When purchasing flanges, you must consider the flange material in addition to physical measurements and bolt hole alignment. Flange material selection is determined by the metal’s chemical composition and physical properties, and you can look to a combination of standards to guide your decision.
Pipes and flanges must be durable enough to withstand heat and pressure, vibrations, and corrosion, and must provide a sufficient seal. While the flange class helps determine bolt hole alignment, pressure and temperature rating, and dimensional standards, flange material specifications must also be considered:
Related to materials is how the flange is manufactured, via plate, cast, or forged methods.
Plate flanges are manufactured when metal slabs are sent through rollers until they reach the desired thickness. A plate flange can costs less, but sacrifices strength and compatibility with other materials.
Cast flanges are manufactured by pouring molten metal into a flange mold. The metal cools and hardens, and then the flange is removed from the mold and machined to the appropriate specifications. This lower-cost option offers plenty of flexibility, but is not the strongest option.
Forged flanges are made through a process of heating and forming the material, and then machining the part to the proper specifications. This creates a stronger flange, but at a higher cost.
Choose the right flange material based on its intended use and the requirements specific to that application. Generally, your flange material will match your pipe material, but this is not always the case. Consider the strengths and weaknesses of each material when designing a piping system; the material should suit the application requirements or it may fail prematurely.
Pipe material is chosen based on variables associated with an application, including:
Certain fluids, for example, fuel or corrosive liquids, require pipes and flanges manufactured of stainless steel, alloy, or other non-corrosive materials. Pipes and flanges used for air or other non-corrosive applications may not require the same non-corrosive materials as acidic or caustic liquids. Similarly, for fuel, oil, or gas transport, the material must suit the application. In these cases, select a flange material that is compatible with both the pipe that will connect to it and the intended application.
The standards dictate the chemical composition, dimensions, and other specifications for flanges. Generally, your flange and pipe material should meet the same standards.
American Society for Testing and Materials (ASTM) standards—displayed as the "grade" of the material used to manufacture the flange—is determined by the metal’s chemical composition. More specifically, this standard dictates how much carbon and other metals are allowed to make up the raw material.
Q235B is a low-carbon steel manufactured in China. The structure allows adequate welding and bolt connection. This steel exceeds AWWA strength requirements and is considered the China comparable material to DIN EN S235JR and ASTM A36 standards (but with slightly lower strengths).
American Water Works Association (AWWA) standards include specifications for steel and stainless steel. AWWA flanges include:
American National Standards Institute (ANSI) and American Society of Mechanical Engineers (ASME) are the industry standards for pipeline flanges in the United States. These standards include B16.1, B16.5, and B16.47 and cover steel, forged, or cast flanges.
Deutsches Institut für Normung (DIN, German Institute of Standardization) is an international standard that applies to steel and stainless steel metric flanges and commonly in maritime applications.
Consider the pipe material, pressure and temperature ratings, flange dimensions, and tolerances, to determine the appropriate flange material. ANSI ratings provide information on pressure and heat tolerances.
Fitting type is an important consideration as well. Does your fitting require welding? If so, the material you use should allow welding. For non-welded styles, such as lap joint or threaded flanges, weldability is less of a concern, and other requirements will take precedence.
When choosing the ideal flange material, refer to the standards required for your intended application, consider the pipe material that will connect to the flange, and ensure the flange material you choose is rated for the temperature and pressure it must withstand. Or, contact API International, Inc. for assistance with standard fittings or custom machined parts or for further information.