Types of Flanges in Pipe Fittings: Standards, Installation, Faces and Gaskets

Quick answer: The main types of flanges in pipe fittings include weld neck, slip-on, blind, socket weld, threaded, lap joint, plate, reducing, orifice, and ring-type joint flanges. They are used to connect pipe, valves, pumps, pressure vessels, instruments, and equipment while allowing assembly, inspection, cleaning, isolation, or future removal.

What Are Flanges Used For?

Many engineers and buyers search what are flanges used for because flanges look simple but serve several functions at once. A flange creates a bolted joint between two components, compresses a gasket, allows alignment during installation, supports inspection and maintenance, and can provide a removable connection where welding alone would make future service difficult.

Flanges are common in refineries, chemical plants, power stations, water treatment systems, marine piping, pressure vessels, HVAC, food processing, mining, and general industrial pipelines. Their value is not only mechanical strength; it is the ability to make a controlled joint that can be opened when the system requires maintenance.

What Are the Types of Flanges?

The answer to what are the types of flanges depends on the standard and industry, but the most common industrial categories include weld neck, slip-on, blind, socket weld, threaded, lap joint, and plate flange designs.

Flange type	Typical use	Key selection note
Weld neck flange	Critical pressure, temperature, cyclic, or high-load piping	Strong hub transition and butt weld connection
Slip-on flange	Moderate service where installation convenience matters	Requires correct fillet welding and alignment
Bride aveugle	Line closure, vessel openings, future expansion points	Must be checked for pressure, gasket, and bolt loading
Bride soudée par emboîtement	Small-bore high-pressure piping	Gap control and weld quality are important
Threaded flange	Small-bore systems where welding is not preferred	Thread standard and service limitations must be verified
Lap joint flange	Systems requiring frequent disassembly or alloy stub ends	Works with a stub end, not by itself
Plate flange	Low to moderate pressure utility and project-specific systems	Not automatically suitable for high-pressure duty

What Is the Standard Used for Flanges?

Buyers often ask what is the standard used for flanges. There is no single global standard for every project. Common choices include ASME B16.5, ASME B16.47, EN 1092-1, DIN, JIS, API, MSS, AWWA, and project-specific pressure vessel drawings.

The question what type of flange is ASME is slightly different. ASME is not one flange type; it is a standards organization and document family. ASME B16.5, for example, covers dimensions and ratings for many pipe flanges and flanged fittings within its size range. ASME flanges may be weld neck, slip-on, blind, threaded, socket weld, lap joint, or other listed forms depending on the document.

Slip-On Flange Installation and Dimensions

Slip on flange installation requires the flange to slide over the pipe, align with the mating flange, and receive proper fillet welds according to the approved procedure. The pipe end is usually set back from the flange face to allow internal welding without interfering with gasket seating. Weld size, cleaning, inspection, and distortion control should be handled by qualified personnel.

Slip on flange dimensions should be taken from the applicable standard and class, not copied from a similar-looking part. Outside diameter, thickness, bolt circle, bolt hole size, hub dimensions, bore, raised face, and tolerance all matter. A common mistake is matching only the bolt holes while ignoring bore or facing differences.

Slip-On Flange vs Weld Neck Flange

The comparison slip on flange vs weld neck flange is about installed performance as much as product price. Slip-on flanges are often easier to align and may cost less initially. Weld neck flanges provide a smoother stress transition through the tapered hub and are preferred in many severe, high-pressure, high-temperature, or cyclic applications.

For critical service, the lower unit price of a slip-on flange may not justify added lifecycle risk. For moderate utility service, a weld neck flange may be unnecessary. Always let the piping specification and service conditions decide.

Raised Face vs Flat Face Flange

The phrase raised face vs flat face flange refers to the gasket seating surface. A raised face concentrates gasket load on a smaller area and is common in many steel flange systems. A flat face has a full flat gasket seating plane and is often used when mating to cast iron, nonmetallic, or equipment faces that could be damaged by excessive localized bending.

Do not mix face types casually. The mating equipment, gasket style, bolt load, material, and standard must be compatible.

How to Choose a Blind Flange

How to choose a blind flange begins with pressure class, size, material, facing, gasket, bolting, temperature, and whether the blind closes a pipe end, nozzle, inspection port, or pressure vessel opening. Blind flanges carry bending load from internal pressure, so thickness and material are critical.

Lap Joint, Threaded, and Socket Weld Details

How to use lap joint flanges: pair the loose backing flange with a compatible stub end. The stub end contacts the fluid, while the lap joint flange provides the bolting force. This can reduce alloy cost and simplify alignment in systems that are dismantled frequently.

Threaded flange advantages and uses include installation without welding, usefulness in small-bore piping, and convenience in some low to moderate service conditions. Limitations include thread leakage paths, corrosion in threads, and restrictions in severe cyclic or hazardous service.

Socket weld flange installation requires correct pipe insertion depth, a small expansion gap, proper weld procedure, and inspection. It is common in selected small-bore high-pressure systems but should be avoided where the crevice created by the socket is unacceptable.

Flange Gaskets and Weld Neck Advantages

Different types of flange gaskets include nonmetallic sheet gaskets, elastomer gaskets, spiral wound gaskets, jacketed gaskets, grooved metal gaskets, and RTJ metal rings. Selection depends on flange face, pressure, temperature, fluid, bolt load, and standard.

Weld neck flange advantages include good stress distribution, strong connection to the pipe, better suitability for severe service, and compatibility with butt-weld inspection methods. These advantages explain why weld neck flanges appear frequently in oil and gas, power, petrochemical, and high-pressure piping.

FAQ

Are plate flanges suitable for high pressure?

A plate flange for high pressure should only be used when the design standard and engineering calculation approve it. Forged weld neck designs are more common in demanding high-pressure services.

Can a lap joint flange seal without a stub end?

No. A lap joint flange is designed to work with a stub end or compatible lapped connection that provides the sealing surface.

Which gasket is best for steam?

The answer depends on pressure, temperature, flange face, bolt load, and code requirements. Spiral wound or other engineered gaskets are often considered for higher duty, but project specifications should control the choice.WhatsApp : +86-18658777855
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