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.

The Most Common Flanges in Pipe Welding: A Comprehensive Guide

The most used flange types per the ASME B16.5 are Blind, threaded, lap joint, socket weld, slip-on, and welding neck flange. Here you will find a short description and definition of each type.

common flanges

Welding neck flange

The easily recognizable long tapered hub of a welding neck flange provides an essential reinforcement of the joint. It is helpful for elevated, sub-zero, or high pressures applications.

The taper on this flange type offers a smooth relocation/transition of stress from flange thickness to pipe or fitting wall thickness. It is crucial under repeated bending conditions caused by the line expansion or other variable forces.

Slip-on flange

If we compare the slip-on flange with the welding flange, likely, it is not as durable. However, it has two-thirds less calculated strength under internal pressure and around one-third of the life span.

They come at easy installation and low material cost, best suited for low-pressure applications with little risk of leaking.

A few other advantages of the slip-on flanges are that it doesn’t require a sizeable longitudinal space in the line to be mounted. Also, they are less aligned with a wide variety of diameters available and do not require accurate cuts in the pipe.

Socket weld flanges

Socket weld flanges were initially developed for high-pressure, small piping. The static strength of the socket weld flange is equal to the slip-on flanges, but their fatigue strength is 50% high compared to the double-welded slip-on flanges.

Before welding, a space between 1/16” and 1/8” needs a creation between the fitting or flange and pipe. It allows you to expand the pipe on the inner side of the weld and reduces the residual stress, helping to prevent the crack weld on the fitting.

Lap joint flange

Lap joint flanges share the same features as the other flanges. However, it does not have a raised face. They are connected to a lap joint stub end.

These flanges are nearly identical to the slip-on flange, except for a curved radius as the bore. It helps accommodate the flanged portion of the stub end, and you can slide it over the pipe. The pipe is usually welded to the stub end, allowing free movement of the lap joint flange.

The strength is similar to the slip-on flange as they have a fatigue life of around one-tenth compared to the welding neck flanges.

Stub end

As a backing flange, a stub end will be used with lap joint flange applications. However, they are also helpful with slip-on flanges.

Stub ends are available in almost all pipe diameters. There are three different kinds available A, B, and C.

  • Type A is something you can machine to fit the standard lap joint support flange.
  • Type B is designed to be used with a standard slip-on flange.
  • Type C is useful with either a slip-on or lap joint flange.

Threaded flange

The top advantage of the threaded flange is that no welding is required in connection to the pipe. It is done using corresponding threads. However, a seal weld is sometimes applicable in conjunction with the flange’s threaded connection.

Threaded fittings are used exclusively in smaller pipe sizes up to around 4”; however, most pressure ratings and sizes are still available.

A threaded fitting or flange only suits applications that use a thicker wall thickness due to the presence of the thread.


This guide offers a solid foundation of the common top flanges in welding, however, with the wide range of stainless steel flanges and other flange materials available.

You can contact us if you want assistance choosing the right welding equipment for your welding project.


Why Is Flange Face Protection Important?

Pipework and pipelines incorporate welded joints and flanges of varying materials, designs, and sizes. Evidence suggests that piping systems, including valves and flanges, collectively continue to be a source of unnecessary hydrocarbon releases, with piping being one of the largest contributors. Proper flange face sealing and inspection is an excellent solution to this issue.

Purpose of flange protectors

Flange protectors protect the entire pipe flange surface. If you close the pipe assembly completely, you can eliminate the risk of contamination. These protectors help to ensure these structures are in fact completely sealed off from their surroundings.

Why flange protection is essential

When we talk about the gas, oil, and utility industry, pipe flange and thread protection are two essential things. It is not just contamination during and after storage you need to worry about, but damage during transport and manufacturing treatments. Lack of the right solutions could result in high-cost repairs. You may even have to replace oil-well pipes and drills.

The flange face is the gasket that seals the surface of the flange connection. The connection can be a vessel, valve, and a multitude of other mechanical equipment. The surface is typically machined where the gasket seals and sets the connection of the piping system.

Types of face flange protectors

Below are few types of flanges that you can find out:

Raised face flange protectors

Raised machine face on your flange is the critical area that requires protection. The flange protectors help you maintain the optimum condition and prevent leakage in storage or before the installation.

Features : Available in 3 key profiles: Adhesive, Plug, and Studded. All are easy and quick to install and stand up to sandblasting.

Material: Petroleum or weather-resistant commercially available grades

Specification: Protects ANSI and DIN flanges. Solutions are available in different sizes.

Suitable for: Easy fitting face protection

Full Face Flange protectors

Keep your flanges in top condition for a perfect fit while guarding against dirt and corrosion ingress during transport around the factories and shipyards.

Features: Protects the entire surface of the flange or leaves bolt holes/bolt accessible. It is available in 5 key profiles: Bolthole, Push-in, Adhesive, Plug, and Studded.

Material: PE gives protection during transit, storage, and finishing. Bolt hole flange protectors’ PP material is cost-effective and offers good chemical and fatigue resistance.

Specification: Available in a range of sizes to support DIN and ANSI  flanges.

Types of Caps and Pipe Plugs – Benefits

When you store or transport the pipes, it is vulnerable to contact and possible damage with other pipes and corrosion can occur on specially machined threads. The pipe caps and plugs are vital to seal pipe ends and provide drill pipe protection.

Pipe Plugs

Eliminate costly downtime by preventing debris from entering the pipe and damaging the vital threads.

Features: Ribbed pipe plugs are available in two styles with flexible ribs of different diameters to fit multiple schedules of drill pipe and NPT.

Material: Tough LDPE offers chemical and weather resistance.

Specification: The straight wall on the plug’s O.D. helps to provide a secure friction fit with the mating pipe’s Inside Diameter for good protection against contaminants. Compatible nominal pipe diameters range from .217in – 24.606in (5.5mm – 625mm)

Suitable for: Drill pipe and NPT line pipe

Pipe Caps

You must minimize the threat of pollution and rust to the pipe and its contents by preventing the entry of foreign objects and contaminants with a pipe end cap.

Features: Flexible pipe caps offer a tight fit while recessed caps that protect coatings, internal walls, and bevels from damage during clamping by crane hooks.

Material: Flexible pipe caps made of PE material are lightweight, durable, and strong. Recessed pipe caps are made of LDPE for excellent chemical resistance to esters, bases, alcohols, and acids.

Specification: Flexible pipe caps fit nominal pipe diameters. It ranges from 64in – 2.374in. Recessed Caps are usually compatible with nominal pipe diameters that range from 48in – ½in.

Suitable for: Pipes transported by crane hooks.

Flange damage prevention

Excessive rust, ding, dent, or scratch in this area can cause a failure of the flanged connection if not corrected before the final bolting. It is not uncommon for a high quantity of improperly inspected flanges to resurface with issues on a project and cost hundreds of thousands if not millions of dollars. The greatest impact of flange damage on these projects is the delay in the construction schedule that costs the owner-operator weeks, months, and years of lost revenue opportunity.


Protection of your flange faces is essential to the success of your project. It is where the magic happens. Get it right, and you’ll be the hero that delivers the project on schedule. If you get it wrong, you may end up looking at more cost overruns, project delays, and sometimes unhappy clients.

If you have any further inquiries related to the importance of flange face protection, 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.

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!