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Technical
MASTERING HEAT EXCHANGER LONGEVITY THROUGH A FOCUS ON WATER CHEMISTRY( PART 1)
By Eamonn Ryan
In a SAIRAC Cape Town Centre TechTalk, Marcelle de Waal, a senior consulting engineer at One Eighty Materials Engineering Solutions( Pty) Ltd, shed light on the critical aspects of corrosion analysis and prevention in heat exchangers, highlighting the importance of water quality and its impact on heat exchanger longevity, particularly given the financial implications of failures. This is part one of a two-part series.
De Waal provided an overview of common industrial heat exchanger types, such as shell-and-tube and plate designs, made from both ferrous and non-ferrous materials. These are widely used in applications from boilers to chillers, essentially any system transferring heat.
The core of De Waal ' s talk revolved around water chemistry, pinpointing it as a primary driver of corrosion in heat exchangers, particularly on the water side of the heat exchanger design. He identified several key elements and parameters in water analysis that significantly contribute to corrosive processes:
• High or low pH levels can accelerate chemical reactions between water and certain metal alloys, speeding up corrosion and reducing the expected lifespan of the heat exchanger. Similarly, elevated electrical conductivity can create a runaway reaction, especially in bimetallic systems that become susceptible to galvanic / bimetallic corrosion.
• Leaks of ammonia into the system or overall increased ammonia content can lead to significant corrosion, particularly in copper alloys, causing dealloying and embrittlement.
• High calcium content can lead to scale formation, which in turn promotes crevice corrosion and reduces overall thermal heat transfer efficiency.
• High chloride levels are extremely aggressive towards stainless steels, which typically result in pitting corrosion and stress corrosion cracking.
• As a system degrades, iron content from ferrous based alloys components( such as carbon steel) can leach into the circulating water supply, increasing the electrical conductivity and accelerating the likelihood and rate of galvanic corrosion in bimetallic systems.
• Copper content and sulphates are often linked to microbialinduced corrosion, that consequently leads to pitting corrosion and blockages caused by excess fouling.
• Turbidity, typically an indicator of suspended solids in the water supply, can introduce a plethora of elemental constituents that inevitably lead to the formation of scale, corrosive attack, blockages and more.
De Waal noted that heat
Marcelle de Waal, a senior consulting engineer at One Eighty Materials Engineering Solutions.
exchanger manufacturers meticulously design their equipment to operate within a narrow pH range, often between 6.8 – 8.9, as significant deviations can cause various corrosive issues, or be partially contributable. Often, as with almost any commercially available piece of hardware, manufacturers typically issue guidelines to their clientele in order to ensure the best optimal conditions and promote longevity of their product. He also referenced the SANS 241 code for potable water, which outlines allowable water quality parameters that are safe for human consumption and closely aligns with general manufacturers guidelines that are adjusted to a stricter quality standard.
The most aggressive corrosion parameters depend on the material. For stainless steels, high chloride content is particularly detrimental, which is due to the electrochemical reactions that strip the stainless steel of its sub-nanometer thin protective passive oxide layer. Without this passive oxide layer, the stainless-steel alloying elements are able to react with the chemical components of the water, resulting in corrosion. In copper tube systems, ammonia poses a significant threat, leading to dealloying and
Image by Supplied by One Eighty Materials Engineering Solutions
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RACA Journal I October 2025 www. refrigerationandaircon. co. za