XVII.

METHODS OF INSULATING UNDERGROUND SYSTEMS

OF STEAM PIPING.

(BY R. C. CARPENTER, ITHACA, N. Y.)

(Member of the Society.)

The following paper states in a concise way the results of the writer's experience with several methods of protecting systems of steam piping which are laid underground. The paper does not pretend to be a compendium of all the methods which have been used for this purpose, but simply contains a description of those which have come under the writer's observation.

There are, in a general way, two methods of insulating pipes, when used to convey steam long distances underground; these may be specified as the tunnel system and the trench system.

In the tunnel system a conduit lined with brick or masonry of sufficient size for the pipes and for a person to enter for examination or repairs is constructed. In this the pipes are carried on suitable hangers, and then wrapped with some insulating substances or covering. A sufficient number of expansion joints or equivalents are used to prevent injury to the line by expansion due to heating and cooling. While this system possesses many advantages over the trench system and is usually to be preferred, its cost is so great as to be in many cases simply prohibitive and some method of trench construction is necessary.

The first system of underground steam piping which the writer saw constructed was put in about 1879. This system was about one-half of a mile in length and was intended to convey high pressure steam for operating a steam pump which was located at about that distance from the boiler. The system was constructed in a very crude manner, very little attention being paid either to the effects of expansion or to protecting the pipe from surface water from the soil. In constructing the line a deep trench was dug, the steam pipe was screwed together, and joints of wooden pump log was placed over the steam pipe for insulation. The trench was then back filled.

The line was used for the purpose intended for three or four

years, but it was not at any time considered a success. The surface water at times covered the pipe, so that large masses of steam apepared at the man-hole; several breaks were also caused by expansion and contraction. After three or four years of use expansion joints were put into the pipe and a tile drain was laid by its side to remove the surface water. It was then used successfully for some years afterwards, in fact as long as it was needed. The next system was constructed in 1880 under the general directions of the writer. This system had a total length, including

Fig. 30.-PIPE WITH WOODEN TUBE INSULATION.

branches, of about one mile, and consisted of two independent lines of trenches, each containing main steam and return pipe. This system was used to convey the steam for heating purposes írom a central boiler plant to a number of buildings belonging to the same public institution. The method of construction was very similar to that used at that time for conveying steam from central boiler plants through the streets of a city for heating purposes. For these special lines very careful surveys were made, and the line was laid with a continual descent from the buildings to be heated to the boiler house. After the trench was constructed a drain of 6-inch tile, such as is used for farm drainage was constructed, so as to be about six inches lower than the steam pipe lines. The

A.

B

STEAM MAIN. B. RETURN MAIN. C. DRAIN.

Fig. 31.-SECTION OF PIPE LINE.

steam pipe lines were insulated from heat loss by a wooden tube with a shell four inches in thickness. The diameter of the tube was two inches greater than that of the pipe and the pipe was held in a central position by iron collars. The tube joints were made by driving a tenon on one end of the pipe into a mortise on the other end of the adjacent pipe.

The wooden tubes which were used for this purpose were made

by special machinery out of large pine logs. The tubes were eight feet in length. The logs from which they were made were first placed in a large lathe and the external circumference shaved off by a knife the full length of the pipe. This operation required a great deal of power and sometimes the logs broke during the process of turning, in which case they were thrown with great force against the sides of the building. After the logs were turned to the proper size they were then bored, the auger for this purpose being a tube which cut away enough wood only to make clearance sufficient for its own motion. The core which was cut out from the interior log could be bored in a similar way with a smaller auger and thus form smaller pipes without loss of timber. After the pipes had been turned and bored they were then placed in a lathe and strongly wound with a hoop-iron, arranged in a spiral form. This added very much to the bursting strength. They were then rolled in hot tar and covered with a coating of saw-dust. Before the pipes, were finished the ends were bored out for a short distance to form the mortise joint, and a short tube, which was allowed to project about six inches was placed in one end to form the tenon. These pipes made in this way would withstand considerable water pressure, and many successful systems of water works have such pipes in use.

