Plate flanges are made by cutting from a flat steel plate, usually carbon steel or stainless steel. After that, they are machined to precise dimensions, including the bolt holes and the center bore. Unlike forged flanges, which are shaped under high pressure, these flanges begin simply as a flat piece of metal. They are commonly welded to pipe and are widely used where a standardized, economical flanged connection is needed. In practice, the term most often refers to plate-style slip-on (ring-type) flanges and blind flanges used in waterworks and general industrial piping.
Standards Used For Plate Flanges
The most important point for buyers and engineers: “plate flange” is a manufacturing route, not a single universal dimension set. The dimensions, drilling, facing, and pressure/temperature basis come from the standard you build it to.
| Standards Organization | Standard / Specification | Typical Use Environment | Why It Matters |
|---|---|---|---|
| AWWA | AWWA C207 / AWWA C228 | Waterworks service | Common for municipal and industrial water systems. C207 addresses steel pipe flanges for waterworks service, while C228 covers stainless-steel pipe flange joints for water service applications. |
| DIN / EN | DIN EN 1092-1 (PN-rated) | Metric / European systems | Uses PN ratings (e.g., PN10, PN16, PN25) with metric drilling and dimensions for DN piping systems, so bolt patterns and flange geometry differ from ASME Class-rated flanges. |
| ANSI/ASME | ASME B16.5 (Class-rated) | Industrial piping (NPS 1/2–24) | Uses ASME pressure classes (e.g., Class 150, 300, etc.) with standardized dimensions, facing options, and bolt patterns for flanged joints in industrial piping systems. |
Different Types of Plate Flanges
Ring-type slip-on plate flange
- A flat ring flange that slips over the pipe OD and is welded to the pipe (common in waterworks and general service).
- Often specified under waterworks ring-type flange categories (for example, AWWA C207 ring-type slip-on)
Blind plate flange
- A solid flange (no bore) used to seal the end of a line/nozzle or to create an isolation point.
- Explicitly included under waterworks flange standards (AWWA C207 describes blind flanges)
Exhaust Flanges
- Flat plate connectors used to join sections of ducting or exhaust piping with a bolted, gasketed connection.
- Common in low-pressure airflow and exhaust applications, where the goal is a secure mechanical joint rather than a pressure-rated piping flange.
Lightweight Flanges
- Reduced-thickness plate flanges engineered for low-pressure service where full-weight, pressure-rated flanges are unnecessary.
- Typically used on utility and non-critical piping where weight, cost, and ease of handling are priorities.
Reducing / specialty plate flanges
- Reducing flanges are used when you need a bolt pattern and face to match one side, but a different bore size or specialty geometry.
- Commonly used as a transition flange to connect equipment or piping with mismatched sizes or drilling, while keeping one side standard.
What is a Plate Flange Used For?
Plate flanges are used anywhere you need a bolted, gasketed joint for assembly, maintenance, or equipment tie-in:
- Waterworks piping (pump stations, treatment plants, distribution piping): ring-type slip-on and blind flanges are core categories in AWWA C207.
- Stainless water service: stainless flanged joints built to AWWA C228 for stainless piping systems.
- Low-pressure piping systems: ideal where extreme strength and high-pressure ratings are not required (up to ~300 psi, depending on the standard, material, and temperature).
- Municipal water pipelines: used for water supply, irrigation, and treatment systems.
- Industrial gas pipelines: suitable for distributing natural gas and low-pressure industrial gas (where applicable and permitted by the governing spec).
- Ventilation and exhaust lines: common in HVAC, industrial vents, and exhaust stacks.
- Structural utility connections: for general industrial setups where cost savings and ease of handling matter.
- General industrial piping where the system design basis (pressure, temperature, loads, cyclic service) and the governing spec allow plate-style fabrication.
How Are Plate Flanges Welded?
This mainly applies to slip-on / ring-type plate flanges, which attach to pipe by welding.
Typical slip-on plate flange welding (conceptual)
- The flange is fit over the pipe OD and positioned to the correct stand-off/face alignment.
- The attachment is commonly done with fillet weld(s) at the pipe-to-flange junction.
- The exact weld configuration (one-side vs two-side fillet, weld size, inspection/NDE) is dictated by the governing piping code, project specification, and the approved WPS/PQR (welding procedure qualification).
Plate Flanges vs Forged Flanges
A plate flange is cut from plate; a forged flange is formed by forging and then machined. That manufacturing difference affects cost, lead time, and in some cases performance under certain loads and services.
Comparison table
| Factor | Plate flange (cut from plate) | Forged flange |
|---|---|---|
| Manufacturing | Cut from plate + machined | Forged + machined |
| Typical advantage | Cost-effective, flexible for custom geometry, common in waterworks ring-type | Strong standard choice for high integrity / high load services |
| Typical limitation | May be restricted by spec/service; suitability depends on loads, fatigue, and project code | Often higher cost; may be unnecessary for low/moderate service |
| Where commonly specified | Waterworks ring-type slip-on + blind (AWWA C207/C228) | Many ASME B16.5/B16.47 industrial flange applications |
Why Choose Plate Flanges?
Plate flanges are selected when they align with the project’s specification and service conditions:
- Cost-effective for the right scope: Cutting from plate is often an efficient manufacturing route for ring-type and blind styles where the governing spec permits plate construction.
- Direct alignment with waterworks practice: Plate-style ring-type slip-on and blind flanges are standard categories in waterworks flange specifications and are widely used on municipal systems.
- Simple, proven connection method: Slip-on plate flanges attach by straightforward fit-up and fillet welding, creating a common bolted, gasketed joint for assembly and maintenance access.
- Custom transitions are practical: Plate machining makes it feasible to build reducing/transition flanges that keep one side standard (bolt pattern/facing) while changing the bore or geometry.
- Material selection supports corrosion control: Plate flanges are commonly produced in carbon steel or stainless steel so the flange material can be matched to water chemistry, environment, and project requirements.
- Best choice when loads/service allow: For low-to-moderate service where high-load forged styles aren’t required by spec, plate flanges can meet project needs without over-specifying.
Common Plate Flange Specification Errors
Use the checks below to avoid fit-up problems and to ensure the flange you order matches the governing standard, rating system, and service conditions.
- Assuming Class 150 drilling equals any Class 150 flange: bolt-hole patterns can be similar, but dimensions and facing details are standard-dependent (ASME vs AWWA vs DIN/EN) and may vary by product type.
- Mixing PN and ASME Class ratings: PN (metric) and ASME Class (inch) are different rating frameworks with different drilling/dimension conventions, and they are not automatically interchangeable.
- Treating pressure rating as a single PSI number: allowable pressure is material- and temperature-dependent (and may also be affected by service and design basis), so always confirm the correct rating table for the specified standard/material.
Conclusion
Plate flanges are a practical, widely used solution when you need a reliable flanged connection with economical fabrication and flexible materials. Our sales team at API International can answer any questions about your flange requirements and guide you toward the best solution for your system. You can also explore our full range of plate flanges in our online product catalog, or contact us for custom flange options designed to meet your project specifications. Get connected with a dedicated sales representative today, or call us at 503.692.3800