Protecting Exposed Water Pipe Against Damage
Pipes on Railway and Waterway Bridges—Defects in Wooden Coverings —Sheet Metal and Felt Box Used—Protection of Hydrants and Valves
MANY pipes and mains in the distribution system of a municipality must of necessity be laid in exposed position or where they are liable to fracture, freezing or other vexatious troubles. This is especially true where lines cross bridges over railroads or waterways. The following paper gives some valuable hints to superintendents as regards problems of this nature:
The natural location for a water pipe is at a suitable depth underground, resting upon a bed of uniform resistance. There it is protected from frost, shock and vibration, from variation in atmospheric temperature, and if not disturbed, or the earth removed from under it and some rigid bearing substituted, it will render service for its natural life without unusual incident. Certain conditions, of course, expose it to corrosion, internal and external, also electrolysis; and a recent event reminds us of a very rare, but very serious danger, that of earthquake. Whether a pipe underground is more liable to damage from earthquake, than one overground is a question difficult to decide. Data on this subject, hereabouts at least, are scarce. Possibly in California they are able to speak with authority in the matter.
During the unusual sensation of the quake, there were two thoughts that occupied my mind almost simultaneously: one for my own personal safety and the other for the pipes in our system. I had a picture of a great many breaks occurring in different locations and in pipe lines of large and small diameter. I immediately called up our emergency headquarters and as I listened to the telephone connections being made without difficulty or delay, I felt somewhat relieved, and when I got my man and asked him if he had received any reports of broken mains and he answered that he had not, I felt doubly relieved. However, I was not entirely at rest until I learned that the pressures indicated by the high and low service gages were normal. The possibilities of a severe earthquake shock are quite disturbing to say the least, and provisions for meeting them from a water works standpoint should make an interesting and valuable study.
Pipes on Railroad and Waterway Bridges
To revert to the subject. Almost all cities are more or less intersected by railroads and water-ways. To afford means for foot and vehicular traffic these waterways and railroads are bridged over. The bridges serve in a great many cases to provide for the carriage of water and gas pipes, electric and telephone cables. In Boston there are many such pipe crossings. To be exact, 102 pipe lines are carried on bridges over railroads or water. They cross usually on one or the other side of the bridge, either under the foot-paths, between the foot-path and vehicle lane, or just outside the bridgeway proper, supported on arms or brackets attached to the bridge-structure. Where there are draws in the bridges, the pipe line is carried under the draw-way by means of an inverted siphon enclosed in masonry or wood.
In carrying a water pipe across a bridge, provision should be made to protect it from freezing and from the impact of wildly driven automobiles, tugs, lighters, etc. The liability to freeze varies according to several factors —the diameter of the pipe, the velocity of flow during the period when consumption is at its lowest, the exposure of the pipe to wind, the position of the pipe in relation to the sun, etc.
“Almost all cities are more or less intersected by railroads and water-ways. lo afford means for foot and vehicular traffic these water-ways and railroads are bridged over. The bridges serve in a great many cases to provide for the carriage of water pipes.”
For many years it was the practice of the Boston water works to enclose its exposed pipes in double wooden boxes. The inside box was square in shape, simply made and fitted close to the pipe. The outside box was sheathed and had a pitched root. If the box was exposed to the roadway a hard pine timber was placed outside as a fender.
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This type of box served the purpose for many years until the price of lumlter, paint and labor advanced, and the small boy become more destructive. It became more costly and difficult to keep the boxes in certain localities in repair. As soon as a slight opening was made in any part of the box, it was only a short time when the rest of it was ripped apart and the lumber stolen. They frequently caught fire and we found that where large pipes were enclosed over railroads that the blast from tbe locomotives loosened the flooring and then the interior of the box became filled with smoke and soot and cinders.
The soot lodged on the pipe and any water that leaked through the box would mix with the soot and form an acid that ate into the iron pipe, pitting it quite deeply and causing us some apprehension as to how long the pipe would last. The loosened floor boards fell upon the tracks and made more or less trouble, so it was decided to give the pipes ventilation and remove the boxing entirely from those directly exposed to the blast of locomotives.
