25 May 2005
6. Drain the heat exchanger.
7. Neutralize remaining acid by circulating a 1% sodium carbonate (soda
ash) solution (about 3.6 kilograms per 38 liters [8 pounds per 100 gallons])
for about 10 minutes.
8. Rinse thoroughly with water until the pH of the rinse water is pH 8 to 10.
Fill and Soak Method
1. Prepare an inhibited dilute acid solution (see paragraphs 9-2.2 and 9-2.3)
in a container of suitable size.
2. Depending on the item to be cleaned and the types of scale involved, you
may want to place an agitator (mixer) in the tank or install a pump outside
the tank to circulate the acid solution. A method to heat the acid may be
required, such as a steam coil. All equipment must be explosion-proof and
3. Immerse the item to be cleaned in the dilute acid solution. Continue
soaking until the reaction is complete as indicated by foam subsidence or
4. If the scale is not completely removed, check the acid strength (see
paragraph 9-2.6). If it is less than 3%, add additional acid and continue
soaking the items until the remaining scale is dissolved. Usually 1 to 2
hours of soaking is adequate.
5. Remove item from tank.
6. To neutralize remaining acid, immerse the item in a 1% sodium carbonate
(soda ash) solution (about 3.6 kilograms per 38 liters [8 pounds per 100
gallons]) for 2 to 3 minutes.
7. Rinse the item thoroughly with water.
Checking Acid Solution Strength. The initial strength of the dilute
inhibited acid will vary from 5 to 20%, although 10% is typical. As the acid is consumed
by dissolving the scale, the strength of the acid decreases. The strength of the acid
solution should be measured periodically during a cleaning operation. When the acid
strength falls below 3%, the solution may be discarded since most of its scale-dissolving
capability will have been used. Use the following procedure to check the acid strength:
Burette, 25 milliliters (0.8 ounce) automatic (for sodium hydroxide solution)