Assessment of Corrosion in Offshore Structures through Inspection Reports and Experiments

Corrosion in Marine and Offshore Structures such as Jacket platforms and jetty piles
is one of the issues to be considered during the design and maintenance. The current
corrosion allowance in the splash zone for structural element is l2mm (PTS 20.073).
Currently, no studies had been done on determining the appropriate corrosion
allowance for offshore steel structures in Malaysia. This issue is crucial because
many of the around 200 offshore structures in Malaysia are reaching their design life
and a lower corrosion allowance would mean that they can be continued to be used
without strengthening the structures. There are five zones at the seawater
environment which include subsoil, continuously submerged, tidal, splash zone
above high tidal and atmospheric zone. The rate of corrosion varies in different
zones.
The goal of this project is to define corrosion allowance and evaluate the
effectiveness of the cathodic protection and anodes on offshore structural members
from PETRONAS inspection reports. This goal is achieved in three stages :
collection and analyse the PCSB Underwater Inspection Maintenance data from
various platforms, conduct an experiment which involves fabricating of samples of
different types of tubular members and immersing the same in different seawater
zones at BOUSTEAD shipyard at Lumut. The samples will be inspected periodically
and measurements will be taken to determine the nature and rate of corrosion. The
results will be compared with the recommended values in the current code.
The implementation of the correct corrosion allowance would benefit PETRONAS
in terms of cost reduction and excellent structure integrity in all circumstances. Case
study on all the reports for the platform in Sabah showed that data was not available
from earlier inspection which could have been missed during platform handover.