A new report commissioned by Australasian Corrosion Association (ACA) examines the economic impact of corrosion, estimating the degradation of infrastructure and assets caused by corrosion at 3 to 5 per cent of GDP each year. This represents an annual cost of many billions of dollars to the Australian and New Zealand economies.

ACA’s report, Corrosion Challenges - Urban Water Industry by Greg Moore quantifies the cost of corrosion to the water industry with the impact on water distribution and sewerage collection pipework and infrastructure affecting many areas of the economy and covering wide ranging assets owned and operated by urban and rural water utilities, industry, agricultural and domestic environments.

For instance, during a pipeline failure event, there are intangible costs that can have a significant effect on the wider community including disruptions due to flooding, road closures and loss of trade. These costs have been estimated at $91M per annum to the Australian urban water industry. The total estimated annual cost of corrosion to the industry and the wider community in Australia is $982 million, equating to an approximate annual cost of $60 for every adult in the country.

The report estimated corrosion failure costs and identified causes that might be attributable to industry practices, industry skilling and regulatory frameworks. The report also examined some potential cost reduction strategies that could be implemented.

Pipelines and treatment plants are some of the main infrastructure assets owned and operated by water authorities. Moore's report shows that the Australian water industry faces many challenges, particularly in the areas of asset management of ageing infrastructure and the required training to support the prevention and remediation of corrosion. The cost attributable to the maintenance and repair of sewage treatment plants is also considerable.

The failure of a major pipeline or reservoir could have far reaching consequences from immediate catastrophic impacts to the surrounding area to long term economic impact on water, and possibly power supplies to cities and towns in addition to high repair and rebuilding costs.

Conventionally, the water industry adopts a reactive approach to maintenance whereby the pipes are run to failure, with individual pipe failures repaired until the failure rate reaches a predetermined level, at which point the entire section of pipeline is replaced. For smaller pipes this is still considered ‘best practice’ for the industry, but a more proactive approach is being adopted for larger critical pipelines.

The report recommended that water authorities needed to increase pipeline condition assessment to predict occurrence of failures. Pipe materials such as grey cast iron and asbestos cement make up a large proportion of reticulation pipes in Australia and many of these are reaching replacement point. In some cases, where the consequence of failure is very high, condition assessment is used to evaluate replacing the pipeline before any failures occur. However, there will always be difficulties in any proactive approach to manage buried assets where there is limited technology to carry out condition assessments. Most water utilities have active CCTV inspection programs where internal corrosion of non-pressure sewer pipes can be assessed and repairs, renovations or replacements of these sewers implemented before major collapses occur.

Pipelines typically consist of pressure pipes used for the conveyance of water and sewage, and non-pressure pipes for the conveyance of sewage. Pipelines are made of a variety of materials and include plastic pipes that do not corrode as well as cast iron, ductile iron, steel, concrete and asbestos cement pipes, all of which are susceptible to both internal and external corrosion to varying degrees.

The performance of all pressure pipes is reported in the Water Services Association of Australia (WSAA) National Performance report as the number of water main breaks per 100km per year. The average reported number of 19 per 100km equates to approximately 26,700 breaks per year over the 139,000+ km of water mains in Australia. Even though this figure includes both major pipe failures and minor leaks, water main break is still an enormous problem for water companies.

Major urban water utilities also operate 260 water treatment plants and 442 sewage treatment plants. While some water supplies are only disinfected, the majority of supplies are also filtered and treated to remove impurities so as to ensure the water quality meets the Australian Drinking Water Guidelines (ADWG). The consequences of failure of a water treatment plant are usually not as serious as a pipeline failure, but the facilities still require ongoing maintenance and repair.

Sewage treatment plants deal with raw sewage and are subjected in most cases to more aggressive environments than water treatment plants, primarily due to the presence and corrosive effects of hydrogen sulphide.

Additionally, there are many other assets such as manholes, sewer vents, tanks, reservoirs, and pumping stations associated with water and sewerage systems, which also have costs associated with corrosion. These costs can be high, especially where repairs and recoating of steel water tanks and other complex steel structures are required.

Civil assets comprised approximately 87 per cent of the reported depreciation costs for the water treatment plants discussed in Moore's study. Using this data and the premise that all of the civil depreciation was due to corrosion, an average annual depreciation figure of $600,000 per plant was estimated. All treatment facilities have an ongoing programme of replacement and repair to their infrastructure. It can be assumed, therefore, that this figure, or a proportion of it, could be used as a representative annual cost of corrosion.

Sewage treatment plants are exposed to a more corrosive environment than water treatment plants due to the presence of hydrogen sulphide gas. Many sewage treatment plants are also located in or near marine environments, adding to the increased corrosiveness of the sewage treatment plant.

The water industry utilises the skills of a wide range of staff to manage, operate and design water and sewerage systems but there are very few training courses available to impart information on corrosion and its impact on the water industry.

ACA organises educational activities such as seminars and training courses to inform and guide organisations and practitioners about topics including the latest protective technologies and processes.

Moore's report recommends accredited training courses designed for water industry personnel and covering topics such as corrosion basics for the water industry; materials and corrosion control for use in conjunction with the Water Supply Code of Australia and the Sewerage Code of Australia; and identification and assessment of pipeline failures in the water industry. The report also emphasises increased training in cathodic protection technologies, especially as applied to aging steel water mains, tanks and other structures.