Skip to content

5 Different Types of ANSI Flanges

If you are unfamiliar with the terminology, ANSI Class Flanges are simply components crafted under the regulations of the American National Standards Institute.

Whether small, medium or large in diameter, they come in a selection of models which process engineers across many industries utilize. 

ANSI Flanges


Here will look at five different types of typical ANSI-compliant flange designs.

1.  Socket Weld Flange

To install a socket weld flange to pipes, a single weld is required along the external face of the flange, unlike slip-on flanges,

which necessitate two welds. Per ASME B31.1, properly attaching the flange to the pipe must first be inserted into the socket until it touches the bottom.

Afterward, the pipe must be slightly lifted off the bottom by 1.6 mm before being welded in place. The gap must be left so the pipe can be placed within the flange socket after solidifying the weld.

Socket Weld Flanges are ideal for smaller-diameter, high-pressure piping applications that involve non-corrosive liquids. A space between the pipe’s end and the socket’s shoulder can cause corrosion in these flange types. They are much less common in sizes larger than NPS 4.

Compared to slip-on flanges, the static strength of socket weld flanges is equal. However, their fatigue strength is superior as they have only one fillet weld rather than two.

2. Threaded Flanges

Threaded flanges have become a favorite amongst many, as they are simple to attach to an assembly and do not necessitate welding. Plus, if the flange is undamaged, it can often be salvaged and used again when the assembly is removed.

Threaded flanges are connected to pipes without welding. The pipe is screwed into the flange with NPT threading per ASME B1.20.1. In a few cases, small welds are added for additional strength.

Threaded flanges can range up to four inches and come with varying pressure ratings. These flanges are predominant in low-pressure and low-temperature pipe connections, such as water and air utilities.

Flanges threaded together are necessary for environments prone to explosions, such as gas stations and plants, due to the hazard of attempting welded connections in those areas

3. Slip On Flanges

These ANSI flanges are extensive in applications that remain firmly in place and not be taken apart. Although welding is required, they are simple to position and align correctly.

A slip-on flange is connected to the pipe or fittings with two welds internal and external, forming a fillet within the flange cavity.

Slip-on flanges have a bore size larger than the outside diameter of the pipe fitted into the flange and connected with a fillet weld.

Commonly dubbed “Hubbed Flanges,” Slip-on flanges are easily identifiable for their slim, petite silhouette.

Slip-on flanges used in flanged joints are less durable than welded with welding neck flanges in comparable settings. Without hubs, they are sometimes called “plate flanges” or “plate slip-ons,”

Slip-on flanges offer several benefits, including their low cost and ease of alignment. Due to their simplistic design and reduced materials required, they are generally more affordable than other flange varieties.

Rotatable around the pipe, they can be realigned with ease, thus making them ideal for more confined spaces. 

Despite their advantages, slip-on flanges may not be suitable for extreme temperature and pressure settings. Thus other varieties, such as weld neck and socket weld flanges, are likely to be a more appropriate choice.

4. Blind Flanges

Designed to obstruct the termination of a flanged pipeline, valve, or pressure vessel, the blind flange gets utilized in various applications that do not require an outlet. These ANSI Flanges are named due to their lack of an opening.

Unlike all other flange varieties, blind flanges lack a central aperture and are utilized to cover and seal a pipeline, valve/pressure vessel, or impede fluid movement.

Blind flanges can be installed and removed, making them an ideal choice for maintenance and repair work.

They can be used as a test point: Blind flanges can be used as a test point to check the pressure of the pipeline without having to dismantle the entire pipeline.

Blind flanges must possess considerable resistance to mechanical pressure generated by system pressure and bolting force demands.

Blind flanges provide an access opening to the pipeline, as they can quickly be detached and provide an interior area of the pipe where the operator can complete their activities.

They are also often utilized as manholes on pressure vessels. Interestingly, despite its simple production process, this variety of flange is sold at a higher price per kilogram than the others.

5. Lap Joint Flanges

Compared to other flange varieties, ANSI Flanges such as Lap Joint Flanges necessitate an external connection piece and are not connected directly to the pipe, valve, or product.

Although it involves a few more steps, the capability to rotate the flange makes it advantageous for situations requiring consistent disassembly for upkeep and cleaning.

Featuring a flat face, lap joint flanges are combined with a stub end. With a form similar to that of slip-on flanges, lap joint flanges have a radius in the crossing point between the bore and the flange face.

The bolts provide the flange pressure needed to hold the lap joint flange and stub end together.

To economically create stainless steel or nickel alloy pipelines, lap joint flanges, and stub ends can be used.

Generally, the lap joint flange is designed of a cheaper material than the stub end, which must be the same as the pipe grade in contact with the conveyed fluid.

The advantages of this setup are twofold: it cuts down on the expense of flanges since fewer costly materials are used, and it makes bolting simpler as the lap joint flange can be spun around the pipe for easy bolt alignment.


ANSI flanges have become ubiquitous in various industries owing to their proven trustworthiness, interoperability, and versatility. Having a standardized design,

ANSI flanges are effortlessly exchanged between different manufacturers, making them suitable for petrochemicals, oil and gas, water treatment, and other industrial applications.

Their strength and thermal stability contribute to their attractiveness. They can withstand high pressure and temperature, guaranteeing secure and efficient performance in pipelines, pumps, valves, and other equipment. What’s more?

These flanges come in different materials, sizes, and ratings, thus allowing for personalization to meet a customer’s specific needs and requirements.


0 0 votes
Article Rating
Notify of
Newest Most Voted
Inline Feedbacks
View all comments
ERP Software
10 months ago

Good effort on sharing such an informative piece of content on flanges.

10 months ago

It’s interesting to learn about the various types of ANSI flanges and their applications. The detailed explanation for each type helps clarify their strengths and limitations.”

10 months ago

What are the advantages of using lap joint flanges compared to other types of flanges?