A look at the fundamentals of clean-in-place technology
By Tim Bowser, PhD, PE, Oklahoma State University
Clean-in-place, commonly referred to as CIP, is an automated method of cleaning processing equipment without disassembly using validated procedures. Examples of equipment cleaned via CIP are tanks, process piping systems, filter housings, ductwork, conveyors, homogenizers, centrifugal separators, and heat exchangers.
Prior to the advent of CIP, manual cleaning was the state-of-the art for processing equipment. Piping systems and processing equipment were disassembled and cleaned by hand. After cleaning, parts were reassembled and sanitized, and because of this, equipment size was severely limited. Pipe lengths of more than 10 feet were not possible because of handling limitations associated with manipulation of the pipe, power-brush cleaning, and wash-tank dimensions. Product storage tanks were also limited to a height of about 8 feet to allow an average-sized person to scrub ceilings and upper surfaces of walls with a brush on a pole.
The need for CIP systems surfaced as a result of World War II, during which shortages of metals forced dairies to substitute Pyrex glass tubes for product transport. Dairy owners and operators actively sought a method that would help them clean the glass tubing without disassembly and the associated breakage. The first automated CIP system was installed in a family-operated dairy in 1953 and CIP was widespread in diary plants by the mid-1960s.
Today, the functional goals of CIP include uniform, effective cleaning of equipment; prevention of product contamination with cleaning chemicals; improved personnel safety; and increased productivity, including reduced downtime and process equipment maintenance, as well as reduced expenses for energy, water, and cleaning chemicals.
CIP fundamentals
Most CIP cleaning cycles include one or more of the following steps: rinsing, washing, sanitizing, and drying. The first step is often rinsing, in which heated or unheated water is used to remove loose soils and residues from surfaces. Rinse water may be recycled or sent to the waste drain depending on the concentration of soils and chemicals in solution and/or suspension.
Washing with cleaning solutions (chemicals) and agitation removes attached soils. The cleaning chemicals are carefully selected for effectiveness on the soil type and the nature of the surface to be cleaned. Agitation may come from one or more of several sources, including spray impingement, hydraulic flow, mechanical agitation (mixers), ultrasonics, and air bubbles. Sanitizing is used specifically to kill and prevent growth of bacteria on surfaces of cleaned equipment. Pumpable or water-soluble agents are left in contact with surfaces to accomplish sanitizing goals. Drying is normally accomplished with compressed air, which is sometimes heated, or with an inert gas such as nitrogen. This step removes water from product contact surfaces to prevent bacteria growth and dilution of product during start-up.
CIP cycles are usually designed to clean a particular soil from a given set of processing equipment. A typical CIP cycle could include pre-rinse, caustic wash, rinse, acid rinse, sanitization, and post-rinse steps.
Basic system configurations
Two major types of CIP systems are in use today: single-use and reuse. Single-use systems (see Fig. 1) discard all liquids to the drain after use, while reuse systems store cleaning waters for reuse in subsequent cleaning cycles. Single-use systems consist of the following major components: recirculation tank; CIP supply pump; water heater; controls; sensors to monitor control variables; and chemical feed equipment. Reuse systems have all of these components but include additional holding tanks for cleaning waters that will be reused (see Fig. 2).
 Figure 1. A single-use CIP system. Photo courtesy of FoodMech, LLC, Stillwater, Oklahoma. |
The control and documentation of five variables is critical to the operation of CIP systems. These are temperature, velocity, pressure, concentration, and time. The temperature of CIP solutions is determined by the process requirements and cleaning chemical activity. Temperature is recorded throughout the temperature-critical steps of the process (e.g., wash) to document cleaning.
Maintenance of turbulent flow in pipes is another important factor in cleaning effectiveness. Turbulent flow promotes hydraulic “scrubbing” of surfaces. As a rule of thumb, a fluid velocity of at least 5 feet per second in pipelines will maintain turbulent conditions. CIP fluid flow rates are normally recorded for process verification. Pipe geometry must also be carefully designed to insure that the cleaning fluid completely wets surfaces for cleaning.
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Adequate pressure in CIP fluid circulation systems is necessary to ensure the reliable performance of spray devices. Pressure also serves as an indication of flow (CIP solution pressure is proportional to the square of its velocity). Many CIP control systems record pressure for documentation of proper cleaning.
Cleaning chemical concentration is also an important measurement of cleaning effectiveness. Concentration values can be measured manually or automatically using a conductivity probe. Optimal chemical concentration levels are recommended by the chemical supplier.
