Title: Understanding Corrosion in Electric Heater Element Evaporator Trays: Beyond the Blame Game

In response to the significant interest in my previous article on condensate corrosion in copper gas loop evaporator trays, I’ve received many questions regarding corrosion in electric heater element evaporator trays. While cleaning chemicals are often the go-to culprit, it's essential to recognise that corrosion can stem from various sources. This article explores the causes of corrosion in stainless steel evaporator trays, supported by research from corrosion experts. I’ll address aluminium evaporator trays in a future article.

The tendency to blame cleaning chemicals oversimplifies the issue. Galvanic corrosion, anodic corrosion, localised heating, and environmental factors also play crucial roles, and these need more attention within the industry. When corrosion issues arise, finger-pointing can overshadow the need for a deeper understanding of material science, water chemistry, and heat distribution.

This article aims to shed light on these overlooked factors to foster a more comprehensive approach to corrosion prevention.

When stainless steel is coupled with heated copper, several factors can contribute to corrosion, mainly through galvanic corrosion and environmental conditions:

1. Galvanic Corrosion: Stainless steel can corrode when in contact with copper in the presence of an electrolyte (like water), especially if the two metals have a significant electrochemical potential difference. Copper is more cathodic (noble), and stainless steel acts as the anode, leading to its accelerated corrosion. This is apparent in the images where the corrosion starts near to where the brass meets the stainless steel at the connection point.
2. Localised heating from the copper heating element can create hot spots on the stainless steel surface. These hot spots can disrupt the protective chromium oxide layer on stainless steel, making it more susceptible to corrosion. Mechanism: Increased temperature near the heating element can lead to accelerated oxidation and degradation of the stainless steel surface, especially if the protective oxide layer is not able to repair itself due to lack of sufficient oxygen.
3. Electrolyte and Contaminant Interaction - Cause: The presence of electrolytes or contaminants in the water or environment can exacerbate corrosion. For instance, if the water contains chlorides or other corrosive ions, it can accelerate the corrosion of stainless steel, particularly when in contact with heated copper. Mechanism: Chlorides and other aggressive ions can penetrate the protective oxide layer on stainless steel, leading to pitting or crevice corrosion. Heated copper can increase the rate of dissolution of these contaminants into the water, further accelerating the corrosion process.

It is worth noting here, that the tray in the picture was in a cabinet installed 6 months prior, and had never been cleaned, or had any cleaning chemicals on any surface, (Or condensate drain tablets!) so that debunks the cleaning chemical theory. Cleaning chemicals can exacerbate corrosion in stainless steel evaporator trays by breaking down the protective chromium oxide layer that shields the metal from environmental damage. If these chemicals contain aggressive agents like chlorides or strong acids, they can accelerate pitting or crevice corrosion, especially in localized areas where the protective layer is weakened. When combined with heat and moisture from the evaporator environment, the chemicals can intensify the corrosion process, particularly in areas near copper heating elements where galvanic corrosion is already a risk. Proper chemical management is crucial to mitigate these effects.

This article delves into the causes of corrosion in stainless steel electric heater element evaporator trays, challenging the common assumption that cleaning chemicals are the primary culprit. It highlights the significant roles played by galvanic corrosion, localised heating, and electrolyte interaction, especially when stainless steel is coupled with copper. By examining these factors, and the many other factors in a food retail environment, the article aims to encourage a more comprehensive approach to corrosion prevention, moving beyond simple blame and focusing on the complexities of material science and environmental conditions. I would again hope that the Institute of Refrigeration UK and the British Refrigeration Association (B.R.A) publish more information on this matter for service teams in the field.

Gel-clear are the leading manufacturer of HVACR drainage solutions for the food retail cold chain. Gravity or pumped, Gel-clear has solutions proven to reduce drain maintenance costs by 2/3rds. Contact us at [email protected] for free trial, product samples, or more information on this article or anything condensate drain related.

Nick Cumings Chris Harvey-Jones F.Inst.R.

References;

D.E.J. Talbot, J.D.R. Talbot,?Corrosion Science and Technology?(CRC Press, Cambridge, 2018)

D. Landolt,?Corrosion and Surface Chemistry of Metals?(EPFL Press, Lausanne, 2007)

M.G. Fontana,?Corrosion Engineering?(Tata McGraw-Hill Education, New York, 2005)

B.N. Popov, Evaluation of corrosion.?Corros. Eng.?1–28 (2015)

S.D. Cramer, S.A. Matthes, B.S. Covino, S.J. Bullard, G.R. Holcomb, Environmental factors affecting the atmospheric corrosion of copper. ASTM Spec. Tech. Publ.?1421, 245–264 (2002)