Scaffolding structures exposed to saltwater can lead to unexpected consequences when ‘galvanic corrosion’ raises its head. John Beck and Kevan Herbert from Apollo Scaffold Services have dealt with these issues for more than 20 years.
Galvanic corrosion is an electrochemical process where one metal corrodes at a faster rate when in contact with a dissimilar metal in the presence of an electrolyte (saltwater). Scaffold contractors working in offshore environments need to be aware of the consequences.
In 1761, The Royal Navy experimented with copper plating fixed to the hull of HMS Alarm with iron nails. On return from a long voyage, the copper plating was in good condition but had become detached from the hull. Many iron nails had dissolved, freeing the copper plating, but the nails that had been isolated from the copper by water-resistant brown paper trapped under the nail heads were in good condition. The Admiralty issued a report stating that iron should not have direct contact with copper in seawater.
The UKCS has produced Offshore Specific Scaffold Guidance which covers this issue. The main concern is the periodic inspection of scaffold fittings attached to aluminium beams and spigot pins used for joining the beams. The guidance stipulates that to retain structural integrity, scaffolds erected under deck should be dismantled every six to 12 months.
Mr Beck has developed aluminium spigot pins to overcome the problems caused by steel pins corroding and expanding, splitting the aluminium beams from within. He has tried various coatings on the beams and fittings to reduce the effects of corrosion and has successfully installed beams that have been in situ for over two years with little degradation.
On the topic of life expectancy and inspection procedures, Mr Herbert suggests using sacrificial droppers and fittings. If a scaffold was expected to be in service for two years, he suggests putting 48 fittings onto a beam and removing two a month for inspection, giving a good indication of the structural integrity of the installed components. This reduces the need to dismantle/re-erect the scaffold installation and the sacrificial droppers can be raised and inspected without operatives working at height.
DOWNLOAD THE SCAFFOLDING GUIDANCE