1-805-484-2992
Quotes - Engineering - SalesAdding a jacket to a tank without welding on it
A clamp-on tank jacket is a set of single-embossed pillow plates rolled to the tank's outside radius, bedded on heat-transfer mastic and pulled tight against the shell with stainless bands or threaded straps. The flat sheet of each plate faces the tank; the inflated side carries glycol, hot water or low-pressure steam. The vessel is never welded, never re-rated and never emptied for more than the time it takes to strap the plates on, which is why it is the retrofit of choice for a tank that cannot be replaced or taken out of service for a shop jacket.
Contact, mastic and straps
The trade is thermal contact. A welded dimple jacket shares metal with the tank wall; a clamp-on plate transfers through two surfaces and whatever sits between them. Heat-transfer mastic fills the gap, and with it a clamp-on jacket reaches a useful fraction of a welded jacket's performance. Without it, an air gap of a few thousandths of an inch cuts the heat flow to a small fraction, and the jacket looks fine while the tank refuses to reach temperature.
Grade is decided by the outside of the tank, not the product in it. The plate never touches product, so 304L serves glycol and hot-water loops in a dry process room. Where the tank is washed down with chlorinated sanitizer, stands near a brine line, or lives in a coastal plant, 316L keeps the plate from pitting under the straps where water collects and dries.
Clamp-on jackets are 304L for glycol and hot-water loops on a dry tank exterior and 316L where washdown, brine spray or a coastal plant keeps the outside wet. The Material & Construction page compares the grades.
What a clamp-on retrofit includes
- Single-embossed plates rolled to the tank radius you measure or we survey
- Sheet 0.05 in. for glycol and hot water, heavier where steam or handling calls for it
- Rated 100 psig for glycol and hot water; low-pressure steam only after review
- Heat-transfer mastic supplied with the plates, with a coverage figure on the drawing
- Stainless banding or threaded strap sets sized to the shell diameter
- Stub connections turned away from the tank so piping clears the straps
- Insulation cleats on the outside face where the jacket will be lagged over
under the straps on washdown tanksWater collects and dries under each strap, so a tank in a washdown room gets 316L plates even when the loop inside them is plain glycol.
What to send us for a clamp-on jacket
A clamp-on quote starts with the tank, because the plates are rolled to it and the duty is limited by how much of the shell they can cover. A photograph with a tape measure in frame answers more questions than most drawings.
- Tank outside diameter, straight-side height and whether the shell is flat, rolled or dished
- Obstructions on the shell: nozzles, manway, lifting lugs, legs, level gauges
- Product in the tank, batch volume, and the temperature change and time required
- Utility available: glycol or hot water supply temperature and flow, or steam pressure
- Whether the tank is agitated, which roughly doubles what a jacket can deliver
- Washdown, sanitizer and ambient conditions around the outside of the tank
- Whether the jacket will be insulated over, and the clearance to walls and other tanks
Call and talk it through with an engineer: 1-805-484-2992
A formed pillow plate strapped to the outside of an existing tank, with heat transfer cement filling the gap so heat crosses the tank wall without a weld to the vessel. It is the usual way to add heating or cooling to a vessel already in service.
Getting a clamp-on jacket to perform
The first rule is coverage. A jacket that wraps the lower third of a tank heats the lower third; convection carries some of that upward, but a tall unstirred tank will show a temperature difference top to bottom that no amount of flow in the plates will fix. Plan the plate layout around the nozzles and the manway, and if the usable shell is small, say so early, because the honest answer may be a larger glycol temperature difference or an in-tank immersion plate instead.
The second rule is the mastic. Heat-transfer mastic is a filled compound troweled onto the tank or the plate before the straps go on. It is the only thing bridging the microscopic gap between two rolled surfaces that will never match perfectly, and its coverage is specified on our drawing for that reason. Skip it, or let it skin over before the plate goes on, and the jacket will transfer a small fraction of its rated duty. Apply it fresh, pull the straps in sequence from the center outward, and torque the straps again after the first heat-up.
The third rule is the radius. A plate rolled to a slightly tighter radius than the tank sits on its edges and leaves a gap in the middle; one rolled too loose rocks on its center line. We roll to the measured outside diameter and leave the sheet thin enough to conform under strap tension. Flat-sided tanks and square tanks take flat plates, which is easier; dished heads take segmented plates or a seperate bottom coil.
Steam in a clamp-on jacket is possible and usually a mistake. The plate is rated for it, but the mastic has a temperature limit, the tank shell expands against the straps on every cycle, and condensate management on a plate strapped to a tank is harder than on a plate hung in it. Hot water at 180 to 200°F or glycol at 30 to 40°F is where clamp-on jackets do their best work; a steam retrofit is better served by an immersion plate through the manway.
The retrofit we are asked to put right most often is a cooling jacket in 304L strapped to a tank in a washdown area. The glycol never touched the plate exterior, but the sanitizer rinse did, every shift, and it dried under the straps. Pitting started along each strap line within a year. The replacement plates were 316L, with the straps padded where they cross the plate and a drain gap left at the bottom edge so rinse water runs off instead of wicking in.
No mastic, no jacket: the air gap carries the heat, and air does not.
A clamp-on plate on fresh heat-transfer mastic reaches a useful fraction of a welded jacket's duty; on bare metal it reaches almost none.
Request a QuoteClamp-on jacket questions
Less than a welded jacket, so we size it for clamp-on contact and tell you the batch time it gives. With mastic properly applied and the straps tight, a clamp-on plate transfers a worthwhile fraction of what the same plate would do welded to the shell, enough to hold temperature and to heat or cool a batch over a reasonable time. It is not the right choice for a fast heat-up or a large steady load.
Not when the tank is stainless and the straps are stainless with the plate bedded on mastic. Carbon-steel bands on a stainless tank leave rust streaks and a crevice; mixed metals under a wet strap set up a galvanic cell. We supply stainless bands or threaded 304 or 316 straps, with a thin pad where the strap crosses a plate edge, so the shell carries only compression.
On carbon steel, yes, with the same mastic and straps, and the plate grade still follows the outside environment. On polyethylene or fiberglass the plate works but the tank wall conducts poorly and softens with heat, so the duty is low and warm water held below the tank's rated temperature, often 120 to 140°F on polyethylene, is the hottest utility we use. Tell us the tank material and we will size to it or recommend an immersion plate through the top instead.
Yes. The plates come off by cutting or releasing the straps, the mastic cleans off with a scraper and solvent, and the tank is unchanged underneath. Refitting needs fresh mastic every time, because the old compound will not re-wet the surface. That is the main reason to specify the jacket with its mastic supplied rather than sourcing a compound locally that may not match the temperature range.
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