How to Pick Out the Right Pipe Flanges for Your Project

Oil and gas plants are large, complex environments with thousands of miles of interconnected piping. The Pipeline and Hazardous Materials Safety Organization estimates that there are 160,521 miles of liquid petroleum pipeline and 1,585,672 miles of natural gas pipeline in the United States. Pipe flanges are a critical part of the piping systems, interconnecting pipe fittings to other equipment.

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Flanges come in various standard dimensions, according to different publications from organizations such as ASME, API, MSS, and others. Projects in the oil and gas sector are unique, necessitating specific pipe flanges to perform the job.

Nearly all flanges are round discs that interconnect valves, pipes, strainers, and fittings. Different shapes such as rectangles, squares, or oval are specific to speciality equipment such as hydraulics. Knowing the different types and standard dimensions can assist you in ordering the correct flanges for your piping systems. Here are some steps to take to pick out the right pipe flanges for your project.

1. Define Your Standard or Specification

Originally, pipe flanges came in standard weld neck, threaded, or blind configurations. As fittings came into the oilfield, standard dimensions became necessary for functional interchangeability. The late s saw the American Petroleum Institute (API) adopt the ASA B16.

Over the years, more standards, sizes, definitions, and pressure classes were added. Most of the standards represent the dimensions, tolerances, and chemistry of the materials. Details of the standard dimensions include the number, size, and diameter of bolt holes, as well as the flange face.

Standard dimensions are the same for all materials used. However, the specifications are regularly revised, broadened, and updated. Standard classifications often used in the oil and gas industries include:

• 150#
• 300#
• 600#
• 900#

Each of these standards classifies flanges by pressure class, facing, pipe size, and connection.

2. Figure Out the Flange Facing

Defining the facing of your flanges is one of the first steps to ordering the industrial pipe fittings. The face of the flange is the sealing surface. The most common types of flange faces include:

• Raised face
• Lap joint
• Large male and female
• Ring-type face
• Flat face
• Full face

The raised face is the most common industrial flange facing. The standard dimensions may vary depending on the classification. Class 150# and 300# have a 1/16-inch raised face. Class 400# to # have a 1/4-inch raised face. Lap joint types have flat faces and are used together with a stub end. Flat face flanges utilize the whole face for sealing and are popular for low-pressure applications. The ring-type face uses a metal ring gasket that fits into the groove in the flange. You can modify your flange faces as long as the minimum standard dimensions are maintained.

3. Pick Out the Correct Pressure Class

The pressure class of a flange standard determines its dimensions. The pressure class rating may fall within 125 to 900 psi. Four factors that influence the pressure limits of the flanges within the oil and gas industry include:

• Dimensions, thickness, number, and size of bolts
• Internal and external temperatures
• Material used
• Flange sizes

You may need to consult your fitting distributor to determine the right flange pressure class for your project.

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What Are Pipe Flanges and How Do They Work?

Offering a reliable way to connect pipe systems with the various equipment, valves, and other components of virtually any processing system, flanges are the second most used joining method after welding.

Using flanges adds flexibility when maintaining piping systems by allowing for easier disassembly and improved access to system components.

A typical flanged connection is comprised of three parts:

• Pipe Flanges
• Gasket
• Bolting

In most cases, there are specific gasket and bolting materials made from the same, or approved materials as the piping components you wish to connect. Stainless Steel flanges are some of the most common. However, flanges are available in a wide range of materials so matching them with your needs is essential.

Other common flange materials include Monel, Inconel, Chrome Moly, and many others depending on the application.

The best option for your needs will depend on both the system in which you intend to use the flange and your specific requirements.

Common Flange Types and Characteristics

Flanges are not a one-type-fits-all sort of solution. Sizing aside, matching the ideal flange design to your piping system and intended usage will help to ensure reliable operation, a long service life, and optimal pricing.

Here’s a look at the most common flange types available.

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Making the Connection: Flange Facing Types

Flange design is only the start when considering the ideal flange for your piping system. Face types are another characteristic that will have a major impact on the final performance and service life of your flanges.

Facing types determine both the gaskets needed to install the flange and characteristics related to the seal created.

Common face types include:

• Flat Face (FF): As the name suggests, flat face flanges feature a flat, even surface combined with a full face gasket that contacts most of the flange surface.
• Raised Face (RF): These flanges feature a small raised section around the bore with an inside bore circle gasket.
• Ring Joint Face (RTJ): Used in high-pressure and high-temperature processes, this face type features a groove in which a metal gasket sits to maintain the seal.
• Tongue and Groove (T&G): These flanges feature matching grooves and raised sections. This aids in installation as the design helps the flanges to self-align and provides a reservoir for gasket adhesive.
• Male & Female (M&F): Similar to tongue and groove flanges, these flanges use a matching pair of grooves and raised sections to secure the gasket. However, unlike tongue and groove flanges, these retain the gasket on the female face, providing more accurate placement and increased gasket material options.

Many face types also offer one of two finishes: serrated or smooth.

Choosing between the options is important as they will determine the optimal gasket for a reliable seal.

In general, smooth faces work best with metallic gaskets while serrated faces help to create stronger seals with soft material gaskets.

The Proper Fit: A Look at Flange Dimensions

Apart from the functional design of a flange, flange dimensions are the most likely factor to impact flange choices when designing, maintaining, or updating a piping system.

However, you must consider how the flange interfaces with the pipe and the gaskets in use to ensure proper sizing.

Common considerations include:

• Outside diameter: The distance between two opposing edges of the flange face
• Thickness: A measure of the thickness of the outer attaching rim
• Bolt circle diameter: The distance between opposing bolt holes when measured from centre to centre
• Pipe size: A designation of the pipe size with which the flange corresponds
• Nominal bore size: A measurement of the flange connectors inner diameter

Flange Classification & Service Ratings

Each of the above characteristics will have an influence on how the flange performs across a range of processes and environments.

So how can you tell which flanges are up to the task and which are not?

Flanges are often classified based on their ability to withstand temperatures and pressures.

This is designated using a number and either the “#”, “lb”, or “class” suffix. These suffixes are interchangeable but will differ based on the region or vendor.

Common classifications include:

• 150#
• 300#
• 600#
• 900#
• #
• #

Exact pressure and temperature tolerances will vary by materials used, flange design, and flange size. The only constant is that in all cases, pressure ratings decrease as temperatures rise.

Flange Standards and Markings

To help make comparison easier, flanges fall under global standards established by the American Society of Mechanical Engineers (ASME) -- ASME B16.5 & B16.47.

If you’re attempting to replace or verify existing parts, all flanges must include markers -- typically on their outer perimeter -- to aid in the process.

These markers also follow a strict order:

• Manufacturer logo or code
• ASTM material code
• Material Grade
• Service rating (Pressure-temperature Class)
• Size
• Thickness (Schedule)
• Heat Number
• Special designations, if any -- for example, QT for Quenched and tempered or W for repair by welding

This guide offers a solid foundation of the basics of flange design and how to choose the ideal flange for your piping system. However, with a wide range of stainless steel flanges and other flange materials available, it is impossible to list every configuration, detail, or consideration.

Should you have questions, the Technical Sales Experts at Unified Alloys are ready to help. Serving industries and businesses across North America and Canada for more than 40 years, we understand the complexities of alloy piping and the needs of your industry. Call us today for additional information and to find the ideal flange, piping, and components for your next project.

Contact us to discuss your requirements of Steel Pipe Flanges(ru,fr,kk). Our experienced sales team can help you identify the options that best suit your needs.