ABB pressure transmitters resist chemical attack 11 October 2011

Inorganic chemicals manufacturer William Blythe reports saving thousands of pounds and several days of production time since switching to ABB pressure transmitters.

Andy Fort, control and instrumentation engineer at the plant, explains that the plant manufactures several products including a halide compound, which is extremely corrosive.

"We found that the pressure transmitters we used suffered chemical damage to the seals," states Fort. "The problem was particularly acute if a small amount of moisture was present, because this caused the chemical made on the plant to attack the metal contact parts."

Corrosion problems, he says, meant two or three transmitters out of the eight installed on the plant needing to be replaced at least every 12 months – costing around £1,000 each as well as plant downtime.

"Each transmitter took between six and eight hours to replace," says Fort. "Maintenance staff also needed to wait for the vessels to cool before they could be worked on. After the replacement, there was a warming time as well to get the vessel to the correct working temperature, so each replacement could mean a full working day of 24 hours was lost."

And to make matters worse, as the transmitters were based on 4—20mA signalling, there was also no diagnostic information available, so failures occured without warning.

Fort contacted WH Good Automation, an ABB Instrumentation Alliance member, which helped to specify the correct seal arrangements and materials – based on ABB 264HD pressure transmitters with Hastelloy 2000 seals.

A six week trial of the product convinced Fort that it was the right transmitter and the company replaced two units on its reaction vessel, two on the receiver tank, one on the still and one on the storage tank. Two more are still to be installed.

Fort says the seals have maintained their integrity, and that having HART intelligent capabilities is easing diagnostics. .

"We are looking at a site-wide SCADA system and this feature will help us drill down and interrogate the transmitters for more information on their operation and status," he says.

Brian Tinham

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