March 2013 17 What is corrosion and why is it important to insurers By Peter Moore, David Jones and Lloyd Sparey, Minton, Treharne & Davies Corrosion is most simply defined as the degradation of a material through a reaction with its environment. All materials can corrode in one way or another, but corrosion is most associated with metals due to their higher tendency to corrode in what can be considered normal environments. The cost of corrosion Corrosion is recognized as a highly significant problem within industrialised nations and is of growing concern to developing countries. The cost of corrosion is immense. The corrosion of metals is estimated to cost approximately 3-4% of an industrialised nation’s GDP annually, which equates to a worldwide cost of between $1.3 and $1.4 trillion. This figure represents the cost of maintenance, prevention and the replacement of products damaged or contaminated through corrosion. However, corrosion scientists have determined that additional corrosion control methods could save up to 25% of the annual cost of corrosion. Corrosion and insurance Insurance policies typically contain the word ‘corrosion’ as part of their exclusionary language and can specify corrosion as either an absolute or a qualified exclusion. Therefore, if corrosion is found to be the cause of a failure or event, the resulting claim could well become disputed. It is not the subject of this article to review Insurers’ detailed reasoning for wishing to exclude corrosion related events, but it is no doubt related to the fact that to some extent corrosion is inevitable. In most circumstances, corrosion cannot ever be completely eliminated, but it can usually be controlled and/or monitored successfully through various methods. Given that a finding of corrosion as the root cause of an incident may well bring the parties to an insurance contract into dispute, possibly litigation, it is of utmost importance that any failure investigation involving corrosion as a possible cause be carried out to forensic standards. Factors influencing corrosion Corrosion can occur in a number of different ways, and there are many factors that can influence the rate of corrosion. These are: The Structure of the Material – Controlling heat input during manufacturing and/or welding is very important to ensure that the microstructure of the metal will not be susceptible to corrosion. For example a coarse microstructure can result in segregation of elements at the grain boundaries that can lead to corrosion. The service environment – The environment that a material is subjected to can greatly affect the rate at which it corrodes. Corrosive environments include the atmosphere, aqueous solutions, soils, acids, bases, solvents, salts, and the human body. Careful consideration must be given to ensure the right material is selected for a particular environment. The variables that can arise in corrosive environments such as operating temperature and fluid velocity can also have a marked affect the rate of corrosion. Galvanic differences between two metals – When two metals are in contact in the presence of an electrolyte (e.g. sea water) galvanic corrosion can occur. The more reactive metal (anode) will corrode at an accelerated rate whereas the less reactive metal (cathode) will not corrode. This effect can be beneficially exploited by the use of reactive metals as sacrificial anodes to protect a structure made from a less reactive metal (i.e. zinc or aluminium anodes on a steel structure). Residual and Service Stresses – A stressed material is more susceptible to corrosion, however this effect is © 2013 Xchanging