Corrosion Management for Different Metals in Closed-Loop Chiller and Mold Cooling Water

Why Do Different Metals Create a Risk in the Same Circuit?

Although the water volume seems constant in closed circuit chillers, plastic/metal injection mold cooling and induction heating-cooling lines, the risk of corrosion does not disappear on its own. The presence of carbon steel pipes, copper/brass collectors, stainless plate heat exchangers and aluminum mold channels in the same water circuit creates a galvanic double effect. Especially trace amounts of copper ions dissolved in water from copper surfaces can trigger local pitting corrosion when transported to aluminum or steel surfaces. Additionally, since aluminum is an amphoteric metal, it can corrode rapidly at high pH values ​​(>8.5). Just the fact that the water appears clear at first filling is not sufficient for safe operation.

Selection of Multi-Metal Compatible Inhibitors

In program design, the list of all metals in the system, operating temperature, filling (make-up) water quality, presence of glycol and sealing status should be examined together. Elif Çevre Kimya's cooling tower and closed circuit page lists nitrite-free molybdate for chiller, mold cooling, and closed heating circuits, TTA/BTA azoles for yellow metals, and organic film-forming polycarboxylate combinations. Where classical nitrite-based products can be susceptible to bacterial degradation (nitrite-consuming bacteria) or aluminum incompatibility, molybdate-azole-organic hybrid formulations can offer a wider pH and temperature window in multi-metal circuits.

Makeup Water Leaks and Trend Following

If the inhibitor balance level is rapidly decreasing in a closed circuit, water leakage and uncontrolled raw water ingress in the system should be detected rather than continuing to add chemicals. pH, conductivity, turbidity, iron/copper/aluminum transport, microbiological load and active inhibitor level should be recorded periodically. Constant dosage is not guaranteed without reviewing water analysis and circuit data.

Field Control and Monitoring List

Chemical dosage and system capacity decisions should be determined by analysis and facility conditions; There is no guarantee of fixed dosage or performance.

• Inventory of all metals and alloys (especially the presence of aluminum and copper) in the circuit
• Maintaining the pH limit (usually neutral/slightly alkaline band) in die circuits containing aluminium.
• Monitoring the weekly/monthly amount of make-up water entering the closed circuit with the water meter
• Periodic analysis of active inhibitor (molybdate/azole), dissolved iron and copper concentrations
• Control against anaerobic and aerobic bacterial growth in circuits containing nitrite/glycol