Another role that engineer-divers play is in maintenance inspections of marine structures, especially when it comes to looking for signs of accelerated low water corrosion (ALWC). ALWC is a form of microbial induced corrosion that occurs in tidal and brackish waters on sheet piles and other steel marine structures.

Steel that is used in the low water zone is designed to corrode at between 0.08 and 0.17mm per year. But in ALWC affected structures the real rate can be up to 1mm per year. This can cause a loss of structural integrity in the steel and the loss of fill material through holes, possibly creating large voids under quayside pavements.

With the recent publication of CIRIA guideline C634, which recommends that port owners arrange regular inspections, ALWC management has never had a higher profile. In one recent project for example, Royal Haskoning undertook an inspection of a 1km length of quay wall for a UK port that was planning to install additional cargo handling equipment on the quayside.

The port needed to know if the structure could take the extra load.

'We found that most of the steel work was in relatively good order, said Andy Harvey, leader of the team of engineer-divers.

'But in some places we identified the first stages of ALWC. Our solution was cathodic protection.'

MJInformation No: 22226