When must a belt be replaced?

A belt must be replaced when it shows visible damage or coating deterioration because these indicators signify that its integrity has been compromised. Visible damage, such as cracks, tears, or fraying, can lead to reduced performance and potential failure during operation. Coating deterioration, which might manifest as peeling or chipping, can expose the underlying material to further wear and environmental factors. This degradation not only affects the belt's functionality but also poses safety risks if not addressed promptly.

In contrast, the other options do not establish a reliable basis for replacement. Simply using a belt for a year does not automatically indicate that it has reached the end of its service life. Also, replacing a belt only after an elevator experiences a malfunction overlooks the preventative nature of maintenance; ideally, components should be replaced before they fail. Lastly, a change in color alone does not necessarily mean a belt needs to be replaced unless it coincides with visible damage or performance issues.