A procurement-friendly guide for getting flanges right the first time
Pipe flanges look simple, but they’re one of the most common sources of delays on industrial, municipal water, irrigation, and fire protection jobs—because “a 6-inch flange” isn’t a complete specification. Pressure class, flange standard, facing, material, drilling pattern, gasket selection, and even coating choices can determine whether a flange bolts up cleanly, seals reliably, and passes inspection. This guide breaks down how to specify pipe flanges in a way that’s easy for engineers to approve and easy for procurement teams to purchase—especially when you’re buying for multiple U.S. cities or exporting.
Start with the 5 questions that prevent 90% of flange mismatches
When a quote request just says “pipe flanges,” your supplier has to guess. Instead, confirm these five items up front:
1) Which standard? ASME (common in industrial/process) vs AWWA (common in waterworks).
2) What pressure rating? ASME “Class” (150/300/600…) vs AWWA “Class” (often water-service working pressure categories).
3) What facing? Raised Face (RF), Flat Face (FF), Ring-Type Joint (RTJ), etc.
4) What material + compliance? Carbon steel, stainless, ductile iron—plus required test reports (MTRs), coatings, and markings.
5) What connection style? Weld neck, slip-on, socket weld, threaded, lap joint, blind—selected based on service conditions and install approach.
ASME vs AWWA: same nominal size does not mean “bolts up”
Industrial projects often reference ASME B16.5 for pipe flanges and flanged fittings (NPS 1/2 through NPS 24) and use ASME “Class” designations such as 150, 300, 600, 900, 1500, and 2500. (asme.org)
Waterworks projects frequently reference AWWA C207 for steel pipe flanges used in water service. The important field takeaway: ASME and AWWA drilling patterns and dimensions are not interchangeable in many common cases, so mixing standards can create field-fit issues and rework.
If your job includes private fire service mains, the flange standard may be driven by the overall system design, available valves/hydrants, and the governing installation standard (often referenced by the engineer of record). When in doubt, align your flange selection with the exact standard called out in the project specifications and the mating equipment.
Procurement tip: If a submittal or RFQ says “ANSI flange,” ask the engineer to clarify whether they mean ASME B16.5 (industrial) or AWWA C207 (waterworks). “ANSI” is commonly used as a shorthand in the field, but it can hide a critical mismatch.
Flange facing: RF vs FF vs RTJ (and why it matters)
The flange facing is the sealing surface where the gasket sits. Choosing the wrong facing can lead to persistent leaks, damaged gaskets, or bolt-up conflicts.
Raised Face (RF) is widely used for general industrial piping because it supports many common gasket styles and is easy to source. (wermac.org)
Flat Face (FF) is commonly used where you want full-face gasket contact across the entire flange face area (including to the bolt holes), often seen in lower-pressure or certain equipment connections. (blog.projectmaterials.com)
Ring-Type Joint (RTJ) uses a machined groove and a metal ring gasket for higher-pressure and more demanding services. It’s a different sealing method than RF/FF—so it must be specified intentionally and matched on both sides. (sciencedirect.com)
Quick comparison table: choose the right flange face for the job
| Facing | Typical use | Gasket notes | Common pitfalls |
|---|---|---|---|
| RF (Raised Face) | General industrial/service piping; common ASME B16.5 builds (wermac.org) | Works with many gasket types (confirm spec and media compatibility) | Mating RF to equipment that requires FF; wrong gasket ID/OD |
| FF (Flat Face) | Select equipment and low/moderate pressure services where full-face contact is desired (blog.projectmaterials.com) | Often paired with full-face gaskets to spread load (blog.projectmaterials.com) | Mating to RF without an approved plan; gasket blowout from poor selection/torque |
| RTJ (Ring Type Joint) | High-pressure / demanding services requiring metal ring gaskets (sciencedirect.com) | Requires correct ring type/size and groove match—both sides must be RTJ (sciencedirect.com) | Incorrect ring selection; mixing RTJ with RF/FF; damage to groove during handling |
Pressure class isn’t “psi”: how to avoid the most common misunderstanding
A frequent mistake is assuming an ASME “Class 150” flange means 150 psi. In ASME systems, “Class” is a pressure-temperature rating category that depends on the material and operating temperature, not a single fixed psi value. ASME B16.5 covers pressure-temperature ratings and related requirements for flanges across the common class series. (asme.org)
What to do instead: match the flange class to the piping spec (line class), design pressure, design temperature, and material. If your job is waterworks-focused, confirm whether the project uses AWWA working pressure classes and what temperature assumptions apply.
How to write a clean flange specification (copy/paste templates)
If you want quotes that come back accurate (and comparable), give your team a consistent flange callout format. Here are two practical templates:
Industrial / process (ASME) example:
“Flange: ASME B16.5, NPS 6, Class 300, Weld Neck, Raised Face (RF), ASTM A105, bored for Sch. 40, with MTRs, quantity __.”
