High temperature resistant stainless steel by special order. Such tubes can be used for above-atmospheric pressures, as standalone outer enclosing tubes, or as a safety container around a ceramic enclosing tube when this is subjected to above-atmospheric pressures or explosive/toxic/corrosive gases that must not escape in case of breakage of the ceramic tube. 

The tube is made of the alloy 253 MA. This alloy has good oxidation resistance to 1100°C in dry air.

The tubes are welded to outer flanges, and are fastened to the outer thread of the base unit, against the Viton O-ring. The tubes can be delivered closed (welded) in the hot zone, or in various types that go through the entire furnace and are open or closed (welded) in the cold zone outside the furnace. The tube fits in furnaces with 50 mm working diameter. It can enclose 39-40 mm outer diameter ceramic tubes if these have close tolerances with respect to straightness, roundness, and diameter.

The tube can be used as standalone outer tube. It then has wider working space inside (up to 40 mm) than the ceramic tubes. For pressure and temperature tolerances, see below. If closed (by welding) it can contain a ceramic tube, for safety, and/or for increased pressures. It then serves two purposes: It is closed a few millimeters above the top of the ceramic tube and thus stops the ceramic tube from the possibility of being pressed up by the pressure. Secondly, it holds everything in place if the ceramic tube breaks from the overpressure or unforeseen incidents. The metal tube may give increased shielding against noise in electrical measurements.

If used as stand-alone tube the 253 MA tube we provide can nominally be operated for 10,000 h at 15 atm overpressure at 900°C, 10 atm overpressure at 1000°C, and 2.5 atm overpressure at 1100°C.

Precautions: Operation of ProboStats above atmospheric pressure - even with a steel outer tube - is done entirely at the user's risk and responsibility, and requires that the user understands the principles of operation and the possible sources of failure and danger, and installs safety precautions as required. The steel tube conducts heat from the furnace to the base unit more efficiently than with only ceramic tubes. Thus, ensure that water cooling of the base unit is in operation. Oxygen is a potentially dangerous gas in pure form at atmospheric and higher pressures: It may ignite organic materials and metals, especially if they are hot. This is a potential danger for the materials of the base unit. Thus, limit pressures of oxygen, and ensure that water cooling is in operation. The steel tube is in danger of touching or short-circuiting the heating element for some types of furnaces. Ground the base unit if electrical hazards cannot be excluded. Do not attempt to force a ceramic tube into the steel tube u