This method involves filling a system with a chemical cleaning solution and circulating it with a pump. This is the most common method used for chemical cleaning in the industry. It is important to keep the fluid velocity in a certain range to avoid corrosion. Furthermore, the concentration and temperature of the cleaning solution have to be monitored during the entire operation. As with any pickling method, it is recommended to apply this method in three different stages: degreasing, pickling, and passivation.
Degreasing usually refers to an alkaline wash of internal surfaces on the process equipment to remove, above all else, organic matter. If incorporated with filtration, it can be used for debris removal from a system during the pre-operational cleaning. Some of the most commonly used chemicals for degreasing purposes, to prevent foaming, and/or to improve heat transfer on process equipment include: sodium hydroxide, tri-sodium phosphate, sodium meta-silicate, sodium carbonate, and non-ionic surfactants.
The type of solvent used for solvent cleaning should be based on laboratory studies of the deposit sample found inside the system. This will help ensure that the expected result of the chemical cleaning is achieved at minimum expense and risk to the system. If the system volume is large, a cutter fluid can be used to reduce the cost of a potentially expensive solvent.