Abstract
Three generic-type non-chromate chemical treatments based upon zinc and/or polyphosphate together with organic scale control agents are currently employed in open recirculating, fresh water cooling systems at ten Esso refineries in Europe. These treatments control the fouling tendency of the cooling water and also protect carbon steel components from corrosion. In addition, specific copper corrosion inhibitors are used where copper-alloys are present while chlorination forms the basis for microbiological control with all treatments. In a well-designed and well-operated system with close control of cooling water chemistry and chemical inhibitor injection, all treatments effectively control corrosion, scaling and fouling to maintain process throughput and system operating reliability. In particular, pH/alkalinity control is critical with all treatments to avoid exceeding the treatments' scale control capability at high pH, and its corrosion inhibition capability at low pH. Oil ingress is the most common operating upset which can not only foul the system but can also interfere with corrosion inhibition and microbiological control.