Cleaning cycle time refers to the amount of time that cleaning solutions are in contact with the surfaces being cleaned while required conditions (e.g., temperature, flow, pressure, concentration) are met. Cycle time is determined by many factors, including line availability (considering for example, production and labor factors), chemical concentration and cost, soil amounts and characteristics, and composition of flexible seals and metal and plastic surfaces.
Spray devices
Spray devices are used to apply CIP fluids to the surface being cleaned. Two general types are available: static and dynamic. Static spray devices are motionless heads with drilled or fixed nozzles. Popular versions include spray balls (see Fig. 3), tubes and bubbles. Spray tubes and bubbles are essentially the given shape with drilled spray holes. Static spray balls are normally designed for 20 to 30 gpm and 20 to 30 psi pressure drop. The effective cleaning diameter of a static spray ball is about 8 feet.
 Figure 3. Fixed spray balls. Photo courtesy of the Food and Agricultural Products Center, Oklahoma State University. |
Dynamic spray devices have a moving spray head or body, which is driven by the cleaning media (see Fig. 4) and/or mechanical means. Spray balls are normally left in the tank during processing. Table 1 lists advantages and disadvantages of static and dynamic spray devices.
 Figure 4. Fluid-driven dynamic spray devices. Photo courtesy of the Food and Agricultural Products Center, Oklahoma State University. |
Fixed spray balls can be drilled in a variety of patterns to match the cleaning requirements of the process equipment (see Fig. 5). Equipment that is carefully designed can be cleaned with a minimum of strategically placed spray balls.
 Figure 6a. Photos of a spray device coverage test for an agitated vacuum tank. Indicating dye under black light is shown on the left; |
Spray device coverage tests document that there is proper fluid coverage of the surfaces being cleaned. Tests are performed by coating dye (e.g., riboflavin) on the surface to be cleaned and then washing it off using pure water applied through the spray device. The dye is easy to spot because it fluoresces under black light (see Fig. 6). Dye removal is visually observed and the system is adjusted until all dye is consistently removed. Spray device coverage tests are recommended when the equipment is still at the manufacturer’s shop and just after installation.
Cleaning agents
Chemical cleaning agents make use of mechanisms such as wetting, dissolving, saponification, emulsification, dispersion and sequestering. Formulated cleaning compounds often include multiple cleaning agents. Wetting agents are found in most cleaning formulations; their purpose is to lower the surface tension of the liquid, which helps to increase the contact area between the liquid and the surface area being cleaned, reducing the amount of cleaning agents needed. Dissolution of residues is one of the primary mechanisms of cleaning agents. The objective is to dissolve the soil into the cleaning solution. Factors such as pH, temperature, agitation, and physical form of the residue affect solubility. Acids, bases, surfactants and solvents may be added to make soils more soluble.
Acidic additives (low pH) are used to dissolve soil residues. Phosphoric, acetic, citric, and nitric acids are examples of acidic cleaning agents. Saponifiers are alkaline substances with high pH values that hydrolyze fat to form soap and glycerol. Examples are sodium hydroxide, potassium hydroxide, soda ash, and trisodium phosphate. Emulsifiers break up liquid soils into smaller droplets that can be suspended in the cleaning fluid when the two do not mix. Dispersants are similar to emulsifiers, but act on solid particles. Sequestrants render minerals soluble. Chelants are a type of sequestrant often used to remove minerals from unsoftened make-up water. Other cleaning agents include enzymes, catalysts and solvents.
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Cleaning agents are often complex formulations of chemicals that are custom-designed for a specific situation. Typical soil residues include protein, carbohydrates, fat, salt and organisms. Contact surfaces in most processes consist of a variety of stainless steels, plastics and elastomers. A custom formulation starts from a base recipe that is adjusted then fortified with additives to address the end-user’s needs. Examples of specific needs are unique soil residues, process equipment geometry and physical composition, water-quality, safety, environment, budget, and time available. Given the complexity and highly specialized nature of the task, formulation of cleaning solutions should be the responsibility of persons that have practical experience and in-depth knowledge of the subject.
System validation
End users must determine their own acceptance criteria for equipment cleanliness. For single-purpose equipment without cross-contamination issues, a visual inspection may be adequate (Bismuth and Neumann, 2000). Multipurpose equipment may require specific analytical acceptance criteria for target residues in the product and on equipment surfaces (LeBlanc, 2000).
Selection of sampling methods is critical to system validation. Samples must be representative of the system as a whole or in a worst-case scenario. Four types of sampling methods are: direct surface, swab, rinse and placebo. The state-of-the-art for direct surface sampling is visual observation. Swab sampling uses a fibrous material to wipe over the surface to remove residues. The residue is then extracted from the swab and analyzed.
