Seamless Tee

What is a Seamless Tee?

A seamless tee is a one-piece T-shaped branch fitting formed from a seamless tube without any longitudinal weld in the fitting body. It is manufactured by heating a seamless pipe section and extruding or pushing the branch outlet from the pipe wall. The seamless construction provides uniform wall thickness and superior pressure integrity, making these tees preferred for critical high-pressure and high-temperature service.

Standards and Specifications

Seamless tees are manufactured to ASME B16.9 and ASME B16.28, conforming to MSS SP-75 and ASTM A234. Available in equal and reducing patterns. Sizes range from NPS 1/2 to NPS 24, with wall schedules from SCH 10 to SCH XXS. The branch is extruded from the run pipe wall, creating a continuous grain flow through the junction.

Materials and Grades

Carbon steel A234 WPB is standard for general service. Stainless steel 304/304L and 316/316L provide corrosion resistance for chemical and marine applications. Alloy steel WP11, WP22, and WP91 grades handle high-temperature refinery and power service. Low-temperature A420 WPL6 is available for cryogenic piping. All starting material is certified seamless tube.

Pressure and Temperature Ratings

Because the tee body has no longitudinal weld, seamless tees offer higher pressure integrity and longer fatigue life than fabricated tees. They are rated for pressure classes 150 through 2500, with temperature ranges matching the selected material. Each tee is normalized, solution-annealed for stainless grades, and hydrostatically tested.

Applications

Seamless tees are used in high-pressure oil and gas systems, refinery process piping, power plant steam lines, chemical injection systems, hydraulic pressure circuits, and cryogenic service. They are specified wherever the fitting body weld would be a potential failure point, such as in sour service, hydrogen service, or fracture-critical piping.

Advantages

The seamless, one-piece construction eliminates longitudinal weld weakness. Continuous grain flow at the branch junction delivers higher strength and better impact toughness. Uniform wall thickness ensures predictable pressure performance. Seamless tees require no body weld inspection, reducing fabrication cost on critical projects.

Manufacturing and Installation

Seamless tees are induction-heated and the branch is extruded from the run pipe wall using a hydraulic press. The ends are beveled for butt welding. On installation, prepare the pipe ends, align the tee, and complete the full-penetration welds with matching filler metal. Apply preheat and post-weld heat treatment as required.

Quality Assurance

Each seamless tee is marked with size, grade, heat number, wall thickness, and manufacturer's stamp. Inspection includes ultrasonic wall thickness measurement, dimensional checks, PMI, hardness testing, and NDE when specified. Material test certificates to EN 10204 3.1 or 3.2 are provided. Tees are coated with rust-preventive oil and bevel ends are capped for shipping.