What issue may arise from a horizontal pipe not being properly supported?

When a horizontal pipe is not properly supported, water hammer can occur. Water hammer is a phenomenon that happens when a fluid in motion is forced to stop or change direction suddenly, causing shock waves to travel through the pipe. This situation can be exacerbated by the improper alignment or lack of support for the pipe, as it can lead to excessive movement or vibration of the piping system.

Specifically, if the pipe is not adequately secured, the sudden pressure changes, such as those caused by valves closing quickly or pumps starting and stopping, can create a loud thumping noise and can potentially harm the piping system. This can lead to pipe damage, joint failure, or even leaks due to the stress placed on unsupported sections.

In contrast, issues like priming, foaming, and flashing do not directly relate to the structural support of horizontal pipes. Priming involves the unwanted accumulation of liquid in a system due to incorrect pipe slope or configuration, foaming refers to bubbles in liquids that can lead to operational inefficiencies, and flashing typically involves the rapid vaporization of a liquid under pressure. These issues arise from different factors and do not stem from the lack of proper support for horizontal piping installations.