AWWA Standards and Their Application to Flanges

ANSI / ASME Flange Pressure Ratings: Class 150 to 2500

The Standard Types of ANSI/ASME Flanges

How Do ANSI/ASME Flanges Work?

Slip-On vs Weld Neck Flanges: Pros and Cons

1. The Role of AWWA Standards

When engineers and utilities design water systems, every pipe, fitting, and connection must meet various standards to ensure safety, compatibility, and long-term reliability. In the United States, this type of guidance comes from the American Water Works Association (AWWA). For more than a century, AWWA standards have provided the technical foundation for water infrastructure, as it covers materials, dimensions, performance limits, testing methods, and installation practices. AWWA standards for flanges are C207 (steel flanges), C110 (ductile-iron flanged pipe), and C228 (stainless-steel flanges).

The American Water Works Association (AWWA) develops consensus-based standards accredited by ANSI. These standards define enforceable minimum requirements for materials, dimensions, performance limits, inspection, and documentation for water sector products and practices.

First issued in 1908, today there are 190+ active standards
Standards are developed by volunteer expert committees and approved through ANSI-accredited procedures.
Regularly updated to reflect technological changes and best practices

1.1 What These Standards Typically Contain

Most product standards include: scope and intended use, material specifications, dimensional requirements and tolerances, pressure/temperature applicability or performance limits, inspection and testing requirements (mechanical, visual, sometimes hydrostatic or coating tests when relevant), and marking and documentation. Exact details vary by product standard.

1.2 Categories of Requirements for Flanges

Requirement Area	Examples in AWWA Standards
Manufacturing	Material grades (steel, ductile iron, stainless steel), allowable impurities, fabrication methods (C207, C228, C110)
Performance	Pressure classes (e.g., 50–300 psi for flanges), stress limits, corrosion resistance
Testing	Hydrostatic pressure testing, tensile/yield strength, chemical composition checks
Installation	Flange bolt torque, gasket selection (NSF/ANSI 61 compliant), alignment tolerances
Design	Dimensional standards (OD, bolt circles, thickness) ensuring interchangeability

2. The AWWA Standards For Flanges

Below are the two flange-related AWWA standards most specifiers use.

2.1 AWWA C207 — Steel Pipe Flanges for Waterworks Service

Covers ring-type slip-on flanges and blind flanges for steel water pipe and appurtenances,

Minimum requirements for AWWA C207 Flange:

Materials & fabrication: steel plate/forgings suitable for water service; machining tolerances; flat-face requirement for mating to waterworks equipment. Carbon steel (typically ASTM A36, ASTM A516 Grades 60,65,70, ASTM A283 Grade C, Q235, or GB/T 700).
Performance: the standard uses class-based working pressure limits (see table below) sized for water utilities.
Design basis: AWWA C207 – Steel pipe flanges for waterworks service from 4″ to 144″ NPS
Interchangeability: for many sizes, AWWA ring-flange drilling (pressure classes A,B,D and E) aligns with ASME Class 150 patterns; F pressure class aligns with ASME Class 300.

AWWA C207 class working pressures

Class	Typical working pressure	Notes
A	up to 50 psi	Light-duty or open-ended applications.
B	up to 86 psi	Low-pressure distribution.
D	up to 175 psi (4–12 in), up to 150 psi (>12 in)	The “standard” municipal choice.
E	up to 275 psi	Heavy-duty applications.
F	up to 300 psi	Highest AWWA class.

2.2 AWWA C228 — Stainless-Steel Pipe Flange Joints for Water Service

Standard covers stainless-steel ring-type slip-on flanges and blind flanges, 2–72 inches, for use with stainless pipe/fittings. Pressure limits tied to conditions/temperatures customary in water and wastewater applications.

Minimum requirements for AWWA C228 Flange:

Materials & fabrication: The standard “provides minimum material requirements and dimensions for a variety of stainless-steel flanges (typically ASTM A240, 304/304L, 316/316L, or duplex alloys)”
Performance: Pressure ratings are equivalent to C207. C228 covers Class SA (50 PSI)
Design basis: AWWA C228 – Stainless steel flanges for corrosive environments, 2″ – 72″ (smaller sizes available when compared to C207)

2.3 AWWA C110 — Ductile-Iron and Gray-Iron Fittings

AWWA standard describes 3–48 inches in ductile-iron and gray-iron fittings for potable, wastewater, and reclaimed water service. It states working pressures and provides guidance on casting, fabrication, and inspection. (AWWA C110-21)

Working pressure: 250 psi maximum; ≤24 in flange joints with ductile-iron flanges may be rated 350 psi.
Why it matters: You can use flanged DI spools in higher-pressure distribution where steel C207 ring flanges would be Class E/F.

2.4 Quick Reference

3. Why AWWA Standards Are Used For Water Service

AWWA standard	Material system	Size range	Typical working-pressure classes	Intended use / notes
C207	Carbon/steel plate or forgings	4–144 in	A (50), B (86), D (150–175), E (275), F (300) psi	Ring-type slip-on & blind flanges for steel pipe; drilling often aligns with ASME patterns.
C228	Stainless-steel slip-on & blind	2–72 in	Pressure ratings are equivalent to C207. Plus C228 covers Class SA (50 PSI)	For stainless systems under water/wastewater conditions; corrosion-resistant builds.
C110	Ductile-iron pipe w/ threaded DI or GI flanges	3–64 in	250 psi, ≤24 in up to 350 psi	Flanged DI spools for potable, wastewater, reclaimed water service; casting/fabrication/inspection guidance.

Water-Specific Design: Unlike ANSI/ASME B16.5 flanges (used in oil/gas, up to thousands of psi), AWWA flanges optimize for large diameters and moderate pressures in waterworks.
Material Confidence: By defining exact steel strengths, stainless grades, and iron casting properties, AWWA ensures reliability in potable and wastewater applications.
Interoperability: Uniform bolt patterns and dimensions allow flanges from multiple suppliers to fit interchangeably.
Cost-Effectiveness: AWWA flanges use less material than industrial ANSI/ASME flanges, reducing cost.

4. Conclusion

AWWA standards are technical rulebooks, not just broad guidelines and they define:

Design geometry (bolt circles, thickness, diameters up to 144″)
Material properties (tensile, yield, chemical composition)
Performance limits (pressure classes, stress levels)
Testing requirements (hydrostatic, tensile, coatings, inspections)
Installation practices (bolt torque, gasket standards, alignment)

Understanding the AWWA standards for flanges is a critical step in choosing the right components for any water pipeline system. Our sales team at API can answer any questions about your flange requirements. Depending on its application, they can also recommend alternative products that may be better suited for your system. We also provide custom flange solutions tailored to your project specifications. Get connected with a dedicated sales representative today! Or call us: 503.692.3800