This invention relates to steel and iron-making injection lances, and more particularly to such lances which are protected by refractory concrete Steel and iron-making injection lances protected by refractory concrete have heretofore been known, illustrative of which are those which are generally offered for sale by Inland Enterprises, Inc. of Cleveland, Ohio. Typically, such lances comprise an inner steel pipe through which injected gasses pass for injection into molten steel or iron and a refractory concrete coating which is provided to protect the steel piping from the intense heat associated with molten steel.
In certain commercial applications, injection lances are inserted into the molten steel or iron bath through the slag cover that usually floats on top of the liquid bath and which serves to partially protect the molten metal from the environment. In other applications, care is taken to prevent contact between the environment and the molten metal which could cause undesirable gas incorporation or reoxidation of the metal.
It has been found that refractory coatings as typically employed on steel-making lances undergo preferential erosion at the slagline due to a reaction between the basic slag on the surface of the molten steel and the acidic alumina material within the concrete coating of the lance. Such reaction dissolves the concrete, thus creating a slagline cut which renders the lance unusable after a short period of time even though other areas of the lance (i.e., tip and top) have sufficient remaining concrete thickness to provide additional service. As an example, treatment lances with conventional exterior refractory concrete coatings typically are usable under service conditions for only about 160 minutes, at which time the lance is removed from service due to slagline cut and then discarded. Obviously, it would be highly desirable to extend the life of such lances since typical steel mills may employ 1,000 or more each year at a cost of $1,000 or more per lance.