Blind Flange Application and Safety Operation Specifications
Publication Date:
Jul 30,2026
Author:
Dacheng Jiaye
Blind flanges, also named blank flanges, are an important category of flange pipe fittings, applied to block pipeline ends
Blind flanges, also named blank flanges, are an important category of flange pipe fittings, applied to block pipeline ends, isolate equipment sections and provide interfaces for pipeline pressure testing. Structurally, blind flanges are solid circular plates with bolt holes matching paired flanges, without central flow holes. Their main functions include temporary pipeline closure during system maintenance, permanent sealing of idle pipeline branches, and forming closed testing sections for hydraulic or air pressure tests. Different pressure grades and material blind flanges correspond to various working conditions. Flat blind flanges are widely used for low-pressure isolation, while spectacle blind flanges integrate blind plate and through plate. Operators can switch pipeline connection status by rotating spectacle blinds without disassembling integral flange connections, which greatly improves operation efficiency for pipelines requiring frequent switching. Spectacle blind flanges are popular in chemical process pipelines. Thickness design of blind flanges follows strict calculation standards. Under internal pipeline pressure, blind flanges bear large bending load. Thin blind plates will produce elastic deformation or even rupture under pressure, leading to serious safety accidents. Therefore, blind flange thickness is usually larger than common welding flanges under identical pressure standards. Safety operation specifications cannot be ignored during blind flange installation and replacement. Before disassembly, operators must cut off medium supply, release pipeline internal pressure and drain residual fluid inside pipelines. Residual pressure is the primary cause of accidental ejection of blind flanges. Operators should stand on the side of flange surfaces instead of facing directly during disassembly to avoid injury caused by sudden medium ejection. Marking identification is strongly recommended for blind flange positions. Operators can hang warning tags to remind maintenance staff about isolated pipeline sections and prevent wrong operation. Many safety accidents occur when workers mistakenly open isolated pipelines with blind flanges. For high-risk medium pipelines, double blind isolation schemes are adopted. Two blind flanges are installed with vent sections in between to guarantee thorough isolation between equipment and pipelines. Blind flanges need regular thickness inspection. Long-term service under pressure causes material fatigue, and medium corrosion reduces effective plate thickness. When thickness is lower than design threshold, blind flanges must be scrapped immediately and cannot continue service. Temporary testing blind flanges and permanent isolation blind flanges should be distinguished clearly. Testing blind plates are only allowed for short-time pressure test usage and cannot be left permanently in pipeline systems. After pressure testing, testing blind flanges should be removed and replaced with standard pipe fittings or permanent sealing blind flanges.
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