Alumina furnace tube sizes: our stock tubes next to the work tubes furnace makers list

We keep 12 alumina furnace tube sizes in stock, from 30×20 to 80×70 mm (OD × ID), cut to the length you order. 40×30, 50×40, 60×50 and 80×70 have the same nominal OD and ID as work tubes Nabertherm or MTI list for their tube furnaces. Carbolite Gero lists only the largest tube OD each furnace takes, so measure the ID on the tube you are replacing.

Our stock furnace tube sizes

These are open at both ends. The last column only compares dimensions with the makers' lists further down; it says nothing about the material.

Long tubes are in stock too: OD 80, 75, 70, 65 and 60 mm at 1–1.2 m; 50, 45 and 35 mm at 1.5 m; 40 and 30 mm at 2 m. We slip-cast tubes up to 100 × 90 × 1000 mm (OD × ID × length). In air our tubes are used up to 1,750 °C hanging vertically and 1,650 °C lying horizontally, the usual position in a tube furnace.

All are 99.5% Al₂O₃ (C799) as standard, and 95% white alumina where a drawing names C 610. We confirm the grade and maximum temperature in each quotation. Other ODs and walls are made to drawing, usually in 25–30 days.

Nabertherm work tubes

Nabertherm publishes one table of working tubes for its R, RS, RHTC, RHTH and RHTV tube furnaces, by material, with the standard and optional tube for each model:

Two things to read from it. The same 50×40 and 80×70 come in three ceramics, and C 530 is porous and C 610 is mullite, so a size match with our alumina says nothing about the grade. And Nabertherm's vacuum tubes have ground ends for water-cooled flanges. If yours do, say so on the request, so the end finish is confirmed in the quotation.

MTI tubes

MTI sells its alumina tubes by OD × ID × length, and states the tube that comes with each furnace:

MTI's own pages show how loose “60×50” can be: ±4 mm on both diameters for TA-60D-M1200. If your flanges are tight, measure the old tube and put the measured figures on the request.

Carbolite Gero furnaces

Carbolite Gero lists the largest work tube OD each furnace accepts, not a tube ID. Its TF tube furnaces take work tubes of 32 to 125 mm OD:

The tube is longer than the furnace. For the TF1 12/60/300, Carbolite recommends a 580 mm tube for use in air and 750 mm with a modified atmosphere, where end seals sit on the tube ends. Its stainless end seals are made for tube ODs of 32, 46, 60, 86, 100, 150 and 200 mm, and it gives an acceptable tube OD tolerance of +1.5 mm to −1 mm. Our 32×25 and 60×50 have the OD of two of those seal sizes.

Tolerance matters here. Our through-tube orders in 2026 were written with ±2 mm on the OD at 34 to 65 mm, which is wider than Carbolite's seal tolerance. If the tube goes into end seals, put the seal's OD tolerance on the request and we'll confirm in the quotation whether we can hold it. The full figures are in alumina tube tolerances.

Measuring the tube you replace

• OD and ID with calipers at both ends, two readings at right angles at each end.
• Overall length, and how far the tube sticks out of the furnace at each end. With end seals or flanges it is longer than the heated length.
• Whether the ends are plain, ground or slotted, and anything fitted to them.
• The furnace make and model. The diameter in a model name can be the tube OD or its ID (see the first question below).

The grade and the heating rate matter as much as the size. Furnace makers' temperature and vacuum limits for alumina and quartz tubes are compared in alumina or quartz tube for a tube furnace, with the boats that pass through each of our tubes. Why a tube cracks on heating, and the ramp rates makers give, is in alumina thermal shock.

What to put on the request

• OD × ID × length, measured or from the furnace maker's tube, with the OD tolerance your seals or flanges need.
• The furnace make and model, and the end finish.
• Maximum temperature, atmosphere, vacuum or not, and your heating and cooling rates.
• Grade: 99.5% (C799) as standard, or 95% white alumina where a drawing names C 610.
• Quantity.

Stock sizes ship in about 3 days for a small order and about 7 for a bulk one. Every size is on the furnace tubes page, or send the tube specification directly.

Questions buyers ask

What size alumina tube does a 50 mm tube furnace take?

Check which diameter the 50 is. Nabertherm's R 50/250 lists a 50 mm outer tube and comes with a 50×40×450 mm tube, while its RT 50/250 lists 50 mm as the inner tube diameter. Carbolite Gero's model names give the largest tube OD the furnace accepts. Measure the old tube's OD and ID before ordering.

Do you make 50×40 and 80×70 alumina furnace tubes?

Yes, both are among our 12 stock sizes, cut to the length you order. They have the same nominal OD and ID as the C 799 work tubes in Nabertherm's table. Ours are C799 alumina as standard.

How long should a tube furnace work tube be?

Longer than the furnace. For its TF1 12/60/300, Carbolite Gero recommends a 580 mm tube for use in air and 750 mm with a modified atmosphere, where end seals sit on the tube ends. Copy the length of the tube you are replacing, or the furnace maker's figure.

What OD tolerance do your furnace tubes have?

Our 2026 through-tube orders were written with ±2 mm on the OD at 34 to 65 mm. Carbolite Gero gives +1.5 mm to −1 mm for tubes in its end seals, so if the tube goes into seals or flanges, put their tolerance on the request and we confirm in the quotation whether we can hold it.

Sources

1. Nabertherm: Working tubes for tube furnaces, sizes by material and model (pages 32–33)
2. Nabertherm: Laboratory catalogue, tube furnace tables (outer and inner tube diameters)
3. MTI Corporation: alumina processing tubes and tube furnaces (TA40D700, TA-60D-M1200, TA80D1000, OTF-1500X; read 15 October 2026)
4. Carbolite Gero: Laboratory & Industrial Ovens & Furnaces, catalogue E-01-2026 (tube furnace tables, work tubes p. 102, end seals p. 106)
5. Our own figures: the factory’s standard-size list, 2026 orders and test report, as recorded in our product catalog.