01What the duty actually asks for
Temperature targets
Pre-rinse ambient, caustic wash 65-85°C, acid wash 50-60°C, final rinse hot water 70-80°C. The heating load is concentrated on the caustic and final-rinse steps.
Water volume and time
kW = volume (m³) × 1.16 × ΔT (K) ÷ hours. A 3 m³ tank from 10°C to 80°C in 90 minutes is 3 × 1.16 × 70 ÷ 1.5 ≈ 162 kW. In four hours the same tank needs 61 kW. The recovery time is a business decision, not a physics one.
Heat carried back
A recirculating CIP returns most of its heat to the tank, so the running duty after the first fill is mostly loss plus the incoming cold water. Sizing on the first fill alone gives an oversized bank that cycles.
Steam and water hammer
Where live steam injection is also used, an electric bank and a steam sparger fight each other unless the control is sequenced. Pick one primary heat source and the other as back-up.
The most common specification error in this duty is a heat-up time copied from a steam system. Electric heating is slower to first temperature and cheaper to hold; if the schedule genuinely needs a 40-minute heat-up, pay for the kW and for the supply capacity, and arrange the bank in steps.
02Materials in detergent and acid
Caustic (NaOH)
316L stainless handles hot caustic well at normal CIP concentrations. Carbon steel does not. Stress-corrosion becomes a concern at high concentration and high temperature, which is a reason to hold the element surface load low.
Acid (nitric, phosphoric blends)
Nitric acid passivates stainless; hydrofluoric or chloride-bearing acid blends do not, and 316L can pit badly. Where halogen-bearing cleaners are used, titanium or a specified alloy is the conversation to have early.
Chlorine sanitisers
Hypochloride at CIP strength attacks stainless at elevated temperature. Sanitise at the low end of the temperature range and rinse; do not soak a hot element in chlorine.
Hard water and scale
Scale on the sheath is both an insulator and a trap for the next cleaning cycle. In hard-water plants, lower watt density plus a scheduled descale beats any anti-scale device.
Ask for the actual cleaning-chemical datasheets and their use concentrations. Element material is a chemistry decision, and the supplier cannot make it from the words "food grade".
03Surviving the drained phase
Low-level trip
A CIP tank is routinely run down between cycles. The heater must lose power on a level that is above the element, on an independent device from the control float.
Watt density in tank duty
1.5-2.5 W/cm² for immersion in a still or slowly circulating tank of water or detergent. Above that, the surface boils locally, scale forms faster, and the element cycles thermally.
Terminal and head
Steam and detergent in the head space are hard on terminals and gaskets. Use a raised terminal head, IP-rated covers and heat-resistant leads; the failures in this duty start above the liquid line.
Drain and clean-in-place of the heater itself
An element that cannot be pulled without a tool becomes a hygiene issue. Specify withdrawal clearance and a sanitary flange or tri-clamp fitting where the standard requires it.
A drain valve left open with the heater armed is the classic CIP element loss. The level trip is the only defence that works when nobody is watching.
04Control and energy
Two or three steps with a modulating final step holds wash temperature within a couple of degrees without the contactor wear of a single on/off band. In a plant running six CIP cycles a day, that band is the difference between a five-year and a fifteen-year contactor.
Insulate the tank and the pipework. A 3 m³ unlagged wash tank at 75°C in a 15°C room can lose 2-3 kW continuously, which is most of the difference between a 60 kW and a 100 kW bank.
If the plant has a heat-recovery opportunity, the rinse water is the place to look: the last rinse leaves hot and clean, and a plate exchanger on it can preheat the incoming fill.