Annealing heats steel to a very high temperature so that bonds weakened during rolling can reform, strengthening the overall structure of the metal. A high-thermal-conductivity hydrogen atmosphere is used inside the oven to help retain this heat, and moisture in that atmosphere is continuously measured to safeguard product quality. High moisture content in the hydrogen-rich furnace gas causes oxidation of the steel surface, resulting in an undesirable finish.

Application

In the past, electrolytic-type moisture cells proved unreliable in this application because of a recombination effect in the hydrogen atmosphere, which disturbs the water/hydrogen/oxygen reaction the cells rely on and produces ambiguous readings. Modern aluminum oxide and TDLAS sensors avoid this problem entirely.

Solution

For moisture measurement, the proven AlOx (aluminium oxide sensor) technology can be used. The sensor is typically installed in a properly designed sample conditioning system that continuously monitors the moisture content in the furnace hot zone or in the exhaust gas; in some applications, the furnace inlet gas is also monitored. As the gas passes through stainless-steel sample lines, it naturally cools to below 50 °C (120 °F) before reaching the measurement cell. Panametrics builds on decades of experience in combining AlOx moisture analyzers with properly designed sample handling and conditioning systems, including the removal of submicron particulate matter.

However, when the fastest possible measurement response and virtually maintenance-free operation are the priority, TDLAS technology is the preferred solution. The Aurora RM analyzer uses Tunable Diode Laser Absorption Spectroscopy (TDLAS) and is available in a 19″ rack-mount configuration. TDLAS is therefore an ideal choice for applications where a rapid response to changes in moisture content is critical.