How are Flanges Categorized Based on Their Faces?

As contact surfaces for seating the sealing gasket material, various flange faces are useful. ASME B16.47 and B16.5 describe many types of flanges, such as raised face, male, and female face flanges, and matching facings are made with identical dimensions to give a large contact surface.

The small and big tongue-and-groove flange facings, as well as the ring joint face designed for ring joint-type metal gaskets, are also covered by these standards.


Raised Face (RF)

The raised face flange, also known as a standard type used in process plant applications, is easy to identify. It is referred to mainly as the raised face because the gasket surfaces are raised above the bolting circle face. The face type allows wide combinations of gasket designs, including flat ring sheet metallic composites and double jacketed and spiral wound types.

The purpose of the RF flange is to concentrate more pressure on the smaller gasket area. It thereby helps to increase the pressure containment capability of the joint. Height and diameter are in the ASME B16.5, defined by diameter and pressure class. Flange pressure ratings determine the height of the raised face.

The typical flange face finish for the ASME B16.5 RF flange is 125 to 250 µin Ra (3 to 6 µm Ra).

Raised face height

If we talk about the height measures which is H and B of all described flange dimensions, if we keep in mind the exception of the Lap Joint flange, it is crucial to remember the following things:

. In pressure classes 150 and 300, the height of the raised face is approximately 1.6 mm (1/16 inch). In the two pressure classes, almost all the flanges suppliers are shown in the brochure and catalog; the H and B dimensions include the raised face height.

. In pressure classes of 400, 600, 900, 1500, and 2500, the raised face flange height is approximately 6.4 mm (1/4 inch). Many suppliers show the H and B dimensions in these p

Flat Face

The flat face flange’s gasket surface is in the same plane as the bolting circular face. Flat face flanges are widely used in applications where the flanged fitting or mating flange is constructed of a casting. Bolting flat face flanges to raised face flanges is never a good idea.

According to the ASME B31.1, when connecting flat face cast iron flanges to carbon steel flanges, remember to remove the full-face gasket. It prevents the thin, fragile cast iron flange from being sucked into the gap created by the carbon steel flange’s elevated face.

Ring type joint

At high pressures, ring-type joint flanges are used. They have grooves carved into their faces, and steel ring gaskets are included. The flanges seal with the tightening of bolts to compress the gasket between the flanges into the grooves. This process will deform the gasket to make intimate contact inside the grooves and create metal to metal seal.

A ring-type joint flange may come with a raised face with a ring groove machined into it. However, the raised face does not serve any part in the sealing mechanism itself.

Ring-type joint gaskets

Ring-type joint gaskets are metallic sealing rings that suit high-temperature applications and high pressures. They are always applicable to special, accompanying flanges, which ensure good, reliable sealing with the right material and profiles.

Ring-type joint gaskets are designed to seal by “initial line contact” or welding action between the mating flange and gasket. Then, with the pressure on the seal interface through bolt force, the ‘softer’ metal of the gasket flows into the microfine structure of the more complex flange material and creates an efficient and tight seal.

Tongue-and-groove (T&G)

The Tongue and Groove faces of the flanges need to match properly. One flange face has a raised ring (Tongue) machined onto the flange face, while the mating flange has a matching depression (Groove) machine into the face.

Tongue-and-groove facings are standardized in both small and large types. They differ from males and females in the inside diameter of the tongue, and the groove does not extend into the flange base. This helps in retaining the gasket on its outer and inner diameter.

Male-and-female (M&F)

A flange must match this flange category. For example, one flange face comes with an area that extends beyond the normal flange face (Male). However, the other flange or mating flange comes with a matching depression (Female) machined into its face.


The above description clearly shows the flange characterization based on their faces. If you want to learn more about flanges, can contact Texas Flange today!

Difference Between ANSI and ASME

American Society of Mechanical Engineers (ASME) and American National Standards Institute (ANSI) are important organizations in the flange industry. Each of them plays an integral role in developing the standards and codes that govern the industry.

Many people usually fail to understand the difference between the two or realize that these organizations are technically two distinct non-products that work separately and impact the flange industry.

Here in this blog, we’ve tried to make it clear about the difference between the two. Before that, we must explain the meaning of each term.

Meaning of ANSI

ANSI was established in 1918. The focus of ANSI is to oversee standards for services, systems, processes, and products offered in the US. The organization consists of members from organizations and corporations, as well as scholars from different academic fields, companies, and government agencies.

The primary purpose of ANSI is to work in a way to solidify the position of the US in the global market by establishing the standards for services and products. The goal is to ensure that the performance and feature levels of items created in the US are consistent and up to par.

Adding on, ANSI accredits organizations that train personnel and produce products to meet their established requirements and standards. They always keep an eye on and check if the services and products are meeting their standards well. They need to consider and update these performance requirements as per the need. They also play a huge role in some initiatives about environmental conservation.

Meaning of ASME

ASME was founded decades before ANSI in 1880 and is one of the oldest standards to develop the organizations in existence. The establishment of society happened after numerous failed occurrences of steam boiler pressure vessels that were devastating. The main focus is to create standards and codes for mechanical equipment.

In the industry, especially the ASME code, it is also called ASME Boiler & Pressure Vessel Code. The main reason for its establishment is to regulate the manufacturing, development, and design of the boilers utilized in various industries.

ASME serves as one of the leading international developer codes and standards to regulate the mechanical engineering industry. It is one of the private organizations to promote multidisciplinary engineering, science, art and encouraging collaboration across engineering disciplines. ASME also involves various industry and periodicals publications, education courses, professional development, and conferences.

