Stocking Program

Size Range | 1/2″ – 36″ NPS (Larger sizes available upon request)


Classes | ASME/ANSI 150, 300, 600, 900, 1500, 2500


Stainless Steel Grades | 304, 304L, 316, 316L, 316L, 317L, 321 , 347, *


Special Alloys | 2205, 254SMo, Monel, Inconel, *


Chrome Moly | P5, P9, P11, P22, P91, *


Standards | ASTM / ASME / ANSI


*-Not all grades available are listed or have a full inventory managed

General information

ASME/ANSI B16.5 & B16.47 – Pipe Flanges and Flanged Fittings

The ASME B16.5 – Pipe Flanges and Flange Fittings standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings. The standard includes flanges with rating class designations 150, 300, 400, 600, 900, 1500, and 2500 in sizes NPS 1/2 through NPS 24, with requirements given in both metric and U.S units. The Standard is limited to flanges and flanged fittings made from cast or forged materials, and blind flanges and certain reducing flanges made from cast, forged, or plate materials.

Pipe Flanges and Flange Fittings in sizes over 24″ are to be referenced under ASME/ANSI B16.47.

Flange Types

Slip-on Flanges

The slip-on flange are the most common flange in which Unified Alloys stocks a full line of ANSI Class 150, 300, 600,1500 & 2500 up to 24″ NPS.  We stock stainless grades F304/304L,  316/316L, F317/317L, F321, F347 and duplex grade 2205 ( in which they are “slipped over” the end(s) of pipe or the end(s) of a fitting, and welded in position. On the pipe or fitting they are set so the inserted end of the pipe or fitting is set back to the wall plus 1/8” allowing for a fillet weld to be made inside the flange, and back (outside) of the flange is also welded with a fillet weld.

Slip-On flange also exist as a reduction where a larger slip-on flange blank is cut out to accommodate a smaller connection size. The slip on reducing flange is used when reducing the line size in areas where there are space limitations.

Weld neck flange:

Weld neck flanges are visually different from other flange types by their long tapered hub and smooth transition of thickness up to where the butt weld joins to a pipe or a fitting. A full penetration weld is utilized to connect it to the pipe or fitting. The tapered hub provides reinforcement, and the added length helps for resistance to dishing during the welding process. Weld neck flanges are typically used in severe service conditions, whether loading conditions are substantially constant or fluctuate between wide limits.

Lap Joint Flange:

A Lap Joint Flange is used in conjunction with a stub end where the flange is slipped over the stub end fitting which is then connected to either to pipe or another fitting by welding or other mechanical means.

The flange itself is not fixed and is left loose for proper alignment with the connection it is matching to. The benefits of this assembly is if there is frequent or rapid disassembly and assembly during maintenance of the piping system. The ability to spin and position the flange compensates for any misalignment of the bolt holes during reassembly.

Backing flange:

A backing flange does not have a raised face, and typically is used with backing rings which are a cheaper version of a stub end with similar installation benefits of the lap joint / stub end pairing.
Threaded (Screwed) Flange:

Threaded flanges are bored out initially to match a specific pipe inside diameter. The reverse side of the flange is then machined with the desired tapered sized pipe thread. Threaded flanges are primarily used to make flanged joints in the smaller bore pipe size ranges.

Socket Weld Flanges:

Socket Weld flange looks like a Slip-On flange, however the key difference is the Socket Weld flange is machined out to match a specific pipe size socket to take the pipe O.D. Once the pipe is set in place, the back side of the flange and pipe is fillet welded to finalize the connection. Socket weld flanges are primarily used to make flanged joints in the smaller bore pipe size ranges.

Blind Flanges:

Blind flanges are made to the sizing specification as all flanges, but there is no center hole or place to connect piping components. The flange is typically used to close or block the end of a piping system.

Forged flanges are stocked up to 24″ NPS in accordance to ASTM A / ASME SA182 and ASME B16.5 rating class 150, 300, 600, 1500 and 2500. Standard stainless material grades F304L, F316L are stocked with F321, F347 along with Duplex UNS31803 (2205) and Chrome Moly grades F5, F9 and F11 Material grades ASTM 321, 347 along with Duplex UNS31803 (2205) and Chrome Moly P5, P9 and P11 stocked in industry tailored size ranges.. Carbon Steel in Accordance to ASTM A105.

Cast flange products are stocked in 150 class T2 coated steel.

Technical data below: