Flange FAQ, Answered

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Flanges can be welded or screwed on, depending on the type of flange and piping system requirements. When selecting a flange type, some important aspects include pressure capacity, pipe size, and intended application.

Common flange types include:

• Ring or slip-on flanges
• Lap-joint flanges
• Threaded flanges
• Socket weld flanges
• Weld neck flanges
• Blind flanges

A raised face (RF) flange is a type of pipe flange where the gasket surface is raised above the bolting circle face. This design concentrates sealing pressure on a smaller gasket area, creating a tighter and more reliable seal.

Yes. Raised face flanges are designed to be used with gaskets placed on the raised portion of the face. Sealing is achieved by compressing soft, flat, or semi-metallic gaskets (such as spiral wound or ring gaskets) between the mating flange faces.

• RTJ (Ring Type Joint) flanges use a machined groove with a metal ring gasket to achieve a metal-to-metal seal, making them suitable for very high-pressure and high-temperature service.
• RF (Raised Face) flanges use a gasket compressed on the raised surface area, making them more common in general industrial applications with moderate to high pressures.

A flange gasket is a sealing component placed between two flanges to prevent leaks. It fills small surface imperfections and creates a tight, reliable seal under pressure, temperature changes, and vibration.

Common standards include:

• ASME B16.5 (NPS 1/2 to 24): The most common industrial flange standard for steel/alloy flanges.
• ASME B16.47 (NPS 26 to 60): Used for large-diameter industrial flanges. Includes Series A (more common) and Series B (different/lighter bolt pattern).
• AWWA C207 (steel ring/plate flanges) — widely used for larger-diameter, plate-style flanges in industrial service (including the lumber industry).
• AWWA C228 (stainless steel pipe flanges) — commonly specified when stainless steel construction is required for corrosion resistance and waterworks-style bolt-up compatibility.

AWWA flanges are primarily used in waterworks applications and cover larger size ranges (up to 144″ in diameter) but lower pressure ratings.

ANSI/ASME B16.5 flanges are designed for industrial systems with higher pressure requirements and cover smaller diameters (up to 24″ in diameter).

ANSI / ASME B16.47 flanges cover the remaining sizes from 26″-60″ in diameter.

Pressure classes are defined in AWWA as B, D, E, and F for carbon steel and as SA, SB, SD, SE, and SF for stainless steel. In ANSI/ASME pressure classes, the pressure classes are defined as 150, 300, 400, 600, 900, 1500, and 2500.

ASME / ANSI Class 150 and Class 300 are pressure classes that indicate the flange’s allowable pressure capability at a given temperature. In general, Class 300 is rated for higher pressure service than Class 150, and it typically has heavier dimensions (thicker flange, different drilling by size) to support that duty.

The American Water Works Association (AWWA) provides two main standards for flanges for water-work applications:

• AWWA C207 – carbon steel flanges
• AWWA C228 – stainless steel flanges

These standards also define dimensions, drilling patterns, pressure ratings, and material properties.

It depends on the nominal pipe size and material, but waterworks flange classes are commonly chosen in ranges that support lower to moderate working pressures. For AWWA carbon steel and stainless steel waterworks flanges, typical working pressures are often specified: up to 50 psi (Class SA) through up-to 300 psi (Class F), depending on nominal pipe size and class.

Flange “Class” (e.g., 150, 300, 600) is a pressure–temperature rating system. Selection should be based on the design pressure and design temperature, then verified against the applicable ANSI / ASME B16.5 (standard sizes) or ANSI / ASME B16.47 (large diameter) pressure–temperature rating tables. Higher temperature services often require a higher class.

Common waterworks practice is full face gaskets on flat faced joints, especially in valve and municipal service. The ideal gasket material depends on water chemistry (chloramines, ozone, temperature), pressure class, and whether it is potable service.

Flanges are commonly used where you want a rigid, bolted joint and easy equipment removal (pumps, strainers, valves). Grooved couplings are often chosen to speed installation and help manage vibration/noise in mechanical rooms and long pipe runs.

