ASME B16.9 Butt Welding Fittings

Scope, Codes & Pressure Ratings

The ASME B16.9 standard covers all dimensions, tolerances, ratings, testing, and marking for factory-made wrought butt-welding fittings in sizes NPS 1/2 through NPS 48 [DN 15 through DN 1200]. It also covers pipe fittings made to special dimensions, sizes, shapes, and tolerances by agreement between the manufacturer and the purchaser. Fabricated laterals, saddles, and other fittings employing circumferential or intersection welds are considered pipe fabrication other than ASME B16.9 fittings. However, fabricated lap joint stub ends are exempt from the above restrictions, provided they meet all the requirements of the applicable ASTM material specification.

A glimpse of the packing workshop of a butt-welding-fittings manufacturer, in Mengcun county, Hebei Province, China.

The ASME B16.9 pipe fittings can be used under the jurisdiction of the ASME Boiler & Pressure Vessel Code (BPVC) as well as the ASME Code for pressure piping. Referencing pressure ratings of flanges per ASME B16.5, they can be designated as Classes 150, 300, 600, 900, 1500 and 2500. The allowable pressure ratings for ASME B16.9 pipe fittings may be calculated as for straight seamless pipe of equivalent material in accordance with the rules established in the applicable sections of ASME B31 Code for pressure piping.

Design of Fittings

The design of butt welding pipe fittings made to ASME B16.9 shall be established by one of the following methods: (a) mathematical analyses contained in pressure vessel or piping codes; (b) proof testing; (c) experimental stress analysis with hydrostatic testing to validate experimental results; (d) detailed stress analysis with results evaluation.

Standard Marking

Generally, ASME B16.9 pipe fittings shall be marked to show the following details: “trademark + material grade + wall thickness + size + heat number”. For example, “M ASTM A234 WP5 SCH80 6″ 385“. When steel stamps are used, care shall be taken so that
the marking is not deep enough or sharp enough to cause cracks or to reduce the wall thickness of the fitting below the minimum allowed.

Material & Manufacture

The ASME B16.9 fittings may be made from an extensive range of mateirals covering (1) carbon and low-alloy steels in accordance with ASTM A234 and ASTM A420; (2) austenitic and duplex stainless steels in accordance with ASTM A403 and ASTM A815; (3) nickel alloys in accordance with ASTM B366; (4) aluminum alloys in accordance with ASTM B361; and (5) titanium alloys in accordance with ASTM B363.

ASME B16.9 90° elbows L/R SCH80 DN500, ASTM A234 Gr. WP22, for a coal-fired power plant in South Africa.

The butt welding fittings shall be manufactured by a “wrought” process denoting that fittings made of pipe, tubing, plate, or forging. The fittings can be made from a hot forming or cold forming process, in welded or seamless pipe. It may be a standard fitting that meets all dimensional requirements of ASME B16.9; It may be a special fitting in conformance with ASME B16.9, except that dimensional requirements are as agreed between purchaser and manufacturer.

Dimensions & Tolerances

The standard ASME B16.9 butt welding fittings can be furnished in various product forms covering elbow (90°, 45°, long radius, short radius, 3D radius, reducing), 180° return (long radius/ short radius), tee & cross (straight or reducing), lap joint stub end (long pattern or short pattern), cap, reducer (concentric or eccentric). The wall thickness of the fitting is often specified by a schedule number, which is a dimensionless number that is widely used as a convenient designation for use in ordering pipe and fittings. These schedule numbers are generally specified in ASME B36.10M and ASME B36.19M.