Standards Reference
Built to Code. Across Every Standard.
From 86 PSI municipal water flanges to 20,000 PSI wellhead connections, flanges are built to the codes your specs require. This is a working reference for the flange standards that come up most often.
The Standards That Matter Most
A 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 flange work.
ASME B16.5
Pipe Flanges 1/2" - 24"
The workhorse spec for industrial flanges through 24 inches. Classes 150 through 2500, raised face, flat face, and RTJ.
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ASME B16.47
Large Diameter Flanges 26" - 60"
Series A (MSS SP-44 lineage) and Series B (API 605 lineage). Same nominal size, very different bolt patterns. Not interchangeable.
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AWWA C207
Steel Pipe Flanges for Waterworks
Class B (86 psi), Class D (150/175 psi), Class E (275 psi), Class F (300 psi). Sizes 4" through 144". The waterworks backbone.
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ANSI B16.1
Cast Iron Pipe Flanges
Class 25, 125, and 250 cast iron. Critical for retrofit and HVAC work because Class 125LW steel flanges share its bolt pattern.
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DIN / EN 1092-1
European Steel Flanges
PN 6 through PN 400. Eleven flange types covering weld neck, slip-on, blind, lap joint, and loose configurations.
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API 6A / 6BX
Wellhead and Christmas Tree Flanges
Pressure ratings to 20,000 psi. The other end of the spectrum from AWWA Class B. Sour service and ultra-high-pressure applications.
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MSS SP-44
Steel Pipeline Flanges
Large diameter pipeline flanges that fed directly into the ASME B16.47 Series A standard. Common on transmission pipelines.
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NACE MR0175
Sour Service Materials
Not a flange standard - a materials standard. Governs hardness and chemistry for H2S environments. Required across upstream oil and gas.
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Why Standards Matter
Interchangeability
Bolt patterns, face thickness, and OD must match the mating flange. A B16.5 Class 150 flange and an AWWA Class D flange in the same nominal size do not always share the same bolt circle. The standard is what makes parts swap without a redesign.
Pressure Ratings
Pressure-temperature ratings are derived from the material group and the flange class. ASME and API ratings derate as temperature climbs. AWWA flanges have a single working pressure tied to the class. Knowing which curve applies is non-negotiable.
Traceability
Code-compliant flanges carry marking that ties heat number, material grade, manufacturer, size, and class to a mill cert. When an inspector asks where the metal came from, the standard is what makes the answer possible.
Cross-Reference Quick Hits
- ASME B16.5 Class 150 roughly aligns with DIN PN 20. Roughly. 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 Class 125LW steel flanges remain so popular in waterworks retrofits.
- ASME B16.47 Series A uses fewer, larger bolts than Series B. They will not swap. Specify clearly on every order.
- API 6A flanges at 5000 psi and above are fundamentally different geometry from B16.5. Do not assume a B16.5 Class 2500 is the same animal as an API 6BX 5K.
Browse the Texas Flange flange types page for an overview of flange types, or jump to the tools section for dimensional lookups and bolt charts.
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