Blind Flange

Blind flange, also known as blank flange, is an indispensable pipe closure component in industrial piping networks. Unlike connecting flanges such as weld neck flange and slip on flange, it features no central bore and serves to seal pipeline terminals, isolate branch pipelines or block certain sections of piping systems. Installed between two flanges with gaskets and bolts, blind flanges enable convenient temporary shutdown, equipment maintenance and pipeline testing without cutting the whole piping circuit. Owing to reliable sealing performance and flexible operability, blind flanges are widely applied in various industrial fluid transportation projects as critical isolation fittings.

Blind flanges are manufactured in compliance with international authoritative standards, mainly ASME B16.5, ASME B16.47 and GB/T 9113. A comprehensive range of material grades can be supplied to match diverse working conditions. A105 carbon steel blind flanges possess outstanding cost advantages and stable mechanical properties, widely used for pipelines conveying water, steam, fuel oil and compressed air. Stainless steel blind flanges in grade F304 and F316L deliver excellent corrosion resistance, suitable for pharmaceutical, food and chemical pipelines with corrosive media and strict hygiene requirements. Alloy steel blind flanges including A182 F11, F22 and F91 are specially produced for high-temperature, high-pressure working environments in thermal power plants, oil refineries and coal chemical facilities. Multiple pressure classes from Class 150 to Class 2500 are available. The most common sealing surface type is raised face (RF); ring type joint (RTJ) blind flanges are selected for ultra-high pressure critical service.

Hot forging is the primary forming process for blind flanges. Qualified steel billets are heated and forged into solid circular blanks. Subsequent precision machining processes involve processing sealing surfaces and drilling standard bolt holes according to dimension drawings. Heat treatment including normalizing and tempering is carried out to eliminate internal forging stress and optimize metal grain structure. Each finished blind flange undergoes strict quality inspection procedures, covering dimensional tolerance measurement, hardness testing, visual surface inspection and non-destructive testing. These inspection items effectively detect hidden defects such as cracks, laminations and inclusions to ensure safety under long-term pressure load.

The core function and prominent merit of blind flanges lie in flexible pipeline isolation and reliable sealing. When maintenance, cleaning or pressure testing is required for downstream equipment, installing blind flanges can completely cut off medium circulation, avoiding the risk of medium leakage. Compared with valves used for isolation, blind flanges achieve absolute shut-off effect. Valves may suffer internal leakage after long-term operation, while solid blind flanges provide more secure isolation for hazardous, flammable and toxic media. Besides, blind flanges can be removed and reused repeatedly, helping enterprises lower engineering operation costs.

Engineers should also notice relevant limitations during application. Blind flanges bear continuous static pressure load inside the pipeline. Improper thickness selection will lead to plate deformation and medium leakage. Therefore, designers must confirm pressure class and nominal size strictly in accordance with design specifications. In addition, construction teams need to mark installed blind flanges clearly to prevent accidental retention after maintenance, which may cause pipeline blockage and production failure.

Blind flanges cover extensive application fields. They are widely adopted in petrochemical plants, natural gas stations, thermal power generating units, municipal water supply networks, fire protection systems, seawater desalination equipment and storage tank piping. Stainless steel blind flanges are preferred for purified water and biochemical production lines. Carbon steel blind flanges dominate conventional industrial and municipal projects. Alloy steel blind flanges undertake isolation tasks for high-temperature steam and high-pressure process pipelines.

In pipeline system design and daily maintenance, blind flanges play an irreplaceable isolation role. Proper specification selection and standardized installation greatly improve the safety of pipeline overhaul. With complete specifications and mature forging production technology, high-quality blind flanges provide stable and absolute sealing solutions. As an essential supporting flange product, blind flanges guarantee controllable and safe operation of fluid conveying infrastructure across all types of global industries.