Meaning and Types of Flange Faces

The flange face is the surface area that receives the gaskets. The material of the gasket seats over the flange face and creates an effective sealing under pressure.

Forged Flanges

The flange face is designed per the ASME B16.6 for flanges up to 24 inches and ASME B16.47 for 26-inch flanges and larger. To prevent leakage problems, many kinds of flange faces are produced.

Meaning of flange face finish

The ASME B16.5 code needs the flange face (flat face and raised face) to come with a specific roughness. It ensures that the surface is compatible with the gasket.

It helps provide a high-quality seal. A serrated finish, either spiral or concentric, is required, with 30 to 55 groves every inch.

It comes with a resultant roughness between 125 and 500 micro inches. It allows for many grades of surface finish that should be available by the flange manufacturers for the gasket contact surface of the metal flanges.

In this blog, we will learn about various flange faces and types of flange face finishes.

Types of Flange Faces

The ASME B16.47 and ASME B16.5 standards refer to 6 different flange faces. These are:

Lap joint flange

The lap joint flange comes with a flat side that is not useful in sealing the flange. Instead, the joint accommodates the back of the stub end. The sealing surface has a stub end and can be either raised or flat.

Ring joint flange (RTJ)

Ring-type connection flanges come with high pressure (class 600 and above) and high-temperature applications above 800°F (427°C). They come in a groove cut into the faces that are steel ring gaskets.

As the tightened bolts force the gaskets between the flanges in the groove, the flanges seal and deform the gasket to seal it in the groove. It creates a metal-to-metal seal.

The RTJ flange comes with a raised face with a machined annular groove. The raised surface doesn’t act as a sealant.

In the case of O-ring sealing RTJ flanges, the raised faces of the flanges are clamped and mated together that may come into contact.

In this case, the compressed gasket doesn’t usually carry the load beyond the bolt tension, movement, or vibration. It will also not crush the gasket and reduce joint stress any further.

Raised face flange (RF)

Raised face flanges are the most common in the identifiable and plant application process. It is called raised face, as the sealing face is higher than the circular bolt face.

The face type enables a wider range of gasket design combinations such as double wall type, spiral wound type, flat ring sheet type, and other metal composite materials.

Flat face flange (FF)

Flat-face flanges have a sealing surface in the same plane as the circumferential bolt surface. Therefore, flat face flanges need to come with bolted-to-raised face flanges.

In addition, a soft type (non-metallic) full-face gasket is usually useful in the two flat-face flanges while it makes a joint connection. The type of flange face is also known as the plain face.

Flat-face flanges are preferable in low-pressure applications. These flanges are not suggested to mate with the RF flange.

Male and female flange (M&F)

Male and female flanges need flange adjustments. The flange face possesses an area beyond the normal (male) flange face. The mating or other flange comes with a matching recess (female) machined in the face.

The female face is 3/16” deep, and the male face is ¼” high. It comes with a smooth finish. The outer diameter of the female face is used to hold and locate the gasket.

The two available versions are large and small M&F flange. In addition, custom male and female shrouds are often found on the heat exchanger shells that cover and channel the flanges.

Large and small tongue-and-groove flange (T&G)

The groove and tongue surfaces of the flanges are essential to match. For example, one flange face has raised ring (Tongue) machined into the flange face. The mating flange has a matching recess (groove) machined into the face.

Tongue and groove facings come in both small and large sizes. They differ from female and male threads in the inner diameter of the groove and tongue. It does not protrude into the flange base by retaining the seal at its outer and inner diameters. These are found commonly on cam and pump covers.

Contact Texas Flange today if you have any questions about Flange’s face.

What Is A Flange Coupling And What Types Of Flange Couplings Are There?

The purpose of a flange coupling is quite simple. It is a driving coupling between rotating shafts that consists of flanges, one of which is fixed at the end of each shaft. The two flanges bolted together with a ring set of bolts completes the drive connection.

Flange coupling

Flange coupling involves bringing the two tube ends together in a flush, sealed manner. The two-piece coupling unit consists of a keyed receiving side for the flanged end to be fastened. The reason being it may be married to the opposing tube end, which also has a flanged end.

Most flange coupling assemblies have either a female or male coupler opening so that when the two ends are brought together, they are aligned without causing drag or resistance in the material being passed through them. The female or male coupling method also creates a stable connection, resistant to shifting, keeping the flange coupling sturdily in place.

A flange coupling is useful in pressurizing the piping systems where tubing ends or two pipes need to come together. The connecting methods for flange couplings are usually quite strong. The reason is either the pressure of the material or the sometimes hazardous nature of the materials passed through many industrial piping systems. Bolt connections and high thread count nut are used to securing the flange coupling place. These bolts and nuts are usually made from tempered alloys or steel to provide the enduring strength and ability to tighten to the utmost level and ensure that the piping system doesn’t leak at any flanged junction.

Flange Couplings


Keys are machine elements used to prevent any relative rotational movement between a mounted shaft and the parts mounted on it.

