Blind Flanges Guide: Blind Pipe Flanges, Pipe Blind Types and Selection for Piping Isolation

Blindflansche are solid flanges used to close the end of a pipe, valve, vessel nozzle or equipment connection. Unlike weld neck, slip on or threaded flanges, a blind flange has no center bore for flow. It is designed to stop the line, isolate a section, reserve a future connection or support pressure testing.

Buyers use many names for the same idea: blind pipe flanges, pipe blind, blind pipe flange, blind flange pipe, pipe blind flange, piping blind or blind flange on pipe. The wording may change, but the function is the same: a bolted closure for a piping system.

Blind flange type	Main feature	Typical use	Buyer note
Plain blind flange	Solid disc with bolt holes and gasket face	Closing pipe ends, valves or vessel nozzles	Most common blind for pipe isolation
Raised face blind flange	Raised gasket seating area	Steel piping, process systems, oil and gas	Match gasket and mating raised face flange
Flat face blind flange	Full flat gasket surface	Waterworks, cast iron mating flanges, low-pressure systems	Use full-face gasket where required
RTJ blind flange	Ring groove for metal ring gasket	High-pressure critical service	Requires correct RTJ ring and groove inspection
Tapped blind flange	NPT or other tapped hole added	Gauge, vent, drain or instrumentation point	State tap size and location clearly
High hub blind flange	Extended hub for stiffness	Large diameter or high-pressure service	Often drawing- or standard-specific

What Is Blind Flange?

What is blind flange? A blind flange is a bolted end closure with no through hole. It bolts to a mating flange with a gasket between the faces. Because it does not allow flow through the center, it is used to terminate, isolate or reserve a pipe connection.

A blind flange is not the same as a cap. A cap is usually welded, threaded or otherwise attached directly to pipe. A blind flange is a detachable bolted part. That makes it useful when a line may need to be opened later for inspection, maintenance, hydrotesting or future expansion.

When to Use a Blind Flange on Pipe

A blind flange on pipe is used when a piping system needs a removable closure. Common situations include the end of a pipeline, a spare nozzle on a vessel, a temporary shutdown point, a valve outlet reserved for future flow, a hydrotest connection or a maintenance isolation point.

For permanent welded closure, a pipe cap may be enough. For a connection that may be opened, inspected or modified later, a blind flange gives more flexibility. The tradeoff is that the bolted joint needs gasket selection, bolt tightening and periodic inspection.

Blind Flange Types by Facing

The most common blind flange types are classified by face design. Raised face, flat face and ring type joint designs are selected to match the mating flange and gasket system.

• Raised face blind flange: common in ASME steel piping with ring gaskets or spiral wound gaskets.
• Flat face blind flange: used when the mating flange is flat face, especially cast iron, ductile iron or waterworks service.
• RTJ blind flange: used where a metal ring gasket sits in a machined groove for high-pressure sealing.

Do not choose the facing by preference. It must match the mating flange, gasket type and project standard. A raised face blind bolted against a fragile flat face casting can concentrate load and damage the equipment.

Pressure Class and Thickness

Blind flanges carry pressure differently from flanges with a bore. Because the disc has no hole, pressure acts across the full closed area and tries to bow the blind outward. That is why thickness matters. A higher pressure class usually means a heavier and thicker blind flange.

For ASME flanges, size, class and material group define the rating. The blind flange does not increase the rating of the joint. It must match the mating flange class and service temperature. If the line is Class 300, the blind should be Class 300 unless the engineering specification states otherwise.

Blind Flange vs Spectacle Blind

A blind flange is installed at the end of a pipe or nozzle. A spectacle blind, also called a figure-8 blind, is installed between two flanges and can be rotated between open and closed positions during shutdowns. If a line will switch regularly between flow and isolation, a spectacle blind or paddle blank may be more practical.

Use a blind flange when the end connection is closed and may be opened only when needed. Use a line blank or spectacle blind when the system needs positive isolation between two flanges as part of operating or maintenance procedures.

Materials for Blind Pipe Flanges

Blind pipe flanges can be supplied in carbon steel, stainless steel, alloy steel, duplex stainless steel and other materials. ASTM A105 carbon steel is common for general industrial service. Stainless grades such as 304, 304L, 316 and 316L are selected for corrosion resistance. Low-temperature or high-temperature systems may need special grades.

The material should match the service medium, temperature, corrosion risk and mating flange. For export projects, buyers should also request material certificates, heat number marking and inspection reports when required.

Gasket and Bolting Notes

A blind flange uses the same bolting pattern as the mating flange of the same size and class. The gasket must match the face type and service. Raised face blinds often use ring gaskets or spiral wound gaskets. Flat face blinds often use full-face gaskets. RTJ blinds require the correct metal ring gasket.

Because a blind is often heavier than other flange types, plan lifting and handling for larger sizes. Protect the gasket face during transport and installation. Dents, scratches and corrosion on the sealing face can create leak paths.

How to Specify a Blind Pipe Flange

RFQ detail	Example	Why it matters
Standard	ASME B16.5, ASME B16.47, EN 1092-1, JIS	Controls dimensions and bolt pattern
Size	NPS 6, DN150	Matches pipe and mating flange
Pressure class	Class 150, 300, 600, PN16	Defines thickness and rating
Face type	RF, FF, RTJ	Must match gasket and mating flange
Material	A105, LF2, 304L, 316L, alloy steel	Matches strength, temperature and corrosion
Modification	Plain, tapped, drilled, high hub	Controls machining and drawing requirements
Documentation	MTC, dimensional report, PMI, NDT	Supports quality control and project approval

Common Mistakes to Avoid

• Ordering a lower pressure class blind than the mating flange.
• Using raised face blind flange against cast iron flat face equipment.
• Forgetting that a large blind flange can be heavy and needs lifting planning.
• Ordering the correct size but wrong face type.
• Assuming a tapped blind flange can be drilled on site without engineering review.
• Reusing old gaskets after removing a blind flange.

Anwendungen

Blind flanges are used in oil and gas piping, chemical plants, water treatment systems, power generation, pressure vessels, pump stations, tank nozzles, marine systems and industrial skids. They are also common in pressure testing because they create a removable closure at the end of a pipe or spool.

Songhai Flange can support standard and custom blind flange requirements, including stainless steel blind flanges, carbon steel blind flanges, tapped blinds, RF/FF/RTJ facings and export documentation for industrial piping projects.

FAQ About Blind Flanges

What is a pipe blind?

A pipe blind is a closure used to block a pipe connection. In many purchasing contexts, pipe blind means a blind flange or pipe blind flange.

What is the difference between blind flange and blind pipe flange?

They usually refer to the same product: a solid bolted flange used to close off a pipe or nozzle.

Can a blind flange be tapped?

Yes. A blind flange can be tapped for a gauge, vent, drain or instrument connection when the design allows. The tap size and location should be specified before production.

What are blind flange types?

Common blind flange types include raised face, flat face, RTJ, plain blind, tapped blind, reducing blind and high hub blind flange.

When should I use blind for pipe isolation?

Use a blind for pipe isolation when the line or nozzle must be positively closed and may need to be opened later for maintenance, testing or future expansion.

Final Thoughts

A blind flange is one of the simplest and most important parts in a piping system. It closes the line, protects future connections and provides removable isolation. To order the right blind pipe flange, confirm the standard, size, class, face type, material, gasket, bolting and any machining requirements before production. Good specification prevents leakage, mismatch and costly site rework.