US Patent 9506812 Temperature indicator

There is disclosed a temperature indicator (10) in the form of a substrate (12) with multiple coating layers (14-22). Each coating layer (14-22) is visually or chemically distinct from the substrate (12). The material makeup of each coating layer (14-22) is different such that each coating is tailored to undergo failure at a different temperature. The presence or absence of coating layers (14-22) can provide a lasting visual indication of a temperature experienced by the indicator (10) in use. The temperature indicator (10) may be beneficial where the use of conventional temperature sensors is problematic, such as within reactor vessels or other sealed enclosures.