If you want to make the joint, grooves or keyways are cut on the surface of the shaft and in the hub of the part to be mounted.

Mounting at an intermediate location on the shaft, the key is placed firmly in the keyway of the shaft, and then the part to be mounted is slid, until it gets fully engaged.

Types of Flange Coupling

The need for couplings arises after purchasing a heavy working costly motor and pump for it because they both need to be well-connected and ensure to be utilized properly while protecting the other components at the same time.

It is unavoidable to couple both the shafts, and it would be simple if they could be seamlessly aligned, and shafts never moved because of the machine vibrations.

Usually, there are 3 types of flange couplings; they can be classified as protected, unprotected, and marine flange coupling.

Protected Flange Coupling

If you want to make it protected, this kind of flange coupling, the protruding nuts and screws are shielded by flanges on both parts of the coupling. This kind of course of action helps to sidestep risks for the laborers.

Marine Flange Coupling

When it comes to Marine Flange Coupling, flanges are formed integrally with the shafts. Depending on the perimeter of the shafts, the number of bolts used is decided. It ranges from 4 to 12 bolts. These types of flange coupling elongated bolts without a head are used to hold the shafts together.

Unprotected Flange Coupling

When we talk about unprotected flange coupling, each shaft is entered in the main flange with a security key that modifies into the keyways of both shafts and the essential flange of the machine. The flanges are consolidated with the assistance of bolts and screws.

If we talk about these types of coupling, about three to six screws are utilized to affix the flanges. Keyways may cause a debilitating impact on the flange coupling by making a gap. If you want to moderate the equivalent, the keys are balanced at the correct point along the perimeter of the shafts.


The growing industrialization and an upsurge in need of technological advancement and engineering tools are taking place worldwide, and specific large companies have built up new industrial applications around them. We at Texas Flange are the leaders in manufacturing a wide range of products, and though couplings are not our specialty, we love to help our customers find what they need.

If you have any further inquiries, contact Texas Flange today!

How to Remove Exhaust Flange Bolts Easily?

Although not in our supply chain, we have had a few questions regarding other types of flange bolting and installation. Here is a basic guide to exhaust flange assembly.

Exhaust flanges consist of a pair of metal sections that join your exhaust pipe together. They are helpful in conjunction with an exhaust set of bolts and gaskets. The usual options of exhaust flanges are the 3 bolt or 2 bolt types. Usually, m10 with the 2 bolt option is helpful, and an m8 bolt for the 3 bolt. The recommended grade of bolts is 8.8 tensile or higher so that you can tighten them without stretching or breaking the bolts. There is also the use of locking nuts, Loctite, or spring washers. It helps to prevent the nuts from vibrating loose.

How Exhaust Flanges Work

Exhaust flanges work with the use of a set of bolts and gaskets to join them together. When you set up a wastegate pipe or exhaust for ease of fitment, you must use v bands or exhaust flanges to enable the sections to re-fit or pull off for access. You can also use exhaust flanges without gaskets, and for that, you need to use automotive-grade silicon.

How to Remove Exhaust Flange Bolts Easily

Welding Exhaust Flanges

Welding exhaust flanges are almost the same thing as welding v band flanges. The essential factor to start with is tack welds every 20-30mm. It helps prevent distortion stitch weld the flange and let it cool down between welding.

How to Remove the Exhaust Flange Bolts

The changing temperatures from cold to hot of the exhaust system together without changing the moisture conditions can result in speeding up the rusting of the flange bolts. If the rust progresses, it could reach the threads, and these may go useless. It is essential to replace and release the flange bolts. You need to apply heat to remove the rust from the threads. If the threads are unusable, you need to cut the bolts from the flange.

Here are a few easy steps to remove the exhaust flange bolts easily:

Keep a check if the area on the flange bolts has no fuel lines as well as combustibles. Clearance of all the combustibles underneath the vicinity for safety is essential.

Use gloves and goggles to protect your hands and eyes.

It is better to have a fire extinguisher closer in case the fire starts.

Ignite the torch carefully. Make sure that the bright blue flame is half or one inch long.

The tip of the torch must be 6-8 inches away from the flange bolt until it has a dull orange color. You need to turn off your torch. Heat the bolt slowly and do not use air to trigger it.

It is better to let the flange bolt cool down and place the socket that fits the bolt to the ratchet.

Slide the socket to the nut that is at the flange bolt. If the bolt loosens, continue with the same process for the rest of the bolts. If it doesn’t budge, go to the next step.

Keep the tip 3-4 inches further and set the flames again.

Heat the bolt once again and when it turns to a bright orange glow, use the air to trigger and blow out more oxygen. Bolt would then start to meltdown.

Turn your torch off and quickly hammer the threaded side of the flange bolt. Repeat the process until the bolt is out of the exhaust.

Let the hot bolt cool down for around thirty minutes. Make sure no combustible materials are lying around before you leave the area.

