Lightweight Flanges.
Heavyweight Performance.
Class 125LW, AWWA C207, and ASME B16.47 steel pipe flanges engineered for waterworks, industrial piping, and large-diameter service. Sizes 4" through 144". Built in Houston.
What Are Lightweight Flanges?
Reduced-weight flanges that maintain full bolt compatibility with ANSI B16.1 Class 125 cast iron patterns, designed for applications where full-thickness steel is overbuilt for the pressure requirements.
Lightweight flanges, designated Class 125LW, use the same outside diameter, bolt circle, and bolt hole pattern as standard ANSI/ASME B16.1 Class 125 cast iron flanges. The difference is in the cross-section: thinner flange rings and shorter hubs reduce material weight without compromising the bolted joint integrity required for low-to-moderate pressure service.
These flanges are manufactured from steel plate, bar, or forgings conforming to AWWA C207 material specifications. They are commonly supplied in slip-on, blind, and weld neck configurations for nominal pipe sizes from 4 inches through 144 inches, making them the standard choice for municipal waterworks, cooling systems, and general industrial piping where cast iron weight and brittleness are undesirable.
Three Configurations. Every Size.
Each type serves a different connection method. All share the same bolt pattern for interchangeability with Class 125 cast iron flanged equipment.
Slip-On Flanges
The workhorse of lightweight flange applications. The pipe slides through the bore and is fillet-welded on both sides. Lower alignment precision required during installation makes these ideal for field work on large water mains and cooling lines. Available in flat face and raised face configurations.
Blind Flanges
Solid discs that seal the end of a flanged pipe, valve, or pressure vessel nozzle. Used for system testing, future expansion points, and permanent dead-ends. Lightweight blinds reduce the load on support structures while maintaining full bolt-pattern compatibility with adjacent slip-on or weld neck flanges.
Weld Neck Flanges
The tapered hub provides a smooth stress transition from pipe wall to flange ring, distributing mechanical and thermal loads more evenly than slip-on designs. Specified for service where cyclic loading, vibration, or elevated temperatures demand a stronger joint. Full penetration butt weld to the pipe.
Built to Recognized Standards
Every flange we ship traces back to a published specification. Here are the primary standards governing lightweight flange design and manufacture.
AWWA C207
The American Water Works Association standard for steel pipe flanges in waterworks service. Covers Class B (86 psi), Class D (150-175 psi), Class E (275 psi), and Class F (300 psi). Sizes 4" through 144". This is the primary governing specification for lightweight flanges in municipal water and wastewater systems.
ANSI/ASME B16.1
Defines the dimensional standard for Class 125 cast iron flanges. Lightweight steel flanges share the same bolt circle, bolt hole count, and outside diameter as B16.1 Class 125, ensuring drop-in compatibility with existing cast iron flanged connections without modification.
ASME B16.47
Covers large-diameter steel flanges in NPS 26 through NPS 60. Series A (derived from MSS SP-44) uses fewer, larger bolts for higher-load service. Series B (derived from API 605) uses more, smaller bolts with a tighter bolt circle. Not interchangeable between series.
Cut, Drilled, Welded in Houston
Every lightweight flange starts as raw steel and leaves our facility as a finished, inspected product with full material traceability. Our fabrication capabilities cover plate flanges cut from A36 and A516-70 stock, forged flanges from A105 billets, and welded bar ring flanges for the largest diameters.
Bolt holes are CNC-drilled to AWWA C207 tolerances. Faces are machined to the specified finish. Every flange ships with a material test report traceable to the heat of steel.
Precision Fabrication
Every weld, every hole, every face finish built to spec.
Where Lightweight Flanges Work
Anywhere you need steel flange reliability at reduced weight and cost, without exceeding moderate pressure requirements.
Municipal Water & Wastewater
Treatment plants, distribution mains, pump stations, aeration systems, and chemical feed lines. AWWA C207 Class D and Class E are the standard selections.
Power & Industrial
Cooling water intake and discharge piping, HVAC chilled water loops, fire protection mains, and general plant utilities where pressure stays below the Class D/E threshold.
Built for Heavy Industry
From water treatment to power generation, our flanges are in the field.
Precision-Engineered to Print
Every flange we manufacture is backed by full dimensional drawings with bolt patterns, bore sizes, and face tolerances called out to ASME standards.
32" Lightweight Flange
20x 1.375" bolt holes, 29.5" bolt circle, 32" OD
96" NOM 125LW-FF-SO Flange
68x 2.438" bolt holes, 108.5" bolt circle, 113.25" OD
AWWA C207 Pressure Ratings
Working pressure limits by class designation per AWWA C207.
| Class | Working Pressure | Size Range | Typical Application |
|---|---|---|---|
| Class B | 86 psi | 4" - 144" | Low-pressure water distribution |
| Class D | 175 psi (≤12") / 150 psi (>12") | 4" - 144" | Standard waterworks service |
| Class E | 275 psi | 4" - 144" | Higher-pressure transmission mains |
| Class F | 300 psi | 4" - 144" | High-pressure industrial service |