Flanges / BL
Blind Flange
Used for line termination, maintenance isolation, and pressure testing.
Technical Specifications
Key Features
- Complete sealing
- Enables pressure testing
- Maintenance isolation
- Reusable
- High pressure capacity
- Easy assembly/disassembly
Applications
- Line termination
- Tank nozzles
- Maintenance covers
- Test points
- Boiler connections
- Future expansion points
Dimension Table
| Nominal Size | Outside Diameter (mm) | Thickness (mm) | Bolt Circle (mm) | No. of Bolts | Bolt Size |
|---|---|---|---|---|---|
| 2" | 152 | 19 | 120.7 | 4 | 5/8" |
| 4" | 229 | 24 | 190.5 | 8 | 5/8" |
| 8" | 343 | 29 | 298.5 | 8 | 3/4" |
| 12" | 483 | 33 | 431.8 | 12 | 7/8" |
| 16" | 597 | 37 | 539.8 | 16 | 1" |
Technical Notes
- 01Thickness varies with pressure class.
- 02High-class blinds can be heavy.
- 03Observe correct bolt torque during assembly.
- 04Gasket selection is critical for sealing.
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Contact UsWhat is a weld neck flange?
A weld neck flange has a long tapered hub that is butt-welded to the pipe. Because the hub transfers stress gradually from flange to pipe, it is the most reliable connection for high pressure, high temperature and cyclic loading. Other main types are slip-on, blind, threaded, socket-weld and lap-joint. Standards: ASME B16.5 (NPS ½–24), ASME B16.47 (large diameter) and EN 1092-1.
Choosing flange type, material and face
Type follows service conditions: weld neck for critical lines; slip-on for economical low-pressure assembly; blind for line ends; threaded where welding is not possible; socket-weld for small bores. Material follows the fluid and temperature: A105 (carbon steel, general purpose), A350 LF2 (low temperature), A182 F304/F316 (stainless), A182 F11/F22 (high temperature). Face types are RF (most common), FF and RTJ (high pressure); the rating is specified as Class 150–2500 or PN6–PN100.
Frequently Asked Questions
Weld neck vs slip-on flange — what is the difference?+
A weld neck is butt-welded and develops full pipe strength — preferred for high pressure/temperature and fatigue. A slip-on slides over the pipe with inner and outer fillet welds: cheaper and easier to align but lower rated.
What is A105?+
ASTM A105 is the forged carbon-steel flange material for ambient and moderate-temperature service — the standard grade for carbon-steel piping.
What does the flange rating (Class/PN) mean?+
Class (150–2500, ASME) and PN (6–100, EN) are pressure-temperature ratings; the allowable pressure derates as temperature rises.
Which standard is used where?+
ASME B16.5/B16.47 dominates North America and oil & gas; EN 1092-1 is common in Europe. Always match the standard and rating of the mating flange.
Related Blog Posts
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Flange Types Guide: The 7 Main Flange Types and How to Choose
We explain weld neck, slip-on, blind, socket weld, threaded, lap joint and orifice flanges — their construction, facing types (RF/FF/RTJ), pressure classes and selection criteria.
Steel Material Selection Guide for Petrochemical Plants
A guide to selecting the right steel material for petrochemical and refinery plants. Step-by-step material determination based on temperature, pressure, corrosion mechanisms, and ASTM standards.