Typically about a 10% concentration of hydrochloric acid
with a corrosion inhibitor and some added penetrating and wetting agents
added. This allows for a better cleaning of machinery and especially
heat exchangers because often the scale in mixed up with silica and
other contaminants. These additives reduce the corrosion on the metals
and cut through and loosen up these other materials mixed with the scale
for faster and more thorough cleaning.