'This process will rapidly compromise the integrity of affected structures and will lead to significant costs for repair or replacement, in addition to having serious implications for the safe operation of the structure, ' notes CIRIA.

The newly completed report, CIRIA Research Project RP693, which was prepared for CIRIA by Mott MacDonald, in partnership with BAC Corrosion Control Ltd, Nuttall John Martin, and The Corrosion and Protection Centre at The University of Manchester, provides a comprehensive guide to the phenomenon of ALWC and its management, condition appraisal, repair, protection and monitoring, and is aimed at infrastructure owners, operators and their advisors, specialist engineers and asset and maintenance managers in ports, harbours and other marine locations.

As the report highlights, currently the only reliable method of detecting ALWC is by visual inspection together with residual wall thickness measurements. 'The strategy for management of ALWC will depend on whether a structure is new build (where the aim will be to take measures to minimise the risk of ALWC occurring) or an existing structure in the early, intermediate or advanced stage of attack, ' says the report, noting that design, inspection, structural analysis, repair, protection and on-going monitoring of maritime structures must now be done taking ALWC into account.

CIRIA makes the following recommendations to ports and harbours seeking to protect themselves against ALWC: for new build structures: include cathodic protection in any design;

apply a heavy duty, protective coating system to at least the exposed part of the structure;

record all design data including specific minimum thickness requirement at the critical low water zone; institute a monitoring programme to confirm the efficacy of the protection used.

For existing structures, ports and harbours should: where necessary, seek independent, professional advice; inspect all structures as soon as possible and establish the presence of any metal wastage or holing; if ALWC is the cause, identify the generalised levels of steel loss and, for the attack found, re-analyse the factor of safety against overstress, instability or collapse; establish a priority work programme, and keep and update regularly a condition database; propose a programme of remedial measures and calculate potential loss of asset value at collapse or for reduced loading use; and carry out priority repairs and make emergency repairs a priority.