A pipe flange looks like a simple disc with bolt holes, but selecting the wrong one can cost a project weeks of rework — or worse, a leak that takes a whole system offline. After more than three decades supplying flanges to petrochemical plants, shipyards, power stations, and water diversion projects, EZ Steel Industrial has seen almost every failure mode a procurement team can face. This guide condenses what we wish every buyer knew before signing that purchase order.

Start with the Operating Conditions, Not the Catalog

Flange selection begins with four numbers: design pressure, design temperature, the fluid being conveyed, and the pipe size. Everything else — material grade, facing type, pressure class — flows from these. Buyers who start by browsing catalogs tend to over-spec or under-spec. A 150# flange on a high-temperature steam line will deform; a 900# flange on a chilled water line wastes money and complicates bolt-up.

Pick the Right Material Family

Material choice determines corrosion resistance, temperature ceiling, and weldability. The four families most buyers encounter are:

• Carbon steel (ASTM A105, A350 LF2): The default for water, steam, oil, and gas at moderate temperatures. Cost-effective and easy to source.
• Stainless steel (ASTM A182 F304, F316): Specify when the fluid is corrosive, hygienic, or when the environment includes chloride exposure.
• Alloy steel (ASTM A182 F11, F22, F91): For high-temperature and high-pressure service in power plants and refineries, where carbon steel loses strength.
• Duplex and copper-nickel: For seawater cooling, offshore platforms, and aggressive chemical service. Our copper nickel alloy line covers 90/10 and 70/30 Cu-Ni grades built to EEMUA 234 and ASTM B466.

If you are pairing the flanges with carbon steel pipe for a low-pressure water line, there is no reason to step up to stainless flanges — that is wasted budget. Conversely, a stainless pipeline that ends with carbon steel flanges will rust at the joint first.

Match Flange Type to the Job

Within a single project you will usually specify several flange types, each chosen for a specific function. The most common are:

When you need to connect the flange to matching pipe fittings (elbows, tees, reducers), make sure the material grade, standard, and wall thickness line up. A common mistake is to buy ASTM A105 flanges and then connect them to A234 WPB fittings made to a different tolerance — they will bolt together, but the gasket seating surfaces may not align perfectly.

Don't Overlook the Facing and the Gasket

The facing is the sealing surface of the flange, and the wrong combination is the single most common cause of field leaks. A quick guide:

• Raised Face (RF): The default for most services. Pairs with spiral-wound or compressed non-asbestos gaskets.
• Flat Face (FF): Use only with cast iron or soft gaskets at low pressure. Never bolt an FF cast iron flange directly to an RF steel flange — the faces will not seal.
• Ring-Type Joint (RTJ): For high-pressure, high-temperature hydrocarbon service. Requires machined RTJ grooves and metal ring gaskets.
• Tongue & Groove / Male & Female: For applications needing precise self-alignment and a controlled gasket compression.

Make sure your stud bolt length accounts for the gasket thickness. Our gasket stud bolt nut kits are packaged to match common RF and RTJ combinations so the field crew does not have to improvise.

Standards and Traceability You Should Insist On

For international projects, the four standards that cover most flange purchases are:

• ASME B16.5 — Pipe flanges from NPS ½ through NPS 24. The most widely specified standard worldwide.
• ASME B16.47 — Large-diameter flanges (NPS 26 through NPS 60), Series A and Series B.
• EN 1092-1 — The European standard; required for CE-marked assemblies.
• API 6A / 6D — For wellhead and high-pressure pipeline gate assemblies.

Insist on full traceability. Every flange should be marked with the manufacturer, material grade, size, pressure class, and a heat number that ties back to a mill test report. EZ Steel's flanges are produced in an ISO 9001 certified facility, and every shipment is accompanied by MTC 3.1 certificates to EN 10204. We also stock a full steel flanges range in carbon, stainless, and alloy grades — including quick-ship options for common Class 150 and Class 300 sizes.

A Few Mistakes We See Every Month

Even experienced procurement teams make these:

• Ordering flanges to a standard (for example, ASME B16.5) but mixing in fittings made to a different standard (GB/T, JIS) without checking dimensional compatibility.
• Specifying "stainless" without naming the grade — F304 and F316 behave very differently in chloride environments.
• Forgetting the bolt material. B7 studs on a low-temperature carbon steel flange are fine; the same studs on a stainless flange can gall. Specify B8 or B8M studs for stainless.
• Buying on price alone. The cheapest flange often arrives without traceability documents — which is a problem the first time an inspector visits the site.

Why Source From a Project-Oriented Manufacturer

Since 1994, EZ Steel Industrial has supplied flanges, pipes, fittings, and valves as bundled packages to projects like the South-to-North Water Diversion and the West-East Gas Pipeline. We hold 480,000+ units of annual capacity, and our inventory team keeps the most-asked grades — ASTM A105, A350 LF2, A182 F304/F316, F11/F22 — on the shelf for fast dispatch. That matters when a contractor has a six-week welding window and cannot wait for a mill run.

Our project teams can also coordinate the full piping package — flanges, stainless steel pipe, fittings, gaskets, and industrial valves — under a single quality plan, single set of MTCs, and single delivery schedule. One supplier, one point of accountability.