“Flange: ASME B16.5, NPS 6, Class 300, Weld Neck, Raised Face (RF), ASTM A105, bored for Sch. 40, with MTRs, quantity __.”
Waterworks example:
“Flange: AWWA C207 steel pipe flange, NPS __, class per drawings/spec (working pressure), flat face per spec, drilling pattern per mating valve/equipment, coating requirements __, quantity __.”
“Flange: AWWA C207 steel pipe flange, NPS __, class per drawings/spec (working pressure), flat face per spec, drilling pattern per mating valve/equipment, coating requirements __, quantity __.”
When your project spans multiple facilities or cities, use the same callout format across all POs. It reduces substitution risk and makes partial shipments easier to reconcile.
Did you know? Quick flange facts that help in the field
• ASME B16.5 covers dimensions, tolerances, materials, marking, and pressure-temperature ratings for common flange classes. (asme.org)
• Raised Face is a common industrial default because it works with many gasket styles and is widely stocked. (wermac.org)
• RTJ is a different sealing system (groove + metal ring gasket), not just “a better RF.” (sciencedirect.com)
• “Nominal pipe size” isn’t the same as OD—so bore, schedule, and mating pipe spec still matter for fit and flow.
Where pipe flanges show up across IFW Supply’s typical scopes
Buyers often associate flanges only with PVF, but they are a cross-discipline item:
Industrial (PVF + instrumentation tie-ins): flanged valves, spool pieces, strainers, pump connections, skid interfaces, maintenance isolation points.
Waterworks & irrigation: flanged valve trains, meter vault assemblies, hydrant accessory interfaces, pumping/booster station connections.
Fire protection: flanged valves and specialty equipment where the design calls for flanged joints for inspection access or equipment connection.
Safety & facilities: emergency water supply and washdown infrastructure where durable, serviceable joints are preferred.
United States sourcing note: keep multi-city projects consistent
IFW Supply supports buyers across the United States—often with projects running simultaneously in Boise, Salt Lake City, Denver, Phoenix, and Seattle. Multi-site programs benefit from a single, approved flange “playbook”:
• Standardize naming: use one callout format (standard + class + type + facing + material).
• Lock mating equipment early: valve and equipment flange drilling/facing should drive the purchase.
• Plan submittals/MTRs: confirm documentation expectations before ordering, especially for critical infrastructure or export shipments.
• Reduce field variance: keep gasket style/brand equivalency and torque practices aligned with the engineer’s intent.
CTA: Get help specifying pipe flanges (and avoid reorders)
If you’re sourcing pipe flanges for industrial, waterworks/irrigation, or fire protection scopes—especially with export documentation, mixed standards, or tight lead times—IFW Supply can help you align the flange standard, facing, and class with the mating equipment and project requirements.
FAQ: Pipe flanges
Are ASME B16.5 and AWWA C207 flanges interchangeable?
Not reliably. They can differ in dimensions and bolt patterns; your safest approach is to match the project’s specified standard and the mating equipment’s drilling/facing requirements.
Does “Class 150” mean 150 psi?
In ASME systems, “Class” is a pressure-temperature rating category that depends on material and temperature; it’s not a single fixed psi number. ASME B16.5 defines pressure-temperature ratings and related requirements. (asme.org)
What’s the default flange facing for most industrial piping?
Raised Face (RF) is a common default in industrial/process applications and works with a wide range of gasket designs. (wermac.org)
Can you mate an RF flange to an FF flange?
It depends on the equipment and engineering approval. Sometimes a full-face gasket strategy is used in flat-face systems, but facing mismatches should be resolved by the project spec and the equipment manufacturer’s guidance (not assumptions).
What details should I include on a flange RFQ to get accurate pricing quickly?
Include: standard (ASME/AWWA), NPS, pressure class, type (WN/SO/THD/etc.), facing (RF/FF/RTJ), material grade, bore/schedule, coating/finish, documentation needs (MTRs), quantity, and required ship-by date.
Glossary (pipe flange terms)
ASME B16.5
A widely used standard covering pipe flanges and flanged fittings (within defined size ranges), including dimensions, materials, marking, and pressure-temperature ratings. (asme.org)
AWWA C207
A standard for steel pipe flanges used in waterworks service; commonly referenced for municipal water and related infrastructure where water-service working pressure classes apply.
Facing (RF / FF / RTJ)
The sealing surface geometry of a flange. RF (Raised Face) is common in industrial piping; FF (Flat Face) provides full-face contact; RTJ (Ring-Type Joint) uses a groove and metal ring gasket for demanding services. (wermac.org)
Pressure Class (ASME)
A pressure-temperature rating category (e.g., Class 150/300/600) that depends on material and temperature—not a single “psi equals class” rule. (asme.org)