City of Chino, CA vs. Parkson Corporation
Ft. Lauderdale, FL
A moderate earthquake dislodged a large Archimedes screw conveyor causing a misalignment of the screw axis. Although loud squealing noises from the roller bearings were witnessed and recorded, operators failed to report or address the unusual condition. Eventually the unit failed and a lawsuit was brought against the equipment vendor. A three dimensional structural and fatigue analysis of the unit was performed including the additional forces induced by the misalignment. A stress-time graph was constructed and demonstrated that the additional loads were sufficient to cause a shaft fatigue failure, consistent with the analysis of the material samples. The report indicated the operating manuals clearly prescribed correction of such conditions and therefore negligent maintenance practice was concluded. The lawsuit was dropped upon receipt of the report.
Ohio Health Corporation vs. Holdridge Mechanical
Grove City, OH
A thermal expansion tank ruptured resulting in catastrophic water damage to an entire office floor and adjacent building structure. Highly experienced experts holding Ph.D., metallurgy, and specialty credentials were hired by both sides to provide a thorough forensic failure analysis. Each side provided conflicting conclusions and the stalemate continued well after depositions. After being hired by the defendant, a thorough mechanical, structural, and corrosion analysis was conducted along with a review of the conflicting reports. The report included a quantitative analysis absent in either of the previous reports. These calculations provided certainty as to the failure mechanisms and sequence. The plaintiff dropped the lawsuit with three weeks of receipt of the report.
Petrochemical Tank Explosion
Alberta, Canada
Analysis of explosion caused by hydrocarbon fumes present during downstream welding operation. Cover of bolted pressure vessel projected 200ft and internal damage noted and photographed. FEA analysis of cover and structural analysis of vessel indicated an impulse of nearly 2000kip. Analysis demonstrated that plastic hinges formed as designed to protect the structural integrity of the unit. Also, proper ASME design of flange resulted in failure of bolts rather than shell. Equipment vendor released of any liability as a result of analysis and report.
Cooling Tower Failure
Sante Fe, NM
Leaks in the heat exchanger coil were detected at the weld-tube interface during startup of a five year old unit. Three different HVAC specialists inspected the unit, each with a different diagnosis. The varying theories included manufacturer defects, weld distortion, fatigue failure, corrosion, freezing, and a combination of these. Additionally, contrasting preventative maintenance procedures were given by the various parties. The coil bundle was deemed irreparable and was subsequently replaced. Investigation questions included: Which failure theory was correct; what was the actual sequence of the failure modes; which was the correct preventative maintenance procedure; why did the unit not fail in the prior four years; what miscommunication occurred to allow the failure; and could the coil bundle have been repaired rather than replaced. The failed portions were cut, removed, and shipped for laboratory inspection. Extensive interviews were conducted with all parties. Calculation on thermal expansion, tube buckling, weld failure, and freezing effects were presented and compared to cross-sectional photos taken during examination. Expansion due to freezing was isolated as the cause, failure at the weld as the weak point, and subsequent atmospheric corrosion as a side effect. The investigation revealed that conflicting inputs of several HVAC service personnel misinformed the owners, resulting in a faulty winterizing procedure.
Coupling Failure
Anthem, AZ
A leak originating from a fractured plastic coupling resulted in a $30k residential loss. Infrared spectroscopy identified the coupling material as polyacetal, implicated in widespread plumbing failures. Fractographic analysis of the failure surfaces indicated crack origin at the stress concentration area of the thread-cap interface. The surface also revealed slow fracture over a period of time climaxing in sudden fracture and catastrophic failure. Calculations demonstrated that a nominal hand torque was sufficient to produce a craze origin and predicted failure at the exact location noted in the micrographs. The manufacturer was subsequently deemed liable for the defect and subrogation ensued.
Faucet Failure
Tucson, AZ
A kitchen faucet failed after only three years of service resulting in $50k damage to a foothills home. A joint inspection of the faucet ensued wherein careful examination, pressure testing, and digital microscopy was performed. Leakage was isolated to an o-ring area revealing a deformed and prematurely aged rubber surface. Rubber fractography revealed drying, cracking, and ozone damage to the rubber interfaces. The o-ring material was found to be deficient and the result of material misselection. Inspection of the manufacturer’s newer model indicated a complete seal redesign including a new gasket configuration and material. The failure analysis, coupled with the manufacturer’s admission of a previously inferior design, was sufficient to allow subrogation of the losses.
Gas Tubing Explosion
Phoenix, AZ
An employee was injured in a gas explosion after a contractor (client) completed formwork in the vicinity of the burner. The site was inspected, plans examined, and personnel interviewed. No violations of code or procedure were found. Subsequent pressure testing of the entire gas line revealed a solitary leak in the corrugated stainless steel tubing located in the control box. Microscopy indicated arc damage, the result of substandard control box design coupled with a damaged CSST surface. The cause of the explosion was shown to be unrelated to the formwork and the client was absolved of any wrongdoing.
Ina Wasterwater Treatment Plant
Tucson, AZ
Concern by public works director and mayor about potential overflow conditions in Tucson warranted site visit and investigation. Data was collected from over 20 U.S. installations of similar bar screen conveyors. Detailed research, curve-fitting, and uncertainty analysis resulted in complex 3-level hydraulic algorithm suitable for projecting overflow conditions. As a result, drastic construction retrofit countermeasures were averted, freeing the vendor of any potential liability and expense.
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