The relative merit of iron and steel has been a mooted question wherever steel has supplanted iron in any branch of engineering construction or mechanical installation. The two metals, however, have finally been assigned their proper values for the construction of bridges, skeletons for tall buildings, and plates and tubes for boilers, but owing to a widespread prejudice against steel pipe it never has been accorded its right place in plumbing and heating practice.

At the time that steel pipe was first put on the market, imperfections in its manufacture prevented a perfect weld being made; consequently, when a length of the pipe was subjected to a severe torsional stress during the process of threading or when being screwed into place, it often opened for several feet along the seam. As the welds could not be depended on to remain tight under the internal pressures and outside stresses to which they would be subjected in practice, steel pipe naturally fell into disfavor. Furthermore, the grade of metal used at the time steel pipe was first manufactured, lacked the soft quality characteristic of the present day grade of pipe steel, and in chilling it sometimes took on a temper in spots that was noticeable when cutting and threading the pipe with hand tools.

In addition to the unsuitability of the early grade of pipe steel for the manufacture of pipe, the time of its introduction was extremely inopportune. Steel pipe was first put on the market about twenty years ago, coincident with the introduction of electric railways. At that time imperfect return conductors, or the absence of return conductors, permitted the flow of numerous currents of electricity through the earth back to their respective dynamos; and in following the line of least resistance those vagrant currents often traveled for a certain distance along a line of gas or water pipe to a point where a suitable condition of moisture and soil permitted their return again to the earth. At the numerous points where the electric current flowed off the pipes, electrolysis occurred which caused the pipes to pit and corrode, and as prior to that time pitting was unknown in wrought-iron pipe (the only-known kind of welded pipe up to that time used) it seemed a logical deduction that all pipes that pitted were made of steel.

Time and investigation, however, have disproved that deduction. A material so extensively used and of such vast importance in mechanical installations could not long rest under the stigma of being unsuitable for its purpose without attracting the attention of impartial experimenters - seekers after truth - anxious to learn the relative value of the new material as compared with the old, that it might be assigned its right place in the list of pipe materials. Numerous experiments have been made to determine the relative strength, workability and durability of wrought-iron and steel pipe. The result of these experiments, however, are scattered through various publications, some of which are not easy of access, and it is with the object of collecting the various data, digesting their substance, and giving in concise form the results of various experiments or of drawing from them logical conclusions that will help busy men to form a correct estimation of the value of soft steel for a pipe material, that this article is written.

It might be interesting here to note that the bulk of welded pipe now used in this country is made of steel. Of the 1,400,000 tons of pipe and tubes manufactured annually, about 1,000,000 tons, or over 70 per cent., is made of soft steel, and the remainder, 400,000 tons, about 30 per cent., is made of wrought-iron. It might be stated further, without fear of contradiction, that many contractors use steel pipe in their daily practice under the mistaken impression that it is wrought-iron pipe. The reason for this belief is that the name "'wrought-iron" to a certain extent among dealers has been extended to include all kinds of welded pipe, and is used as a synonym for either wrought-iron or steel pipe, so that unless "strictly wrought-iron pipe" is specified, the order might be filled indifferently with either wrought-iron or steel pipe. In view of this fact, the suggestion has been made that wrought-iron pipe and steel pipe each be designated by the term wrought pipe, a generic term, to indicate the kind or type of pipe without specifying the material of its composition; and as for most purposes neither material has an advantage over the other, the suggestion seems a good one.

To arrive at a true estimation of the value of a material, some standard of comparison must be assumed by which to measure the various qualities of the new material, and in proportion as the qualities rise above or fall below the assumed standard, the new material must be considered either better or worse. In the case of wrought-iron and steel pipe, wrought-iron having been first on the market, must be accepted as the standard with which steel pipe is to be compared, and comparisons made of the relative strength, workability and length of life of equal thickness of the two materials.