ZIP probe takes hot dips to ensure integrity of zinc kettles

Galvanized steel is used in numerous sectors but the zinc coating that gives the metal alloy its longevity has to be heated to around 450°C in kettles that need periodic inspections.

Zinc Immersion Probe
Zinc Immersion Probe

Hot dip galvanizing involves immersing chemically cleaned steel products into zinc kettles that need to be checked for rates of corrosion throughout the equipment.

Those corrosion wear rates vary depending on volumes, dip sizes and the amount of production at each plant and monitoring techniques have included draining the molten zinc from the kettles to another device, or leaving the kettle to cool before physically sampling the kettle’s surface.

Now, Zinco UK is about to introduce an ultrasonic probe that monitors such kettles in situ. The Hereford-based company and Sonemat have signed an agreement to use the ultrasonic probe technology developed from research first conducted at Warwick University.

In use, the probe is mounted onto a steel framework that sits on top of the hot dip galvanizing kettle said David Watkins, managing director Zinco UK. It is inserted into the zinc by a vertical motor drive or manual operation.

He added that the heart of the probe contains a novel high temperature ultrasonic sensor that is capable of launching ultrasonic waves into and from the molten zinc. All the internal components of the ultrasonic transducer inside the sensor are designed to survive temperatures of 450°C without any cooling.

“Typically [for] an inspection of average sized galvanizing plant, the probe would be submerged into the zinc for approximately six hours,” he said. “The ultrasonic signals are transmitted through a specially designed cable that is capable of operating at high temperatures that is connected to a laptop computer at the customer’s premises. The ultrasound signal is interpreted by the technician on site and the data captured is saved for future use.”

The company states that readings in a high-velocity kettle are focussed at the end containing the heat shield as this is usually the area of greatest corrosion.  Alternatively, on a flat flame or electrically heated furnace readings will be taken directly in front of the heat source and in between the heating elements.

After use, the Zinc Immersion Probe (ZIP) cools down naturally and has a thin layer of zinc at the tip of the probe.

“The equipment travels from site to site and is carefully reinserted into liquid zinc the next time it is required,” said Watkins, who added that the probe has a design life of in excess of 30 inspections as long as it properly maintained and not subjected to large thermal shocks.

The ZIP probe has so far been used to measure galvanizing kettles in Africa, Malaysia, Middle East, Scandinavia and Europe.

“We are confident that this new resource will lead to us serve at least 30 per cent of the world-wide market”, said Watkins.