Rinse sampling involves taking a sample of the final CIP rinse water, or separate rinse water, and analyzing it for contamination. Placebo sampling originated in the pharmaceutical industry and involves manufacturing a placebo product (drug without the active substance) following a normal product manufacturing and CIP cycle. The placebo is analyzed for residual values of the active substance (LeBlanc, 2000). This technique is effective for validation of food processing systems when selected ingredients are removed from the product to make a placebo.
Valid analytical methods must be stable, accurate, precise, selective for the particular contaminants, and have a limit of detection of at least 25 percent of the target residue limit in the sample (LeBlanc, 2000). The chromatographic methods (LC/MS, GC/MS and HPLC) are often preferred for cleaning validation studies (Bismuth and Neumann, 2000).
Operations, utilities and maintenance issues
Many operations, utilities and maintenance issues are often overlooked in CIP systems-with disastrous results. Gaskets are a chief example. Gaskets become worn and lose their elastic properties over time and should be replaced periodically. Over-tightening of gaskets (especially at leaky joints) can result in their extrusion into pipelines and product flow paths. Extruded gaskets form minute pockets that are difficult to clean and that promote bacterial growth. Torque limiters, improved fittings (e.g., Swagelok’s TS Series Biopharm fittings), and better gasket materials help to solve problems. Color-coded gaskets can aid gasket replacement procedures.
Steam used in CIP systems should be dry, clean and supplied at ample pressure. Condensate separators can be used to remove moisture before steam reaches control valves. Bypasses and shut-off valves should be included in systems to facilitate maintenance activities. Duplex strainers and dirt legs should also be included. Steam lines may need to be cleaned in systems where steam is injected directly into the product.
Compressed air is frequently used in CIP systems to operate controls and to blow dry lines, vessels and equipment. Oil, bacteria, particles and moisture should be eliminated from the system and adequate filtration and traps installed. UV lamps can be incorporated to kill bacteria. The compressed air system should be inspected and cleaned periodically.
Softened, filtered water is recommended for CIP operations. Minerals in hard water can interact with soil, cleaning agents and stainless-steel surfaces, and mineral content can vary throughout the year with regard to water quality, causing process changes that are difficult to track and identify.
It’s important to recognize that stainless steel is not invincible. Any stainless steel can pit or corrode if subjected to iron (or other metal) contamination. Water that is high in chlorides or sulfur should not be used. Cleaners or sanitizers should remain on stainless steel surfaces for more than 20 minutes. Sudden temperature changes should be avoided, and recommended concentrations of chemicals must be followed. Initial passivation and clean-up of stainless steel equipment is critical to ongoing performance.
In future, look for trends in CIP such as more widespread use and mandated requirements for CIP processes. Also expect more powerful and directed cleaning agents. Smoother product contact surfaces with fewer harborage and attachment points for bacteria will also be a trend, together with coatings for product contact surfaces that improve cleanability. Finally, look for improved validation equipment and improved methods of mechanical cleaning.
Tim Bowser is an associate professor of biosystems and agricultural engineering in the Food and Agricultural Products Center at Oklahoma State University (Stillwater, OK). He can be reached at [email protected].
References
- Bowser, T.J. CIP workshop materials. Food and Agricultural Products Center, Oklahoma State University, Stillwater (2005).
- Bismuth, G. and S. Neumann. Cleaning Validation, a Practical Approach. CRC Press, New York, pp. 35-61 (2000).
- LeBlanc, D.A. Validated Cleaning Technologies for Pharmaceutical Manufacturing CRC Press, New York, pp. 135-191 (2000).
- Seiberling, D.A. “CIP Sanitary Process Design” in Handbook of Food Engineering Practice. K.J. Valentas, E. Rotstein, R.P. Singh, editors. CRC Press. New York (1997).
- Seiberling, D. A. Web site: http://www.seiberling4cip.com/evol&dev.htm, viewed on January 16, 2007.
Ten precepts of CIP system operation (Bowser, 2005):
- Time, temperature, flow, pressure and concentration work together to clean and sanitize.
- Follow validated SOPs.
- Follow safety procedures for chemical handling.
- Record significant CIP events; otherwise, they did not occur.
- Remove and reposition fittings to make swing connections to prevent pinched gaskets.
- Never over-tighten gaskets (even if leaking). An extruded gasket may cause product recall.
- Inspect and replace gaskets according to schedule.
- Use approved chemicals at the required concentration.
- Trust your own senses before machine sensors.
- Report system quirks immediately to your supervisor and in writing.