25 May 2005
cooling towers, evaporative condensers, and other equipment containing
galvanized steel. In general, sulfamic acid can be applied to equipment
while it is operating but should be drained from the system after a few
hours, and the concentration of the normally used corrosion inhibitor
should be increased several-fold to protect the metal surfaces.
Commercially prepared descaling compounds consisting of concentrated
or diluted inhibited acid (containing 7 to 28% of the acid and inhibitor) may
be purchased under various trade names at prices 4 to 30 times the cost
of the ingredients themselves if purchased as generic chemicals.
Advertisements of some of these products may contain claims that cotton
clothing and skin are not attacked by the acid. These claims are usually
based on a very dilute solution of the acid that causes a minimal attack on
clothes and skin; however, the cost of the cleaning process may be
increased because a higher quantity of dilute product may be needed. Be
aware that handling acid in any strength must be performed with
considerable care, caution, and adherence to safety procedures.
The cost of diluted acid is expensive; therefore, concentrated acid of
government specifications should be purchased and diluted to usable
strengths. The necessary corrosion inhibitors can be added to the dilute
acid solution. Users of small quantities of acid cleaners (possibly less than
38 liters [10 gallons] of diluted acid per year) may not be able to justify
purchasing undiluted acid and spending the time, cost, and effort to
prepare the cleaning solution; therefore, consider the specific
requirements before ordering.
Cleaning Preparation. The unit to be cleaned must be isolated from other
parts of the system. For systems that cannot be isolated by the closing of valves,
isolation may be accomplished using rubber blankets, wooden bulkheads with seals,
inflatable nylon or rubber bags, rubber sponge-covered plugs, or blind flanges and steel
plates with rubber seals. Long lines may require auxiliary connections for chemical
cleaning. The following information should be considered before the cleaning process is
Decide whether to clean using a soaking process or by circulating the
cleaning solution (see paragraph 9-2.5). In either case, temporary piping
or hose lines will be required to connect the cleaning solution mixing tanks
or trucks to the unit, with return lines to tanks or drains. Proper
precautions and adequate provisions must be made to protect equipment,
isolate control lines, replace liquid level sight glasses with expendable
materials, and provide suitable points for checking temperatures. It may
be necessary to remove selected system components if the cleaning
process might damage them.