In the system described double expansion joints were placed at distances of 240 feet and man-holes were left at these points for inspection and for the repair of the joints.

The expansion joint used was somewhat heavier than that ordinarily sold and was provided with an inside lug, so that under no condition could the parts of the joint pull entirely apart.

The wooden logs which were used for insulating purposes were very badly charred in five years from the date of laying and contained a great many season checks, so that water could freely run from the soil onto the pipes. This reduced the efficiency of the line in a great measure.

This line was anchored in each man-hole midway between the two expansion joints, and although ́steam was turned off every night at ten o'clock and on again every morning at six, no leaks whatever were ever traceable to this cause.

This line is still in use, and for the first ten years after its construction did not require any repairs or any expenditures whatever, except such as related to the annual inspection and repacking of the expansion joints.

The system next described was constructed in 1885 and in this both main steam and return pipe were used, the return pipe being

laid in the center of the main steam, so that the pipes were concentric. The outer pipe was wrapped with asbestos and over the entire system a tube of sewer pipe was laid. The lengths of sewer pipe were split longitudinally, the upper half being put in place after the steam pipes were in position, the joints being protected by concrete.

This system has proved very successful in use and is still in service. The expense of running the return pipe in the center of the main steam is considerable and while it tends to prevent all heat losses from the return is very difficult to construct. With this system the water would be received into the boiler at the temperature of the steam, and the work of the boiler would be simply to cvaporate water into steam of the same temperature. The heat used in the building would be essentially that which is given out in the condensation of steam without change in temperature, the entire losses being those due to radiation from the steam main. Except for the difficulties of construction the system is perfect.

A system of underground steam piping was constructed by the writer in 1878, in which both main and return pipes were laid in a wooden box covered with concrete. The pipes were supported on suitable hangers and provided with proper expansion joints and were loosely wrapped in coverings of sheet asbestos and hair-felt. A drain was laid underneath the trench to carry away the soil water. The general method of construction is shown in Fig. 32 and was as follows: After excavating the trench a layer of concrete four inches in thickness was then spread over the bottom and was made about six inches wider than the box to contain the pipes. The box, which was made of pine plank, was slipped in place without top and in sections. The pipe hangers were then put in place and the steam and return pipes laid. These pipes were then tested for leaks, then wrapped with the covering, as described. The top of the box was then put in place and the whole box surrounded on top and sides with a layer of concrete four inches in thickness.

This system has proved successful and has superior insulating powers to any of those previously described. In the pipe systems protected with the wood pipe, sufficient heat escapes in practice to thaw any snow which falls on top of the ground. Our experience with the construction described, through several severe winters has shown that the ground is not thawed nor is the snow melted; this would indicate that the heat loss is quite small, as the snow is melted with a very slight escape of heat.

The cost of the latter construction is much less than that of the wood pipe system of insulation.

The writer believes that an improvement in the system described could be made by supporting the pipes by hangers resting on the concrete; this would add much to its permanency. Wood used in underground construction of this character rots very soon, and if it is used in such a manner as to form an essential part of the support of the pipe line, its decay may affect the alignment of the whole system and in that way interfere with the economic operation. Wood is, however, a very excellent insulating substance and would no doubt be useful for such purposes for a long time after its power of supporting the pipe had been lessened by decay or by carbonization.

The buildings of Cornell University were heated with steam, which passes through a system of underground piping, in 1888

In the system first used the boilers were situated in a building near the highest part of the campus and but little of the return water could flow back by gravity. Consequently no attempt was made to return the water of condensation, except from the group of buildings immediately surrounding the boilers. In most of the buildings the return water was passed through a large cooling coil placed in a ventilating shaft and as much heat as possible was extracted in warming the air used in ventilation. In this system. the expansion of the pipe lines was taken up by variators constructed by the Holley Mfg. Co. In the variator one end of the pipe was supported by a movable diaphragm and the expansion and contraction of the pipe was compensated for by motion of this diaphragm. These were placed at intervals of about 50 feet along