Occurrence of Massive Magnetite Formations in the Unheated Economizer Tubes of High-Pressure Boilers

Abstract

Six instances are reported of massive magnetite formations occurring in the unheated tubes connecting the economizers to the steam drums of three high-pressure boilers. Two resulted in failure of the tubes concerned. The reaction involved was not the well-known iron-steam direct combination, but one of a number of others known to be feasible at much lower temperatures involving several intermediate steps. While it has not been possible to identify the mechanism of formation of the deposits observed, the circumstances and environment in which such formations become possible have been recognized and are described. The measures taken to prevent the occurrence of further formations are described, and some suggestions are made regarding the plant conditions under which attack of this kind is likely to arise. Some information is given regarding the ultrasonic methods which were used to detect the presence of magnetite at tube sites which were inaccessible to visual examination.