Two prevalent methods are used to monitor corrosion in aqueous and non-aqueous liquid streams in pipes and vessels:
• Electrical resistance (ER).
• Linear polarization (LPR) methods.
Both started out in the 20th century as primary laboratory procedures and one — LPR — is based on electrochemical theory developed and refined over the past 200 years.
About 60 years ago, these techniques were moved out of the laboratory and into the process streams and vessels for a semblance of online monitoring. These older online systems were essentially black-boxes with recorders and wires going out to probes with corrosion monitoring transducers: resistance elements for ER and electrodes for LPR. There enclosures were relatively big and bulky compared to the transmitter housings of today.
As online monitoring evolved from the ’60s, vendors made improvements both in the housing sizes and in the methods of communication with data storage and analysis devices. Up until about 15 years ago, the typical method of online monitoring was to use a hand-held corrosion analyzer and datalogger, or to use a proprietary digital protocol to bring corrosion monitoring signals back to a central monitoring.
That brings us to today, where proprietary protocols have been replaced by standard 4 to 20 mA signals with the open Hart protocol. In many cases, line-powered wired devices have been replaced with battery- or solar-powered wireless devices. These devices are available for both ER and LPR monitoring methods.
Related: Keeping an Eye on Corrosion
Corrosion is the result of a metal’s reaction to its environment. Effective corrosion monitoring helps users keep an eye on water quality to help prevent the corrosion that leads to failed equipment.