Blind Flange

Blind flange is a type of plate flange used to seal the end of a pipeline, without a central through-hole, and is fully sealed by connecting it to the pipeline flange with bolts. It is widely used in pipeline systems that require temporary or permanent isolation of medium flow. Its structure is simple yet crucial, effectively blocking medium leakage and ensuring equipment maintenance safety.

Structure and Characteristics

Blind flange is usually a circular flat plate structure with a thickness much greater than that of ordinary flanges (such as Class 150 blind flanges with a thickness about twice that of welded flanges of the same specification), with evenly distributed bolt holes at the edges that perfectly match the bolt holes of the matching flange. There are various forms of sealing surfaces, including flat (FF), protruding (RF), concave convex (MFM), etc., which are suitable for metal or non-metal gaskets (such as wrapped gaskets, rubber gaskets), and achieve absolute sealing through bolt pre tightening force.

The material should be selected according to the characteristics of the pipeline medium: carbon steel (A105) is suitable for room temperature and low pressure systems; Stainless steel (304/316) is used in corrosive environments; Alloy steel pipe (WP22) is suitable for high temperature and high pressure scenarios (such as power plant steam pipelines). Large caliber blind plates (DN1000 and above) are often forged to ensure material density and avoid deformation under high pressure.

Core role

Isolation medium: During pipeline maintenance and equipment upkeep, blind flanges can completely cut off the flow of the medium (such as cutting off the connection between oil and gas pipelines and storage tanks), which is more reliable than valve closure and prevents safety accidents caused by valve leakage.

End sealing: used for terminal closure of pipeline systems (such as unused reserved interfaces) to prevent debris from entering or medium leakage.

Pressure bearing: Blind plates need to withstand the full pressure inside the pipeline, so the thickness increases with the pressure level (such as Class 2500 blind plates with a thickness of over 100mm), ensuring that they do not rupture under high pressure.

Installation and Applicable Scenarios

Attention should be paid during installation:

Gaskets must be installed between the blind plate and the matching flange, and the bolts must be evenly tightened (in diagonal order) to prevent local leakage;

High pressure blind plates need to be equipped with high-strength bolts (such as 8.8 grade, 10.9 grade) and coated with anti seize agents to avoid difficulty in disassembly.

Typical application scenarios include:

Isolation of inlet and outlet of oil storage tanks (blocking oil products during maintenance);

The backup interface of the chemical reaction kettle is sealed;

Temporary sealing of high-pressure steam pipelines (Class 900 and above pressure rating).