AN EMPIRICAL-MODEL TO DESCRIBE THE NONISOTHERMAL AGING BEHAVIOR OF FEROPLUG MATERIALS

Feroplug is a new temperature indicator developed by the authers and c o-workers. The device makes use of the characteristics of ferrite tran sformation in duplex stainless steels, and has the following advantage s over conventional methods of temperature measurement: (1) It is a pi ece of stainless steel, with no delicate parts, and can be used in ver y hostile environments; (2) It does not require any cables such as tho se in the case of thermocouples;(3) It is very much cheaper than therm ocouples. This invention has been patented in the USA, UK and Europe w ith financial and legal support provided by the British Technology Gro up, UK. Patent application in Japan is still pending. The invention is particularly useful for life assessment purposes in power and petroch emical plants. The underlying physical principle of the Feroplug is ba sed on the transformation of ferrite, which is ferromagnetic at room t emperature, into other phases such as carbide and sigma which are non- feromagnetic at room temperature. The amount of transformation depends on the temperature and duration of exposure. If the amount of transfo rmation and time of exposure is known, the temperature of exposure can be deduced. Thus, the Feroplug makes use of the change in the amount of ferrite, which can be easily detected by room temperature magnetic measurement, to indicate the temperature of exposure. A model has been developed which can describe the ferrite transformation behaviour of Feroplug materials under non-isothermal conditions. The agreement betw een experimental data and the model is good at temperatures above 550 degrees C.