A recurring question is: what is a flange? How to define flange? Flanges are products used to connect pipes to pipes, or pipes to valves, fittings, noozles, chokes, pumps and other devices within pipelines or piping systems. Steel flanges allow easy access to the pipeline for cleaning, inspection or modification activities (example pipeline extension or retrofit). The most common standards for flanges are: ASME B16.5 / ASME B16.47-type A/B, API 6A, EN 1092 and various BS/UNI/DIN specifications. These norms set standard dimensions and tolerance that are used as reference by piping designers and flanges manufacturers.

Flanges are available in multiple material grades, from forged carbon steel (ASTM A105 for high temperature service and ASTM A350 for low temperature) to stainless steel, duplex / superduplex and nickel alloys (ASTM A182). As a general rule, the material of the flange shall match the material of the piping system. For specific applications, non-ferrous flanges are also used (copper, bronze, cupronickel, aluminium). 

In some cases, flanges are painted on the external surface or are internally lined with protective materials (such as Polyprophylene, PTFE, PVDF, etc). Lined flanges are generally used in combination with lined pipes and fittings.


Pipe flanges

Most used flanges for pipelines and for the petrochemical industry


The following parameters have to specified to order (or request estimates) for flanges:

  • Flange type (welding neck, slipon, threaded, lap joint flange)
  • Dimensional norm (ASME, JIS, EN, UNI, DIN, etc)
  • Diameter (generally between 1/2" - 60")
  • Flange rating: the rating of flanges (defined class) ranges from 150 to 2500 for ASTM, from 5k to 30k for JIS B2220 flanges and KS1503 flanges; from PN 6 to PN 100 for european flanges (DIN, UNI, EN 1092-1, GOST 12820 / 12821-80); Class 600/3, 1000/3, 1600/3, 2500/3, 4000/3 for SANS / SABS flanges (south african standard for flanges)
  • Schedule (only for welding neck / socket weld flanges)
  • Flange facing: according to ASME B16.5, raised face is the standard facing for flanges (different facings, like RTJ or flat face FF have to be ordered specifically)
  • Flange surface finish (smooth, stock, concentric serrated, etc)
  • Material grade
  • Quantity
  • Accepted origins for forgings and finished product



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Useful links: ANSI | ASME | ASTM | API | MSS | BS | DIN | ISO