Tees are used to form branch connections. Suppose the size of the branch is the same size or one or two sizes smaller than the run pipe. In that case, a tee or reducing tee is usually used, as cutting a fishmouth can weaken the pipe and require the application of a butt welding tee, as specified in ASME B16.9.

This ensures that the joint will comply with the rated pressure of the adjoining pipe, without the need for further calculation. Tees are often used for cleanout access or the installation of components like thermowells.

The tee is installed where an elbow would otherwise be used, and the thermowell is inserted into the run of the pipe at the end of the tee.

Pipe Tees Types and Functions

There are two types of piping tee connections

• Equal Tee
• Reducing Tee

Equal Tee

• Both the branch and run pipe have the same diameter.
• Used when equal distribution of flow is required.
• Common in oil and gas, and water supply networks.

Reducing Tee

• The branch outlet has a smaller diameter than the main pipe.
• Used when the flow needs to be directed to a smaller line.
• Efficient in reducing the velocity and pressure of the fluid.

Other Important Types are

• Cleanouts
  • These are providing access for maintenance and cleaning purposes.
  • This type of tee is used to remove blocks in the lines.
• Lateral Tees
  • A lateral tee is a pipe fitting that allows one pipeline to branch off from another at an angle, usually 45 degrees.
  • This angular connection differentiates it from a standard tee, which typically branches at a 90-degree angle.
  • The lateral tee is used when a smoother flow direction is needed to minimise pressure drops, turbulence, and flow disruptions in the pipeline.
  • This type of fitting is especially useful when fluids need to be diverted or mixed gently without causing significant resistance or back pressure within the system.
  • Branch Angle: Typically 45°, though custom angles may be used depending on design needs.
  • Benefits of Using Lateral Tees
    • The angled branch reduces flow disruption compared to 90° tees.
    • Suitable for systems where pressure conservation is important.
    • Smooth transitions reduce internal wear and fluid noise.
    • Particularly beneficial in high-velocity and high-volume pipelines.

Materials Used for Pipe Tees

• The material selection depends on temperature, pressure, and the nature of the fluid.
• Common materials include
• Carbon Steel (ASTM A234 WPB): For general industrial applications
• Stainless Steel (ASTM A403 WP304/316): For corrosive environments
• Alloy Steel (ASTM A234 WP11/WP22): High temperature and pressure applications
• PVC/CPVC: For non-metallic applications like water treatment or agriculture
• Brass/Copper: Often used in plumbing and HVAC systems.