A pipe flanges is a small but critical link in any industrial piping system. It is the bolted connection that lets you assemble, inspect, isolate, and ｒｅｐｌａｃｅ sections of a pipeline without cutting the line. Choose the wrong flange type, the wrong material, or the wrong standard, and the connection becomes the weakest part of an otherwise well-designed system — usually discovered during hydrostatic test, hot commissioning, or worse, in service.

At EZ STEEL INDUSTRIAL, we have been manufacturing and supplying flanges and complementary piping products since 1994. Our work spans copper nickel alloy, marine shipbuilding, power plants, and large municipal projects such as the South-to-North Water Diversion and the West-East Gas Pipeline. This article walks through the practical decisions that drive a correct flange selection, and shows where our stock and custom supply can shorten your lead time.

1. What a Pipe Flange Actually Does

A flange is a disc-shaped collar, welded or screwed to the end of a pipe, that mates with another flange through bolts and a gasket. That three-part assembly — flange, gasket, bolting — is what creates a leak-tight seal at pressures from vacuum to above 2500 psi and at temperatures from cryogenic to over 600 °C.

Beyond sealing, the flange also has to handle three mechanical jobs: hold the pipe in place, transfer operating loads (pressure, weight, thermal expansion) into the pipe or vessel, and allow the line to be opened for cleaning, inspection, or repair. The flange type you ｓｅｌｅｃｔ determines how well it does each of these jobs.

2. The Six Flange Types You Will See Most Often

Most published standards (ASME B16.5, EN 1092-1, JIS B2220, GOST) define the same family of flange structures. Each one is a trade-off between cost, ease of installation, and mechanical performance.

• Slip-On (SO / SORF) — Slides over the pipe and is fillet welded front and back. Cheapest to install, good for low to medium pressure. Our most common stock item for general service lines.
• Weld Neck (WN / WNRF) — Welded to a pipe with a matching bore. The hub carries stress smoothly into the pipe, which is why it is the default for high pressure, high temperature, and cyclic service. Always our recommendation for power plant and refinery main runs.
• Blind (BL) — A solid disc used to close a pipe end, vessel nozzle, or valve body. It also doubles as a test flange during hydrostatic testing.
• Socket Weld (SW) — The pipe sits in a socket and is fillet welded at the hub. Smooth bore, suitable for small-bore high-pressure systems, but limited in size by ASME B16.5 to NPS 2 and smaller.
• Threaded (TH / NPT) — Tapered internal threads let the flange be attached without welding. Useful where hot work is restricted, but not for high-cycle or high-temperature service.
• Lap Joint (LJ) — Pairs with a stub end. The flange can rotate, which makes bolt-hole alignment easy on large-diameter or lined systems.

3. Choosing the Right Material

Material selection usually matters more than flange type, because the flange has to survive the same fluid, pressure, and temperature as the pipe it is attached to. Three families cover the vast majority of industrial use:

3.1 Carbon and Carbon Alloy Steel

ASTM A105, A350 LF2, A694, and alloy grades such as A182 F5/F11/F22 dominate oil & gas and power plant service. They are the cost-effective default for temperatures up to about 540 °C, paired with carbon steel pipe in grades like ASTM A106, A53, API 5L, and ASTM A333.

3.2 Stainless Steel

ASTM A182 F304/F304L, F316/F316L, and duplex F51/F55 are specified for corrosive service, hygienic lines, and offshore platforms. They are typically paired with stainless steel pipe to ASTM A312, A249, or EN 10217 standards.

3.3 Copper-Nickel Alloys

90/10 and 70/30 Cu-Ni are the materials of choice for seawater cooling, firewater, and shipboard piping because they resist biofouling and chloride attack. They are also the standard for many offshore and shipbuilding projects. EZ STEEL INDUSTRIAL supplies copper nickel flanges to EEMUA 234, ASTM B466, and GB/T 8890, covering most marine classes.

4. Standards, Pressure Classes, and Faces

A flange is defined by three numbers: the standard, the pressure class, and the facing. The standard dictates the dimensions and tolerances; the class dictates the pressure-temperature rating; the facing dictates how the seal is made.

4.1 Facing Types

• RF (Raised Face) — Default in ASME B16.5. Adds a 1/16" or 1/4" raised ring to concentrate gasket load.
• FF (Flat Face) — Used with cast iron and EN 1092-1 Type 01 flat flanges, paired with soft gaskets.
• RTJ (Ring Type Joint) — Machined groove for a metal ring gasket. Standard for high-pressure oil & gas and wellhead service above 600#.
• Male & Female / Tongue & Groove — Less common today, but still used in some process plant specifications.

5. Don't Forget the Bolting and the Gasket

A flange is only as good as what sits between the two faces. A complete specification should always name:

• Gasket type — spiral wound, ring joint, compressed non-asbestos, graphite, PTFE, or rubber. EZ STEEL INDUSTRIAL supplies gasket stud bolt nut packages matched to the flange class and fluid.
• Bolt material and stud length — ASTM A193 B7/B7M for high-temperature carbon service, B8/B8M for stainless, B16 for high-pressure, B16M for low-temperature.
• Nut grade — ASTM A194 2H, 2HM, 8, 8M, etc., matched to the stud.
• Gasket stress and torque — checked against the gasket manufacturer's recommended seating stress, not just the bolt torque.

Specifying the gasket and bolts together with the flange is the single most common way to avoid leaks during commissioning.

6. Where Each Flange Configuration Fits Best

Different services put very different demands on a flanged joint. The table below summarizes what we typically recommend, and what we keep in ready stock.

7. How EZ STEEL INDUSTRIAL Supports Your Project

We are a 500+ person integrated manufacturer with annual capacity above 480,000 metric tons, working from raw material inspection to finished goods. For flange buyers, that translates into a few practical advantages:

• Full material traceability — Mill Test Certificates and full MTC packs, with optional third-party inspection (SGS, BV, TUV).
• Standards coverage — steel flanges in ASME, EN, JIS, GOST and BS series, plus Cu-Ni to EEMUA 234 and ASTM B466.
• Project packaging — Flanges, gaskets, stud bolts, pipe fittings, and industrial valves supplied as one matched package, with line-by-line tagging, to keep site assembly fast and traceable.
• Inventory of common grades — A106, A53, A312, A333, A335, API 5L, plus matching flange sizes in 150# / 300# / 600# classes — the items you usually need on short notice.

Our flange, pipe, fitting, and valve lines have been qualified into national projects such as the South-to-North Water Diversion and the West-East Gas Pipeline, and into shipbuilding and offshore contracts across Asia, the Middle East, and Europe.