Importance

Loading Importance Indicators...

Abstract

Methods and solutions useful for removing iron oxide-containing scale from the interior surfaces of steel. An aqueous cleaning solution containing formic acid and at least one carboxylic acid having at least two carbon atoms wherein the weight ratio of formic acid to higher carboxylic acid is greater than about 4:1 is contacted with the scale in the absence of an oxidizing agent. Preferred carboxylic acids are the mono-, di-, hydroxy-, and polyhydroxy-carboxylic acids having from two to six carbon atoms. More preferrably, the aqueous solution includes about 0.5-10.0 percent-by-weight in total of such acids wherein the weight ratio of formic acid to higher carboxylic acid is from about 4:1 to about 9:1, together with an effective amount of an organic acid corrosion inhibitor and, optionally, a scale dissolution accelerating agent. Preferrably, contact is under a reducing atmosphere, at a temperature in the range of about 150.degree.-200.degree. F. and a pH less than 7. More preferrably, the cleaning solution is circulated through the vessel for a time less than 30 hours. These high ratio formic/carboxylic acid solutions are capable of holding more iron in solution than low ratio solutions, especially in a reducing atmosphere where iron is maintained in the ferrous state.

Loading the Abstract Image...

First Claim