How It Works
InstantMPY analyzers measure corrosion with linear polarization resistance (LPR), an electrochemical method the oil and gas industry has trusted for 60 years, adapted and refined for drinking water since 2012.
The method, in plain terms
Corrosion is an electrochemical reaction. The analyzer applies a small voltage (about 10 millivolts) across the metal tips of the probe and measures the current needed to hold that voltage. That current is directly related to how quickly the metal surface is corroding. From it, the analyzer calculates polarization resistance and, using Faraday's law and the Stern-Geary relationship, converts it to an instantaneous corrosion rate.
The result is displayed in mils per year (mpy), the standard unit for reporting corrosion in drinking water. One mil is a thousandth of an inch: a reading of 5.0 mpy means the metal is losing five thousandths of an inch per year. Over 20 years, that is one tenth of an inch of metal gone.
The measurement is recognized by ASTM International
The LPR method used by InstantMPY analyzers is Test Method B of ASTM G96-90 (2018), the Standard Guide for Online Monitoring of Corrosion in Plant Equipment. Among its documented advantages: corrosion rate measurement within minutes, early warning of corrosive upsets, and a clear signal for when inhibitor feed needs adjustment.
Better than coupons
Corrosion coupons give one averaged reading per 90 days. An InstantMPY analyzer produces a reading every 60 seconds: thousands of data points across the same period, revealing the swings a coupon averages away. The mpy number it reports is the same unit coupons report, so your historical records still line up.
Frequently asked questions
Can this help me monitor seasonal fluctuations?
Yes. Corrosion rates are typically lower in cold months and higher in warm months. Lower feed rates when the water is less corrosive saves money; higher feed rates when the water is more corrosive protects the system when it matters most.
I use LSI. How is this different?
The Langelier Saturation Index predicts the scaling tendency of water with respect to calcium carbonate. It does not measure the corrosion rate of water on metals. LPR measures the actual corrosion rate, quantified in mpy.
How long until readings are meaningful?
Corrosion probes need 3 to 5 days in the water to stabilize. After that initial period, readings are accurate and meaningful, and rates fully settle within about a week.
What maintenance does it need?
None, and no calibration either. Replace the electrode tips about once a year (about $30) and the analyzer keeps working; useful instrument life is 10 years.