Black pipe cross tee have several common applications in plumbing and HVAC systems:
Branching off of main black iron water supply lines.
Cross tees are often used to create branches for water supply lines to fixtures like sinks, toilets, boilers, etc.
Connecting multiple black iron pipes together at a junction.
Cross tees can join three black iron pipes together at an intersection. This allows pipes to split off in multiple directions from one point.
Providing access openings in pipes.
Cross tees create an opening in the side of a pipe which provides access for valves, gauges, drains or other connectors to be installed.
Serving as pipe couplers.
Cross tees can couple or join two black iron pipes together end-to-side or side-to-side. They provide an easy and inexpensive coupling solution.
Use in emergency sprinkler systems.
Cross tees are suitable for use in fire sprinkler systems where water needs to be distributed from a primary supply line to multiple branch lines.
HVAC applications.
Cross tees are also commonly used in heating, ventilation and air conditioning systems to split refrigerant or air flows between multiple branches.
Gas pipe applications.
For gas pipe systems, cross tees provide an easy way to divide the gas flow from a main line to multiple branch lines supplying gas to appliances like heaters, stoves, fireplaces, etc.
Drain piping.
Cross tees are sometimes used in drain piping systems to create branching in soil, waste or vent lines.
Steam pipe systems.
Cross tees can also be used to branch steam supply lines into multiple distribution lines. However, threaded pipe fittings may be slightly more common for high-pressure steam.