Sanitary Shell and Tube Heat Exchangers

Designing a sanitary shell and tube for the duty in front of it

Tube size follows the product, not the catalog

The first number fixed on a sanitary shell and tube job is the tube OD, and it is chosen from what flows through it. Clear liquids and water-like products run in 3/4" tubes, which give the most surface per shell diameter and the highest tube-side velocity for a given flow. Products with small particulates, light pulp or a tendency to foul move up to 1" tubes. Anything with soft solids, or that must be brushed between runs, goes to 1-1/2". Wall thickness is usually 16 or 18 gauge; thicker walls only cost heat transfer and add nothing to a 150 psig design.

Velocity, fouling and the CIP return

Tube-side velocity is the second decision. Between 4 and 8 ft/s keeps most food products turbulent enough to scrub the wall and keeps CIP effective; below about 3 ft/s a milk or juice unit will foul early and the cleaning cycle will not reach the back of the fouling layer. Passes are added until the velocity lands in range, with the trade-off that each added pass raises product-side pressure drop. On the shell side the same thinking sets baffle spacing so the utility actually crosses the bundle instead of short-circuiting along it.

CIP is normally run at 160 to 180 F with caustic and acid cycles, and the design velocity in CIP mode should be at least 5 ft/s in every tube. A shell and tube unit sized on product flow alone can have tubes near the outer rows that see less CIP velocity; a good design checks both cases.

Joints, heads and where the crevices hide

Rolled tube joints are the classic sanitary failure: the tube-to-tubesheet gap traps product and is unreachable by CIP. On the product side every tube is seal welded to the tubesheet, usually by orbital TIG for repeatability, and the weld is ground and polished flush. Channel heads are machined from a single piece so there is no inside corner weld; the head-to-tubesheet joint is a tri-clamp or a sanitary flange with a food-grade gasket rather than a raised-face bolted joint.

Where product runs on the shell side instead, which is common for viscous product heated with hot water in the tubes, the shell interior is polished and the baffles are cut and pitched so the shell drains through a low-point outlet. That configuration is rarer and needs a longer conversation about baffle design.

• Orbital TIG seal weld on every product-side tube joint
• Heads machined from solid, polished to the tube finish
• Tri-clamp or sanitary flange head closure, no raised-face bolting
• Low-point drains on both sides in the installed orientation

Materials, finish and what is on the record

304L is standard for food and dairy; 316L is standard for pharma and for any product carrying chlorides, brine or acidified sauces. Tubes are seamless or welded-and-drawn with the weld bead removed so the internal finish holds 32 Ra or better across the full length. The unit is passivated after fabrication and electropolished if the spec calls for 20 Ra or lower. Material test reports, weld maps, hydrotest and profilometer readings ship with the unit so the validation package writes itself.

A sanitary shell and tube unit that is sized to the actual flow, tubed for the actual product and welded rather than rolled will run for decades. Call and talk it through with an engineer: 1-805-484-2992

Standard steam-to-water units and spare bundles

Two catalogued ranges sit under this section for the buyer who needs a stock unit rather than an engineered one. The steam-to-water units are 6" and 8" sanitary shell and tube heaters in 304 or 316 stainless with tri-clamp process connections, rated 150 PSI and 375°F, in 54" to 96" tube lengths. The matching replacement tube bundles drop into those shells when a bundle has fouled or been damaged, so the shell, heads and piping stay in place. Each part number has its own page with the connection sizes, surface area and ratings.