In 2023, The American Water Works Association (AWWA) has issued a specification revision affecting the bolt hole diameter for 22″ Class-F flanges. This revision is applicable to Carbon Steel (AWWA C207 Class F) and Stainless Steel (AWWA C228 Class SF) materials, in both Slip-On and Blind configurations. It means that engineers, procurement teams, and contractors working with this size and class should review the change and confirm alignment with current drawings and inventory.
What Changed for AWWA Class F Flanges?
For 22″ AWWA Class-F flanges, the diameter of bolt specification was revised (affecting the bolt hole diameter):
- Previous Spec: Bolt size: Ø 1.25″ (Bolt hole diameter: Ø 1.375″)
- New 2023 Spec: Bolt size: Ø 1.500″ (Bolt hole diameter: Ø 1.625″)
This change applies to both flange styles: Slip-On (Ring) and Blind.
! Note on Compatibility: Bolt hole diameter directly affects bolt pattern compatibility. Connecting flanges from different production runs, or replacing a single flange in an existing system, requires verification of bolt hole sizing across the full joint. Mismatched diameters can cause improper assembly or compromise joint integrity. Specifications should always be confirmed before procurement.
Background: AWWA C207 and C228 Standards
- Dimensions — outside diameter, inside diameter, bolt hole circle, resultant bolt hole diameter (based on bolt diameter), and thickness
- Pressure classes — Classes B (SB) through F (SF), covering pressure ratings from 86 psi up to 300 psi. There is also Class SA, which covers a 50 psi pressure rating.
- Material requirements — carbon/mild steel (C207) and stainless steel in 304/304L or 316/316L grades (C228)
- Drilling compatibility — bolt patterns that align with ASME/ANSI Class 150 (Classes B–E) or Class 300 (Class F)
These standards cover flanges from 4″ through 144″ nominal pipe size. They are the most widely used specifications in municipal water, treatment plant, pump station, and industrial pipeline applications.
AWWA Flange Pressure Classes
AWWA flanges are organized into pressure classes, each designed for specific service conditions:
| Class | Pressure Rating | Bolt Pattern |
|---|---|---|
| Carbon Steel — AWWA C207 | ||
| B | 86 psi | ASME/ANSI Class 150 |
| D | 150–175 psi | ASME/ANSI Class 150 |
| E | 275 psi | ASME/ANSI Class 150 |
| F | 300 psi | ASME/ANSI Class 300 |
| Stainless Steel — AWWA C228 | ||
| SA | 50 psi | ASME/ANSI Class 125/150 |
| SB | 86 psi | ASME/ANSI Class 150 |
| SD | 150–175 psi | ASME/ANSI Class 150 |
| SE | 275 psi | ASME/ANSI Class 150 |
| SF | 300 psi | ASME/ANSI Class 300 |
Class F is the highest-rated AWWA class, designed for up to 300 psi service, which makes bolt hole accuracy especially critical. At 300 psi, joint integrity depends on proper bolt engagement across all holes.
What Is Bolt Hole Alignment and Why Does It Matter?
Bolt hole alignment refers to the precise positioning and sizing of bolt holes around the bolt hole circle (B.H.C.) of a flange. Every bolt hole must:
- Match the correct bolt hole diameter (Ø B.H.) for the specified bolt size
- Be positioned accurately on the bolt hole circle — the centerline diameter on which all holes fall
- Be symmetrically spaced so that mating flanges align when brought together in the field
When a spec revision changes bolt hole diameter (as this AWWA update does for 22″ Class-F), the bolt size required to fill and thread through the hole changes accordingly. A Ø 1.375″ hole accepts a different bolt than a Ø 1.625″ hole. For systems where new flanges are being introduced alongside flanges manufactured to the previous specification, bolt sizing must be evaluated across the full joint.
