Flanged immersion heaters — electric heater assemblies for boilers and tanks

What is a flanged immersion heater

A flanged immersion heater is an assembly of one or more hairpin tubular heating elements brazed or welded to a common threaded fitting or plate flange, forming a single drop-in unit for boilers, tanks and pressure vessels. All connections are sealed at the flange face — the heating elements are fully submerged in the medium.

In GOST 13268-88 documentation these assemblies carry letter codes depending on the heating medium:

• SEV — water (or air) heating assembly;
• SEM — oil heating assembly;
• TENB — universal, any medium.

These codes appear in the model number and on the rating plate. A separate thermowell tube for a thermocouple or RTD sensor can be integrated with the heating elements — essential for automatic temperature control.

Important: The active (heated) sections of adjacent elements must never touch. Contact between adjacent heated sections creates a hot spot that accelerates sheath failure.

Construction

Each element is a standard tubular heater: a nichrome resistance coil centred in a metal sheath tube, with compacted MgO (magnesium oxide) powder as insulation. Elements are bent into a hairpin (U-shape) so that both terminal pins exit from the same end and are brazed or welded to the flange. This concentrates the heated length inside the vessel and keeps all electrical connections outside.

Flange types:

1. Threaded fitting — BSP (G) or metric thread screwed into the vessel wall. Compact, low cost. The most common type for domestic and light-industrial boilers and water heaters.
2. Plate flange (bolt flange) — flat steel or stainless plate bolted to the vessel with M8–M12 studs. Hole pattern to ANSI B16.5 or EN 1092-01, or to customer drawing. Used for large industrial tanks and high-pressure vessels.

Number of elements

The number of elements in one assembly is determined by two constraints:

• Physical fit — how many hairpin elements can be mounted on the flange and immersed without mutual contact;
• Phase balance — 3-phase assemblies must have a number of elements divisible by three (3, 6, 9…) for balanced star or delta loading.

Individual element ratings are available in 0.5 kW steps. Typical values: 0.5 · 1 · 1.5 · 2 · 2.5 · 3 · 4 · 5 · 6 · 9 · 10 · 12 kW. Combined, total assembly power can reach 100 kW. For loads below 1 kW, a single-element screw plug heater is more practical than a multi-element assembly.

Watt density and heating medium

Watt density — the power dissipated per unit of element surface area — is the most critical design parameter of any immersion heater. Too high a watt density for the medium leads to film boiling, carbonisation or premature sheath failure.

The medium also determines sheath material. GOST 13268-88 assigns a letter code per material/medium combination:

• J — water, stainless steel AISI 304/316;
• X — water, copper;
• P — water, carbon steel;
• Z — oil, carbon steel C10;
• R — aggressive media, titanium or PTFE-coated.

This letter appears in the model number (see Marking section below).

Water-service heaters

Water is the best heat-transfer medium for immersion heaters. Watt density can be as high as 12 W/cm² (77 W/in²) — water removes heat from the sheath rapidly, and the 100 °C boiling point at atmospheric pressure caps the sheath temperature. A 12 kW water-service assembly in 13 mm sheath tube is only 30–40 cm long. Typical applications:

• Electric heating boilers (50–400 m² coverage);
• Indirect-coil and direct-type storage water heaters;
• Industrial process tanks;
• Radiators and hydronic systems.

Oil-service heaters

Oil is a poor heat-transfer medium. Watt density must be kept below 2 W/cm² (13 W/in²) — at higher densities oil carbonises on the sheath surface, forming an insulating coke layer that traps heat and causes the element to fail. Even at a client's request, exceeding 3 W/cm² in oil is not recommended. Oil-service assemblies use carbon steel C10 sheath.

Voltage and phase configuration

Any supply voltage from 12 V to 600 V can be specified; DC supply is available on request. Standard values: 220 V, 230 V, 380 V, 400 V. Single-phase assemblies operate on 220/230 V. Two- or three-phase assemblies on 380/400 V. All 3-phase assemblies have element counts divisible by three — the terminal block is wired in star (Y) or delta (Δ) as specified.

Order worldwide

Custom-manufactured to drawing — from 3 days, from 1 piece. Worldwide shipping via DHL, FedEx, SDEK. 1-year warranty on all products. In business since 2010. To order, Send us a sketch, a photo of an existing heater, or describe your requirements — we will work out the specifications and provide a price within 15 minutes during business hours.

Certification: GOST 13268-88, on request — DIN, IEC, ASTM. TEN-Miass, ul. Shota Rustaveli 82a, Tashkent, Uzbekistan 100000. Phone: +998 50 090 19 24.