A Complete Guide to Steel Flanges

Explore our comprehensive guide on steel flanges, designed to give you a deep understanding of what steel flanges are and how they can be chosen based on your specific application needs.

Steel flanges are typically attached to other pipe fittings using welding and are sealed with bolts and gaskets. They play a crucial role in connecting various components used in industrial processes, such as water pipelines, oil filtration machinery, food processing equipment, and pressure vessels.

Over the years, these industrial elements have been manufactured in various specifications, each serving an important role across multiple industries.

Ensuring that pipes are connected safely is essential to prevent leaks in the piping system. Flanges help maintain accurate connections and ensure safe operation over extended periods.

Steel Flanges Specification

Manufacturing standard of pipe flanges is ASME B16.5

It includes NPS ½ to NPS 24 metric inches, which covers pressure-temperature ratings, dimensions, tolerance, materials, sizes, tolerances, marking, testing, and opening method of flanges.

The flange class rating includes 150, 300, 400, 600, 900, and 1500, available in sizes from NPS ½ to NPS 24 metric inches. Class 2500 is available up to NPS 12 in both metric and U.S. units, with bolt and flange hole diameters specified in inch units.

ASME B16.5 flanges are made from forged or cast materials. Blind flanges and certain reducing flanges are fabricated from forged, cast, or plate materials. This standard also includes requirements for bolting, gaskets, and flange joints.

Different Types of Flanges

Weld Neck Flanges		This kind of flange is welded to the pipe ends at the neck Typically butt welded to a pipe Applied in high pressure situations Greater longevity than slip-on flanges when subjected to stress
Slip On Flanges		This pipe flange slips over the pipe Lower Price than weld neck flange Manufactured with an ID that is slightly bigger than the pipe’s OD
Socket Weld Flanges		It has a female socket in which pipe is fitted Fillet welding is done from OD on the pipe Similar to slip-on flange, but with a bore and a counter bore dimension Counter bore is than the O.D. of the matching pipe Suitable for pipes with a nominal dia of 150 or less
Lap Joint Flanges		Used on piping fitted with lapped pipe (lap joint stub ends) Having two components: stub end and a loose backing flange Stub end Similar to a slip-on flange, but with a radius where the flange face and bore meet
Threaded Flange		Also known as screwed flange Possessing a thread within the flange bore that aligns with the pipe’s male thread Used in utility services such as air and water Like to the Slip-On flange, but the bore is threaded
Blind Flange		A blind flange is a round plate with no centre hole and all the necessary boltholes Used to close off the ends of a piping systems
Orifice Flange		Used with orifice meters Measuring the liquid or gas flow rate in the appropriate pipeline
Long Welding Neck Flange		Has a very long neck Has a tapered neck and a bevel end Has a straight short pipe as the neck of a long weld neck flange
Weldoflange and Nipoflange		A Welding Neck flange combined with a purported Weldolet or Nipolet
Expander and Reducing Flange		Used to increase or decrease the bore size of a pipeline A strong substitute for butt weld reducers

Steel Pipe Flange Material Grades

Reducing weld neck flange have pressure rating of class 150 to class 2500

ASME creates the flange class, taking into account there are several pressure and temperature ratings. There are seven classes i.e. 150, 300, 400, 600, 900, 1500 and 2500. And the reducing weld neck flange can be worked at this pressure rating of class. The pressure rating specifies the highest tolerable pressure at a stated temperature. For instance, a class 2500 flange can resist more pressure and it is heavier compared to 1500 flange. Here, the class 2500 flange signifies that the flange is workable at this rated temperature without getting crack or damaged.

Galvanized Pipe Flange Working Pressure

Standard size range of socket weld and slip on flanges is 1/2″ to 24″

The range of standard size socket weld and slip on flanges are important for several industries as it gives fastening to the piping system. Socket weld and slip on flange are usually manufactured in the standard from ½” to 24”.

The categorization and distinction between the flanges from countries to countries are important to understand for flawless combination and consistency in global projects.

Flange standardization gives safety and similarity in the broad range of global industries. It enables global trade by offering a common base for fabricators, suppliers and consumers. 

Steel Flange Dimension Chart

WNRF Flange Weight Chart