1-805-484-2992
Quotes - Engineering - SalesThe dimple jacket as part of the tank, not an addition to it
A jacketed tank built with an integral dimple jacket has a thin stainless outer sheet spot-welded in a grid directly to the tank shell and seam-welded around each zone. The shell itself is the inner face of the jacket, so there is no plate, no mastic and no second wall between utility and product. Steam, glycol or cooling water flows in the dimpled space, and the tank heats or cools through one thickness of metal. It is the jacket to specify when the tank is new and the duty is serious.
Zones, pressure and the shell
Zoning is where a dimple jacket earns its place against a conventional jacket. Because each zone is its own welded pocket, a tank can carry a steam zone on the lower side wall, a glycol zone above it and a separate cooling-water zone on the dished bottom, each with its own connections and control valve. A half-filled batch is heated by the zone it covers, not by a jacket wasting steam on empty shell, and a cook-then-chill cycle switches zones instead of flushing one jacket from steam to glycol.
The dimple pattern also lets the jacket run at 100 to 150 psig on sheet of 0.05 to 0.075 in., where a plain annular jacket of the same rating would need a thick outer shell. Tight spot-weld pitch holds the thin sheet; the tank shell takes the rest. The jacket sheet can be 304L on a 316L tank, because inhibited glycol and clean steam condensate do not usually ask for molybdenum, and that is the usual pairing.
A jacketed tank is 316L on the product shell with the dimple jacket in 304L for glycol and steam, or 316L throughout where the plant insists on one grade. The Material & Construction page compares the grades.
What the integral jacket build includes
- Jacket zones laid out on the approval drawing to match fill levels and duties
- Spot-weld pitch and sheet gauge set for 100 psig glycol or 150 psig steam
- Dished-bottom jackets for cooling water or glycol, separately valved
- Jacket inlet at the top of each zone for steam, at the bottom for glycol
- Condensate outlet at the lowest dimple of each steam zone, with trap and vacuum breaker shown
- ASME Section VIII stamp on the jacket and shell where the specification requires it
- Insulation and cladding over the jacket, with stand-off cleats welded before cladding
jacket sheet for 150 psig steamA 0.075 in. jacket sheet on a tight spot-weld grid carries 150 psig steam against a tank shell that would otherwise need a far heavier outer wall.
What to send us for a jacketed tank
The tank and the jacket are designed together, so the quote needs the vessel data as well as the heat duty. Where the tank is already drawn, send the drawing and we will lay the zones onto it.
- Tank volume, diameter, straight side, head style and the minimum and maximum fill levels
- Product, viscosity, solids and whether it scorches on a steam-heated wall
- Heating duty: batch volume, start and target temperatures, time allowed
- Cooling duty, if any: target temperature, time, and the glycol or water supply available
- Steam pressure at the tank and whether it is modulated or on-off
- Agitation: type and speed, because it sets the inside film coefficient
- Code requirements: ASME stamp on the shell, the jacket or both, and any CRN or PED registration
Call and talk it through with an engineer: 1-805-484-2992
A thin outer sheet spot welded to the tank shell in a regular pattern, so the utility flows in the narrow space behind it and the welds carry the pressure instead of a heavy outer wall.
Laying out the zones and picking the utility
A jacketed tank is sized from the inside out. The batch, its temperature change and the time allowed give the duty; the agitator and the product viscosity give the inside film coefficient; the jacket utility gives the outside one. Steam at 15 psig condensing at 250°F against a stirred water-like product is the easy case and needs the least jacket area. A viscous product with a slow sweep agitator and 180°F water in the jacket is the hard case, and it is why some tanks carry a jacket over the whole straight side and the bottom head.
Zone boundaries follow fill levels. The lowest zone covers the minimum batch so a small batch heats on its own zone without baking product onto an uncovered wall above it. Upper zones add area for full batches. On a tank that both cooks and chills, the steam zones and the glycol zones can be the same pockets, switched with a changeover manifold, or separate pockets so one utility never enters the other's space; separate pockets cost more sheet and less headaches.
Steam zones are piped with the inlet at the top and the condensate outlet at the lowest dimple, with a trap sized for the cold start-up load and a vacuum breaker so the zone drains when the valve closes. Glycol zones flow upward, inlet at the bottom, so the pocket fills and vents. A dished-bottom zone is nearly always glycol or cooling water, because steam on the bottom head scorches whatever settles there.
The grade question is simpler on an integral jacket than on an immersion plate. The tank shell is the product-contact surface and follows the product: 316L for dairy, food, beverage and anything with chloride sanitizers, 304L for clean water and inhibited glycol batches. The jacket sheet sees only utility, so 304L is normal even on a 316L shell. A plant that runs tower water through a jacket, or a jacket zone that will see a brine chiller, moves the jacket sheet to 316L and the chloride limit to roughly 1,000 ppm.
The error that reaches us is a jacket run on cooling tower water or untreated well water without anyone checking chlorides. Tower water at 4 to 6 cycles can reach 600 to 900 ppm chloride from a 150 ppm makeup, runs warm, and full of deposits, and a 304L jacket pitted from the utility side leaks into the product with no way to see it coming. Specify a closed glycol loop for cooling, or 316L jacket sheet with a chloride limit written into the water treatment spec.
Zone the jacket to the fill level, not to the tank height.
A small batch heated on a full-height jacket bakes product onto the dry wall above the liquid line.
Request a QuoteJacketed tank questions
A dimple jacket for almost every steam, glycol and cooling-water duty: it carries 150 psig on thin sheet, zones easily and costs less. An annular or half-pipe jacket is the right call for very high jacket pressures, for thermal oil above the dimple sheet's comfortable range, or where the owner's standard already specifies one. We build both and will say which the duty needs.
Yes, if the tank comes to the shop, the shell is thick enough to take the spot welds, and the owner accepts a re-rating of the vessel. Field welding a jacket onto a tank in place is not something we offer. For a tank that cannot move or be re-rated, a clamp-on pillow plate jacket gives heating or cooling without a weld on the vessel.
Batch heating is a race between jacket area times temperature difference and the batch's thermal mass. Each gallon of water-like product raised 1°F stores about 8 Btu, so a 1,000 gallon batch heated 100°F needs about 800,000 Btu plus losses, and the jacket must deliver that in the time allowed. Send the batch, the rise and the clock time and we return the jacket area and utility flow.
Where the specification or the jurisdiction requires it, the jacket is designed and stamped as a pressure chamber in its own right under ASME Section VIII, separately from the shell. Many jurisdictions require it for steam above 15 psig. We design to the code either way and apply the stamp as specified; say in the inquiry whether the shell, the jacket or both must carry it, and whether CRN or PED registration applies.
Related
Embossed Plate
Energy Recovery Banks
Banks of single-embossed plates on spacers recover heat from exhaust gas, dryer air and warm waste water, with the grade set by whether the plate runs wet or dry.
+ Learn More
Embossed Plate
Clamp On
Retrofit heating or cooling on a stainless tank you already own: curved pillow plates, straps and heat-transfer mastic, with no weld and no code re-rating.
+ Learn More
Embossed Plate
Drip Elimination
Pillow plates run below the room dew point pull moisture out of the air over product lines and in cold rooms, with a gutter and drain so nothing reaches the floor.
+ Learn More
