When specifying steel pipe flanges for oil, gas, power, and water transmission pipelines, two primary American National Standards govern dimensions and pressure-temperature ratings: ASME B16.5 and ASME B16.47. While they share similar pressure classes and metallurgies, their nominal size limits and dimensional profiles differ substantially—most notably the distinct divergence between Series A (MSS SP-44) and Series B (API 605).
Covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24 (DN 15 through DN 600).
Covers large diameter steel flanges from NPS 26 through NPS 60 (DN 650 through DN 1500).
ASME B16.47 absorbed two previously competing industry standards, designating them as Series A and Series B. They are dimensionally incompatible and cannot be bolted together:
| Characteristic | ASME B16.47 Series A (MSS SP-44) | ASME B16.47 Series B (API 605) |
|---|---|---|
| Originating Standard | MSS SP-44 (Pipeline Standard) | API 605 (Refinery / Compact Standard) |
| Flange Weight & Thickness | Heavier, thicker hub and body | Lighter, thinner, more compact |
| Bolting Pattern | Fewer, larger diameter bolts | More numerous, smaller diameter bolts |
| External Bending Resistance | Superior resistance to soil load & bending | Moderate; ideal for compact valve stations |
| Common Industry Use | Cross-country oil/gas pipelines, offshore | Refinery units, tank farm headers, compact skid piping |
The single biggest RFQ error in large bore piping is requesting an "ASME B16.47 NPS 36 Class 300 flange" without designating Series A or Series B. Because their bolt hole circles, bolt diameters, and overall outside diameters do not match, valve manufacturers and pipe fabricators cannot mate them in the field without costly on-site re-machining.
No. ASME B16.47 strictly standardizes only Weld Neck and Blind flanges. At nominal diameters of 26" to 60", slip-on or socket-weld joints cannot provide adequate fatigue resistance against pipeline flexure and internal pressure loads.
Most pipeline ball valves and check valves in sizes 26" and larger are built with end flanges conforming to ASME B16.47 Series A (MSS SP-44) because the heavier flange dimensions withstand pipeline settlement and soil movement without flange distortion.
Remax Forge manufactures heavy ring forgings and large-diameter flanges in ASME B16.47 Series A & B, ASTM A105, A350 LF2, and high-yield pipeline grades (F52, F60, F65, F70).