Technical note

Does electrochemical treatment corrode pipes?

Risk comes from anodic chlorine and cathodic scaling. What is controllable, which materials matter, and what to monitor for acceptance.

This is the question customers ask most often, and rightly so: if you pass direct current through circulating water, will it “electrolyse” the heat exchangers? The answer depends on three things — how the current is applied, how the water flows, and which materials are present. Once the mechanism is understood, the risk is manageable rather than a matter of luck.

1. What happens at the two electrodes

The equipment runs on a side-stream loop. Scale-forming species — calcium carbonate, magnesium hydroxide — deposit on the cathode, which is what we want. At the anode, oxygen or chlorine is generated. The risks come from both ends: near the cathode, pH rises and fast scaling can blind the plates; oxidants generated at the anode (free chlorine, ozone) enter the system and can attack carbon steel and copper. So “will it corrode?” cannot be answered in general terms — first ask what the free chlorine is controlled to, what the anode material is, and whether copper is present.

2. Three material groups, three concerns

Carbon steel piping and exchangers are most sensitive to free chlorine and low pH. Under normal control the uniform corrosion rate depends on chlorine concentration and water temperature; in practice free chlorine is kept low and total iron is monitored. Copper (condenser tubes, brass valves) is more sensitive, especially where ammonia and chlorine coexist — selective corrosion can occur, so copper systems need tighter control of oxidants. Stainless steel has low uniform-corrosion risk but is susceptible to chloride pitting and crevice attack; selection should be based on chloride concentration, not just the grade name.

3. Control measures — the equipment alone is not enough

Four measures are normally combined: limiting chlorine generation through current density, polarity reversal and duty cycle; monitoring free chlorine and pH with automatic power reduction on exceedance; periodically reversing polarity or mechanically cleaning the cathode to prevent blinding; and, where necessary, using a corrosion-resistant anode (for example a titanium substrate) so that the oxidation risk is confined inside the equipment rather than released into the system. Write these into the control logic and the risk becomes controlled.

4. What to monitor for acceptance

Set up monitoring during commissioning: corrosion coupons or resistance probes, total iron and total copper, free chlorine, pH, conductivity, and exchanger inlet/outlet temperatures. Record weekly for the first month, then monthly. The criterion is not a number printed in a manual but whether the corrosion rate and heat-transfer performance are worse than before the retrofit. If total iron keeps rising or free chlorine exceeds the limit, reduce power and inspect the anode before blaming water quality.

5. When we would advise against it

Systems with substantial aluminium internals, or processes extremely sensitive to oxidants, need a separate assessment. Where chloride is high and ordinary stainless exchangers are used, fix the material issue before discussing electrochemical treatment. The equipment is not a master key; stating the limits is more responsible than promising that nothing will ever corrode.