CIP and SIP Design

Building for cleaning and sterilizing

Velocity and pressure drop

CIP works by chemistry and by shear. The chemistry is handled by the skid; the shear is handled by the exchanger geometry and the CIP pump. In sanitary tube a velocity of about 5 ft/s is the common target for turbulent flow that lifts soil from a 32 Ra surface, and on a unit whose process flow gives only 2 ft/s the CIP flow has to be more than double the process flow. That raises the tube-side pressure drop by a factor of four or more, and the tube-side design pressure and the head gaskets have to be rated for it. On plate exchangers the equivalent rule is 1.5 to 2 times process flow, and the port velocity, not the channel velocity, is what limits it.

• Give both process and CIP flow rates on the specification
• Multi-pass tube arrangements raise velocity at the cost of pressure drop; three or four passes are common on small units
• Product on the shell side is hard to clean at velocity; keep it in the tubes

---

Caustic, acid and the metal

One to two percent caustic at 180 F does nothing to 304L or 316L; it is the reason the exchanger is stainless. The acid step is where care is needed. Nitric acid is passivating and is the safer choice for the metal. Phosphoric acid is common and acceptable. Chlorinated sanitizers and any acid step with chlorides in the water are where 304L begins to pit, and a plant that uses them should be on 316L for the product side.

---

SIP and thermal cycling

Sterilize-in-place at 250 F for 30 minutes is a modest condition for the metal and a hard one for the assembly. Between a cold product run and a steam hold the bundle grows about 0.1 inch per 10 feet per 100 F, and on a fixed-tubesheet straight-tube unit the shell and tubes fight over that difference at every cycle. Three answers exist: a U-tube bundle that expands freely, an expansion joint in the shell, or a shell-and-tube design short enough that the stress stays within the ASME allowable. The fabricator's thermal design should show which one was used and the number of cycles it was checked against.

Gaskets see the same cycle. Each SIP compresses and heat-ages the elastomer; EPDM that lasts two years on CIP alone may need replacing yearly with weekly SIP, and silicone or a steam-grade EPDM is chosen for joints that are steamed often.

---

Cleanability by construction type

A gasketed plate exchanger is the easiest to verify clean: open the frame, look at every plate, swab if the program calls for it. It is also the one with the most gaskets and the tightest channels, so particulates and burn-on can bridge a channel and the CIP flow goes around it. A shell-and-tube unit with product in polished tubes cleans reliably at velocity and can be borescoped through the heads, but cannot be opened for a full visual without pulling the bundle. A tube-in-tube unit has one product channel with no bypass path and is the best choice for viscous or fouling product, at the cost of surface per dollar.

---

Writing CIP and SIP into the specification

Give the CIP chemistry and temperatures, the CIP flow rate, the SIP temperature and frequency, and the sanitizer. Those five items fix the material, the gaskets, the design pressure, the pass arrangement and the expansion provision. Call and talk it through with an engineer: 1-805-484-2992 The case for automating the cleaning cycle in the first place is set out on our advantages of clean-in-place page.