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Tank Heaters
Flange Immersion Heaters
Bolted to a mating flange on the tank nozzle. This is what you use when the load is large, the vessel is closed or pressurized, or the heater has to be a permanent part of the tank.
What it is
A flange immersion heater is a bundle of hairpin elements welded into a flange. The flange bolts to a mating flange on the tank or vessel nozzle, and the element bundle extends into the liquid. All electrical connections sit in a terminal enclosure on the dry side of the flange.
This is the construction we have built the most of. Large flanged heaters have been core work here across more than fifty years — big chemical and process tanks, high-kilowatt bundles, difficult chemistries and awkward nozzle geometry. If the job is large and flanged, it is squarely what this company was built around.
Because the flange is a structural, gasketed joint, this is the only immersion style that works in a pressurized or sealed vessel. It also carries far more power in a single unit than a screw plug or over-the-side heater, which is why large storage tanks, process vessels and heat transfer systems almost always use flanged heaters.
When it is the right choice
- The load is above about 24 kW. A single flanged heater can carry hundreds of kilowatts.
- The vessel is closed or pressurized. A gasketed flange joint holds pressure; a hanging element cannot.
- The tank already has a flanged nozzle. Match the existing flange and the install is bolts and a gasket.
- It is a permanent installation. Fixed asset, fixed heat load, long service life.
- The area is classified. Explosion-proof terminal enclosures are standard on flanged builds.
What it requires from you
A flanged heater needs a mating flange on the tank. If the tank does not have one, it has to be cut in and welded, which means draining, cleaning, and in many cases a code inspection. On an existing tank that cannot come out of service, an over-the-side heater or an external circulation heater gets you heat without touching the vessel.
You also need enough straight clearance inside the tank for the full immersed length of the bundle, and clearance outside for the enclosure and for withdrawing the bundle during service. Both get missed regularly.
Specifications
| Specification | Range or option |
|---|---|
| Rating per unit | 3 kW to 500 kW and above |
| Flange sizes | 2", 2-1/2", 3", 4", 5", 6", 8", 10", 12", 14" |
| Flange standards | ANSI 150 lb and 300 lb raised face, flat face, or custom bolt pattern |
| Voltage | 240 V, 277 V, 380 V, 415 V, 480 V, 575 V, 600 V |
| Phase | Single phase, three phase delta, three phase wye |
| Sheath materials | 316 stainless steel, 304 stainless steel, Incoloy 800 / 840, carbon steel, Monel 400, titanium, Hastelloy |
| Immersed length | Built to the vessel — specify available internal length |
| Element bundle | Hairpin elements, straight or bent, with baffles or supports on long bundles |
| Terminal enclosure | NEMA 1, NEMA 4, NEMA 4X, NEMA 7 explosion proof, NEMA 9, moisture-resistant |
| Instrumentation | Sheath and process thermocouples or RTDs, high-limit cutout, terminal box thermostat |
| Options | Insulated and jacketed enclosure, epoxy-sealed terminals, stepped kW for multi-stage control |
Sheath material by service
| Service | Typical sheath | Note |
|---|---|---|
| Water, closed loop and storage | Incoloy 800 or 316 stainless | Incoloy tolerates dry-fire better and resists scale-related hot spots |
| Steam generation, high temperature water | Incoloy 800 | Standard choice above roughly 250°F |
| Heat transfer fluid, thermal oil | 316 stainless steel or carbon steel | Watt density must come down sharply — see watt density limits |
| Fuel oil, lube oil, hydraulic oil | Carbon steel or 316 stainless | Low watt density to avoid coking on the sheath |
| Caustic and alkaline solutions | Nickel, Monel 400, or 316 stainless | Monel handles concentrated caustic well |
| Salt water, brine, chlorides | Titanium | Stainless pits and cracks in hot chloride service |
| Air and gases in a duct or vessel | Incoloy 800 | Very low watt density because gas carries heat away poorly |
| Aggressive mixed acids | Hastelloy or titanium, application specific | Send a bath analysis — this one is not a chart answer |
Common questions
What is the largest flange immersion heater you can supply?
Single flanged units are commonly built well past 500 kW. The practical limits are the flange size the vessel will accept, the immersed length available inside, and the electrical service feeding it. Very large duties are often split into multiple flanged heaters on separate nozzles so the load can be staged and so one failure does not take the whole system down.
Can a flange immersion heater be installed in a pressure vessel?
Yes, and it is the standard method. Specify the design pressure and temperature so the flange rating, gasket and any code requirements are right. ASME code work and pressure-rated builds are quoted per application.
Do I have to drain the tank to install one?
To install into an existing nozzle, yes — the nozzle has to be open. If a nozzle has to be cut in and welded, the tank must be drained, cleaned and made safe first. When a shutdown is not acceptable, an over-the-side heater or an external circulation heater avoids opening the vessel at all.
What is the difference between a flange heater and a screw plug heater?
Mounting method and capacity. A screw plug threads into an NPT coupling and is generally used up to about 24 kW. A flange bolts to a flanged nozzle, holds pressure more reliably at larger sizes, and scales into the hundreds of kilowatts. Below roughly 24 kW in a non-critical tank, a screw plug is usually cheaper.
Can you match an existing flange so it drops into our current nozzle?
Yes. Send the flange size, rating, face type and bolt pattern, or send photos and a measurement of the bolt circle and hole count. Replacement heaters built to match an existing installation are routine work.
Large duty, closed vessel, or a flange to match
Send the flange spec and the vessel dimensions. If you are replacing an existing heater, photos and a bolt circle measurement are usually enough to start.