Flanges are used to join two joints of pipe

Flanges are used to join two joints of . Each connecting piece of has installed flanges that bolt together with stud bolts and seal with a gasket. SunnySteel is a full-line distributor of flanges, offering carbon steel, stainless steel, and exotic alloys. With sizes ranging from 1/4” to 48″, SSE can provide the flanges required for virturally any piping project.

Sunny Steel Supply can often provide the flanges listed below for a same-day delivery.  Large quantities, custom sizes, and special alloy (Alloy 20, Monel, Hastelloy, Inconel, Titanium, etc) flanges may be subject to a longer lead time for delivery.

Size Range: 1/2″ – 48″ Diameter
Types: Slip On, Socket Weld, Weld Neck, Threaded, Blind, Lap Joint, Long Weld Neck, Orifice/Orifice Plate, and API Flange
Class: 150 through 2500
Carbon Steel: A105, A350, 
Stainless Steel: 304, 310, 316, 321, 347
Exotic Alloys: A20, C276, Duplex 2205, Duplex 2507, AL6XN, A200, A600, Monel, Inconel, Incoloy 800, Incoloy 825, Aluminum, Titanium

There are several things you’ll need to know when purchasing flanges, including diameter, pressure class rating, type of connection, schedule (for weld neck and socket weld), material, face type, and series A or B (only necessary for flanges above 24” NPS).

To couple two joints of pipe, two flanges can be used. For a greater number of joints, the formula will be: # Flanges – 2 X (# Pipe Joints – 1)


  • Standard Carbon (A105): is an ASTM specification dealing with forged carbon steel piping components
  • Stainless Steel Flanges (): This specification covers forged or rolled alloy and stainless steel (304, 304L, ) flanges. This spec also covers other alloys including chrome (i.e. F11)
  • High Yield Flanges (A694): ASTM A694 is the standard specification to cover carbon and alloy steel forgings for pipe flanges, fitting, valves and other parts for high-pressure transmission service. Applications include, but are not limited to, in wellhead and Christmas-tree manifold equipment in oil and gas industry. The two numbers in each grade indicate the yield strength requirements, in ksi.
  • (A350): This specification covers several grades of carbon and low alloy steel forged or ring-rolled flanges (LF2 in low-temp applications).


Weld neck flanges are circumferentially welded into the system at its neck so that the integrity can be easily examined by radiography.

The bore of the pipe and the weld neck flange match in order to reduce turbulence and erosion, thus making the weld neck flange the strongest connection type and the most favorable in critical applications.

Slip on flanges are slipped over the pipe and the fillet welded. Slip on flanges are easy to use in fabricated applications, meaning that the pipeline is predesigned for a particular use. Slip on flanges are often used instead of a weld neck flange when cost or space is a major concern.

Threaded Flanges are used for special circumstances with their main advantage being that they can be attached to the pipe without . Threaded flanges can be removed easily. Sometimes a seal weld is also used in conjunction with the threaded flange connection.

Blind flanges are used to “blank off” pipelines, valves, and pumps. Sometimes, you might hear blind flanges referred to as an inspection cover, or blanking flange.

Socket weld flanges are counter-bored to accept the pipe before being fillet welded. Socket weld flanges are used in 4” and smaller high-pressure systems. The bore of the pipe and socket weld flange match, thus providing good flow characteristics.

Lap joint flanges are always used with either a stub end or taft which is butt-welded to the pipe with the lap joint flange loose behind it. The stub end/taft always makes the face. Lap joing flanges are used in systems that need frequent cleaning.

Lap joint flanges are favored in low-pressure applications because it is easily assembled and aligned. These flanges look very similar to a slip on, but the are distinguished by the rounded interior edge of the flange face. To reduce cost, lap joint flanges can be supplied without a hub and/or in treated, coated carbon steel

These classes include: 150 LBS, 300 LBS, 400 LBS, 600 LBS, 900 LBS, 1500 LBS, and 2500 LBS.

A higher class rating will increase the weight, height, face, and often times change the stud bolts required for installation of the flange. Precise dimensions for each flange, by class, can be viewed in our technical flange specification page.

Bolt chart for flanges by class can be seen here.


Raised face is the most common flange face type. The gasket surface is raised above the bolting circle face and allows for the use of a wide array of gasket designs (Spiral Wound, Cut, etc.).

The primary purpose of the raised face is to concentrate more pressure on a smaller gasket area and thereby increase the pressure containment capability of the joint, creating a more secure connection.

For full face flanges, the gasket surface is on the same plane as the bolting circle face. Full face flanges are often used in applications where the mating flange or fitting is made from a casting since relatively brittle cast iron requires a full-face contact point.

The ring-type joint face (or RTJ) has grooves cut into the face into which the gasket is placed. For ring type flanges, the flanges seal when tightened bolts compress the gasket into the grooves. This is referred to as “coining” the gasket.

Ring type joints excel in high-pressure, high-temperature applications such as oil field drilling equipment. RTJ’s are also used on valves and pipework assemblies.


For flanges above 24″, the flange must be specified for either series A or series B. These are competing specifications that were brought together in B16.47. ASME has incorporated most of the MSS-SP44 spec into B16.47 Series A and most of the API 605 spec into B16.47 series B. Weld necks and blinds are covered under these two specs. For slip-ons over 24”, you must refer to either Industry Standard or Boiler Code flanges.

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