Do you know what types of pipe fittings known as "tees" are classified into?

Pipe tees can actually be sorted by the size of their outlets, which is something a lot of people probably don't think about in daily life

For equal diameter tees, each opening matches in size—it’s as straightforward as it sounds

Reducing tees have a look of their own: while the two connections along the main line stay the same size, the side outlet is noticeably smaller, which stands out as a practical solution in many piping setups

A different way to break it down is by the manufacturing process they go through

Hydraulic Bulging

This approach involves filling a pipe with liquid and squeezing it from both sides using a powerful hydraulic press. The tight squeeze increases the pressure inside, pushing the metal outward into a mould that shapes the side branch. It’s a pretty clever technique that applies both inward force and inner liquid pressure at the same time, guiding the metal to expand into the new branch shape

The biggest draw of hydraulic bulging is that it can produce a finished tee in a single step, which really speeds things up in production. It’s interesting too—both the main pipe body and the saddle where the branch is formed end up with thicker walls, which can matter a lot during use

Yet, to make this work, especially for seamless pipe tees, the machines have to deliver some serious tonnage. It makes sense that factories mostly use hydraulic bulging for standard wall tees at moderate diameters. The usual materials you might see here cover low-carbon steel, low-alloy steel, various kinds of stainless steel that aren’t too hard to work with, and even some metals like copper or aluminium

Hot Press Forming

In hot press forming, the process kicks off with a pipe section that’s actually larger than the finished tee. By compressing it down, the shape gradually comes together

Cold-Drawn Tees

For these tees, things get started by adding an opening right where the branch should be. The blank is heated, slipped into a shaping die, and a punch is inserted where the branch forms. Applying force makes the pipe compress outward and the metal flows right into the branch area, thanks to the punch pulling it along. It’s a coordinated movement where the pipe is squeezed radially and stretched at the branch, forming that familiar tee shape. Unlike the hydraulic process, here the branch takes shape mostly because of how the metal slides sideways—some people even call this the radial compensation method

Hot pressing comes with a nice side perk: the machines don’t have to work quite as hard as with cold forming. This technique works well with a range of steels and is often chosen for bigger tees and those with thicker walls. It’s a handy solution if you’re dealing with pipes that have to handle a lot or need extra robustness

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