Early corrosion failure of copper tubing used in air-conditioning units (original) (raw)

Hot-water corrosion failure of a hard-drawn copper tube

Engineering Failure Analysis, 2013

Deoxidized high phosphorus copper (C12200, DHP-Cu) is the principal construction element in piping in water distribution systems and HVAC (Heating Ventilation and AirConditioning) installations due to its excellent thermal and electrical conductivity, formability, corrosion resistance and antimicrobial activity. However, design and installation deficiencies or aggressive environmental parameters, such as improper water quality, may lead to unexpected failures causing material losses and many times property damage incurring high costs of repair. A corroded copper water tube caused leakage in a hot water hydraulic installation. The leakage was reported after approximately 6 years in service. Tubes were disconnected from a hydraulic installation and samples were taken for failure investigation. Failure analysis findings suggest strongly that the leakage was caused by tube perforation from the inner waterside due to localized pitting corrosion. The main cause of the accelerated tube pitting corrosion was the improper water chemistry (especially high chlorine content and low pH) inducing chemical attack of copper leading to scale layers of cuprite, chlorides and sulfates.

Copper tubing failure due to ant-nest corrosion

MATEC Web of Conferences

Ant-nest corrosion is a type of premature and localized failure, which is observed in Cu tubes used mainly in air-conditioning and heat exchanger units, induced by the presence of organic matter. Leakage takes place within a short period of time after unit installation and frequently causes pipeline and equipment damage accompanied with loss of refrigerant liquid. In the present paper, case histories concerning such type of insidious corrosion phenomena are presented. Metallographic examination on cross-sections revealed that a particular pitting corrosion mechanism is activated, driving to a tunnelling-type "tortuous" pit propagation, causing rapid metal tube perforation and leakage.

Protection of Copper Alloy Condenser Tubes by Coating

Proceedings of 2nd International Multi-Disciplinary Conference Theme: Integrated Sciences and Technologies, IMDC-IST 2021, 7-9 September 2021, Sakarya, Turkey

The protective coating acts as a layer against erosion, corrosion, and fouling associated with scale deposits. In this study, two laboratory test rigs were installed one for the corrosion rate estimation and another for evaluation of the heat transfer resistance. Three different types of epoxy resin were employed for coating tube surface interiors using different ratios of resin to solvent to produce different coat thicknesses. The results obtained from the corrosion rate and heat transfer resistance measurements showed that the epoxy coating type (a) (ratio of 2: 1 epoxy: solvent ) is efficient in reducing the corrosion rate to 21.1x10-2 mpy; for example, the efficiency of 92.2% and the heat transfer resistance increased from 12.88x10-4 to 18.37x10-4 m2K/W compared to other types of coating.

Erosion–corrosion of heat exchanger tubes

Engineering Failure Analysis, 2009

The shell and tube heat exchanger failed before 5 years of operation. The failure was caused by pits on the tube outside surface developing until its perforation. Inside the Cu-DHP tubes in soft temper a cooling agent circulated to cool down industrial water at the shell side from 16 to 4°C. The cooled water was hard, rich in chloride ions with relatively low sulphate ions concentration and pH ranging from 4 to 7. The leaking tubes were subject to standard metallographic examination, hardness measurement, scanning electron microscopy and X-ray energy dispersion analysis. It was found that the tube damage was caused by erosion-corrosion induced by two factors: disturbed flow of water containing suspended solid particles and chemical composition of water rich in chlorides that resulted in loss of stability of protective cuprous oxide layer.

Interactive effect of ant nest corrosion and stress corrosion on the failure of copper tubes

Engineering Failure Analysis, 2018

Premature failure of copper tubes used in airconditioning units is a serious problem for air conditioning manufacturers and customers. Several failure theories were put forward, such as ant nest corrosion and inter-granular stress corrosion. A new opinion is raised in this article that the interaction of ant nest corrosion and stress corrosion cause the failure of copper tubes. This article analyzes the interactive effect through comparing the morphologies of the failure copper tubes in practical application with the samples which were exposed to the concentration of 1 vol% formic acid vapor in airtight glass vessels for different days. The experiment results show that most of copper failures result from the interactive corrosion due to the morphology of interactive corrosion tunnels is thinner than single ant nest corrosion and the corrosion starting points of interactive corrosion tend to distribute at the bottom of internal groove where the tensile stress was concentrated.

Localised corrosion of copper canisters

Corrosion Engineering, Science and Technology, 2014

Copper canisters in a KBS-3-type underground repository will be subject to general corrosion and minor localised attack. The form of the localised corrosion will depend on the composition of the bentonite pore water in contact with the canister surface and, in particular, the pH and chloride, sulphate, and bicarbonate ion concentrations. The presence of a passive Cu 2 O/Cu(OH) 2 layer is a prerequisite for film breakdown and pitting. Literature pitting data have been used to determine whether pitting is possible or whether the environmental conditions will favour active dissolution of the canister. It is concluded that the canister surface will corrode generally and will be subject to only minor localised corrosion in the form of surface roughening.

Root cause analysis of the corrosion-related coiled tubing failure

Journal of Electrochemical Science and Engineering, 2022

Coiled tubing (CT) is widely used in the oil and gas industry. However, corrosion-related failures are frequently reported. Research into the causes of failures leads to improvement in the design of components and processes. In this study, a new CT sample and a CT sample with perforated wall that had failed after a few acidizing operations were selected for analysis. Scanning electron microscope (SEM) images at the fracture site showed that CT damage was caused by the low cycle fatigue. In addition, light and scanning electron microscopy (SEM) showed that a corrosion pit acted as the initiator of the crack. Elemental analysis using energy dispersive X-ray spectroscopy (EDS) indicated the presence of an iron oxide layer and a layer associated with the Sb containing inhibitor. The corrosion damage investigation showed that the internal CT wall pits likely formed during storage due to the acidizing operations in the areas where the remaining liquid was still at the tube bottom.