Pyrosil D® and Incotherm® Alloy TD are the same materials, named differently depending on the manufacturer. We will refer to Pyrosil D®.
Pyrosil D® (a brand name registered to Tyco Thermal Controls) is a nickel-chromium alloy which we use as a specialised heat resistant sheath material for our mineral insulated (MI) thermocouple cables, Type N and Type K. It has a chemical composition of about ± 22% chromium with the addition of (1.4%) molybdenum (silicon). It is suitable for use at extremely high temperatures: a maximum of 1250°C for continuous use.
Aside from being able to withstand high heat, Pyrosil D® cable has a number of other useful properties including:
The excellent resistance of Pyrosil D® to nitridation is the result of two physical properties. Firstly, it absorbs less nitrogen which also makes it much more stable. Secondly, Pyrosil D® does not contain elements such as Nb (Niobium) and Al (Aluminium) which can form internal nitrides. The following graph demonstrates the nitridation of Pyrosil D® in comparison to some other sheath materials.
Oxidation resistance in Pyrosil D® materials is the most notable at higher temperatures. The following two graphs at 1100°C and 1200°C indicate this characteristic and clearly show how Pyrosil D® out-performs other thermocouple materials
The overall mechanical strength of Pyrosil D® is reflected in a number of physical properties: stress rupture strength; tensile strength and the ability to withstand continuous high temperatures. Furthermore, it has a coefficient of thermal expansion close to that of the thermal couple’s core rods meaning there is very little differential expansion which is what usually results in conductor breakage.
The specific chemistry of Pyrosil D® ensures low drift at high temperatures. The diffusion of elements such as manganese (Mn) and aluminium (Al) through the thermocouple sheath can contaminate the wires and over time, affecting the EMF output (drift). However, Pyrosil D® has very low levels of Mn and Al which prevents this cross contamination and thereby minimizes drift. Another contributing factor to low drift is the fact that the composition of Pyrosil® is similar to that of the core rods which reduces the potential for diffusion of elements.
Pyrosil D® mineral insulated cable offers an extremely specialised solution for the high temperature thermocouples used for measurement in challenging environments. It can not only tolerate heat but a variety of atmospheres: vacuum, reducing or oxidising. As such there are many industries where a Pyrosil D® sheath provides the required protection: :
It is also useful to mention some specific applications in industrial processes: Pyrosil D® cable can be used to protect temperature sensors in incinerators and furnaces as well as to monitor the abrasive flue gases that are emitted. An aluminium anode bake furnace would be one example of this.
In gas or steam turbines, high temperature thermocouples often include Pyrosil D® cable for protection. A specific example would include monitoring the temperature of the turbine blade path and the turbine exhaust gas.
In glass and electronic component manufacture it is very important that contamination be kept to low levels. Pyrosil D® exhibits minimal oxide spalling and is therefore an excellent choice for mineral insulated cables in these industries.
Lastly, the significance of Pyrosil D® products is reflected in the fact that it is now considered standard practice for major refinery companies to use Pyrosil D® sheathed thermocouples in furnace applications.
Kamet offers Type K and also Type N thermocouples with a Pyrosil D® MI cable sheath. Type N thermocouples are available in diameters ranging from 0.5mm to 12.7mm. Type K thermocouples are available in diameters ranging from 0.25mm to 12.7mm
Both Simplex and Duplex conductor configurations are available. For both types of thermocouples in Pyrosil D® sheath the following applies:
Kamet is your international supplier of mineral insulated thermocouple cable, RTD cable and other high quality components for industrial temperature sensors. Get in contact with our area sales managers to receive a quote today.
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