meet sanitary sealing standards.

3. Medium strong corrosive media: high chlorine environment in seawater, diluted acid-base, and chemical saline wastewater. Preferred 316L low-carbon stainless steel and 2205 duplex steel, resistant to chloride ion pitting corrosion, with a service life 2-3 times longer than ordinary stainless steel.

4. Strong corrosive and high-risk media: toxic media such as concentrated strong acids, strong bases, hydrogen sulfide, chlorine gas, and phosgene. Preferred special materials include 2507 super duplex steel, Hastelloy alloy, and titanium alloy; Additional requirements: The flange should be equipped with anti-corrosion PTFE gaskets, and the pressure level of flammable and explosive media should be manually upgraded to 1-2 levels.

3、 Comparison table of commonly used flange material parameters in industry (directly applicable to engineering)

4、 Summary of flange operating condition selection and key points for avoiding pitfalls

1. Selection priority: Temperature>Pressure>Medium. Ordinary carbon steel is not selected for low temperature, ordinary stainless steel is not selected for high temperature, and carbon steel is selected for corrosive medium without cost savings;

2. Equipment adaptation points: Select flat welding flanges for atmospheric pressure pipelines, welding flanges for high-pressure vessels/boilers, and RTJ ring sealing flanges for toxic, flammable, and explosive media;

3. Standard adaptation: Domestic engineering prioritizes HG/T chemical flanges and GB national standard flanges, while foreign trade heavy industry equipment is adapted to ASME American standard flanges to avoid size docking errors;

4. Operation and maintenance reminder: The flange material of the same pipeline must match the material of the pipe and valve body to prevent electrochemical corrosion of dissimilar metals and extend the service life of the entire equipment.

Core keywords of this article:

Equipment suitable for flanges, material selection for flange operating conditions, carbon steel flange operating conditions, medium suitable for stainless steel flanges, high-pressure flange material, low-temperature flange selection, chemical flange selection standards