Acid strength control in a steel mill pickling bath

This project was completed for the ArcelorMittal Dofasco steel mill in Hamilton, ON. Before the final finishing process, surface oxidation must be removed from coils of sheet steel in hydrochloric acid pickling baths at 80-95 degrees Celsius. The acid concentration needs to be controlled closely: too little acid leads to a poor-quality finish, while too much acid adds to the cost of production.


ArcelorMittal Dofasco was looking for a better way to control the hydrochloric acid levels in their pickling baths. Our team had to consider the following pain points when designing an analytical solution:

  • The baths contained both acid and iron salts from the steel, making simple measuring devices like conductivity meters ineffective on their own.
  • The steel mill’s on-line titrators were capable of measuring the acid concentration, but the aggressive nature of hot hydrochloric acid created significant maintenance issues.


In order to help the client successfully monitor their pickling baths, Novatech replaced its on-line titrators with a SensoTech LiquiSonic system:

  • The LiquiSonic 40 controller combines a sonic velocity measurement with a conductivity measurement, allowing for a highly accurate acid and iron salt concentration analysis supported by the LiquiSonic 40 software.
  • The Halar coated LiquiSonic sensor and in-line Peek coated conductivity sensors are the only wetted parts.
  • Both sensors are suited for temperatures up to 100 degrees Celsius and can tolerate high volumes of gas bubbles.
  • The first SensoTech installation was in 2014, and measurement reliability has increased thanks to its minimal need for maintenance.


The SensoTech unit provides us with an accurate and reliable reading. Very little maintenance. Mostly cleaning equipment and strainer before the unit. The older on-line unit needed constant maintenance and replacement of expensive parts. Unit had issues with plugging up, fouling of metering pumps and/or pH probe replacements.”

– Dave Howarth,
Pickling and Cold Rolling Instrumentation/Measurement Equipment Specialist,
ArcelorMittal Dofasco, Hamilton ON


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