Pipe Flanges Explained: How to Choose the Right Flange for Industrial Piping Systems

A practical guide to flange types, materials, and standards — from a manufacturer with three decades of full-cycle production experience.

In any industrial piping system — whether it carries steam through a power plant, crude oil across a continent, or seawater through a ship's engine room — the pipe flanges are the unsung heroes. They are the bolted connections that hold the system together, allow sections to be opened for maintenance, and keep high-pressure fluids safely contained for decades. Choosing the wrong flange is one of the most common — and most expensive — mistakes in piping engineering.

This guide walks you through what flanges do, the most common types you will encounter, the materials and standards that govern them, and how to match a flange to your service conditions. It is written from the perspective of EZ Steel Industrial, a Chinese manufacturer with over thirty years of experience supplying flanges, pipes, fittings, and valves to projects ranging from the West–East Gas Pipeline to petrochemical plants and modern shipbuilding yards.

What a Pipe Flange Actually Does

A pipe flange is a forged or plate-cut disc with bolt holes around its perimeter, welded or threaded to the end of a pipe. Two flanges, separated by a gasket and pulled together with gasket, stud bolt & nut sets, form a bolted joint. That joint needs to do four things at once:

• Contain pressure. The flange, gasket, and bolts together resist the internal pressure pushing the joint apart.
• Prevent leakage. A correctly selected gasket and face finish keep process fluids inside the pipe.
• Resist the service environment. Temperature, corrosion, vibration, and fire exposure all influence the choice of material and face type.
• Allow maintenance. Unlike a welded connection, a flanged joint can be unbolted to swap out a valve, repair a pump, or clean a section of line.

The Six Flange Types You Will See Most Often

Different piping duties call for different flange geometries. The six most widely used types cover the vast majority of industrial applications:

Material Matters: Matching Metal to Service

Choosing a flange type is only half the decision. The material grade determines whether the joint survives the chemistry, temperature, and pressure of the line. Common options include:

• Carbon steel (ASTM A105, A350 LF2) — the workhorse for oil & gas, power, and general process piping up to around 425 °C.
• Stainless steel (304/304L, 316/316L, duplex) — used where corrosion resistance or cleanability matters, such as food, pharmaceutical, and chemical service. Stainless steel pipe flanges are often specified to ASTM A182.
• Alloy steel (F11, F22, F91) — for high-temperature service in power boilers and hydrocracker reactors.
• Copper nickel alloy (90/10 Cu-Ni, 70/30 Cu-Ni) — the standard for shipbuilding, offshore platforms, and desalination plants, thanks to excellent resistance to seawater corrosion. Copper nickel flanges are typically specified to EEMUA 234, ASME B16.5, or the relevant marine classification society rules.

Standards You Will See on Every Drawing

Flanges are not a free-form component — they are tightly standardised so that a flange made in one country bolts to a flange made in another. The most common standards in industrial use are:

• ASME B16.5 — pipe flanges from NPS ½ to NPS 24, the dominant standard in oil & gas and chemical plants worldwide.
• ASME B16.47 — large-diameter flanges from NPS 26 upward, in Series A and Series B.
• EN 1092-1 — the European standard for steel flanges, used across the EU and many EPC projects.
• GOST — the Russian/CIS standard, still widely specified for projects in Eastern Europe and Central Asia.
• JIS B2220 — the Japanese standard, common in shipbuilding and in East Asian industrial plants.
• AWWA C207 — the American Water Works Association standard for water and wastewater service.

A steel flanges range that covers all of the above is what allows a single supplier to serve global EPC contractors without surprises on the jobsite.

Pressure Class, Face Type, and Gasket — The Other Three Decisions

Even with the right type and material, a flange can fail if the pressure class, face finish, and gasket are not matched to the service. The most common pressure classes under ASME B16.5 are 150, 300, 600, 900, 1500, and 2500. The face types you will encounter most often are:

• Raised Face (RF) — the default for most process piping, paired with a soft or spiral-wound gasket.
• Flat Face (FF) — preferred when connecting to cast iron or non-metallic flanges, paired with a full-face gasket.
• Ring Type Joint (RTJ) — a metal ring groove machined into the face, used for very high pressure and high temperature.
• Male & Female (M&F) and Tongue & Groove (T&G) — precision-machined faces for applications where precise gasket location is critical.

Frequently Asked Questions

Which flange type is the most widely used?

The weld neck flange. Its tapered hub reduces stress at the pipe-to-flange transition, making it the default for high-pressure and high-temperature service. The slip-on flange is a close second, and dominates low-pressure utility lines because of its lower installation cost.

How do I decide between a raised face and a flat face?

Use a raised face (RF) for most steel-to-steel connections — it concentrates gasket load on a smaller area and gives a more reliable seal. Use a flat face (FF) when at least one of the mating flanges is cast iron, glass-lined steel, or any other brittle material that could crack under the concentrated RF load.

Can I mix materials within a single flanged joint?

You can, but it must be done deliberately. A common combination is a carbon steel backing flange behind a stainless or copper-nickel stub end, which saves cost while keeping the wetted surface in the correct alloy. The two metals must also be galvanically compatible for the service environment.

What documentation should a flange supplier provide?

At minimum: a Mill Test Certificate (MTC) traceable to the heat number, dimensional inspection records, and for pressure-containing service, hydrostatic or pneumatic test reports. For marine and nuclear service, classification society or RCC-M certificates are typically required.

Why the Source of the Flange Matters

A flange is one of the few components in a piping system that, if it fails, brings the entire line down — often with significant safety and environmental consequences. That is why procurement teams are increasingly looking for suppliers who can demonstrate full-cycle control: raw material traceability, in-house forging or plate-cutting, certified machining, and a documented quality system audited by the relevant international bodies.

Working with a manufacturer that also produces the matching pipe fittings, stud bolts, and gaskets simplifies the bill of materials, ensures dimensional compatibility, and reduces the number of vendors the EPC contractor has to manage on a single project.