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Guidelines for Selection of Various Types of Flanges

Flanges are one of the most vital components in a piping system. They connect pipes, pumps, valves, and other equipment to form a complete piping system assembly. Flanges also enable seamless modification, inspection, and cleaning of these systems.

Some aspects to consider when selecting flanges are:

Material grade

Flange face type

Flange finish

Flange thickness and dimensions

Here’s a quick guide to selecting the various types of flanges based on their applications, material standards, and ASTM standards.

Ring-Type Joint vs. Raised Face

Most pressure vessel flanges fall under two categories – ring-type joint and raised. Many manufacturers consider ring-type joint flanges more efficient as they give grooves cut into their faces instead of a plain gasket between connecting flanges.

Upon tightening, a rated metal gasket is compressed into the grooves, providing an extremely tight and leak-proof seal for higher stress service.

The major benefit of using a ring-type joint flange is that the groove is within the flange. When the bolts are tightened, the ring centers itself. An API type flange is a common type of ring-type joint flange.

Raised face flanges are excellent for concentrating more pressure on a smaller gasket area. It increases the joint’s ability to hold pressure. These flanges are widely used in process plant applications. The gasket surface of these flanges is raised above the bolting circle face, hence the name.

Which One to Use: If you need a flange for high-pressure and temperature situations, a ring-type joint flange can be an ideal pick. It can be used for petroleum industry applications, oil fields, and pipework assemblies. On the other hand, raised face flanges are versatile and can be used in all high or low pressure and temperature situations.

Weld Neck Flanges

Weld neck with matching bevel to pipe

A weld neck flange, also known as a tapered hub flange or buttweld hub flange, comprises a circular fitting around the base along with a protruding rim and the pipe connection end.

These flanges are always made from forged construction and then butt-welded to a pipe. It transfers the stress from the flange to the pipe in a more seamless manner with regards to load bearing factors from an engineering design perspective.

You can use weld-neck carbon steel flanges in hostile environments with extreme sources of stress, such as pressure and temperature. These flanges can bear pressures up to 5,000 psi or higher. Weld neck flanges are available in all steel material grades, such as stainless steel, carbon, and alloy. Be sure to choose weld neck flanges with an ASME B16.5 rating for optimal field service.

Blind Flanges

Blind Flanges

The purpose of a blind flange is to block off a section of a pipe or nozzle by covering or closing its end. You can also utilize blind flanges to get easy access to a vessel or line’s interior if it needs to be reopened after getting sealed.

Understandably, blind flanges are suited for specific cases. These flanges are commonly available as both raised flat (RF) and flat faced (FF) styles. They’re best suited for waterworks, petrochemical, pipe engineering, and public services.

As far as material standards are considered, these flanges should follow the same standards as other flanges, such as weld neck flanges. Stainless steel flanges are ideal for corrosive environments where stainless weld necks are often installed with stainless blind flanges to match.

Slip-On Flanges

Slip on Flanges

Slip-on flanges slip over the pipe or tube to which you want to join. These flanges are manufactured with high precision to ensure their inside diameter is slightly bigger than the outer diameter of the pipe. These flanges are then linked to the pipe using a “fillet weld” at the inside, outside, top, or bottom of the flange. The fillet weld makes sure the joint is firm and properly sealed.

Slip-on flanges are best suited for low-pressure applications. They’re available as both raised and flat-faced flanges and are easier to align than weld neck flanges.

These flanges are ideal for design temperatures below 230-degree Celsius and a corrosion allowance of more than 3 mm in comparison to weld necks. For severe cyclic conditions, look for flanges ASME B31.3 or ASME B16.5 Class 600 or higher ratings.

Lap Joint Flanges

Lap Joint Flanges

A lap joint flange assembly consists of two components: a stub end and a backing flange. A pipe is welded to the stub end with a gasket, while the backing flange isn’t welded and is free to move and rotate. It enables you to get the desired alignment when joining it with another pipe or elbow.

You should consider lap joint flanges if your piping system requires regular inspections, cleaning, or dismantling. These flanges can align bolt holes and swivel around, simplifying the assembly of stiff piping with larger diameters. They are best suited for low-pressure applications and may not work well in high load conditions.

Wrapping Up

Each flange is different and has unique applications. It’s critical to understand the features and characteristics of each flange to find the one that best suits your needs.

If you need assistance in selecting the right flange type, get in touch with Texas Flange today!

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