CIP and SIP Explained: Differences, Stages, and Application in Pure Water Systems

Typical stages

1. Pre-rinse: clean water is circulated through the line by a centrifugal pump and sent to drain.
2. Detergent circulation: the solution is heated to the circuit temperature and circulated for the duration required by the procedure.
3. Drainage: once cleaning finishes, the solution is discharged to waste.
4. Final rinse: water is passed through for a defined time until no residue remains.
5. Disinfection (if required): a sanitant is added via a dosing pump and may be left in the lines until the next production run.

Design principles

• High-turbulence, high-flow solution in piping circuits; full wetting with low-energy spray in lightly soiled vessels; high-energy dynamic spray devices in heavily soiled or large-diameter vessels.
• The solution supply unit, supply pump, spray device, return circuit, and return pump are the main components.
• Heating and chemical detergent increase effectiveness; flow velocity must remain high enough to carry dissolved particles away from the surface.
• Fully automated CIP includes a PLC, balance tanks, sensors, valves, heat exchangers, and data acquisition; flow, detergent concentration, temperature, and wash time are monitored continuously.
• Well-designed CIP allows one section of the plant to be cleaned while another is in production and reduces water and chemical consumption.

Cleaning triggers and steps

• Trigger: 10% drop in normalized permeate flow; 5% – 10% increase in normalized salt passage; 10% – 15% increase in normalized pressure drop.
• Six steps: solution make-up, low-flow pumping, circulation, soaking (approximately 1 hour; 10 – 15 hours for difficult fouling), high-flow pumping (30 – 60 minutes), and flushing.
• Flushing: with RO permeate or deionized water; pre-filtered raw or feed water is not used.
• Stages cleaned separately: stages are cleaned individually so that foulants removed from the first stage are not pushed into the second stage.
• Sequence: typically alkaline cleaning first; acid cleaning is started first only when calcium carbonate or iron oxide is present.

Equipment and sanitization

• Cleaning solution pH ranges between 1 and 13; a stainless steel (316) or non-metallic composite pump, polypropylene or fiberglass-reinforced plastic tank, 5 – 10 micron polypropylene cartridge filter, and corrosion-resistant materials are used. Line velocity is kept at or below 3 m/s.
• Cleaning temperature must not drop below 15 °C, as kinetics slow significantly. Tank volume is sized based on the empty pressure vessel volume plus the connecting pipe volume.
• Sanitization: a hydrogen peroxide and peracetic acid mixture is diluted with RO permeate to 0.2% (by weight) peroxide and circulated below 25 °C for 20 minutes; biocidal efficacy and membrane life are more favorable at pH 3 – 4. Free chlorine, chlorine dioxide, and combined chlorine are not recommended.
• In heat-sanitizable RO elements, hot water is raised to approximately 80 °C and held for 60 – 90 minutes; transmembrane pressure must remain below 1.7 bar. This is the preferred method in pharmaceutical and food plants, as it is easy to validate and requires no chemical storage or rinsing.
• In biologically active waters, chemical sanitization is performed every 3 – 5 days in summer and approximately every 7 days in winter; frequency is site-specific.