Final answer:
Tees are pipe fittings used for making branch line connections at 90°. They have an inlet and two outlets, allowing for a perpendicular connection to the main pipeline.
Step-by-step explanation:
The correct answer is d. Tees. Pipe fittings used for making branch line connections at 90° are called tees. Tees have an inlet and two outlets, which allows for a perpendicular connection to the main pipeline. The shape of the tee resembles the letter 'T', with the straight portion of the tee representing the main pipeline and the perpendicular section representing the branch line.
For example, if you have a main pipeline running horizontally and need to connect a branch line vertically, you would use a tee fitting. This allows the flow of fluid or gas to be diverted from the main pipeline and enter the branch line at a 90° angle.
Other options mentioned in the question, such as a nipple, elbow, and return bend, are also types of pipe fittings, but they are not specifically designed for 90° branch line connections.