Failure analysis of Integrated Nozzle Actuating System (INAS) cooling hydraulic pipeline

During post test disassembly of a developmental aero engine, a hydraulic pipeline was found fractured from near weld joint. The pipeline was manufactured from a α–β Titanium alloy and was welded using Tungsten Inert Gas Welding (TIG) technique. The pipeline was in service for approximately 100 h. Fractographic features of the surface revealed transgranular cracking mode with presence of corrosive elements near the outer wall. Crack branching was also observed on the pipeline near to the fractured surface. Evidences of corrosion pits along with microcracks were also present near to the fractured surface. From the evidences, it was corroborated that the pipe failure was due to synergistic effect of corrosion fatigue and stress corrosion cracking.

► Working principle of a hydraulic pipeline and CD nozzle is discussed.
► EDS analysis of the fractured surface and filler rod has been carried out.
► Fractured surface has been observed under SZM, OM and SEM.
► Possible failure mechanisms have been discussed and analyzed.
► SCC and corrosion fatigue concluded as possible causes for failure of this pipeline.