WOOD STAVE PIPE.
Wood pipe for conveying water to and through municipalities has been used “since the memory of man runneth not.” The Romans used it for generations. Many miles of it were laid in the streets of London centuries ago. and last year some of these old pipes were removed from the streets, and were found in a good sound states of preservation. The early waterworks in the United States were built with wood pipe distribution mains; New York and Philadelphia being well known examples. During the building of the New York subways, some of these old wooden mains were encountered and removed. They were found perfectly sound. The pipes above referred to were made by boring pine logs and banding each end with a round wrought iron band. Making the two ends in the form of a tenon and chamber, and driving one into the other. This method of manufacture required the removal of the best part of the wood, and yet the pipes have lasted for centuries. The writer removed several hundred feet of these pipes from the streets of Wilmington some ten years ago, which had been in the ground since 1812, and not only was the wood as sound as the day it was buried, but the wrought iron bands were perfect. These facts are simply mentioned in answer to the oft repeated question, “what is the durability of wood pipe.” It might well he asked “why, if wood pipe was so durable, should cast iron and steel pipe have been substituted.” The answer to that question is that the old method of making a wood pipe limited its inside diameter to the diameter of the log, and thus its place in the modern water installation was necessarily very much limited.
Dimensions. —By the modern, method of making wood pipe the diameter is unlimited. The largest wood pipe known to the writer being 9 feet 6 inches in diameter, made under the direction of Mr. John Birkinbine, of Philadelphia. The quality of the materials entering into the construction of the modern wood pipe are far superior to that used in the ancient installations, The wood is cut out of the solid logs in the form of staves from 1 inch to 3 inches in thickness, and thus the best of the log is utilized, and the inspection of the staves is an easy matter both during construction and thereafter. The steel or iron bands can be properly inspected during manufacture. and their placement properly inspected. So that there is no other character of pipe, whose quality can be better known and observed than wood pipe.
Forms of Wood Stave Pipe.
There are two distinct forms of wood stave pipe in common use. One is termed “continuous,” and the other “machine made.” Both are built of the same character of wood, and the staves are of equal thickness for like pressures. Those built into “continuous” pipe are made of uniform thickness throughout their lengths, with a head on one longitudinal edge and with a saw kerf at each transverse edge into which a metal plate is inserted to make a watertight joint. The bead on the longitudinal edge serves to make a watertight joint by being squeezed into the face of its neighboring stave when the iron bands surrounding the pipe are cinched up. The staves are made in unequal lengths to enable joints to be broken in constructing the pipe. The staves are held together by round iron or steel bands of such diameters and spacing as will retain the pressures required. Each end of the bands passing through a malleable iron shoe and having a thread to which a nut is fitted. Thus the staves can he point in the longitudinal joints, these leaks can occur unless it oozes through the grain of the wood. This form of wood pipe is built in the trench, and from 16 inches to any diameter required, but more commonly used for pipes over 24 inches in diameter. It has one special feature well worth noting, that if the pipe leaks at any point in the longitudinal joints, these leaks can be easily stopped by cinching up the bands near the leaks, or if some defect shows up in the pipe line a few years after building, sections can be easily removed and replaced, by substituting new staves or new bands. The staves built into “machine made” wood pipe have two beads upon one longitudinal edge and two corresponding grooves in the other longitudinal edge. The Extract from a paper by T. Chalkley Hatton, C. E. read at the Rochester meeting of the American Waterworks Association. beads are a little larger than the grooves, and when cinched together the bead crushes into the groove, thus insuring its being totally filled and made water tight. At one end there is a tenon cut 1 inches long, where the staves are one-half the thickness of balance of the walls of the pipe. On the other end there is a chamber cut 4 inches deep. The tenon is smaller in diameter at the end than at the shoulder, and when driven into the chamber makes a watertight joint, even though the two shoulders are not in perfect contact. The staves are cut radially to correspond with the diameter of the pipe, and are held together by a steel band, steel wire or copper clad wire. This band or wire is wound spirally upon the pipe by a machine. The high tension produced by the machine squeezes the beads into the grooves making a longitudinal joint that cannot leak so long as the elastic limit of the bands is not overcome. Where steel is used for banding the pipe it is run through a bath of warm asphalt, which adheres to its surface, thus protecting it from any water which might ooze through the grains of the wood. After the pipe is wound, and the tenon and chamber cut. it is rolled in a bath of hot asphalt which adheres to the outside of the steel and wood protecting them from outside oxidizing agents. It is then rolled in a bed of saw dust. This saw dust enters into the asphalt and forms a protection for it in shipment and handling. “Machine made” wood pipe is made in lengths from 5 to 12 feet and shipped to the work ready to be laid. They are laid by driving one piece into another until the two shoulders are in contact, or nearly so. No skilled labor is required; the inspector standing on top of the trench can readily observe whether the pipe has been driven home by the observing of the two shoulders. This form of pipe is made for diameters from 3 inches to 36 inches. Either form can be laid around curves of from 90 to 200 feet radii, according to the diameter of the pipe.
