Forensics

Furnace Failures

Introduction

Compression cracks in the roof of an aluminium melting furnace. The contractor had omitted the expansion joints.

Furnaces are expensive to build, maintain and repair. They are often the heart of a factory, such that if the furnace stops producing the factory ceases working. Accordingly, furnaces failures are always costly. When they occur the size of the repair costs alone can justify investigation. In addition, quite often there is a need for technical questions to be answered to assist determination of liability.

Types of Failures

A flaw in a toilet bowl, caused by slippage during casting. This type of defect is unrelated to furnace problems.

Furnaces fail in a great variety of ways. Original construction can be faulty and it can be necessary to distinguish between design, overseas or local construction as the proximate cause of failure. When furnaces are relined either partly or completely they are at risk. Perhaps a lesser quality refractory was used for the refurbishment, or the work carried out by a local contractor with less experience than the original installers.

Welding repair by the owner to the frame of a new aluminium melting furnace, in a vain attempt to stop it from distorting. This Italian-designed furnace had been improperly constructed in Malaysia.

Because many furnaces hold tonnes of molten metal or glass, a breakout can have disastrous consequences. Breakouts can be a result of power failure, construction faults or management choosing to continue production when refractory deterioration (and prudence) would dictate otherwise. Molten metal and moisture are a deadly combination, yet in some designs the furnace walls or the product from the furnace are water cooled, setting the seeds for disaster.

Roof damage on a glass furnace.

Sometimes the investigation emphasis is on the consequences of a breakout rather than the cause, with the need to distinguish between damage by fire versus damage by radiation or contact with molten glass/metal. This arises from the practice of some factories of having fire and explosion policies but no breakout policies.

Metal penetration between the bricks of an aluminium melting furnace.

Some furnace failures occur as a result of an external effect. A power failure is one example. Others are contaminated fuel (leading to burner blockage and blackening of product), floodwater entering a furnace, or even a fire brigade responding to a call and putting the 'fire' out inside a furnace. Some furnaces have to be cooled down over many days and any unplanned stoppage (resulting in more rapid cooling) poses great risk to the installation. When incidents do occur, claimed damage may or may not be apparent, with the spectre of future problems being raised unless extensive repairs are carried out.

Long term erosion damage on the wall of a brick kiln.

A further area of argument can be with respect to the product from a furnace. There may be an incident, after which it is claimed that the reject rate has risen. Coincidentally there might be significant changes in staff or methods of heating, and the competing factors have to be unraveled and judged.

The above pot pourri of furnace problems is not a theoretical list. FSM has carried out investigations involving one or other of all the failure mechanisms mentioned.