Forensic Services Newsletter

Corrosion accounts for 15% of the failures we are asked to investigate. It is the second most common reason for general engineering failures (fatigue is the most common). The failure of a Bailey bridge in Sarawak is a timely reminder that corrosion is for all practical purposes inevitable. All metals except gold are unstable under normal environmental conditions and from the moment that metals are won from nature, they begin to revert to their natural state. Painting, electroplating, cathodic protection and environmental control only influence the time of decay, not the end result. If the word corrosion is taken in the broadest sense, it extends to materials such as fibreglass, plastics and wood. There is a general impression that plastics last for ever, but in fact plastic artefacts present the greatest challenge to museum curators desiring to ensure the survival of classic inventions, such as Bakelite radios, Walkmans and the earliest personal computers.

Existing Bailey bridge in left photo, with remains of collapsed Bailey bridge in foreground. The condition of some members can be seen in the photo on the right.

The Bailey bridge was invented during the Second World War for the British army and so successful was the design, they are still being made today. When we were asked to investigate a collapse of one of these bridges in Sabah, Malaysia, we were surprised to find that it had been made in the 1940's. That is not to say that it had necessarily been standing for 60 years, as a feature of these bridges is the ease with which they can be reused at different sites. Another unusual feature of this particular bridge was that it had been re-erected recently, which was quite an engineering accomplishment considering the extent of corrosion damage, as can be seen in the photograph above.

So prevalent is corrosion, that knowledge of corrosion processes is a prerequisite for investigating general engineering claims for insurers. Within our company we have considerable expertise, with published papers and a number of our staff having attended NACE corrosion courses. Some photos of corrosion failures follow

Corrosion failure of a tin roof in Kuala Lumpur, as a result of pitting corrosion on the underneath of the tin sheet, before the building was even finished. Note that we are not using the word 'tin' as a euphemism for zinc-coated steel. The roofing sheet was actually made of tin. Loss of paint of carbon steel tank floor under a stainless steel heating pipe, as a result of galvanic induced corrosion. Pitting corrosion on the bottom of a tank.
Pitting corrosion on stainless steel following a fire. Degradation of fibreglass tank around a nozzle, as a result of vibration of the pipe. Galvanic corrosion of carbon steel shaft of a propeller, with stainless steel blades.
Corrosion cracking of fibreglass laminate. Corrosion cracking of fibreglass laminate.

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