Which patch can only be applied to a pipe that is fully isolated?

• A. Temporary patch
• B. Installed drainage
• C. Slip patch
• D. Welded patch

Answer: (B)

The main idea here is that some pipe repairs require the line to be completely shut off and drained before you work on it, so the repair can be done without any flow or contents in the system. The patch designed for installed drainage is built to be used only on a fully isolated, drained section of pipe. It relies on a dry, clean surface and provides a path to drain any leakage away from the repair area. Because of that drainage feature, you must ensure the entire line is isolated and depressurized before installing it.

Other patches are meant for different scenarios and don’t hinge on having a fully isolated line in the same way. A temporary patch is meant for a rapid, short-term fix while the system is still in service. A slip patch is a mechanical wrap that can be applied to a leaky area with clamps. A welded patch involves hot-work and is done on a depressurized, non-operating section, but its key requirement isn’t the dedicated drainage and isolation setup that the installed drainage patch specifically demands.