Plate Flanges Guide: Steel Plate Flange Types, Materials and Buying Tips

Plate flanges are simple, practical and widely used in industrial piping. A plate flange is usually a flat circular flange made from steel plate, with a center bore for the pipe and bolt holes around the outside diameter. Because the design is straightforward, it can be economical for water treatment, HVAC, general industrial piping, equipment connections and custom fabrication.

This guide explains what a steel plate flange is, how flange plate steel is selected, how flange plates are manufactured, and what buyers should confirm before ordering a standard or custom steel flange plate.

What Are Plate Flanges?

Plate flanges are flat flanges cut and machined from steel plate rather than forged with a long hub. The basic shape includes an outside diameter, inside bore, bolt circle, bolt holes and gasket face. Depending on the application, the flange may be welded to pipe, bolted to equipment or used as a custom connection plate.

In purchasing language, terms such as flange plate, flange plates, flange plate steel and steel flange plate may refer to the same family of flat steel flange products. Clear drawings are important because different markets may use these words slightly differently.

Steel Plate Flanges vs Forged Flanges

Steel plate flanges are often chosen when the service is suitable for a flat plate design and cost efficiency matters. Forged flanges, such as weld neck flanges, usually provide better grain structure and stronger hub geometry for severe pressure, temperature or cyclic loading.

A plate flange can be a good choice for low to moderate pressure systems, especially when the project standard allows it. For high pressure, high temperature, vibration or critical service, engineers should confirm whether a forged flange is required.

Common Materials for Steel Plate Flanges

The most common material for a steel plate flange is carbon steel because it offers strength, machinability and reasonable cost. Stainless steel plate flanges are selected when corrosion resistance, food-related service, washdown or chemical compatibility is important. Alloy steel plate flanges may be used for special temperature or strength requirements.

Material	Typical Use	Key Advantage
Carbon steel	Water, air, utility and general industrial piping	Economical and easy to machine
304 stainless steel	Food, clean water, mild chemical and washdown areas	Good corrosion resistance and availability
316 stainless steel	Marine, chloride, chemical and higher hygiene service	Better pitting and crevice corrosion resistance
Alloy steel	Heat, pressure or special industrial service	Improved strength or temperature performance

How a Flange Plate Is Manufactured

Manufacturing usually begins with plate material selection. The steel plate is checked for grade, thickness and certificate requirements. Blanks are then cut by plasma, laser, waterjet, sawing or other cutting methods depending on size, thickness and order quantity.

After cutting, the flange plate is machined to final dimensions. The bore, outside diameter, bolt holes and gasket face may be turned, drilled, bored, faced or chamfered. For export orders, marking, surface protection and packing are also part of the manufacturing process.

Key Dimensions to Confirm

Before ordering plate flanges, confirm the outside diameter, bore, thickness, bolt circle diameter, bolt hole diameter, number of bolt holes, face type, gasket requirement and pipe schedule. If the plate flange connects to existing equipment, send a drawing or measured dimensions rather than relying only on nominal size.

For custom flange plates, also specify tolerances, surface finish, hole orientation, coating, material certificates and inspection requirements. A small error in bolt circle or bore can stop installation even when the material grade is correct.

Plate Flange Types and Applications

A plate flange may be designed as a slip-on style plate flange, blind plate, backing ring, custom equipment flange, waterworks flange or special adapter. The application determines whether the flange is welded, bolted, used with a gasket or used as a support component.

Common applications include water treatment plants, drainage systems, cooling water, fire protection, HVAC, low-pressure process piping, ducting, tank nozzles, pump connections, valve adapters and OEM equipment. Steel plate flanges are also useful when large diameter or non-standard drilling makes a custom machined solution more practical.

Face Type and Gasket Selection

The sealing face should match the gasket and mating flange. Some plate flanges use a flat face with a full-face gasket. Others may use a raised face or machined gasket seating area. The correct choice depends on pressure, fluid, mating material and project standard.

If the flange is used with cast iron, plastic or other softer mating components, engineers often review bolt load carefully. If the service is higher pressure or chemical duty, gasket material and surface finish become more important.

Inspection and Quality Control

Quality control for steel plate flanges should include material certificate review, dimensional inspection, bolt-hole pattern verification, face finish inspection, marking checks and visual inspection. Depending on the order, additional tests such as ultrasonic testing, magnetic particle testing, liquid penetrant testing or coating thickness inspection may be required.

For stainless steel flange plates, packing should prevent carbon steel contamination and surface damage. For coated carbon steel flanges, the coating should protect the part during storage and shipment without blocking gasket surfaces or threaded areas.

Common Ordering Mistakes

• Ordering by nominal pipe size without confirming bore and pipe schedule.
• Forgetting bolt circle diameter or bolt-hole quantity.
• Using the wrong face type for the gasket and mating flange.
• Specifying only “steel” without material grade or certificate requirement.
• Approving production without a drawing for custom flange plates.
• Choosing a plate flange for service that requires a forged hub flange.

How to Send a Clear RFQ

A clear RFQ for a steel flange plate should include standard, size, pressure or design condition, material grade, plate thickness, bore, outside diameter, bolt pattern, face type, quantity, surface treatment, inspection documents and delivery destination.

For custom work, attach a drawing in PDF or CAD format. If the flange must match old equipment, photos and measured dimensions are helpful. This lets the manufacturer check whether the requested flange plate steel thickness and drilling pattern are suitable before production.

FAQ About Plate Flanges

What is a plate flange?

A plate flange is a flat flange made from plate material, usually with a center bore and bolt holes. It is used to connect pipe, valves, equipment or custom assemblies.

Are steel plate flanges suitable for high pressure?

Some steel plate flanges can be used in approved pressure services, but severe high pressure, high temperature or cyclic loading may require forged flanges such as weld neck flanges. Always follow the design code.

What information is needed for flange plates?

Send material, size, thickness, bore, outside diameter, bolt circle, hole size, face type, standard, quantity, inspection requirement and drawings for custom flange plates.

Need Plate Flanges for Your Project?

Songhai Flange supplies plate flanges, steel plate flanges, flange plates, blind flanges, slip on flanges and custom machined flange products for industrial piping, water treatment, chemical equipment, marine systems and OEM projects. If you need a standard plate flange or custom steel flange plate, our team can support material selection, drawings, machining, drilling, inspection and export packing.