1. ABSTRACT - CORROSION RESISTANCE OF AN ELECTROLESS Ni-P & Ni-P-Al2O3
COATING TO AN OIL AND GAS PIPELINE
The infrastructure of steel pipelines are the most efficient and economical method of
transportation of hydrocarbons within the oil and gas industry. These pipelines must be
mechanically strong and be able to withstand corrosion and erosion. This research will
investigate the corrosion resistance of an electroless Ni and Ni-P-Al2O3 coating to the inside and
outside of a mild steel tube substrate.
Ni coatings were deposited by the process of electroless deposition. The co-deposition of Ni-P-
Al2O3 coatings was produced by the same process. The coating was achieved by using one litre
nickel solution baths, with a deposition time of one hour. The agitation of the baths was carried
out by the means of an innovative process using the magnetic field of the hotplate. This was
used to make the substrate twist and move in the solution. The coating parameters that were
altered were the phosphorous content and the addition of the Al2O3 particle. For the Ni-P-Al2O3
baths the loading was 10 g/l of 2.1µm Al2O3 particles.
The research was to investigate and test the corrosion resistance of the coating developed on
the internal and external surfaces of the pipe substrate, under the different experimental
conditions. The main coating features analysed was the thickness and the corrosion rate. These
were investigated using optical microscopes, scanning electron microscope analysis, and
laboratory testing; hot water porosity test and a semi-immersion test in an aeriated 3.5% sodium
chloride solution. Results obtained from the investigation experiments confirmed that a coating
was present both internally and externally in all samples. Significant results were obtained in the
experiments, this indicating that coating features such as thickness were affected by the two
parameters that were altered to the bath. A major development was that the inclusion of the
Al2O3 particle increased the coating thickness.
The porosity and semi-immersion experiment results, indicated that again the two bath
parameters that were altered had a dramatic effect on the results obtained. A significant factor
was that the inclusion of the Al2O3 particle increased the corrosion resistance of the coating. A
major development was that medium phosphorous had the best corrosion rating results; this
was due to a number of factors such as better bath control. The best results were obtained from
MP-Ni-Al2O3 for both coating properties and corrosion resistance.