How ASME and ANSI differs

At the first look, you can see that ASME and ANSI seem to play similar roles in the industry. But in reality, many things set them apart. You can see it from the description above. Now here are a few crucial distinctions that set the two apart:

1. The foundation of ASME happened decades before ANSI came into existence. ASME was founded in 1880, while ANSI was founded in 1918.

2. The main focus of ANSI is to strengthen the US market position, while the focus of ASME was to develop solutions to mechanical engineering safety issues and problems.

3. ANSI accredits and established quality and performance standards for services and products in a huge variety of sectors, while the primary focus of ASME is on pressure vessels and boilers.

4. ANSI works towards strengthening the position of the US in the global market, whereas ASME works towards finding the solutions to real-time mechanical engineering problems.

5. ASME has developed 600 standards and codes for various mechanical devices, while ANSI has designated approximately 9500 standards.

6. The ASME members include engineering professionals and individual volunteers from other organizations as its members. On the other hand, ANSI members are chosen individuals from organizations, academic fields, government agencies, and corporations.


It is essential to know the difference between ANSI and ASME before anything. If you order a flange fitting at Texas Flange, you will get products that adhere to ASME B16.5, B16.47, or B16.9 per your project requirements.

Use of ASME B16.5 Standards for Flange Pressure Ratings

Engineers rely on ASME/ANSI standards and codes. The construction of the piping system helps to make sure that they meet the prescribed requirements of pressure integrity. The standards and codes help to determine the characteristics of pressure integrity and simplify the design rules.

The difference between the codes and standards is helpful for the designers with detailed flange specifications and designs for the components. Here are the frequently encountered rules and standards:

1. Minimum wall flange thickness

2. Permissible materials for construction

3. Allowable work stresses

Structural behavior is due to the effects of thermal expansion, live loads, seismic loads, deadweight, internal pressure, and other imposed external or internal loads.

However, the piping codes provide no design rules for standard in-line components like standard valves and flange fitting components. The designing of these classes of elements happens through the reference to the industry standards.

1. Pressure-integrity standards: The standards help in providing uniform minimum-performance criteria. The designing and manufacturing of the components to the same standards will be helpful to function equivalently.

It helps to remember that pressure integrity is not entirely synonymous with leakage integrity. During the operation and test, pressure integrity is one assurance when it comes to the leak-tight condition and does not account for the entire risk profile to the structural stability of the pressure boundary or added stresses.

2. Dimensional standards: The standards provide the configuration that helps in controlling the parameters for components. The primary purpose of these dimensional standards is to ensure that the manufacturing of similar parts by different suppliers will be physically interchangeable.

Conformity to the specified standards of ASME flange dimension during manufacturing a product doesn’t imply that the configuration of all such similar products will provide equal performance.

There are many different ASME standards for piping components that provide pressure-temperature ratings in their included “Reference Codes and Standards” sections.

As per the ASME B16.5, 2017, there are:

a. 16 nonferrous metal groups

b. 10 high-alloy steel material groups

c. 8 low-alloy steel and carbon material group

If you want to check the complete lists and tables, you can check them on ASME B16.5, 2017. (Standard: “Pipe Flanges and Flanged Fittings: NPS ½ through NPS 24 Metric/Inch Standard”.)

The flanges with any material in the same group can easily carry the same pressure class of ASME flange and have the same pressure-temperature rating for almost any single material group.

The ASME B16.5 standard provides the 7 pressure classes for flanges. These are – 2500, 1500, 900, 600, 400 (less common today), 300 and 150. Class 75 also exists in ASME B16.47 Series B large diameter.

The rating for flanges in terms of pressure temperature represents all the material groups organized within 44 tables. One table includes the ASME B16.5 2017 ed, for every material sub-group or group.

Table B2.1 is the adaption from ASME Standard B16.5 and is typical of the 34 flange rating tables that provide the pressure-temperature ratings for the flanges in the 2.1 material group.

The tables you will find below are organized as per the pressure classes that you can find at the top. At the left-hand border, you can also find the maximum working temperatures.

During the practice, using ASME B16.5 to determine the rating of the flange is relatively easy. Below is the recommended three-step process:

a. Determine the maximum temperature and operating pressure required for the flange.

b. You can select the material of the flange from the material groups of the 44 listed materials. Be aware of the qualifying notes that concern maximum operating temperatures for various materials that may influence the final material selection.

c. You must consult the right group table of material. You can start with the temperature listed in one increment higher than the desired maximum operating temperature. Try to start with the Class 150 column and then proceed to the right until you find the proper pressure rating for the desired temperature, exceeding or equal to the required operating pressure.

The specified column that can satisfy the requirements can dictate the required pressure class and determine the actual pressure-temperature rating of the flange.

ASTM A182 is one of the chrome-based material specifications from material group 2.2.

If you consult Table B2.2 at a temperature of 650°F (343°C), a Class 600 flange has a rating of 890 psig (6136 kPa gage) at 650°F (343°C).

Table A1.1 Materials Used for ASME B16.5 Flange Construction (Partial Listing)

ASME B16.5 Flange Construction
Table B1.1 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 1.1 Materials

Table B1.1 Pressure-Temperature Ratings
Table B2.1 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 2.1 Materials

Table B2.1 Pressure-Temperature Ratings
Table B2.2 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 2.2 Materials

Table B2.2 Pressure-Temperature Ratings

If you still have any doubts about how to select flanges and what to look for, do let us know in the comment section or call us today!