Yes. Flanged joints are often a practical choice for slurry or farm waste lines because they provide a reliable gasketed seal while still allowing sections of pipe to be unbolted and removed for maintenance. They also simplify tie-ins to pumps, valves, and instrumentation. Because slurry and waste environments are typically corrosive, flanges are commonly specified in stainless steel or with protective coatings, along with appropriate bolting, to improve service life.

DIN flanges are not interchangeable with ANSI- or ASME-rated flanges or piping systems because mismatched flanges cannot be mated.

There is no exact DIN-to-ANSI flange conversion—even if the bolt holes align, there may be a disparity between pressure ratings or other aspects of the standards. While adapters can be custom machined to facilitate matching European standard and American standard piping components, using the appropriate DIN components is a quicker, easier option.

It depends on the line’s duty and maintenance needs:

• Flanges: strong and serviceable, easy to disassemble for maintenance (but require more bolting and gasket management).
• Welded joints: permanent and robust, but slower to modify/repair and harder to service quickly in the field.
• Grooved couplings: commonly used in mines for faster installation and accessibility. Selected product lines are designed specifically for mining services including slurry/tailings.
• Expansion joints: used where the system must accommodate thermal growth, movement, or maintenance needs in long runs. Expansion joints help manage expansion and reduce piping stress when movement is unavoidable.

Raised Face (RF) is common for many plant services. Ring-Type Joint (RTJ) is usually specified for higher-pressure/higher-integrity joints where a metal ring gasket and machined groove are required. The plant spec typically dictates facing based on service criticality.

Flanges and fittings are commonly used across process piping, equipment connections, and specialty components that support lumber operations. They’re widely used by facilities in:

• Pulp and paper
• Veneer
• Plywood
• Dimensional lumber
• ACB utility pole manufacturing

Flanges and fittings are most commonly used anywhere a data center needs serviceable, leak-tight, pressure-rated connections, especially on:

• Cooling systems
• Water distribution and utility piping
• Backup power lines

Common exhaust flange materials include carbon steel, such as ASTM A36 or ASTM A105. They are often used when cost is a priority, and the risk of corrosion is managed. Stainless steel, such as ASTM grades 304L or 316L, is often selected for better corrosion resistance and longer service life.

The main difference is corrosion resistance. Stainless steels contain additional elements including chromium, which forms a protective oxide layer that resists rust and chemical attack, making it ideal for corrosive or sanitary environments. Carbon steel, while stronger and more economical, is more prone to rust and usually requires protective coatings for long-term usage.

Common grades for carbon steel flanges include ASTM A105 (forged carbon steel, used in high-temperature services) and ASTM A36 (low-temperature mid/low carbon steel). These grades ensure the flanges can handle specific pressure, temperature, and environmental conditions.

While both 304 and 316 stainless steel are corrosion-resistant, 316 stainless steel includes nickel and molybdenum for better performance at higher temperatures and improved corrosion resistance. Because it offers better resistance to pitting corrosion from saltwater, 316 stainless steel is preferred for marine environments over 304 stainless steel.

The zinc coating protects against rust and moisture, which makes them more durable and low-maintenance than uncoated or painted flanges.

They provide long-lasting corrosion resistance, are ANSI/ASME-compliant, and extend the service life of piping systems.

Absolutely. Domestic-compliant flanges still meet the same ASME or AWWA dimensional standards and can be used in the same piping systems. The difference is that their material origin and manufacturing processes satisfy AIS, Buy America, or BABA requirements.

A custom flange is designed to meet requirements that standard flanges cannot. This may include unique sizes, bolt hole patterns, materials, or face types tailored for specific piping systems. They provide flexibility when off-the-shelf options do not fit, ensuring a safe and reliable connection.

Lead times for custom flanges vary depending on complexity, material availability, and order size. In many cases, quick-turn manufacturing is available to reduce downtime, while larger or more complex projects may require additional time for design and machining.

A reducing flange connects pipes of different sizes while maintaining the same bolt circle and face dimensions, allowing for smooth changes in diameter without extra fittings.

A hub flange has a reinforcing hub or collar that provides extra strength, centers the pipe during welding, and improves stress distribution between the flange and the pipe.

No—gaskets are designed for one-time use.

Reusing them can cause leaks, uneven compression, or flange damage.