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FORENSIC ENGINEERING SERVICES

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Thermal Failure Mode Analysis
Design Fault Investigation
Forensic Advisors

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Resonant Failure

A third of the 6000 tubes in a large thermal recuperator (erected in Kentucky) failed within 24 hours of start-up. During warm-through, only a very light, temperate flow of combustion products had passed over the matrix. We were commissioned to undertake a design fault investigation, which showed that the Strouhal Number for the tubular array indicated these conditions to correspond with those necessary for vortex-shedding. It was further demonstrated that the frequency at which this occurred coincided with the tubes' natural resonant frequency at the prevailing temperature, causing failure under high cycle fatigue. We presented our failure mode analysis to the State Court of Ohio in Cleveland over the course of a five-day hearing and received commendations from attorneys on both sides.

More on Tubes

As remarked elsewhere, the Environment Agency had acted in response to complaints of excessive plume emissions from the exhaust stack of a biomass-fired shell & tube boiler. While investigation indicated that the system was losing water, visual inspections had showed no defect. Thermal FMEA showed the system to be losing water through faulty boiler tubes. It could not explain why the seam welder had "missed" a significant length of run as the formed section passed through the mill, nor how inspections at tubemill, stockholder, converter and the boiler manufacturer had all passed unnoticed.

A Question of Value

We were appointed by the defence in a criminal prosecution. Its operatives had admitted to sabotaging a high pressure plant for essential oils extraction. Although they claimed it was dangerous, each faced long prison terms - given the owners had said it was worth a seven-figure sum. However, its price was not its value. Site inspection prompted us to undertake a design fault investigation, from which it emerged that the equipment had never worked in commercial production, and could not be made to work save at disproportionate expense; also, that its design presented clear operational risk. The men were released.


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