T. N. THOMSON

THE physical properties of wrought iron and steel pipes have been brought to my attention during the past few years, and I have spent considerable time trying to determine whether mod

ern soft steel pipe is really superior or inferior to modern wrought-iron pipe for heating and plumbing purposes. The matter was originally brought to my attention by the pipe manufacturers, who stated that we are wrong in supposing that steel pipe is less durable than wrought-iron pipe. Indeed, they showed me the results of numerous tests which demonstrated that, as far as corrosion is concerned, the life of wrought iron and the life of soft steel are practically the same when the pipes are subject to the same conditions.

I did not doubt the records of these tests at all, but as they were principally laboratory tests I could not consider them as convincing as the condemnation of steel pipe by steamfitters and contractors. Then we tried to investigate along practical lines. I had not gone far when we found that a peculiar condition of affairs exhibited itself as follows:

(1) A large proportion of the members of the heating trade denounced steel pipe, because, as they said, "It splits, breaks the teeth of the dies and rusts out too quick." Contractors who would acknowledge that they carried steel pipe on stock a few years ago could scarcely be found; they invariably all supposed they carried only wrought-iron pipe.

(2) Engineers and architects very

*Read at the January, 1908, meeting of the American Society of Heating and Ventilating Engineers.

freely specified that "wrought-iron pipe (not steel pipe) must be used, etc., their impression being that the increased cost of wrought-iron pipe over steel pipe was more than compensated for in the greater period of usefulness of the wrought-iron pipe over the steel pipe.

(3) Instructors in trade schools, professors in colleges, and even the writers of text-books were known to emphasize the supposed fact that steel pipe was not as durable as wrought-iron pipe, and that the latter should be used in preference to the former, particularly for underground work.

(4) On the other hand, statistics showed that the makers of steel pipe furnished about 80% of all the welded pipe then used in America. I also found that not only had the makers of steel pipe spent millions of dollars in the development of vast plants, but that they had also made a large number of experiments and tests to determine the relative durability of wrought-iron and steel pipes, and that their findings were invariably to the effect that the life of these two materials is about the same when they are subject to equal conditions.

(5) Wrought-iron pipe and steel pipe resemble each other so closely that many engineers, contractors, architects, and even steamfitters themselves, cannot distinguish a difference. I know this to be a fact, for I have tried a number of high-class representatives of these several vocations, and they almost all acknowledged that they could not determine the difference unless they were first to cut and thread the pipes; then those pipes which appear most difficult to thread they would christen steel pipes, while those which appear more easy to thread they would call wrought-iron pipes. But this process of determining a difference is not reliable, for it is a fact that a man working with sharp and properly designed

dies can thread steel pipe almost as easily as he can thread wrought-iron pipe. This was demonstrated by a series of tests I made for the International Correspondence Schools in 1905, full records of which can be found in the 1905-1906 proceedings of this society.

METHOD OF INVESTIGATION

As by far the greater part of the every-day work of our students in heating and ventilation is principally the manipulation of welded pipes, we considered this subject of sufficient importance to investigate and try to find something absolutely definite regarding the relative corrosion of modern wrought iron and modern mild steel pipes when both are subject to the same actual working conditions as they occur in practice. With this end in view we commenced by quietly circularizing about 300 heat

Cold

wrought iron. An examination of these samples showed that uniform corrosion took place in both the wrought-iron and the steel pipes. An excellent example of uniform corrosion of a 3-inch black wrought-iron underground cold-water pipe came from Chicago. It had been in use three years; fully half of the metal was "eaten off" the outside, while the inside was but slightly corroded. There was no pitting present in this sample.

Another good example of uniform. corrosion was exhibited in a piece of 11⁄2-inch black wrought-iron exhaust pipe from power boilers in Tonawanda, N. Y. This had lain in damp soil and ashes four years before giving out. The thickness of this pipe varied from about one-half the original thickness to tissue paper thickness, but no pitting was present. The

ing engineers and contractors, offering a book to each in exchange for a small piece of corroded pipe which had been in service only a few years, we to pay express charges at our end. Each circular letter was accompanied by a sheet with printed questions relating to the history of the sample, and was provided with blank spaces for the answers.

