Effects of Sa 2 and Sa 2.5 Blast Cleaning Surface Preparation on the Adhesion and Corrosion Protection Properties of Coating

Corrosion is a major problem for oil and gas operators as the cost consumed each
year in fighting corrosion are staggeringly high. Along with the implementation of
cost-effective corrosion prevention methods, the race for reducing cost consumption
still goes on. Protective coating is considered to be one of the most economical
methods there is. However, in the application of protective coating, the cost allocated
for surface preparation exceeds the coating material costs itself by 21 %. The typical
standards currently used by PETRONAS required the steel substrates to be blast
cleaned to the ISO cleanliness standard of Sa 2.5. Thus this project aims for the
practice of a cheaper alternative of cleanliness standards which is Sa 2. Three
samples (carbon steel) are blast-cleaned to the standard of Sa 2.5 and three others to
the standards of Sa 2. All samples are coated based on coating system No. lA in
PTS. Corrosion test (ASTM B117-90) and adhesion test (scratch test) are conducted
exclusively to measure the performance of coating system under different surface
cleanliness standards. Four samples (two samples with Sa 2 and others with Sa 2.5
cleanliness standards) had undergone corrosion test. Remaining two samples, each
with Sa 2 and Sa 2.5 cleanliness respectively, had undergone adhesion test.
Calculation on corrosion rate using mass loss method and visual examination for
evaluating the rust grade are done to determine the corrosion properties. Inspection
using 3D non-contact measurement is conducted to confrrm the critical load
experienced by the coating thus demrmining the adhesion properties. Findings for
corrosion test shows a equal performance of coating between samples prepared under
Sa 2 and Sa 2.5 cleanliness standards - corrosion rate of 0 millimeter per year and a
rust grade of 10. Findings for adhesion test shows the critical load experienced by
sample prepared under Sa 2 is 51N and higher than the sample prepared under Sa 2.5
which is 43N. However, acoustic emission shows a higher intensity profile from the
sample prepared under Sa 2 standards compared to the sample prepared under Sa 2.5.
Thus, for the success implementation of surface cleanliness of Sa 2, the performance
of the chosen coating system are to result in similar or better performance in
comparison to the application of Sa 2.5.