Failure of flexible couplings in environmental control system (ECS) of an aircraft.

Raghavedra, K and Madan, M and Sujata, M and Bhaumik, SK (2021) Failure of flexible couplings in environmental control system (ECS) of an aircraft. Engineering Failure Analysis, 125. ISSN 13506307

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Abstract

There was an incidence of failure of flexible coupling joining the pipelines in environmental control system (ECS) of a military aircraft. Examination revealed that the sleeves of the coupling got detached from the assembly because of fracture in all the rivets with the steel locks. The rivets were made of Al-alloy of specification 5083. Microscopy and fractography studies confirmed that the failure mechanism in the rivets was exfoliation corrosion. In-situ composition analysis of the corrosion products on the fracture surfaces of the rivets showed presence of chlorine (Cl) in quantities as high as 8.9 wt%. In addition, deposits of foreign material were found present on the steel lock surface surrounding the rivets. The observed foreign material contained sodium (Na), magnesium (Mg) and chlorine (Cl) in concentrations as high as 16.3, 10.2 and 14.0 wt% respectively. Considering the application environment, presence of Na, Mg and Cl in such high quantities appeared to be unrealistic. Examination of service records of the ECS revealed that during each time of maintenance, leak checks were performed on the pipe assemblies. As per the standard operating procedure (SOP), a proprietary solution was recommended for this purpose. But, over the years, the manufacturer changed over to usage of commonly used soap solution for leak checks. Chemical analysis showed that the soap solution contained Na, Mg and Cl in large quantities. Failure of the Al-alloy rivets by exfoliation corrosion mechanism was facilitated due to usage of soap solution containing these corrosion species. The root cause responsible for creating the condition for physical failure to occur has been discussed in this paper.

Item Type: Article
Uncontrolled Keywords: Flexible coupling, Al-alloy rivets, Exfoliation corrosion, Root cause of failure
Subjects: CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
CHEMISTRY AND MATERIALS > Composite Materials
Depositing User: Mrs. Usha Kumari
Date Deposited: 03 Aug 2022 11:24
Last Modified: 03 Aug 2022 11:24
URI: http://nal-ir.nal.res.in/id/eprint/13573

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