Device and method for measuring carburization in furnace tubes.

摘要

A device is for monitoring the degree of internal carburisation of furnace tubes and propagates first and second A.C. signals of different frequencies adjacent the outer surface of a furnace tube to be tested. The effective penetration depth of the first signal is at least the furnace tube wall thickness whilst that of the second signal is not greater than the minimum uncarburised thickness of the furnace tube. E.m.f's are induced in a detecting coil by the signals in dependence upon the magnetic permeability characteristics of the furnace tube at the penetration depth of the respective A.C. signals. The difference in level between the e.f's is measured to provide a resultant output. Useful e.g. in steam cracking of hydrocarbon feeds for prodn. of ethylene, where outer surface of tubes are heated to typically 1000-1100 deg.C, the stream passing through them being heated to ca. 850 deg.C. Device can be used to monitor internal carburisation of furnace tubes even in the presence of independently variable amounts of paramagnetic oxides on its outer surface.