CIP Skids: Portable and Fixed Clean-in-Place Systems

A CIP skid is a clean-in-place system built as a self-contained assembly on a structural frame, carrying the solution tanks, supply and return pumps, heating, instrumentation and controls needed to circulate cleaning chemistry through process equipment without dismantling it. It is delivered as one piece, connected to the plant utilities and to the circuits it will clean, and commissioned in place.

In practice the terms are used interchangeably, but a skid specifically means the system was assembled and tested on a frame in a shop rather than built up from loose components in the plant. Every CIP skid is a CIP system; not every CIP system is skidded, because some large installations are field erected around existing structures.

A portable CIP skid is a smaller cart-mounted or castered unit that is wheeled to the equipment it will clean and connected temporarily. It suits plants with a small number of circuits, pilot and development suites, or sites that need to clean a vessel that a fixed central system does not reach. The trade-off is manual connection, which puts more of the cleaning outcome in the operator hand.

A single-tank skid is the simplest and suits single-use chemistry that goes to drain after one pass. Two-tank designs typically hold a caustic solution and a rinse water volume so the detergent can be recovered and reused. Three-tank designs add a separate acid tank where both alkaline and acid cycles run regularly. Tank count follows the chemistry program and the cost of the water going to drain, not the size of the plant.

Single-use sends the cleaning solution to drain after one pass, which is simpler, avoids carry-over between products and is often required where cross-contamination is the controlling risk. Recirculated chemistry recovers the detergent for reuse and cuts chemical and water cost considerably, but it adds tankage, filtration and the need to monitor solution strength. Regulated multi-product facilities usually have the decision made for them.

Sizing starts from the largest circuit the skid has to clean, not the number of circuits. The supply pump must deliver enough flow to reach turbulent velocity in the largest-diameter line in that circuit, and the return path must be able to remove solution at least as fast as it is delivered. Tank volume follows from the circuit hold-up plus the volume needed to keep the pump suction flooded.

A commonly used design target for pipeline cleaning is around five feet per second, which is enough to hold turbulent flow in typical sanitary line sizes. Turbulence is what actually does the work, because it is the shear at the pipe wall rather than the chemistry alone that removes soil. Velocity has to be checked against the largest diameter in the circuit, since that is where it will be lowest.

Vessels are cleaned by spray devices rather than by velocity. A static spray ball floods the surface and relies on a falling film, which suits light soils and is simple and cheap. A rotary jet head produces a directed, higher-impact pattern that covers the vessel in a repeating cycle and is markedly better on baked or tenacious soil. The choice is a soil question, not a vessel size question.

Either by direct steam injection into the tank or by an in-line plate or shell-and-tube heat exchanger. Direct injection is simpler and responds quickly but dilutes the solution over time and requires culinary or clean steam depending on the application. Indirect heating through an exchanger keeps the steam separate from the solution and is normal where the steam quality is not qualified for product contact.

A typical program is a pre-rinse to remove gross soil, an alkaline wash for organic and protein residues, an intermediate rinse, an acid wash where mineral scale is present, a final rinse and, where required, a sanitizing step. Caustic soda is the usual alkaline agent and nitric or phosphoric acid the usual acid. Concentration, temperature, flow and time are the four parameters that define the cycle.

By inline conductivity measurement, which correlates with the concentration of the dosed chemical and lets the controller top up automatically to hold a setpoint. Conductivity is also how the end of a rinse is detected, by watching the value fall back toward the incoming water. It is the single most useful instrument on the skid.

At minimum supply and return flow, supply and return temperature, supply conductivity, and tank level. Return-side temperature matters more than supply-side, because it tells you the far end of the circuit actually reached cleaning temperature. Regulated installations add return conductivity and, where a rinse has to be proven, total organic carbon sampling.

By logging the four cycle parameters against time for every cycle, with the records retained. In a regulated facility those records are the evidence that the cleaning was performed as validated, so the data path from instrument to record has to be as controlled as the equipment itself. In food and beverage the same data is normally kept for traceability rather than for validation.

Product-contact surfaces are normally 316L stainless steel with hygienic connections and a documented interior finish. Where the skid serves pharmaceutical manufacture, construction follows ASME BPE, including the surface finish record and the weld documentation. Food and beverage installations more commonly work to 3-A Sanitary Standards, which govern equipment design for that sector.

They are designed out. Under ASME BPE the permitted unswept length is limited to a length-to-diameter ratio of two, measured from the wall of the main line. The older six-diameter guidance that is still widely quoted comes from legacy FDA material and is considerably more permissive than what BPE now requires, so it should not be used as the design basis for new hygienic work.

Coverage on vessel surfaces is commonly demonstrated with a riboflavin test, in which a fluorescent solution is applied to the interior and the surface is inspected under ultraviolet light after a cycle. Circuit cleaning is proven by swab and rinse sampling against defined acceptance limits. Both belong to cleaning validation, which is a protocol exercise rather than something the equipment alone can deliver.

In pharmaceutical and medical device manufacture, yes, through installation, operational and performance qualification followed by cleaning validation of each cycle against the soils it must remove. Food, beverage and general industrial installations are normally commissioned and verified against a cleaning standard rather than formally validated.

Yes, and most fixed installations do, using a distribution manifold and sequenced valves so circuits are cleaned one after another. The constraint is that the skid must be sized for the largest circuit, and that the schedule has to fit every circuit into the available cleaning window. Where circuits differ greatly in size, a small dedicated unit alongside a central system is often cheaper than oversizing.

It depends entirely on the soil, the chemistry and the number of steps, and it is determined during cycle development rather than assumed. What matters commercially is that the total of all circuits fits inside the plant cleaning window, which is usually the real constraint on how the system is configured.

Return flow that cannot keep up with supply, so the circuit floods; velocity that falls below turbulent in the largest line because sizing was done on the wrong diameter; spray devices chosen for a lighter soil than the vessel actually carries; and temperature measured only at the supply, so nobody notices the far end of the circuit never got hot. All four are design decisions.

Yes. A CIP skid can be supplied as equipment built to a written specification for a site or another contractor to install and tie in, or as a complete scope including the distribution piping, utility connections and commissioning. Which route is appropriate is usually a question of who holds the rest of the project.

The circuits to be cleaned with their line sizes and lengths, the vessels with their volumes and internal fittings, the soils involved, the product regime the plant operates under, the available cleaning window, and the utilities on site. The soil and the largest circuit are the two that determine most of the design.