Why Choose Plate Flanges?

API Marketing
April 7, 2026

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flange connections, Plate Flanges welding

How Plate Flanges Are Welded

Plate flanges are cut or machined from flat steel plate rather than forged from bar or billet. They are widely used in waterworks, selected industrial systems, utility connections, and other applications where ring-type slip-on and blind flange styles are appropriate. In simple terms, plate flanges are often chosen because they provide a reliable way to assemble, isolate, maintain, and connect piping systems without overcomplicating the design. For many projects, that balance of practicality, manufacturability, and fit-for-service performance is exactly what makes them the right choice.

Main Reasons to Choose Plate Flanges:

1. Cost-Effectiveness for the Right Scope

Fabricating flanges from plate is simply a more economical manufacturing route for certain geometries and quantities. Cutting and machining from plate can be a practical manufacturing route for common plate-flange styles, especially ring-type slip-on and blind flanges. When the project does not require the added strength or geometry of a forged flange, plate construction can provide a more efficient solution.

Where the savings are most pronounced:

Flange Type	Plate Manufacture	Forged Manufacture
Blind Flange	Very efficient	Higher cost, longer lead
Slip-On Ring Flange	Efficient	Moderate cost
Weld Neck Flange	Not applicable	Standard route
Long Weld Neck	Not applicable	Standard route

The tradeoff is that plate flanges are generally not suitable for the highest pressure classes or cyclic/fatigue-intensive services — but for low-to-moderate pressure waterworks applications, that’s rarely the constraint.

Note: Cost advantage is most significant in ANSI/ASME Class 150 and Class 300 applications, and in AWWA flange categories where the pressure rating doesn’t demand the enhanced mechanical properties of a forging.

2. Direct Alignment with Waterworks Practice

Plate flanges are a natural fit in waterworks service because they are already familiar, accepted categories in that space. The AWWA C207 standard (Steel Pipe Flanges for Waterworks Service) directly addresses plate-style flanges. The standard defines flange classes (B, D, E, F) by pressure rating and describes both slip-on ring-type and blind configurations that are manufactured from plate. In water treatment plants, municipal piping, pump stations, and water distribution systems, the design intent often prioritizes serviceable bolted joints, maintenance access, and dependable field connections.

Relevant AWWA C207 Flange Classes:

Class	Pressure Rating	Notes
Class B	86 psi	Low-pressure service
Class D	150 psi	Common for distribution
Class E	275 psi	Transmission mains
Class F	300 psi	Higher-pressure service

3. A Simple, Proven Connection Method

Another reason to choose plate flanges is the straightforward nature of the connection itself. Slip-on plate flanges use a simple fit-up and fillet weld arrangement, producing a bolted, gasketed joint that is widely understood and easy to service in the field. Blind plate flanges provide equally practical value where a line, nozzle, or opening must be sealed for operation, maintenance, or future expansion.

The installation sequence is straightforward:

Slide the flange over the pipe end
Position to the correct standoff dimension
Apply fillet welds to both the face side and back side of the flange
Machine or verify the gasket face finish
Bolt up with appropriate gasket and fasteners

Note: The dual fillet weld requirement (both internal and external) is important for structural integrity and leak prevention, and is called out explicitly in ASME B31.3 and related codes. Skipping the internal weld — which happens in sloppy fabrication — is a documented failure point and shouldn’t be accepted on any quality-controlled project.

4. Custom Transitions Are Practical to Fabricate

Plate flanges are also chosen because machining from plate makes custom transitions and specialty configurations more practical. Reducing flanges are a routine product in plate flange fabrication. A reducing or transition flange can keep one side standard in bolt pattern or facing while changing the bore or geometry on the other side. That is especially useful where two connected components do not match exactly but still need a clean, functional flange connection.

Situations where this advantage stands out include:

Mismatched bore sizes
One side requiring a standard bolt pattern
Retrofit and modification work
Special equipment or utility tie-ins

5. Material Selection Supports Corrosion Control

Another major advantage of plate flanges is material flexibility. Plate flanges are commonly produced in carbon steel or stainless steel. This means they can be selected in a way that better matches water chemistry, humidity, external exposure, and project-specific service conditions. In corrosive or moisture-sensitive environments, this becomes an important reason to choose one plate flange material over another.

Plate flanges are routinely produced in:

Material	Common Specification	Typical Application
Carbon Steel (A36)	ASTM A36	Standard water service with protective coating
Stainless Steel (304 / 316)	ASTM A240	Corrosive water chemistry, reclaimed water, coastal
Duplex Stainless (2205)	ASTM A240	High-chloride or high-pressure aggressive service

6. The Right Choice When Service Conditions Allow

Plate flanges are often the best choice when the project’s load and service conditions allow them. This is one of the most important points in the whole discussion. Plate flanges are not universally better than forged flanges. They are better when the actual service conditions do not require the extra performance margin, geometry, or specification framework of a forged alternative.

This advantage is strongest when:

The service is low to moderate rather than extreme
The governing specification allows plate-style fabrication
The system does not justify a heavier forged flange
The goal is fit-for-service performance without over-specifying

Summary Table: Why Choose Plate Flanges?

Reason	Why It Matters	Best Fit
Cost-effective for the right scope	Helps avoid over-specifying the connection	Waterworks, utility, and selected industrial service
Direct alignment with waterworks practice	Matches common service expectations in municipal and treatment systems	AWWA-style piping and water infrastructure
Simple, proven connection method	Supports practical assembly, maintenance, and isolation	Slip-on and blind flange applications
Custom transitions are practical	Makes bore and geometry changes easier in special situations	Retrofits, tie-ins, and specialty connections
Material selection supports corrosion control	Allows better matching to environment and fluid conditions	Carbon steel and stainless service
Best choice when loads/service allow	Provides practical performance without unnecessary complexity	Low-to-moderate service conditions

When Plate Flanges May Not Be the Best Choice

It is also worth being clear about what this post does not mean. Choosing a plate flange is not automatically the right move just because it is economical or familiar. In higher-pressure, higher-temperature, high-load, or more code-sensitive service, the project may call for a forged flange or another connection method altogether. That is why the real question is not simply, “Are plate flanges good?” The better question is, “Do plate flanges fit the actual design basis of this system?” If the answer is yes, they are often an excellent choice. If the answer is no, another flange style may be more appropriate.

Conclusion

So, why choose plate flanges? Plate flanges have a clearly defined and well-supported role in industrial and waterworks piping. They’re cost-effective for ring-type and blind geometries, directly aligned with AWWA waterworks standards, simple to install and maintain, and adaptable to custom transition requirements. They are available in corrosion-resistant alloys and are suitable for most low to moderate-pressure water service applications.

The key is not choosing plate flanges by habit. Rather, choose them when the project scope, service conditions, and governing standard all support them. Our sales team at API International specializes in navigating complex flange requirements to ensure your flanges meet your design specifications. Explore our comprehensive range of plate flanges in our online product catalog, or contact us for custom options tailored to your unique project needs. Get connected with a dedicated sales representative today or call us at 503.692.3800.