Less dismantling of the unit.
Lower cost and labor.
Because the cleaning is more complete, it is possible to examine the unit thoroughly for defects, such as cracks and corrosion pitting.
A more thorough job is accomplished because the acid reaches areas inaccessible to mechanical cleaners.
ACIDS FOR CLEANING. - The following acids are used to clean boilers: hydrocholoric acid, phosphoric acid, sulfamic acid, citric acid, and sulfuric acid.
HYDROCHLORIC ACID is most frequently used for boiler cleaning because it has a relatively low cost and satisfactory inhibitors are available. Also, the chemical reactions of the hydrochloric acid with the boiler deposits usually result in soluble chlorides.
PHOSPHORIC ACID can remove mill scale from new boilers. With this acid, the boiler can be fired directly without producing noxious or corrosive fumes. Direct firing produces good circulation and distribution of the cleaning solution. Another advantage of phosphoric acid cleaning is that the metal surfaces resist corrosion after cleaning. When cleaned with phosphoric acid, you must protect metal surfaces from surface corrosion during draining and before neutralization.
SULFAMIC ACID is available in powder that must be placed in solution. The powdered acid is easier and safer to handle than liquid acids in carbons. It does not produce noxious fumes as it dissolves and it is less corrosive than hydrochloric acid, especially at higher concentrations and temperatures.
CITRIC ACID AND SULFURIC ACID are used for removing boiler waterside deposits. Sulfuric acid is economical and easily inhibited. However, a danger is that the sulfuric acid can form insoluble salts, such as calcium sulfate.
INHIBITORS. - Without inhibitors, acid solutions attack the boiler metal as readily as they attack the deposits. With the addition of suitable inhibitors, the reaction with the boiler metal is greatly reduced. Inhibitors used include arsenic compounds, barium salts, starch, quinolin, and pyridin. Commercial inhibitors are sold under trade names by various chemical concerns. Other inhibitors are manufactured by companies that furnish complete acid cleaning services.
SAFETY PRECAUTIONS - When acid cleaning a boiler installation, you must observe SAFETY precautions as follows:
Before acid cleaning, replace all brass or bronze parts temporarily with steel or steel alloy parts.
Provide adequate venting for safe release of acid vapors.
Close all valves connecting the boiler with other piping or equipment.
Provide competent chemical supervision for the cleaning process.
Do not exceed the specified acid and inhibitor allowable temperature. The inhibiting effect decreases with the temperature rise and the probability of acid attack of the boiler metal increases.
After acid cleaning, be sure to thoroughly flush out all of the tubes that are horizontal or slightly sloping. Obstructions in these tubes can cause poor circulation, overheating, and failure of tubes when the unit is placed in service.
Use goggles, rubber gloves, and rubber aprons when handling acids.
Slowly pour the acid into water when mixing the solutions.
NEVER POUR WATER INTO ACID.
Do not chemically clean boilers with riveted joints.
During acid cleaning, hydrogen gas can develop through the reaction of the acid on the boiler metal. Some of the generated gas becomes part of the atmosphere inside the boiler, and the remainder is absorbed by the boiler metal, then liberated gradually. Because hydrogen air mixtures are potentially explosive, be careful when opening a unit for inspection after acid cleaning. Until the atmosphere within the boiler pressure parts has been definitely cleared of explosive gases, do NOT use open flames. flashlights, lighting equipment. or anything that might produce a spark near the openings to the pressure parts. Do NOT enter the boiler. The unit can be cleared of explosive gases by thoroughly flushing the unit with warm water with a positive overflow from the highest vent openings. The water temperature should be as nearContinue Reading