On the face of it, news that European steel companies now reckon they know how to stop steel sheet piling in marine environments falling victim to accelerated low water corrosion is to be welcomed. ALWC, after all, can knock several decades off the expected life of sheet pile structures and hit port operators and local authorities alike with massive repair or replacement bills.
So to be assured that resistant alloy steels, high performance coatings or various forms of cathodic protection can eliminate this threat must come as a great relief to all concerned (see News).
On closer scrutiny, however, the news is not quite as good as it seems. Unpublished European Coal and Steel Community research on which these assurances are founded has been directed more at finding a practical cure for the problem than identifying its cause.
One of the many strange features of ALWC is its apparently random pattern of attack, with only certain areas on some piles in some parts of some ports suffering. Those hoping the research would address this random attack will be disappointed.
Particularly disappointing is the failure to identify any significant risk factors which would reliably indicate a predisposition towards ALWC occurring. From the port engineers' point of view being able to quantify the risk to existing structures is of more immediate importance than knowing how to prevent new structures being attacked. One of the stated purposes of the ESPC research was to produce a risk-assessment model, and this it has, but with many caveats.
'This simple risk assessment model can only provide an overview of the parameters involved in the ALWC process,' says the ESPC research committee responsible, adding: 'the ALWC phenomenon proved to be highly complex . . . a detailed description of the chemical and biochemical reactions involved is not possible.'
So, if ALWC is still not fully understood, can the construction industry really be certain that the recommended remedial measures will always work? British Steel admits it took more than a year to create the right conditions for bacterial corrosion in its accelerated test tank at Swinden, and that so far test plates exposed at known ALWC sites have not developed the same patterns of corrosion as those on adjacent piles. And the recommendations are based on investigations carried out on affected piles at only 10 European ports.
So there is no absolute assurance that remedial measures will work, and it will be many years before there is enough feedback from users to provide incontrovertible evidence on the relative efficacy of the preventative options now being recommended. In the meantime the ECSC study is finished, although it could be years before it is actually published, judging from the organisation's previous record for sitting on its research. No further investigations are planned.
The extent of the problem is the source of continuing debate. Steel producers are anxious to maintain that ALWC affects only a minority of ports. Others are claiming to have discovered it at dozens of sites throughout Europe and beyond.
While most attention has focused on commercial marine operations, ALWC could logically occur on any steel structure in water that has more than a hint of salinity - instances have been recorded in the brackish Baltic, and in estuaries.
For years steel producers could confidently specify an uncoated mild steel sheet pile for almost any location and predict a 120 year design life. If ALWC strikes this could be slashed to 30 years or less before major maintenance is needed. Insuring against this risk will cost extra money. Advanced alloy steels, high performance coatings and cathodic protection do not come cheap. No-one wants to make that sort of investment without being reasonably sure it will actually pay off.
So more data on exactly where and when ALWC occurs is urgently needed, as is more research into the key factors that govern whether a port will be attacked or not. This research should not be left to steel producers or other commercial interests.
If ever there was a case for independent, government-funded pure research that will have immediate practical application, this is it.