One of the usual questions asked is “what pressure can wood stave pipe safely withstand?” The proper reply to this is that the tensile strength of the material composing the bands represents the pressure the pipe will stand. Wood pipes are made to withstand pressures up to 200 pounds to the square inch, so far as the writer knows. The more the pressure under which the pipes are subjected the more steel or wire required to band them together. As the tensile strength and elastic limit of iron and steel are well known, it becomes a simple matter of computation to determine the gauge and spacing of the bands to make a wood pipe, which will withstand any pressure up to 200 pounds. Beyond this pressure it is likely the water would waste through the pores of the wood so that a higher pressure would not be economical or practicable. The writer has experimented with wood pipe up to a direct pumping pressure of 300 pounds, without fracturing the pipe. This experiment was made to ascertain what a pipe-built for pressures up to 100 pounds would do if it was subjected to a water hammer equal to three times the pressure. At 250 pounds the water oozed through the walls of the pipe. At 300 pounds it spurted in small streams at a few of the longitudinal joints, with a few leaks at the transverse joints. The pressure was suddenly removed to nothing, and gradually brought up to 100 pounds, with the result that the leaks stopped. This showed that, while the steel bands had been stretched, the elastic limit had not been overcome, and the pipe would, under such conditions as frequently exist in a long pipe line, safely withstand a wide range of pressures suddenly applied. Pressures from 100 to 150 pounds are common in machine made wood pipe, while continuous pipe of large diameter is successfully operating under pressures from 80 to 130 pounds It is not the writer’s purpose to advertise any particular manufacture of wood stave pipe, of the materials entering into their manufacture, and he therefore hesitates to name the many pipe lines, both continuous and machine made, with which he is somewhat familiar either as an observer or as designing and consulting engineer Assuming that wood stave pipe is laid where it will be constantly subjected to water pressure, the life of such is entirely dependent upon the life of the material with which it is banded. While the life is somewhat problematical, there are well known illustrations where steel banded pipe has been in continuous operation for 50 years without apparent deterioration. While the writer has industriously made inquiries wherever such might be expected to give reliable information. he has failed to learn of a single case where steel bands have given way; on machine made pipe. The engineer who designs a continuous wood stave pipe provides for at least a factor of safety of 3 in determining the size and spacing of his hands. The manufacture of machine made pipe provides for an equal factor of safety. Now, when steel or iron corrodes, it does so by pitting, and thus it is reasonable to assume that two-thirds of the crosssection of the steel can oxidize before the band will fail under ordinary conditions From the writer s observation, sheet steel, such as composes the bands of machine made wood pipe, pits in irregular spots, and never on a straight line, thus the band may be two-thirds gone before the pipe will fail. Where oxidizing agents are known to exist, such as in salt marshes, through salt water or sulphur deposits, the pipe should be banded together with copper clad steel wire This copper clad wire is cheaper than solid copper wire. It has an elastic limit of about 50,000 pounds per square inch, a tensile strength of from 90,000 to 100,000 pounds, and a coefficient of expansion less than two-thirds that of copper. Thus it becomes a product equal in strength with the steel and far better than copper.
So far as the writer’s knowledge goes, there have been very few well conducted observations made ot the leakage from wood pipe lines. From general observations made by the writer of lines in operation, no leaks of any significance have been apparent. Mr. Campbell, however, conducted careful observations on his lines, and states that after two years, there was no material leakage in the ten miles of 10-inch and 16-inch wood pipeline between the source of supply and the reservoir, while pipe was working under a maximum pressure of 130 pounds. That in the 12.6 miles of 11-inch and 12-inch pipe lines below the reservoir. and subjected to a less pressure, the 11-inch line leaked 17.046 gallons per mile, and the 12 inch about 3,702 gallons per mile. Along the railway, when the maximum pressure was 130 pounds, the 11-inch pipe leaked 120 gallons per mile, and the 8 1/2-inch and 7 1/2-inch pipe leaked 208 gallons per mile. It occurs to the writer’s mind that if there were 103.4 miles of wood pipe in this installation wherein the maximum leakage was 208 gallons petmile, and 8.0 miles wherein the leakage amounted to 17,040 gallons per mile, there must have been some defective joints or pipes in the latter section which needed looking after; that if 90 per cent, of the whole line was practically watertight, the other 10 per cent, could easily be made so. However, from the result of the careful observations made by Mr. Campbell, it seems reasonable to assume that wood pipe, properly made and laid, can be made watertight under a pressure of at least 130 pounds There are many contractors who make a specialty of installing continuous wood stave pipe, and there are several manufacturers of machine made wood pipe in the United States, prominent among whom may be mentioned the Washington Pipe and Foundry Company, on the Pacific slope; the Eastern Manufacturing Company and A, Wyckoff & Son Company, of Elmira, N. Y.; Smith & Son, of Bay City, Mich., and A. Wyckoff & Son Company, of Alexandria. La. To those who are interested in securing detailed information upon wood pipe the writer would refer them to the above named manufacturers.