Aluminium Pipe Tee Fittings

What an aluminium tee does in a piping system

A tee has three openings: two on the run (the straight-through line) and one on the branch at 90°. It can split one flow into two, combine two flows into one, or simply provide an outlet for an instrument, drain or future connection.

Aluminium tees are used wherever the rest of the piping is aluminium: compressed-air and nitrogen networks, vacuum lines, cryogenic and LNG piping, marine fuel and water systems, irrigation, food and beverage process lines, chemical plant handling media that aluminium resists, and lightweight systems in aircraft ground equipment and vehicles. Matching the fitting alloy to the pipe avoids galvanic corrosion at the joint and lets the whole system be welded with one procedure.

Tees are produced in several ways. Small threaded fittings are usually forged or machined from bar. Butt-weld tees are formed from seamless pipe by hydraulic bulging or extrusion of the branch (so-called "drawn-outlet" tees), or fabricated by welding a branch pipe into a header. Very large or special-angle tees are fabricated from pipe or rolled plate. The manufacturing route affects strength and code acceptance, so it should be stated on the order for pressure work.

Types of aluminium pipe tee

Alloys and tempers for aluminium tees

ASTM B361 covers factory-made wrought aluminium welding fittings and lists the alloys that can be supplied, including 1060, 1100, 3003, 5083, 5086, 5154, 6061 and 6063. The table summarises how they are used.

Always match the tee alloy to the pipe alloy, or at least to the same family, so that the welding filler and corrosion behaviour are compatible. A 6061 tee welded into 5083 pipe is possible with ER5356 filler, but the 6061 heat-affected zone becomes the weak point of the joint.

Common butt-weld tee sizes (Schedule 40 and 80)

Butt-weld tees are made to the outside diameter and wall of the pipe they join (ASME B36.10 schedules) and to the centre-to-end dimensions of ASME B16.9. For an equal tee, the centre-to-end distance is the same on the run and the branch. The table gives the main dimensions in inches and millimetres.

Dimensions per ASME B36.10M (pipe) and ASME B16.9 (fitting centre-to-end). Reducing tees keep the run centre-to-end and use a shorter branch dimension listed in B16.9. Schedule 5, 10 and 160 walls are also produced.

Small threaded tees run from 1/8 in to about 4 in. Fittings to MIL-DTL-52618 and similar commercial 150 lb aluminium threaded fittings are rated for low-pressure service; catalogue ratings are typically around 150 psi at room temperature, and the threaded joint, not the body, usually limits the rating.

How tee pressure ratings are determined

A butt-weld tee made to ASME B16.9 is designed so that it is at least as strong as straight seamless pipe of the same material and schedule. In practice, that means the pressure rating of the system is calculated from the pipe (for example under ASME B31.3 for process piping) and the tee does not need a separate rating, provided it is ordered in the same alloy, temper and wall.

• Welded systems in 6061 or 6063: base the calculation on the welded strength, because the heat-affected zone around each tee is weaker than the delivered T6 pipe.
• Threaded tees: the thread root reduces the effective wall, and aluminium threads gall and crack if over-tightened. Keep threaded aluminium fittings to low-pressure utility service and small sizes.
• Flanged tees: the flange class and gasket set the limit. Aluminium flanges follow the dimensions of the corresponding steel standard but carry lower pressure-temperature ratings.
• Fabricated tees: a branch welded into a header needs reinforcement calculations (area replacement) and is less efficient than a formed tee.
• Temperature: aluminium allowables fall above about 100 °C; most aluminium piping runs from cryogenic to around 150 °C.

How to choose the right tee

1. Match the pipeConfirm the pipe OD and wall (NPS and schedule, or metric OD × wall). The tee ends must match exactly for butt welding; a mismatch of wall creates a step that disturbs flow and concentrates stress.
2. Size the branch for flowSelect the branch size from the flow the branch must carry and the acceptable velocity and pressure drop, then decide between an equal tee and a reducing tee.
3. Choose the end connectionButt-weld for permanent, high-integrity lines; socket-weld for small bores; threaded or compression for small utility lines that may be modified; flanged where removal is needed.
4. Check pressure and temperatureConfirm the design pressure, temperature and code (B31.3, B31.1, EN 13480 or class rules) and whether welded allowables apply.
5. Specify standard and documentsState ASTM B361 for wrought welding fittings, ASME B16.9 for dimensions, and the certificate required, normally EN 10204 3.1.

In compressed-air networks, tees are best installed with the branch taken off the top of the main, so condensed water stays in the main and drains away rather than running into tools. See the aluminium air piping guide for layout advice.

Aluminium tees compared with steel and stainless tees

Aluminium wins on weight, clean bore and low-temperature service. Steel remains the choice for high-pressure, high-temperature and fire-exposed lines, where aluminium's lower melting range and strength are limiting.

Custom and non-standard aluminium tees

When the standard range does not fit, tees can be made to drawing. Common requests include tees in metric OD × wall sizes that do not match ANSI schedules, heavy-wall tees for cryogenic headers, lateral tees at 30° or 60°, tees with integral flanges or threaded bosses, and tees machined from solid 6061 bar or forgings for hydraulic or pneumatic manifolds.

Related fittings, pipe and stock

Aluminium (aluminum) pipe tees: frequently asked questions