44
Technical
There are vast a number of relevant industry standards used in corrosion evaluation, typically incorporated during the design conception of the heat exchanger, on a case-by-case basis. The use of standards are not limited to only design but also incorporated in maintenance plans and subsequent failure analysis testing when required. Due to the vast list of standards available, thorough research of the relevant standards are required to ensure systems such as heat exchangers remain operational for their intended purpose.
Addressing preventative measures, De Waal stressed the importance of not interfering with a system unless done by a qualified servicing agent who should know the system ' s specific requirements and limitations, guided by the heat exchanger’ s manufacturer.
De Waal recommended utilising testing laboratories that are accredited( SANAS) for water analysis, evaluating the water chemistry and verifying their compliance with standards like SANS 241 or as specified by the manufacturer. He advised clients to provide the heat exchanger ' s manual, as it specifies crucial water quality parameters for benchmarking. One Eighty integrates such water analysis results with material analysis techniques to offer a holistic understanding of corrosion issues and identify the root cause of the problem.
De Waal highlighted a common challenge: clients often send water samples to water testing laboratories that test against drinking water standards, receiving feedback that the water is‘ within acceptable ranges’. However, potable water standards are often insufficient for the highly specific requirements of heat
exchanger systems. " Your manual will have a very specific range," he stressed, pointing out that heat exchanger manufacturers specify much finer tolerances for certain physical characteristics or chemical properties than what typical drinking water regulations typically offer.
Regarding dissimilar metal corrosion, De Waal explained that the risk of galvanic corrosion depends on how far apart the metals are on the galvanic series chart, which indicates the galvanic potential difference. He noted that zinc, aluminum and magnesium are more anodic, while copper and its alloys are more cathodic. These metal alloys are inherently not corrosive by themselves, but when coupled with an electrolyte( such as water), galvanic corrosion can occur. This happens through an electrochemical reaction, that results in the more anodic metal to corrode. The key is to select bimetallic combinations that are as close as possible on the galvanic series to minimise the galvanic potential difference that would induce corrosive attack. Alternatively, galvanic corrosion can also function as a type of protective system, whereby a low-cost material is‘ sacrificed’ in order to protect a more costly and inherently corrosive susceptible metal from failing. One such example, was citing zinc anodes protecting carbon steel ship hulls that enable the longevity of the carbon steel plates against sea water by using the relatively low cast zinc anode blocks as sacrificial material. Stainless steels systems that consist of similar alloy types, such as 304 or 316, can effectively be paired together to form a type of heat exchanger in order to minimise material cost, without having a significant galvanic potential difference. RACA
Continued in part two …
AIR CONDITIONING
Airstream Components Africa( Pty) Ltd
Unit 17, 178 Barbara Road, Elandsfontein Tel: 011 8221486 | Fax: 011 8221493 Email: cliff @ airstreamafrica. co. za
AIR CONDITIONING
AIR CONDITIONING
AIR CONDITIONING
AIR CONDITIONING AIR CONDITIONING
44
RACA Journal I October 2025 www. refrigerationandaircon. co. za