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Tubular Heaters

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Construction Tubular heaters can be formed into virtually any shape, brazed or welded to any metal surface, and cast into metals. The tubular heater’s basic construction consists of a computer-designed helical coil of 80% Nickel 20% Chromium alloy resistance wire fusion welded to the nickel-coated steel terminal cold pins. This assembly is precisely stretched and centered in the element metal sheath, which is then filled with Grade “A” Magnesium Oxide powder (MgO). The filled tube is then compacted by a roll reduction mill into a solid mass, permanently stabilizing the coil in the center of the tube while providing excellent heat transfer and dielectric strength between the coil and the sheath.

Electrical Limitations and Minimum/Maximum Sheath Lengths

Element Diameter		Maximum Voltage	Maximum Amperage	Resistance in Ohms per Heated Inch		Sheath Length
Element Diameter		Maximum Voltage	Maximum Amperage	Resistance in Ohms per Heated Inch		min		max
in	mm			min	max	in	mm	in	mm
0.26	6.6	250	15	0.1	17	11	279	200	5080
0.315	8.0	480	30	0.06	21	11	279	200	5080
0.375	9.5	480	30	0.04	21	11	279	230	5842
0.43	10.9	600	40	0.04	21	11	279	268	6807
0.475	12	600	40	0.04	21	11	279	275	6985
0.625	15.9	600	40	0.04	17	11	279	255	6475

Sheath and Heated Length Tolerance (applicable for all diameters)

Length		Sheath Length Tolerance		Heated Length Tolerance		Minimum Unheated Length Each End
in	mm	in	mm	in	mm	in	mm
11-20	279-508	±3/32	2	±1/4	6	1	25
21-50	509-1270	±1/8	3	±1/2	13	1-1/4	32
51-80	1271-2032	±5/32	4	±7/8	22	1-1/2	38
81-110	2033-2794	±3/16	5	±1-1/8	29	1-5/8	42
111-140	2795-3556	±7/32	6	±1-3/8	35	1-3/4	44
141-170	3557-4318	±1/4	6	±1-5/8	41	2	51
171-200	4319-5080	±3/8	10	±1-7/8	48	2-1/4	57
201-UP	5081-up	±1/2	13	±2-3/8	60	2-1/2	64

Standard Sheath Materials The selection of a sheath material should be made based on the the chemical composition of the solution being heated, character of materials entering the solution, and the processes controls. A material selection guide can be found on page 16-12 of the Tempco catalog. The following are the most common tubular element sheath materials. For other materials consult TEMPCO. Note: Maximum sheath temperatures refer to the maximum temperature of the element sheath material. Consideration must be given to maximum temperature and watt density the heated material can safely see. .
Incoloy® 800 A Nickel (30-35%), Chromium (19-23%), Iron Alloy. The high nickel content of this alloy contributes to its resistance to scaling and corrosion. Used in air heating (also see Incoloy® 840) and immersion heating of potable water and other liquids. Maximum sheath temperature is 1600°F (872°C).	316 Stainless Steel A Chromium (16-18%), Nickel (11-14%), Iron Alloy with Molybdenum (2-3%) added to improve corrosion resistance in certain environments, especially those which would tend to cause pitting due to the presence of chlorides. Applications include deionized water. Maximum sheath temperature is 1200°F (649°C).
Incoloy® 840 A Nickel (18-20%), Chromium (18-22%), Iron Alloy having about 10% less nickel than Incoloy 800. Used in many air heating applications where it has exhibited superior oxidation resistance at less cost. Maximum sheath temperature is 1600°F (872°C).	Copper Mainly used in clean water heating for washrooms, showers, rinse tanks and freeze protection of storage tanks. Maximum sheath temperature is 350°F (177°C).
304 Stainless Steel A Chromium (18-20%), Nickel (8-11%), Iron Alloy used in the food industry, sterilizing solutions, and many organic and inorganic chemicals. Maximum sheath temperature is 1200°F (649°C).	Low Carbon Steel Applications include fluid heat transfer media, tar, high to low viscosity petroleum oils, asphalt, wax, molten salt, and other solutions not corrosive to a steel sheath. Maximum sheath temperature is 750°F (399°C).
321 Stainless Steel A Chromium (17-20%), Nickel (9-13%), Iron Alloy modified with the addition of titanium to prevent carbide precipitation and resulting intergranular corrosion that can take place in certain mediums when operating in the 800-1200°F (427-649°C) temperature range. Maximum sheath temperature is 1200°F (649°C).