Furnaces

A gas furnace heat exchanger can deteriorate because of overheating, corrosion, repeated thermal cycling, abnormal combustion, airflow conditions, or exposure to corrosive combustion products. An investigation may compare crack location and characteristics with burner operation, airflow, temperature history, corrosion evidence, maintenance records, and the condition of surrounding components. ASHRAE has documented heat-exchanger corrosion associated with combustion air contaminated by substances that can introduce corrosive compounds into the flue gases.

An electric arc furnace investigation may examine the charge material, cooling-water system, furnace vessel and roof, electrodes, electrical equipment, operating sequence, refractory condition, alarms, interlocks, and available operating records. Particular attention may be given to evidence of water or moisture entering areas containing molten metal because contact between water and molten material can produce a violent event. The investigation should also consider electrical, mechanical, thermal, and operational conditions rather than assuming a single cause from the outset.

Electric furnace heating elements can fail because of excessive temperature, electrical overload, contamination, repeated thermal cycling, mechanical damage, poor heat dissipation, or deterioration during service. Relevant evidence may include the condition of the element, electrical measurements, controller settings, temperature records, furnace insulation, mounting conditions, and the location and appearance of the failed section. These findings can help determine whether the failure is consistent with electrical, thermal, mechanical, or environmental factors.