Vessels designed for sanitary service are almost always cleaned in place and/or sterilized in place by a combination of heat, and the circulation of chemicals over all of the surfaces to be cleaned. Crevices, pockets, threads, and non-draining surfaces must be avoided. There are numerous types of sprayballs and spray heads designed for the cleaning of the interior surfaces of vessels. There are many different cleaning cycles used in various industries, but most cleaning cycles involve a pre-rinse of clean water, a heated caustic wash cycle, a post rinse cycle, and some type of sanitizing cycle.
The most common type of cleaning device is the sprayball, a hollow ball with an array of holes which sprays the interior of the vessel. The holes may be designed to spray up only, spray down, spray in a 360 degree pattern, or they may be custom located to hit specific areas. There are 2 types of cleaning actions utilized, there is a cascading action of a large flow of chemicals running over the surfaces, and an impingement action caused by the direct spray. The best type of action depends on the surfaces to be cleaned. Both actions can occur simultaneously. The use of more than one spray device may be required to completely clean all the surfaces. Agitator shafts, baffles, and other common protrusions in the vessel can shadow certain areas in the vessel. The undersides of mixer blades are also a potential cleaning problem. Nozzles and manway openings must also be considered. Sprayballs which have custom drilled holes should have a means of positively locating the sprayball to the correct orientation. Sprayballs are designed and drilled to operate at specific flows and pressures. Too low a supply pressure may result in the spray not hitting the surface with sufficient velocity for cleaning (if it hits at all). Too high a pressure can atomize the spray and lead to inefficient cleaning. Sprayballs can be designed and drilled for a given flow rate and pressure within reason. Some sprayballs are split to allow cleaning of any plugged holes. For critical applications, the flow, temperature, and pressure to a sprayball should be monitored to ensure there are no blockages. Rotary devices often do a very good job of impingement cleaning, but cannot be validated unless the rotary action can be proven.
Caustic chemicals are hazardous and should be treated with respect. Containing the chemicals in the vessel during CIP can be overlooked. Hinged lids without gasketing or a drip lip may not fully contain CIP solutions. Another consideration during CIP is the temperature variation. Large atmospheric vessels with side entry manways are often designed to be CIP’ed with the door open to provide proper venting for the tank. The temperature changes during a CIP cycle can create a vacuum condition. Rapid temperature fluctuations in a vessel can create dangerously high stresses. Try drinking a cup of hot coffee then bite an ice cube to understand the effect. A temperature change of no greater than 10 degrees a minute is recommended.