Waterwall Chordal Thermocouples

Chordal thermocouples are a useful tool for predicting waterwall metal temperature distress. The readings from the mean wall temperature of a chordal thermocouple should be recorded weekly, after installation. If a previous problem of water-side deposits caused overheating to the extent that acid cleaning of the boiler was required, then the use of chordal thermocouples are useful tools to record temperatures on a weekly basis. The chordal thermocouple readings are directly related to heat flow through the tube wall. Therefore, the recording of temperatures should always be at the same high load, with the same burners in operation. Recording the mean wall temperature will provide a trend of water-side deposits. It only takes a thin coating of water-side deposits to increase the temperature of the tube metal. Iron oxide deposits have a heat transfer coefficient of about 1/70th of steel. Mineral constituents have even lower heat transfer coefficients.