Blind Flange
Blind flanges are solid discs used to seal off the end of a pipe, valve, or pressure vessel opening. Unlike other flange types that have a bore for pipe passage, blind flanges are solid plates designed to withstand the full system pressure on one side. They are manufactured to ASME B16.5 with raised face, flat face, or ring-type joint facings, and are available in all standard pressure classes from Class 150 to Class 2500.
Blind flanges are commonly used at pipe ends for future expansion, at vessel manways and handholes, and for hydrostatic test isolation. They allow easy access to piping systems for inspection, cleaning, and maintenance, and can be removed to add future pipe extensions. Our blind flanges are forged with controlled grain flow and undergo 100% ultrasonic testing for material integrity before final machining.
ASME B16.5 / DIN 2527
ASTM A105 / A350 LF2
DN15-DN1200, Class 150-2500
Applications
- Pipe end sealing and blanking
- Vessel and tank manway closures
- Hydrostatic test isolation
- Future expansion tie-in points
- Valve and equipment isolation
Quality Assurance
All Blind Flange products undergo NDT testing with MTC per EN 10204 3.1. Third-party inspection by SGS, BV, TUV available.
Blind Flange Technical Specifications
Blind flanges (BL flanges) are used to seal the end of a piping system, pressure vessel, or valve. They have no center bore and are bolted to a mating flange with a gasket. Blind flanges allow easy access for inspection, cleaning, or future pipe extension.
| Parameter | Specification |
|---|---|
| Standard | ASME B16.5 / DIN 2527 / EN 1092-1 Type 05 / JIS B2220 |
| Size Range | DN15 (1/2") to DN1200 (48") |
| Pressure Class | Class 150, 300, 600, 900, 1500, 2500 |
| Face Type | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ) |
| Thickness | Per ASME B16.5 Table 2 (min. thickness by size and class) |
| Material Grades | ASTM A105, A350 LF2, F304/F316/L, F22, F91 |
| Bolt Holes | Matched to ASME B16.5 bolt pattern (4, 8, 12, 16, 20, 24 holes by size) |
Manufacturing Process
Blind flanges are forged solid with no bore, providing maximum structural integrity for pressure containment:
- Forging: Upset forging of round bar stock creates a solid disc with forged grain flow for maximum pressure resistance.
- Normalizing: Heat treatment at 870-900C to achieve uniform mechanical properties.
- CNC Machining: Precision turning of face, hub (if present), and outer diameter.
- Drilling: CNC drilling of bolt holes with tight tolerance on bolt circle and hole spacing.
- Face Machining: Raised face, flat face, or RTJ groove machining to specified finish.
- NDT: 100% ultrasonic testing for internal defects, magnetic particle on surfaces.
- Hydrotesting: Blind flanges for Class 900 and above may be hydrotested at 1.5x rated pressure.
Applications & Service Conditions
Blind flanges serve critical functions across industries:
- Pipe End Sealing: Temporary or permanent closure of pipe ends during construction or maintenance.
- Pressure Vessel Closures: Manway covers, handhole plates, and inspection ports on vessels.
- Future Expansion Points: Blind flanges installed at tee branches allow easy future connection without system modification.
- Pressure Test Ports: Used as test blanks during hydrostatic testing of piping systems.
- Isolation Points: Used with spectacle blinds or figure-8 blinds for positive isolation during maintenance.
Blind flanges are critical for pressure safety. Our blind flanges are hydrotested and certified to ASME B16.5 dimensional tolerances, with MTC 3.1 certificates documenting material traceability.