Standards Reference
Steel Flange Standards, From 86 PSI to 6,000.
From AWWA Class B ring flanges in A36 plate to F91 chrome-moly forged weld necks for ultra-supercritical steam, we supply steel flanges built to the codes your specs require. This is our working reference for the standards we stock and source every day.
The Standards That Govern Steel
A steel flange is only as good as the specification it was built to. The standard governs dimensions, tolerance, material chemistry, marking, pressure-temperature ratings, and acceptable face finishes. Pick the wrong code and you can end up with a flange that bolts up just fine but is rated for a fraction of the pressure your system actually sees. Below are the eight standards that cover the vast majority of steel flange work we do, from forged A105 weld necks to plate-cut A36 blinds at 144 inches and beyond.
ASME B16.5
Steel Pipe Flanges 1/2" - 24"
The core spec for forged steel flanges through 24 inches. Classes 150 through 2500. A105 carbon, F304/F316 stainless, F11/F22/F91 chrome-moly. Raised face, flat face, RTJ.
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ASME B16.47
Large Diameter Steel Flanges 26" - 60"
Series A (MSS SP-44 lineage) and Series B (API 605 lineage). Same nominal size, very different bolt patterns. Not interchangeable. Both forged and plate-cut production paths.
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AWWA C207
Steel Ring Flanges for Waterworks
Class B (86 psi), Class D (175/150 psi), Class E (275 psi), Class F (300 psi). Plate-cut from A36 and A516-70. Sizes 4" through 144" standard, custom larger on request.
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ANSI B16.1
Cast Iron Pattern Compatibility
Legacy Class 25/125/250 cast iron pattern. The retrofit case for steel plate flanges that drop into the same bolt circle. A36 plate-cut as the modern replacement.
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DIN / EN 1092-1
European Metric Steel Flanges
PN 6 through PN 400 ratings. Type 01 flat ring, Type 11 weld neck, Type 05 blind. P250GH and P265GH carbon steel material designations.
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API 605
Large Diameter Steel Flange Lineage
Older API spec that fed into ASME B16.47 Series B. Still referenced on heritage process vessels and tank nozzles. Lighter cross-section with more bolts on a tighter circle.
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MSS SP-44
Steel Pipeline Flanges
Large diameter pipeline flange spec that fed directly into ASME B16.47 Series A. Still seen on transmission pipeline orders. Heavier bolt loads, larger bolt diameters.
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NACE MR0175
Sour Service Materials
Not a flange standard. A materials standard governing hardness and chemistry for H2S environments. Required across upstream oil and gas work in carbon and alloy steel.
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Why Standards Matter for Steel
Interchangeability
Bolt patterns, face thickness, and OD must match the mating flange. A B16.5 Class 150 steel flange and an AWWA Class D steel flange in the same nominal size do not always share the same bolt circle. The standard is what makes steel parts swap without a field redesign.
Pressure Ratings
Pressure-temperature ratings derive from the material group and flange class. ASME ratings derate as temperature climbs, which is why F22 and F91 exist in the first place. AWWA flanges hold a single working pressure tied to class. Knowing which curve applies is non-negotiable.
Traceability
Code-compliant steel flanges carry marking that ties heat number, material grade, supplier mark, size, and class to a mill cert. When an inspector asks where the steel came from, the standard is what makes the answer possible. Every flange we ship carries that paper trail.
Cross-Reference Quick Hits
- ASME B16.5 Class 150 roughly aligns with DIN PN 20. Pressure regime overlaps. Bolt patterns do not match.
- AWWA Class D (175 psi) shares its bolt circle and hole pattern with ANSI B16.1 Class 125 through most common sizes, which is why plate-cut steel ring flanges remain the default for waterworks retrofit work.
- ASME B16.47 Series A uses fewer, larger bolts than Series B. They will not swap. Specify clearly on every order, on every line item.
- Forged vs plate-cut is a production-path decision, not a standards question. ASME and AWWA both permit plate-cut flanges where the standard allows. We supply both routes on the same project when sizes and pressures justify it.
Browse the steel flange product overview for what we stock, or jump to materials for the grade-by-grade specification reference.
Need a Spec Cross-Check?
Send us your line list or flange schedule. We will confirm the standard, class, material, and face finish before anything ships.