Panametrics Aurora RM TDLAS Analyzer Ensures Reliable Moisture Control in Hydrogen Annealing Furnaces
Summary
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.
| Dew point range | -85 to -50 °C (-121 to -58 °F) |
|---|---|
| Operating temperature | 538 to 1371 °C (1000 to 2500 °F) |
| Operating pressure | 45 psig (412 kPa) |
Benefits:
- Maintenance-free, non-contact TDLAS measurement
- Immune to the hydrogen recombination effect that limits electrolytic cells
- Fastest speed of response among trace moisture technologies
- Rated for the extreme temperature and pressure of furnace hot-zone gas
Challenge
Any moisture analyzer used on hydrogen annealing furnaces must withstand hot-zone gas temperatures that can reach 1371 °C (2500 °F) and pressures around 45 psig, while still delivering a fast, drift-free reading. Electrolytic-type cells, the traditional choice, are prone to unreliable, ambiguous results in a hydrogen-rich atmosphere, and their upkeep adds unplanned maintenance to an already demanding production line.
Solution
An aluminum oxide sensor is typically mounted in a properly designed sample system that continuously monitors the moisture content of the furnace hot-zone or effluent gas; the feed gas to the furnace is monitored in some installations as well. As the gas travels through stainless-steel sample lines it naturally cools to below 50 °C (120 °F) before reaching the sample cell. Panametrics draws on decades of experience pairing its aluminum oxide moisture analyzers with a properly designed sample system that removes sub-micron particulate fines. For the fastest speed of response and maintenance-free operation, the Aurora RM – using tunable diode laser absorption spectroscopy in a 19″ rack-mount enclosure – is the ideal choice.
Source: Panametrics Application Note PANA100AN (panametrics.com) — © Panametrics LLC. Localized and adapted by INTECH CONTROL, official Panametrics representative in the Slovak Republic and Hungary.