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Forensic Examination of Leaking Rubber Hose

Complete materials testing capabilities and in-depth failure analysis by nuclear industry specialists
A leak was identified in an EPDM (Ethylene-Propylene-Diene-Terpolymer) hose which was reinforced by two braids of steeel wire. A yellow hypalon (chlorosulfonated polyethylene) jacket was fitted around the metal braid layers. It was reported that the hose had a pinhole leak, accompanied by blistering of the protective yellow sheath.
Forensic examinations of the leaking hose comprised various tests and activities: First, venting and decontamination was done to reduce radiation hazards to ALARA levels. Then, visual examination of the hose was performed. A bubble leak test and helium leak test were done to investigate any sign of leakage.
Borescope inspection of inner part of the hose was performed to locate any possible leak sites or other defects. The hose was then cut into pieces and the defect location was examined in detail by a stereoscope and SEM (Scanning Electron Microscope). In addition, the elastomeric material of the hose was confirmed by performing FTIR (Fourier Transform Infrared).  Finally, durometer hardness of the hose was measured.
Based on the test results, the immediate cause of the non-metallic hose failure was found to be fatigue cracking.
Multiple fatigue cracks nucleated on the inner side of the hose and propagated outwards towards the outer side. The apparent cause of the hose failure was a manufacturing defect. The EPDM inner hose contained a linear through wall discontinuity that acted as an area of weakness for the fatigue cracks to nucleate and grow. It is speculated that the through wall discontinuity was created during the hose extrusion process. It appears to be a flow line created as the polymer compound separated and recombined as it passed through the die.
If the processing conditions are not optimal, this can result in a zone of partial and weak entanglement of the polymer molecules. At the macroscopic level, such flow lines are usually found to have lower mechanical properties and can have significantly less resistance to high cycle fatigue. A cyclic pressurization test, followed by an internal borescope inspection, is recommended to reveal the presence of similar defects in new hoses.