At just over two metres, one of the world's longest torsional viscometers has recently been shipped to a customer needing to measure the viscosity of fluid in a five-thousand-litre polymerisation vessel.

Previously, samples had to be taken away for offline viscosity measurement in the lab. This was time-consuming, and the properties of the sample were liable to change before the measurement could be made.

Inconvenience aside, the risk was that the polymerisation point would be missed. If that happened, the product would solidify in the reaction vessel. That would be a disaster, as the process would then have to be shut down until the tank could be emptied.

The difficulty was that any in-process viscometer could only be mounted at the top of the reaction vessel. But engineers needed to monitor the viscosity of the fluid at its base. And as the reactor was located in a hazardous area, the instrument would also have to be intrinsically safe.

Fortunately, Hydramotion has extensive experience in the design of long-reach sensors suitable for direct insertion into process tanks. The company was able to supply an XL7 viscometer with a process fitting custom-made to suit the existing port. Both the viscometer and its local display unit are ATEX certified.

Following installation, continuous on-line viscosity measurement has been possible regardless of actual fluid level. This not only saves valuable time and ensures that the process can be monitored throughout, but also avoids the risk of costly disruption.