Compositional Analysis of Soluble Salts in Bresle Extraction from Blocks in Newbuilding Shipyards

Soluble salts, especially NaCl, on the substrate shall cause premature coating failure, promoting osmotic blistering of the coating and underfilm corrosion of the steel. The salt measurement method specified by IMO’s PSPC rule, ISO standard 8502-6 & 8502-9, inherits the shortcoming that the measured value is the amount of Total Dissolved Salt(TDS), and is neither of NaCl nor of chloride ion. In this study, an Ion Chromatography(IC) measurements, which measures specific ion concentration in a solution, is employed to measure exact amount of NaCl in the Bresle extraction water from several blocks in a newbuilding shipyard. By using conductometric methods, 30 ㎎/㎡ ~ 70 ㎎/㎡ TDS was detected for sweep blasted blocks, but NaCl contents of the same extracted solutions from the same blocks, as confirmed by the IC, were measured to be around 20 ㎎/㎡. Comparison of these two methods confirmed that actual content of NaCl was below 60% of TDS, due to the existence of many other anions in the extracted solution, suggesting that ~ 80 ㎎/㎡ TDS corresponds to 50 ㎎/㎡ NaCl.