Throw the cut bolts after another hour or two to ensure that the bolts are at room temperature and won’t cause fires in the garbage bin.


If the problem persists and it becomes impossible to remove the exhaust flange bolts, it is better to consult professionals. Contact your local supplier for more information.

How Are Flange Bolts Tightened?

Bolted flange joints are used widely in water mains. It is the reason why a proper bolt tightening sequence in flanged joints is a must. This precaution helps in controlling the stress variation in flange joint components. If not done right, the chances of leakage are higher at flanged pipe joints during the operating conditions.

There must be a correct bolt placement by tightening them properly and that of gaskets and their placement in a flanged joint that will help ensure a leak-free joint. With the help of proper bolt tightening, it will also help you make sure that there is uniform load distribution in all the bolts without injuring the gaskets. In this blog, you’ll learn how you can properly tighten the bolts of the flange.

Before you begin with the actual flange bolting, the bolts/nuts, gasket, flange need some observation.

Checking points of flange before bolt up

If there is any leakage through the flanged joint, the layout of gasket material prevents the flange surface from any type of imperfection and seals them. You can see the limitations that a gasket can successfully seal. You must review the flange surface thoroughly and make sure there are no gouges or dents. The flange surface finish must exist as per the recommendation of the manufacturer for particular gasket materials.

The recommended values of the flange surface roughness areas follows:

Metal or Jacketed Clad Gaskets: 63-80 rms
Spiral Wound Gaskets: 125-250 rms
Solid Metal Gaskets: 63-80 rms

The meaning of rms stands for root mean square. The specification of roughness is usually millionths of an inch as the average of valleys and peaks measured from the midline of the flange surface. The recommended radius of the flange is usually 1/16″, and the round-nosed tool must have 30-55 serrations per inch in a spiral or concentric pattern.

How Are Flange Bolts Tightened

Now here are a few points to check before the flange bolts are installed.

Ensure proper cleaning of the gasket seating areas before insertion. In case of serration damage, re-serration is a must.
In the case of ANSI B31.3 not meeting the requirements, do not forget the rectification of the piping components.
According to clause no. 335-C in ANSI B31.3, permitted tolerances are as given below:

1. The alignment of the flange faces must be as per the design plane within 1 mm in 200 mm (1/16 in./ft) measurement across any diameter.
2. The alignment of the flange bolts must be within 3 mm (1/8 inch) maximum offset.

Check if the flanges are co-axial or parallel before you insert the gasket in between the flange pipe.

Checking points for the gaskets before tightening flange bolts

Examine the gasket making sure it is free from all defects.
The location of the gasket must help to ensure the full sealing. For instance, the gasket that is on the tube sheet of the exchanger requires a proper location so that the outer periphery of the gasket can match with the OD of the tubesheet at every point.
Make sure that the gasket is of the right dimension with the usage of specified materials.

Bolts for pipe flanges

Bolts must create compressive pressure on the gasket and flanges so that you can prevent leakage. So when you want to select, the temperature variations in service are considered.

Do not avoid the usage of short bolts on the flange joints.
The bolt’s lubrication with molybdenum disulfide is recommended, especially in all the bolts of size 7/8″. You can check the application as the bolt load is developed by torque and depends on the lubrication of threads.
The cleaning of nuts and bolts with suitable solvents is advisable, such as CTC/Diesel with the use of a wire brush, especially in the threaded portion.
Make sure that the material of all the nuts and bolts is specified.

Procedure for flange tightening

It is essential to tighten all the bolted joints in a uniform and diametrically staggered pattern.
In the case of pipe flanges from 12″NB to 8″NB and a pipe with spacer piece with at least two gaskets, the distance measured between the two flanges must be at four locations like 6’o clock, 9’o clock, 12’o clock, and 3’o clock positions and require equal distance for even tightening.
The stud bolts of 7/8″and above can be tightened with the use of a torque wrench. Make sure that the tightening load to every bolt is applied uniformly as possible. You can carry the tightening in three to four stages in the steps of 70, 50, and 30 percent of the final torque value. The fourth stage uses 70 percent again for the final torque value.
For the exchange of heat, final torque can value up to 100, 70, and 30 percent of the final torque value.
Follow the guidelines by the manufacturer wherever you can find the recommendation to use the hydraulic tensioner for bolt tightening.

Wrong practices for tightening flange bolts

There are many times when the plant operators end up following wrong practices for the flange bolt tightening. These are as follows:

Usage of rusted/dirty fasteners without lubricating
Usage of ordinary fasteners and not high tensile ones
Using a lot of gaskets for filling larger gaps between the flanges
Improper storage of gaskets
Reusing old gaskets
Improper sequence of bolt tightening


Flange bolt tightening is not an easy task. You must take care of all the elements required to understand the proper flange bolting, be it flange thickness, bolt sizes, or any other. Also, make sure not to go forward with wrong practices as it’ll put you at risk later.

If you need assistance to know more about the flange bolt tightening or choosing the right type of flange, contact Texas Flange today!