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Chemical cleaning is employed frequently for de-scaling exchangers in combination with other cleaning methods. A customized chemical solution is circulated through the scaled apparatus for certain time following drainage and washing. Many cycles of cleaning may be necessary to reach satisfactory de-scaling level. The composition of the cleaning liquor is very important for efficient de-scaling. The scale from an industrial boiler is treated with four different acid solutions at five different strengths to study their dissolving effect on the scale/deposits in the tubes of the boilers. Results reveal that 5% solution of HCl is the most effective to dissolve the scale in a specified time at room temperature. Sulfuric acid shows very poor de-scaling properties under the test conditions. The order of effectiveness to dissolve the scale deposits is HCL > HNO3> HCOOH> H2SO4. Hydrochloric acid may provide 30-50% savings on the circulation time as compared to HNO3 based on the rate of dissolution.