Scope of Impact
This revision is relevant to any project involving 22″ Class-F flanges, including:
- Municipal water transmission lines using large-diameter flanged connections
- Pump stations and treatment plants with 22″ flanged isolation or connection points
- Replacement or repair situations where new flanges must mate with existing ones
- Design projects currently specifying 22″ Class-F where drawings or BOMs may reference the old bolt hole diameter
Current drawings should be verified against the revised AWWA C207/C228 standard edition, and existing inventory should be assessed before procurement of new flanges for any system where mating compatibility is a factor.
Class-F Flanges Available from API International
API International manufactures and stocks AWWA Class-F flanges in both carbon steel (C207) and stainless steel (C228), in Slip-On and Blind configurations, from 4″ through 48″ nominal pipe size. All Class-F flanges meet the ASME/ANSI Class 300 bolt pattern and are rated at 300 psi at atmospheric temperature. Our 22″ Class-F flanges reflect the current AWWA specification:
- PF2200-F — 22″ Carbon Steel Ring Flange (C207), 300 psi
- PFBL2200-F — 22″ Carbon Steel Blind Flange (C207), 300 psi
- SPF2200-F — 22″ Stainless Steel Ring Flange (C228), 300 psi
- SPFBL2200-F — 22″ Stainless Steel Blind Flange (C228), 300 psi
Review the AWWA C207 & C228 Flanges Spec Sheet or visit our AWWA Flanges page. API International’s engineering team is available to assist with specification questions, compatibility assessments, and procurement support for AWWA Class-F flanges and related components. Contact us for custom options tailored to your unique project needs or call us at 503.692.3800.
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Frequently Asked Questions
What is the difference between AWWA C207 and C228?
What is the pressure rating of AWWA flanges?
Pressure ratings vary by class:
- Class A: up to 50 psi (Stainless Steel Only)
- Class B: up to 86 psi
- Class D: up to 175 psi
- Class E: up to 275 psi
- Class F: up to 300 psi
These ratings apply to water service and depend on flange size and material.
What are AWWA C207 Class F flange dimensions?
AWWA C207 Class F flange dimensions are standardized by size and include the outside diameter, inside diameter, bolt circle, bolt-hole size, number of bolt holes, and flange thickness. Class F sizes are typically covered from 4 inches through 48 inches.
What is the pressure rating of AWWA C207 Class F?
AWWA C207 Class F flanges are rated for 300 psi at atmospheric temperature, making them the highest pressure class within the AWWA C207 standard.
What are the dimensions of AWWA C228 Class SF flanges?
AWWA C228 Class SF flange dimensions are defined by:
- Nominal pipe size (NPS)
- Outside diameter (OD)
- Bolt circle (BC)
- Number of bolt holes
- Hole diameter
- Thickness
Class SF flanges are typically available in sizes from 4” to 48” and follow drilling patterns compatible with ANSI/ASME Class 300 up to 26″ and Class 300 series A bolt patterns from 26″ to 48″. Exact dimensions vary by size and must be referenced from AWWA C228 standard tables.
Why are Class SF flanges typically limited to 48”?
At higher pressure ratings like 300 psi, flange thickness and bolt loading increase significantly. Beyond 48”, maintaining structural integrity, gasket sealing, and bolt stress becomes less practical, which is why larger diameters are typically handled with lower-pressure classes or alternative designs.
Are AWWA C207 and AWWA C228 interchangeable?
Not exactly.
AWWA C207 and AWWA C228 may share similar dimensional patterns in some sizes and classes, but they are different standards with different material specifications. C207 covers carbon steel flanges, while C228 covers stainless steel flanges, so interchangeability should always be confirmed by checking the exact dimensions, pressure class, and service requirements.
How to order AWWA flanges from API International?
To order AWWA flanges from API International, contact our sales team with your required flange class, size, material, configuration, and quantity. Our team can confirm availability, review any special project requirements, and help you select the correct flange for your application. API International stocks common AWWA flange sizes and can also modify stock products through our machine shop when needed.