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What Are Carbon Steel Flanges Used For?

Carbon steel flanges are specified across nearly every industrial and municipal piping sector, from municipal water mains to power plants, chemical processing lines, and structural piping. The grade, configuration, and governing standard vary by application. This guide covers where carbon steel flanges are used, the specific applications within each industry, and the material grades and standards that govern their selection.

Water and Wastewater Systems

Municipal water infrastructure is one of the largest applications for carbon steel flanges. For waterworks service, flanges follow AWWA C207, which covers carbon steel flanges up to 300 psi in Classes B, D, E, and F.

Most waterworks flanges are plate-fabricated from ASTM A36, which is cost-effective and well suited to the waterworks pressure range. Ring-type slip-on and blind configurations are the most common types. For ANSI/ASME-rated water piping at higher pressures, A105 forged flanges are specified instead.

Common applications

  • Municipal water mains and distribution networks
  • Water and wastewater treatment plant piping
  • Pump and valve connections
  • Irrigation and drainage infrastructure
API Flanges for Water Waste Work

Power Generation

Industrial Flanges for Energy Power Generation API

Power generation facilities operate piping systems that carry high-pressure steam, cooling water, and condensate at elevated temperatures. These conditions call for forged A105 carbon steel flanges rated to the appropriate ANSI/ASME pressure class, since the joints must hold under sustained pressure and thermal cycling.

Power piping systems are governed by ASME B31.1, which sets material and testing requirements. Flanges are dimensioned to ANSI/ASME B16.5 for standard sizes and ANSI/ASME B16.47 for large-diameter lines.

Common applications

  • Steam distribution and boiler connections
  • Cooling water and condensate systems
  • Turbine and heat exchanger connections
  • Feedwater and utility piping

Chemical Processing

Chemical plants use flanged connections throughout process piping for easy isolation and servicing. Process piping is governed by ASME B31.3, which requires forged A105 flanges for carbon steel service. Where the media is corrosive or the temperature exceeds carbon steel limits, alloy or stainless steel flanges are specified instead.

Face type matters in chemical service. Raised face is standard, while ring-type joint flanges are used for higher-pressure and higher-temperature process lines.

Common applications

  • Process piping and transfer lines
  • Reactor and vessel connections
  • Pump, valve, and instrument connections
  • Utility and service piping within the plant
PULP AND PAPER INDUSTRY

HVAC and Ventilation

API Industrial Flanges for HVAC Industry

Heating, ventilation, and air conditioning systems use carbon steel flanges to join large-diameter ductwork and connect air handling equipment. Because these are typically low-pressure applications, flanges are usually plate-fabricated from ASTM A36 rather than forged. Large diameters that fall outside standard forged availability are cut from A36 plate.

Common applications

  • Large-diameter duct connections
  • Air handling unit connections
  • Mechanical room and plant piping
  • Exhaust and ventilation systems

Agriculture

Agricultural operations use carbon steel flanges in irrigation mainlines, pump stations, and equipment manifolds. These systems handle water at moderate pressure, so plate-fabricated A36 flanges are the economical and practical choice. Domestic availability and fast lead times matter here, since agricultural projects often run on tight seasonal schedules.

Common applications

  • Irrigation mainlines and distribution
  • Pump station connections
  • Equipment manifolds and headers
  • Water transfer and drainage systems
Industrial Flanges for Agricultural Industry

Construction and Structural

API Industrial Flanges for HVAC Industry

In construction, carbon steel flanges connect structural pipe, handrails, and pipe supports. These are non-pressure applications where the flange provides a bolted mechanical connection rather than a pressure seal. ASTM A36, widely recognized as the most commonly used structural steel grade in the United States, is the standard material for this service.

Common applications

  • Structural pipe connections and frames
  • Handrails and guardrail systems
  • Pipe supports and hangers
  • General fabrication and equipment mounting

Carbon Steel Flange Application Overview

The table below summarizes the primary applications and the grades most commonly specified in each.

Industry

Typical Application

Common Grade

Water and Wastewater

Municipal water mains, treatment plants, irrigation systems

A36 (plate), A105

Power Generation

Steam lines, cooling water systems, turbine connections

A105

Chemical Processing

Process piping, reactor connections, chemical transfer lines

A105

HVAC and Ventilation

Large-diameter duct connections, air handling equipment

A36 (fabricated)

Agriculture

Irrigation mainlines and equipment manifolds

A36 (plate)

Construction

Structural pipe connections, handrails, pipe supports

A36

Conclusion

Carbon steel flanges appear throughout industrial and municipal infrastructure because they balance strength, cost, and availability. Water and wastewater, power generation, chemical processing, HVAC, agriculture, and construction all rely on them. A36 serves fabricated and non-pressure applications, while A105 serves code-rated pressure piping.
API International supplies carbon steel flanges for every one of these industries, fully machined to ASTM A105 material requirements and dimensioned per ANSI/ASME B16.5, ANSI/ASME B16.47, and AWWA C207. Explore our full range in the online product catalog, or contact us for custom machining on nonstandard sizes and configurations. Get connected with a dedicated sales representative today, or call us at 503.692.3800

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Frequently Asked Questions

What are carbon steel flanges used for?

Carbon steel flanges connect pipes, valves, and equipment across water and wastewater systems, power generation, chemical processing, HVAC, agriculture, and construction. They create sealed, bolted joints that can be assembled and serviced over the life of the system.

Do I need mill test reports (MTRs) for carbon steel flanges?

On any quality-controlled or code-governed project, yes. Certified mill test reports (MTRs) confirm that the flange meets the specified ASTM chemistry and mechanical requirements. MTRs are required for ASME code-stamped fabrications and most municipal, refinery, and chemical plant procurement. Request them at time of order.

What grade of carbon steel flange is used in water systems?

Waterworks flanges are usually plate-fabricated from ASTM A36 and follow AWWA C207, which covers carbon steel flanges up to 300 psi. For ASME-rated water piping at higher pressures, forged A105 flanges are specified.

Can carbon steel flanges be used in high-temperature applications?

Forged A105 carbon steel flanges are rated for service up to 800°F (425°C) under ANSI/ASME B16.5. Above that temperature, alloy steel grades such as F11 or F22 are required. This is why power and chemical plants use A105 within its range and switch to alloy for hotter service.

Why is carbon steel preferred over stainless steel for most flanges?

Carbon steel offers strength and weldability at a lower cost, which makes it the default for general-service piping. Stainless steel flanges are specified only where corrosion resistance is essential, such as chemical, marine, or sanitary service, because they cost more.