In a SAIRAC Cape Town Centre TechTalk on 13 May, 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 2 of a two-part series.
ASSOCIATIONS
Mastering heat exchanger longevity through a focus on water chemistry( Part 2)
… continued from Part 1.
De Waal outlined One Eighty ' s systematic approach to root cause analysis for heat exchanger failures:
• Visual on-site inspection: This initial step involves a site visit by one or more of their consulting engineers to assess the equipment, gather background information and collect necessary samples.
• Lab analysis: Depending on the nature of the damage( mechanical or chemical), this typically includes: o Mechanical testing: To check material compliance, particularly if material properties like hardness or strength are within the expected ranges for the given material specification. This is common when large tube arrays collapse without apparent corrosion, or in cases of buckling or shell deformation in boilers. o Chemical testing: To analyse material composition using techniques like Optical Emission Spectrometry( OES) or X-Ray Fluorescent spectroscopy( XRF) to verify the alloy conforms to specifications of heat exchanger designs. o Metallurgical analysis: By examining the microstructure, they can determine the origin of a failure, for instance, whether a perforation initiated from the water side or the refrigerant side, which is critical for identifying the likely source of the problem, understanding the progression of damage, and conduct further tests to identify the root cause.
• Comparison to OEM standards: All gathered information, including water analysis, material properties, and failure mechanisms, is compared against Original Equipment Manufacturer( OEM) standards and specifications. It is crucial to rule out any likely cause that could potentially contribute to the failure, in order to identify the root cause.
By Eamonn Ryan
In a SAIRAC Cape Town Centre TechTalk on 13 May, 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 2 of a two-part series.
• Identification of failure mechanisms and triggers: Based on the evidence, One Eighty identifies the primary failure mechanisms( e. g., corrosion, mechanical failure, ruptures) and the potential triggers that led to them.
• Recommendations: Finally, One Eighty provides clear recommendations based on their findings in order to assist their clients in minimising or ideally eliminating the problem.
De Waal highlighted key visual indicators of potential corrosion-related failure risks that operators should look out for:
• Discoloration or visual defects: Any change in the visual appearance of components in the system, particularly if it deviates from its original commissioned state, signals a need for further investigation to determine the severity and possible consequences.
• Excessive scale formation: Often indicative of poor water quality, this can be seen during maintenance backwashes when water discharge is contaminated, evident by discoloration and / or the presence of solid particles.
• Unusual pressure variation: These can signify blockages or leaks, indicating that corrosion has likely already occurred. Immediate action would be recommended in order to rectify the issue, if possible.
• Decrease in heat transfer efficiency: Excessive scaling can severely impede heat transfer, possibly requiring significant effort or treatment to restore efficiency.
• Deterioration of welds: Clear visual evidence of material loss surrounding welded components would facilitate the need for immediate intervention.
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He also addressed the use and accuracy of |
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in-line pH and electrical conductivity sensors. |
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While useful for indicating problems in heat |
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exchanger systems, De Waal cautioned that |
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temperature shifts could affect readings, |
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depending on the design and type of sensor |
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