www . refrigerationandaircon . co . za RACA Journal I March 2024 41
Contributor
FAILURE INVESTIGATION OF A CORRODED HEAT EXCHANGER ( PART 1 )
By Ryan Rennie , from the Spada-Rennie Group
One Eighty was appointed by an air-conditioning contracting supplier and installer to investigate the failure of a heat exchanger unit .
INTRODUCTION The heat exchanger was operated in a butcher ’ s curing / drying room and was in operation for approximately 18 months before failure .
The heat exchanger allegedly failed due to leakage of the liquid coolant ( glycol ) during operation . An initial attempt was made to repair the leaks using epoxy putty , but the leaks persisted . The initial leak site was unidentified ; however , it was suspected to have originated in the copper tube coils adjacent to the larger copper tube manifold . The unit was clearly corroded ; therefore , it was imperative to determine and identify the corrosion mechanism and the root cause for the failure of the heat exchanger . One Eighty was provided with only a section of the heat exchanger for testing , as shown in the images below . cleaning agents , we selected a set of metallurgical tests that would aid in the identification of the corrosion mechanism for this root cause failure investigation .
These tests included but were not limited to : 1 . Visual inspection 2 . Sampling selection and designation for metallurgical testing 3 . Macro-examination by way of stereomicroscopy 4 . Microstructural analysis by way of light microscopy
5 . Scanning electron microscopy ( SEM ) and Energy Dispersive Spectroscopy ( EDS )
6 . Spectrographic Analysis by way of Optical Emission Spectrometry ( OES ) 7 . Vickers hardness testing
Ryan Rennie , from the Spada- Rennie Group .
Ryan Rennie
RESULTS AND DISCUSSION From visual inspection , it was evident that the entire heat exchanger was subject to corrosive attack . The most affected areas were where the paint coating was damaged . The corrosion was predominantly on the outer surface .
Macro-examination through the tube cross-section showed localised pitting corrosion on the outer surface of the copper tubing , suggesting that the copper was exposed to the elements
Images supplied by One Eighty
APPROACH AND METHODOLOGY Due to the lack of identification of the failure initiation site , the heat exchanger product datasheet , the paint coating material specification and application procedure , or datasheets of any
Corrosion of the copper tubing at the interface with the enclosure plate .
www . refrigerationandaircon . co . za RACA Journal I March 2024 41