Project engineer, CAPCIS MARCH Ltd, Manchester,
Water treatment consultant, Amoco Corporation, Naperville, IL
Associate chemical engineer, Amoco Chemical Company, Alvin, TX
Senior mechanical engineer, Bridger Scientific, Sandwich, MA
Pages: 9 Published: Jan 1994
Corrosion and fouling impact the operation of cooling water systems in terms of reduced heat-transfer capability, increased maintenance cost, loss of plant availability, and water contamination. Conventional test methods have focused separately on measurement of fouling build-up by electrically-heated or pressure-drop apparatus and corrosion detection by electrical resistance or electrochemical methods. A major drawback of conventional fouling monitors has been the inability to indicate real-time corrosion activity beneath surface deposits. Consequently, it has been necessary to destructively evaluate test heat exchanger tubes and/ or rely upon use of corrosion coupons and probes, or both, under nonheat flux conditions. A recent test method, focusing on two simultaneous effects, monitors localized corrosion (pitting, etc.) promoted beneath a fouled heat exchanger tube. The corrosion tendency of a surface under heat flux differs from corresponding surfaces without heat transfer in two respects. First, higher temperature increases the rate of corrosion reaction kinetics. Secondly, scales or biofilms prevent uniform corrosion and promote localized attack, often in the form of pitting. Furthermore, the presence of deposits creates a microenvironment at the heat transfer interface that can prevent the ingress of certain species (inhibitors, biocides) and increase the concentration of others (acidity, bacteria). Contrary to expectation, the presence of scales or biofilms will often exacerbate damage, not prevent it. An overview of the test method and recent field results carried out at Amoco Chemical Company's Chocolate Bayou Plant are presented and discussed.
fouling, under deposit corrosion, on-line surveillance, electrochemical noise
Paper ID: STP12927S