An Investigation of Ant-Nest Corrosion caused by the Leakage of a Copper Tube – Finned Heat Exchanger of an Air Conditioning Unit
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R. Gaedicke
Abstract
Leakages often occur in the copper tube – finned heat exchangers of cooling and air conditioning units, the dimensions of which are on the microscopic scale thus making the location and cause very difficult to determine. In the case presented here the leakages found were located using a Helium leak detector. After removing the fins of the heat exchanger, because the points of failure were not visible to the naked eye, a dye penetrant test was carried out on the affected area (Penetrations test or PT), which led to the discovery of three very small indications on one section of the tube. Subsequent microscopic laboratory examination revealed the cause to be microscopically small holes in the wall of the tube caused by corrosion through from the internal surface of the coolant side of the tube. The corrosion mechanism was identified as Formicary Corrosion otherwise referred to as Ant-Nest Corrosion. For this type of corrosion to occur, which according to the specialist literature is often found in Cooling or Air Conditioning units, an aqueous electrolyte or electrolytic film containing Carbonic acid and Oxygen is required which can lead to damage occurring within weeks to months. In the case described in this article, the unintentional ingress of an aqueous oxygenated acidic solution of Glycol into the heat exchanger was most probably responsible for the damage.
Kurzfassung
An luftgekühlten, kupferberohrten Lamellenwärmetauschern von Kühl- und Klimaanlagen kommt es häufiger zu Leckagen, deren Dimension im Mikrometerbereich liegt, was die Ortung und Ursachenklärung sehr schwierig gestaltet. Im dem hier vorgestellten Fall wurden die ermittelten Leckagen mittels eines Heliumlecktests geortet. Da die Schadensstellen nach dem Entfernen der Lamellen mit bloßem Auge nicht erkennbar waren, wurde an einem betroffenen Bereich eine Farbeindringprüfung (Penetrationstest, Abk. PT) durchgeführt, die an einem Rohrabschnitt zu drei sehr kleinen Farbanzeigen führte. Nachfolgende mikroskopische Laboruntersuchungen ergaben, dass es sich hierbei um mikroskopisch kleine, korrosionsbedingte Wanddurchbrüche handelt, die von der kühlmittelseitigen Rohrinnenoberfläche ausgingen. Als hierfür verantwortlicher Schädigungsmechanismus wurde Formicary Corrosion oder auch Ant-Nest Corrosion (die deutsche Übersetzung wäre Ameisennestkorrosion) ermittelt. Für diese Art der korrosiven Schädigung, die laut Angaben in der Fachliteratur gehäuft an Kälte- und Klimageräten beobachtet wird, ist ein carbonsäure- und sauerstoffhaltiger wässriger Elektrolyt bzw. Elektrolytfilm erforderlich, der in Wochen bis Monaten zu Schäden führen kann. In dem hier beschriebenen Fall war vermutlich der ungewollte Eintrag von wässriger, luftsauerstoffhaltiger Glykollösung in den Wärmetauscher für die Schädigung verantwortlich.
References / Literatur
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© 2015, Carl Hanser Verlag, München
Articles in the same Issue
- Contents/Inhalt
- Contents
- Editorial
- Editorial
- Technical Contributions/Fachbeiträge
- Intermetallic Titanium Aluminides as Innovative High Temperature Lightweight Structural Materials – How Materialographic Methods Have Contributed to Their Development
- Report on the 49th Metallography Conference From 16th to 18th of September in Dresden
- An Investigation of Ant-Nest Corrosion caused by the Leakage of a Copper Tube – Finned Heat Exchanger of an Air Conditioning Unit
- Meeting Diary/Veranstaltungskalender
- Meeting Diary
Articles in the same Issue
- Contents/Inhalt
- Contents
- Editorial
- Editorial
- Technical Contributions/Fachbeiträge
- Intermetallic Titanium Aluminides as Innovative High Temperature Lightweight Structural Materials – How Materialographic Methods Have Contributed to Their Development
- Report on the 49th Metallography Conference From 16th to 18th of September in Dresden
- An Investigation of Ant-Nest Corrosion caused by the Leakage of a Copper Tube – Finned Heat Exchanger of an Air Conditioning Unit
- Meeting Diary/Veranstaltungskalender
- Meeting Diary
