Pipe Flange Supplier – ASME B16.5 & B16.47

Flange Types and Where Each Is Used

The weld neck flange has a tapered hub that transfers stress from the flange to the pipe smoothly and is the standard choice for high pressure, high temperature and severe cyclic service, and for all applications where radiography of the weld is required. The slip on flange is slipped over the pipe and fillet welded at both sides; it is cheaper and easier to align but has lower fatigue life and is not used for severe cyclic service. The socket weld flange is used for small bore lines in the same way as a socket weld fitting. The threaded flange is used where welding is not permitted, typically on small bore utility lines. The lap joint flange uses a stub end, so the flange rotates for bolt hole alignment and the wetted surface is the stub end material, which makes it economical in stainless or exotic material. The blind flange closes a flanged opening and is removable. Selection is governed by the design code, the pressure and temperature class, and whether the joint will be radiographed.

Understanding Flange Classes

The classes 150, 300, 600, 900, 1500 and 2500 in ASME B16.5 are not pressure ratings in psi. They are class designations that define a set of dimensions, and the actual permissible working pressure depends on both the class and the material and the design temperature. For example a class 150 carbon steel flange rated for roughly 19 bar at 38 degrees Celsius derates to about 13 bar at 200 degrees Celsius, and the derating factor differs for stainless steel. The correct procedure is to select the class from the applicable pressure temperature rating table in ASME B16.5 for the specific material and design temperature, then confirm the pipe schedule matches the flange bore. ASME B16.47 covers larger flanges, series A for sizes 26 to 60 inch in the MSS SP-44 tradition and series B for sizes 26 to 60 inch in the API 605 tradition; the two series are not dimensionally interchangeable.

Flanges: what the class and the facing have to match

A flange is not specified by size alone. The pressure class sets the wall and the bolt circle, the facing has to match the gasket and the flange it is bolted to, the bore has to suit the pipe, and the material follows the line. Below the size, those four are the whole specification.

EN 1092-1 Flanges and PN Ratings

In Europe, flanges are most often specified to EN 1092-1 rather than ASME B16.5. The standard covers circular flanges in sizes DN10 to DN4000, and pressure is named as a PN (nominal pressure) value: PN6, PN10, PN16, PN25 and PN40 are the ratings most commonly used on carbon and stainless steel lines. A PN16 flange is not a direct substitute for a Class 150 flange; the bolt circles and drilling can match on common sizes, but the two systems are not dimensionally interchangeable, so the standard must be stated on the enquiry.

EN 1092-1 designates flange types by number. The types most often supplied here are Type 01 plate flange for welding, Type 05 blind flange and Type 11 weld neck flange, with facing forms A (flat face) and B1/B2 (raised face). These have replaced the older DIN 2501, DIN 2527 and DIN 2633 designations that are still named on many drawings.

Plate flanges are flat discs welded to the pipe and used for low pressure, non-critical services such as water, air and general utility lines, typically at PN6, PN10 or PN16. Materials range from carbon steel P235GH and P250GH (1.0460) to stainless 1.4301, 1.4404 and 1.4571.

Enquiry: state the standard (EN 1092-1), DN size, PN rating, flange type number, facing form and material. Flanges are supplied with EN 10204 3.1 certificates, with 3.2 on request.

Grades supplied and minimum properties

The grade fixes the minimum strength and the chemistry. The table below gives the requirements that separate the flange material grades ordered most often; the full composition and mechanical table for each grade is on its own page.

The complete chemistry and mechanical table for each grade, with the notes that qualify it, is on the individual grade page – for example ASTM A105 flange. The stainless grade has the higher tensile requirement but the lower minimum yield strength, which is why flange wall thickness is set from the rating rather than from the material table alone.

Source: specified minimum yield and tensile strength for each grade, per ASTM A105 / ASME SA105 and ASTM A182 / ASME SA182. The standard named against each grade is the governing document.

• A105
• A350 LF2
• A694 F52
• F304
• F304L
• F316
• F316L
• F321
• F11
• F22
• F91

Download Pipe Flange Supplier – ASME B16.5 & B16.47 data sheet (PDF) One page: supply range, grades and key sizes, what to state on the enquiry, and the inspection documents that come with the order. The standard is the governing document.