Corrosion control and the environment

Citation

Sharratt, P. (2001), "Corrosion control and the environment", Anti-Corrosion Methods and Materials, Vol. 48 No. 1. https://doi.org/10.1108/acmm.2001.12848aab.007

Corrosion control and the environment

Corrosion control and the environment

Keywords: Environment, Corrosion

The environmental issues surrounding materials selection were until recent years mostly ignored. The choice of the right material centred on the search for durability, low cost and other properties relevant to performance in the desired application. Times are now changing, and the environmental performance of a material has started to permeate the processes of selection, use and end-of-life treatment or disposal. Pressure is primarily legislative, but there are also influences from public pressure, the environmental pressure groups, the media and financial institutions.

Environmental problems may arise through the use of a material, or in its manufacture or disposal. In-use environmental problems are mostly obvious. Materials failure may result in accidental releases to the environment. Corrosion of pipes and equipment increases the likelihood of failure, and the resultant need to maintain and replace equipment generates waste. However, these problems do not necessarily change our perspective – low corrosion and maintenance are objectives that are already aligned with the "traditional" economic drivers. We need to expand our view to see the emerging issues.

Corrosion products are a potential source of pollution. For example, in chemical processes involving the use of strong acids, corrosion may be inevitable, and the residues from such processes can contain nickel, chromium and other metals that pose an environmental threat. This problem, however, is not always picked up by process designers, and ends up as an effluent treatment problem for the process operators. Polymers have also attracted increased environmental attention – and none more than PVC, with a campaign against its use being orchestrated by environmental pressure groups. A wide range of issues has been raised to support arguments for cessation of manufacture. They include the potential for in-use environmental effects when additives such as lead and phthalates leach from the PVC. However, a key point here is that the arguments have spread to the full life cycle of PVC from manufacture to final disposal of post-consumer wastes.

Legislation now aims to reduce waste generation and to promote reuse and recycling, and is becoming increasingly holistic in its requirements. Already, for some applications the selection of materials may now involve consideration of the overall life-cycle environmental impact. Packaging is one area where legislation is forcing industry to rethink under the influence of European legislation. The car industry is starting to address the end-of-life dismantling and recyclability of it products. The electronics and white goods industries are considering similar questions. It seems likely that soon even the construction industry will be forced to look at the environmental impacts associated with manufacture of its raw materials and disposal of demolition wastes.

Environmental impact has started to be a commercial battleground. Manufacturers of aluminium, steel and plastics promote the environmental benefits of their products in terms of lower energy use in manufacture and use. The debate as to which is best, for example as a soft drinks container, has become heated. The Cooperative Bank produced a biodegradable credit card as an alternative to the usual PVC. Recyclability and low environmental impact have become selling points. While at the moment the environmental benefits associated with such claims should be taken with a pinch of salt, the arrival of new legislation will inevitably sharpen competition, and those materials with higher impacts will ultimately be losers.

Life-cycle assessment (LCA) has emerged as an important tool to support environmental decision making. LCA considers the environmental impacts associated with a particular product, activity or service "from cradle to grave". As such it should support the selection of appropriate materials for a duty taking into account not just local impacts but those arising elsewhere. This is an immensely complex activity, even for a relatively simple subject. While standardisation of the methodology is now taking place, for example through the ISO 14040 series, one of the central difficulties is the lack of detailed information on impacts associated with processing operations. The issues surrounding energy and raw materials use are reasonably easy to define, and LCA often focuses on "big picture" impacts such as contribution to global warming and depletion of non-renewable resources. Detailed impacts such as the local toxic impact arising from corrosion products is probably well outside the expertise of the LCA practitioner. Further, the data to support such an assessment are unlikely to be readily available in the literature.

It is here that the materials science and corrosion communities could make a significant contribution. We do not even yet know what pathways are important contributors to environmental issues. How important is it that wear products from car engines end up in used motor oils and contribute to the difficulty of recycling? Can corrosion of materials in landfills influence leachate composition, and so on? Once the pathways are identified, can we quantify the rates of release? Then there are questions of the environmental benefits and disbenefits from applying particular corrosion control techniques. Which coating or treatment has the least overall impact? Does minimum corrosion mean minimum overall environmental harm?

It is certain that the solution of such problems requires the corrosion community's assistance. However, the answers need to be provided in a way that is usable to the non-specialist. Life-cycle assessment of a product or process will have corrosion as only one among many impact pathways, and the LCA practitioner may be from a range of disciplines. In the first instance, it will be necessary merely to assess whether corrosion provides an impact that is significant, either in absolute terms or relative to the other process/product impacts. Only if the effects were likely to be significant would a more detailed assessment be required.

What also seems certain is that the problem will not go away. Disciplines and industries that ten years ago stood well outside the environmental debate are now having to answer difficult questions and justify their decisions. The ostrich approach – to say that it will not affect me – is one that carries a high risk. The proactive response may unearth some unpalatable problems, but might also identify new commercial and technical opportunities. The choice is yours.

Paul SharrattEnvironmental Technology Centre, UMIST