Sheathed Electric Heaters
Sheathed electric heaters are one of the most rugged heating elements in industrial hydraulic, lubrication, and heat transfer oil systems. Their core advantage lies in the "core-tube separation" structure—when the heating core is damaged, there is no need to drain the oil tank; simply pull out the old core and replace it with a new one, greatly reducing downtime maintenance costs.
Combining Yangzhou's local industrial supporting facilities and the latest selection logic, here is a practical procurement guide for you:
I. Comparison of Mainstream Sheathed Heater Models and Selection
The most common model systems for sheathed heaters are the SRY series and HRY series, with the core difference lying in structural design and applicable working conditions:
Model Series Core Features Surface Power Density Applicable Scenarios Maintenance Method
SRY2/SRY3 Ordinary immersion type, simple structure and low cost ≤1.5–2.5 W/cm² Open/closed oil tanks, hydraulic oil, lubricating oil heating Overall replacement required when damaged
SRY4 High surface load, designed specifically for circulating oil ≤3 W/cm² Flowing or circulating oil, working conditions with good heating effect Overall replacement required when damaged
SRY6/HRY1-7 Core-tube separation, with protective sleeve Core ≤1.8 W/cm², sheath ≤0.7 W/cm² Heat transfer oil, mineral oil, occasions requiring high reliability Only replace the core, no need to drain oil
SRY9-1 With temperature control + oil inlet/outlet, independent control Sheath ≤0.7 W/cm² Heat transfer oil systems requiring precise temperature control, high anti-carbonization requirements Only replace the core, no need to shut down
HRY8-9 With heat dissipation fin protective sleeve type Depends on design Special working conditions requiring larger heat dissipation area Only replace the core
Key Parameter Reminder: Surface power density is the core of selection. For media prone to carbonization such as heat transfer oil, the sheath surface heating power must be controlled at ≤0.7 W/cm²; otherwise, local overheating will cause oil carbonization, adhering to the sheath surface, sharply reducing heat transfer efficiency, or even burning out the element.
II. Procurement Pitfall Avoidance Guide: 5 Core Parameters and Common Misconceptions
Only looking at power, not surface load: For the same 6kW heater, different sheath diameters and lengths result in vastly different surface power densities. During procurement, the sheath outer diameter and immersion length must be confirmed, and the actual W/cm² value calculated. For heat transfer oil working conditions, it must be ≤0.7 W/cm².
Wrong material selection leading to corrosion and leakage: Ordinary mineral oil can use 304 stainless steel or seamless steel pipe; if the medium contains trace corrosive components, it needs to be upgraded to 316L stainless steel; for high-temperature heat transfer oil (>250℃), it is recommended to use Incoloy 800 and other high-temperature resistant alloy sheaths.
Ignoring flange standards and mounting hole dimensions: The SRY6 series protective sleeve diameter is usually φ108mm, and the mounting hole needs to be ≥φ114mm; the SRY2 series mounting hole is ≥φ65mm. Before procurement, the equipment oil tank flange interface dimensions must be verified to avoid buying something that cannot be installed.
Equating "sheathed type" with "explosion-proof type": The protection grade of ordinary sheathed heaters is generally IP54. If used in petrochemical and other flammable and explosive environments, flameproof type must be selected (explosion-proof grade ExdⅡCT4 and above), and an explosion-proof certificate must be obtained.
No temperature control or liquid level protection: Sheathed heaters are strictly prohibited from dry burning. If the oil tank liquid level may fluctuate, a liquid level switch must be provided to achieve automatic power-off at low liquid level; it is recommended to integrate a PT100 temperature sensor + PID temperature controller for precise temperature control.
III. Recommended High-Quality Local Manufacturers in Yangzhou
Yangzhou is one of the core production areas for sheathed electric heaters in China, and procurement and after-sales response are very convenient:
Yangzhou Huateng Electric Technology Co., Ltd.: Specializes in SRY9-1 sheathed heat transfer oil temperature-controlled heaters, with oil inlet/outlet design. During maintenance, only a small amount of heat transfer oil inside the sheath needs to be drained, with no need to shut down, suitable for continuous production working conditions.
Yangzhou Zhili Electric Technology Co., Ltd.: Professionally produces SRY6 series sheathed tubular electric heaters, with a product line covering SRY6-1/2/3 and other specifications. It also provides power testing instruments and can offer an integrated "heating + testing" solution.
Taixing Shuanglong Electric Appliance Co., Ltd. (Taixing, Taizhou, about 1 hour's drive from Yangzhou): Focuses on non-standard electric heaters. Its marine sheathed electric heaters have partially replaced German imported products and are widely used in large projects such as shipyards, steel mills, and power plants, with an annual production capacity of 20,000 units/sets.
Jiangyin Huanyu Electric Heating Equipment Co., Ltd. (Jiangyin, Wuxi, about 1.5 hours' drive from Yangzhou): A veteran electric heating enterprise with over 40 years of history. Its HRY series sheathed heaters have long been supporting manufacturers of thin oil stations, hydraulic stations, and gearboxes. The products have obtained CE certification and support flameproof customization.
IV. Installation and Maintenance Key Points
Dry burning strictly prohibited: The effective heating area must be 100% immersed in the medium. The installation position should be ≥50mm from the bottom/side wall of the oil tank, avoiding dead corners.
Sealing and leak prevention: When connecting flanges, add high-temperature resistant sealing gaskets and tighten bolts diagonally in steps; for threaded connections, use high-temperature resistant raw material tape, and do not twist with excessive force.
Regular carbon removal: If carbon deposits or oil stains are found on the sheath surface, they must be removed before use; otherwise, heat transfer efficiency will decrease and local overheating will accelerate aging.
Insulation testing: Every 6-12 months, use a 500V megohmmeter to measure insulation resistance. If it is below 1MΩ, drying treatment or replacement is required.
Core replacement: When the SRY6/HRY series is damaged, simply pull out the old core and replace it with a new one, with no need to drain the oil tank. This is the greatest maintenance advantage of the sheathed type.
