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Port authorities caught out on steel eating bug

PORT AUTHORITIES are failing to co-ordinate efforts to fight socalled 'steel eating bugs' on sheet pile walls despite knowing that the problem could be worse than first thought, it was claimed last week.

Accelerated biological corrosion is now being tackled by Lerwick harbour in the Shetlands in a long term multi-million pound repair and strengthening operation after a high proportion of its 1.4km of sheet piling was found to be badly affected.

But Lerwick Port Authority deputy chief executive Sandra Laurenson told NCE that the engineers devising a repair had to start from scratch, because harbour authorities have failed to co-ordinate research.

'Other ports are just not talking about what sort of problems they have and how they are being tackled, ' said Laurenson.

'We are getting nothing from the steel producers. Engineers are developing different solutions in isolation.'

The 'steel-eating bugs' can knock decades off the expected working life of sheet piles in harbours and estuaries. They were first discovered in a narrow band close to the low water mark and dubbed accelerated low water corrosion (NCE 5 April 1998).

The phenomenon is characterised by a soft bright orange organic layer hiding a soft black deposit, below which is bright, pitted steel.

However, investigations have discovered biological corrosion much deeper in the water. At Lerwick many of the Frodingham piles were perforated right down to seabed level, a depth of 9m.

The very clear water there might be a factor in this, according to consultant Arch Henderson's Lerwick office manager Andy Sanderson.

He added: 'The question is, does the clear water encourage the corrosion to go deeper - or does it just mean it's easier to find?'

Port engineers contacted by NCE agreed there was little formal collaboration on the issue, but said there was a great deal of informal, liaison between port consultants.

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