MARINE CORROSION OF MILD STEEL AT LUMUT, PERAK

The corrosion rate in marine environments affects economic interest since the loss
of steel in marine structures has impact on structural safety and performance. With
emphasis to maintain existing structures in service, there is increasing interest in
predicting corrosion rate at a given location for a given period of exposure. Various
corrosion allowances are prescribed for structural members by different standards.
There are no studies to determine the appropriate corrosion allowance for offshore
steel structures in Malaysia. A field experiment is conducted for estimating the
corrosion loss of mild steel under atmospheric, tidal zone and immersion zone
corrosion conditions for 2 years in seawater at Boustead Shipyard, Lumut. Parameters
such as pH, temperature, salinity, humidity, seawater quality and fouling effect are
considered in this experiment to better understand the effects of these parameters
jointly on corrosion behaviour. The research objectives are to determine the nature
and rate of corrosion and the effect of immersion depth and microalgae on the
corrosion rate. Two sets of corrosion coupons of Type 3 mild steel were immersed in
seawater. The corrosion rate of the coupon was estimated based on the material
weight loss with time. The corrosion rate is controlled by oxidation in short term and
bacterial activity in long term. Corrosion rate in the splash zone is observed to be the
maximum. The results are also compared with code prescriptions and discussed. A
time based corrosion model is developed for sample 1 using EXCEL. The model for
splash zone is given by y = 1.0455t14165 and for immersion zone is y = 5.8096t0'7971.
Parametric regression model is also developed using SPSS with the parameter pH,
temperature, salinity, fouling load and time elapsed. This agreed closely with results
from model designed using EXCEL.