Specifications

Grades and their matching pipe

Each A234 alloy grade is the fitting equivalent of an A335 pipe grade, so a line built from P22 pipe uses WP22 fittings and F22 flanges, all with the same nominal 2¼Cr-1Mo composition.

Like the forged grades, WP11 and WP22 are offered in strength classes, which must be stated on the order. Composition and properties of the matching pipe grades are on our alloy steel pipes and tubes page.

Fitting types

• Elbows – 45° and 90° long radius and short radius, and 180° returns.
• Tees – equal and reducing.
• Reducers – concentric and eccentric.
• Caps.
• Forged fittings – socket weld and threaded elbows, tees, couplings and plugs.
• Olets – weldolets and sockolets for branch, drain, vent and instrument connections.

Forming and heat treatment

Alloy steel fittings are hot formed from seamless pipe or plate of the matching grade. Forming temperature and the subsequent heat treatment are controlled closely, because chrome-moly steels lose their designed properties if overheated or incorrectly tempered. After forming, fittings are normalised and tempered or otherwise heat treated as the grade and class require, then the ends are machined to ASME B16.25 bevels. For WP91 the heat treatment is particularly critical, and hardness is checked on each fitting or lot to confirm it falls within the specified range.

Testing, marking and documents

Each fitting is dimensionally inspected and marked with the manufacturer's identification, grade and class, size, schedule and heat number. Welded fittings have their welds examined as the standard requires. The mill test certificate shows the chemical composition, mechanical properties and heat-treatment details. Additional hardness testing, positive material identification, magnetic particle or ultrasonic examination and third-party inspection can be arranged on request.

Ordering

Please state the fitting type, standard, size and reducing size, schedule, grade and class (for example WP22 Class 1), seamless or welded construction, quantity and any tests or inspection required.

Installation notes

Alloy steel fittings are welded to matching pipe with preheat, interpass temperature control and post-weld heat treatment to the design code. Because chrome-moly fittings look the same as carbon steel, they should be stored separately, kept with their markings visible, and checked before installation – positive material identification at site is a common requirement on alloy piping. Fittings, pipe and flanges should be ordered with consistent grade and class so that a single welding procedure qualification covers the system.

Choosing seamless or welded alloy fittings

Most alloy steel fittings up to medium sizes are made from seamless A335 pipe, which gives the fitting the same structure and heat treatment response as the line pipe. In large diameters, fittings may be formed from A387 plate and welded; the welds are then radiographed and the whole fitting heat treated. Power plant and refinery specifications often require seamless fittings up to a stated size, so please give this requirement with the enquiry.

Applications and related products

Alloy steel pipe fittings are used in power-station main steam, reheat and extraction lines, boiler and HRSG piping, refinery heaters and hydroprocessing units, petrochemical crackers and fertiliser plants. They connect alloy steel pipes and tubes to alloy steel flanges, bolted with alloy steel fasteners. We also supply alloy steel plates and round bars. See all fitting materials on the pipe fittings page and grade guidance on the alloy steel page.