My object in trying to obtain these samples and their histories was to find how many were wrought iron and how many were steel. I expected to find that at least 80% of the samples of corroded pipe sent to me would be steel, but they were not. Of the samples received only ten gave out within four years of service, six of these being steel and four being

corrosion was chiefly external, and no doubt was due to the moisture and the ashes. But a better example of uniform corrosion was found in a piece of 2-inch steel pipe from Boston, The pipe was used as a wet return for a direct-radiation low pressure heating system, the pressure never exceeding 3 pounds. This pipe was put in February, 1904, and was removed March, 1905. The pipe was run on top of a cement floor over which was a plank floor on which coal was stored. Some of this coal worked down through the wood floor so that the pipe was partially buried in coal. After each heavy rain some surface water would leak through into the coal bin, so that it is probable the coal around the pipe was continually

moist. The pipe was not covered with pipe covering. The corrosion was all external. The inner surface was not corroded in the least.

Three galvanized nipples were received from one party in Newark, N.J. They were reported to have been all taken from the same pipe line, which was used for hot-water circulation between a tank and a heater for a house supply of hot water. Two of these nipples were wrought iron and one was steel. They were all pitted to about the same extent.

A study of the samples received from the trade would lead me to assume that (1) both wrought-iron and steel pipes which convey steam or hot water will corrode very rapidly when buried underground in wet or damp soil or ashes, the corrosion being principally external; (2) both wrought iron and steel pipes which convey hot water become rapidly corroded if the air and other gases naturally solvent in the water are not permitted to escape from the water previous to its passage through the pipes, as in feed-water heater connections and hot-water circulation pipes for plumbing purposes, this corrosion. being principally internal if the pipes are not buried underground. That the life of either wrought-iron or steel pipes subject to both of the aforesaid conditions will be much shorter than if the pipes are subject to only one of them, because the metal will thus become rapidly cor

(3)

Of course no definite conclusion can be drawn from the study of a number of pieces of corroded pipes received from different parts of the country further than the facts we can see in the samples themselves; for instance, the finest sample of uniform corrosion I received was mild steel. It came from Milwaukee, Wisconsin, is 34-inch black steel pipe and is reported to have been used "for heating water in a range boiler for domestic purposes." It was in use two years. The corrosion is practically uniform without a sign of pitting. Part of the original thickness of the metal was corroded from the inside and about two-thirds from the outside. The pipe, which, no doubt, was originally standard weight, is now about 1-16-inch thick at its thickest part and tapers down to tissue paper thickness in several places.

To secure a record of facts regarding the period of usefulness of steel pipe as compared with wrought-iron pipe it is necessary to test a large number of samples of both steel and iron pipes subject to exactly the same conditions, and these conditions must be the same as the conditions of practice.

On March 7. 1906, I installed a number of pieces of wrought-iron and steel pipe for a corrosion test at the ceiling of the engine room in the Instruction Building of the International Correspondence Schools in Scranton, Pa. (Fig. 1), with the ob

roded at both the internal and external surfaces. (I received no samples which show this, neither have I made tests to prove it, but it seems rational to form this opinion at present.) (4) It is not a fact that the destruction of wrought-iron pipes is in the form of a uniform corrosion, while the destruction of steel pipes is in the form of pitting; they appear to be on an average nearly alike, with the difference, if any, in favor of steel.

ject of determining definitely whether steel pipe will last as long, or longer, than wrought-iron pipe, and by how much. The existing conditions were as follows:

A 100-gallon galvanized iron boiler a in the engine room is set horizontally on two cast-iron cradles supported on brick piers. This boiler furnishes hot water to 24 combination cocks at four press-room sinks as at b and four slop sinks c. The