We have watched them closely during cold spells, testing them by means of the air valves and so far have not noticed any signs of ice within, not even during the winter of 1917-18. These pipes range in size from 12″ to 42″. We attribute the freedom from ice to the constant movement of the water. Care has to be exercised to keep all valves open on both sides of the bridges. We have not removed all the wooden boxes as many of the pipes, large and small, still have that type of protection. It serves its purpose well in certain places, removed from locomotive gases, hot cinders and the small boy.
Sheet Metal and Felt Box Replaces Wooden
We are, however, replacing the wooden boxing where it is worn out. or where the pipe line is relaid, by a sheet metal cover over a coating of felt. We find this more durable and less bulky than the wooden box. It consists of a covering of felt three inches thick wrapped around the pipe. Over that is a layer of tar paper to keep the felt dry. The tar paper and felt are kept in place by copper wire. Over that is a galvanized sheet iron cover properly rolled to fit snugly over the felt. Wooden collars three inches deep and two inches wide are placed around the pipe at frequent intervals to support the metal cover.
The cover is screwed to the collars. Along the top is a sheet metal ridge about 1 1/2 inches high to discourage walking or sitting on the pipe. Where the pipe is exposed to vehicular traffic the usual 10 x 10 hard pine fender runs along outside. Where the pipe goes below tbe surface of the ground on each end of the bridge, the metal cover follows it for a few feet. To prevent corrosion and also to protect it from knocks of various kinds, a jacket of brick freely coated with cement is placed outside the sheet iron for a distance of about two feet above and three feet below the surface of the ground. Although galvanized, the sheet iron is painted with a priming coat of red lead followed by a coat of color, usually battleship gray.
Some Special Treatment for Unusual Cases
A recent special treatment of a pipe exposed to the cold was on Neponset Bridge where the pipe ran along under the sidewalk in a space about twenty inches deep, provided for gas and water. The bottom and sides of the pipe-way were of concrete and the top was an artificial stone walk reinforced with wire mesh. We filled the entire space twenty inches deep and about five feet wide with shavings. We have used shavings in several places and found them satisfactory.
We have also used granulated cork. Cork is especially good as it does not absorb moisture.
To provide protection from automobiles we plan as far as possible to lay the pipe in or under the sidewalk of the bridge, using the bridge girder as a fender. If it is necessary to expose the pipe to auto traffic we place a time outside and curve it around both ends of the pipe where it comes up from underground.
Pipes passing over water-ways are exposed to bumps from tugs, lighters, barges, etc. Piling and timbering may be so arranged in the form of fenders as to afford suitable protection.
Leaking of Pipe Joints
Joints are liable to leak due to vibration of the bridgestructure. This varies with the design and method of bridge construction and the kind of traffic passing over it.
A most frequent and serious trouble is settlement at the abutments. The pipe on the bridge structure does not settle but the pipe in the ground where it rises to mount the bridge has a tendency to settle and pull away from the abutment. As a rule, the approach to a bridge is a fill of loose gravel or sand and the vibration from bridge traffic overhead and railroad traffic underneath keeps the sand and gravel in a state of movement. It compacts or crawls and moving away from under the pipe causes the pipe to sag. The joints strain and sometimes blow out. Furthermore, there is an unbalanced pressure to contend with. To counteract all this, the inclined pipe between the upper and lower levels should be strapped together and anchored to the abutment. Concrete piers should be placed back of the curves and otherwise the pipe made as secure as possible. We have had some very serious leaks due to pipe-lines separating at bridge abutments.
Large Feed Lines Should not Cross Bridges
Because of their value and importance large feed lines should not be exposed to the risks of crossing bridges. In Boston we are carrying them under the railroads and water-ways by means of inverted steel siphons enclosed in concrete.
Steel may be considered as a better material than cast iron, to use in large lines crossing over bridges, as it is practically self-supporting. It is, however, more difficult to repair if damaged. On the other hand, cast iron resists corrosion from locomotive gases, moisture, etc. better than steel.
From my experience with pipes in Boston, I am inclined towards the following conclusions:
If practicable all pipes, large and small, should cross railroads and water-ways under and not over.
Method for Large Pipes over Bridges
If not practicable, or for some good reason, it is not desirable to pass under, the pipes, if of large diameter, should be made of steel, well supported and strapped, protected from impact with moving objects, coated to resist acid fumes and liquids, and a velocity of flow maintained within to prevent freezing. If of 12 inches or less in diameter, they may be made of steel or cast iron, properly supported, strapped at points of unbalanced pressures, covered with some non-conducting material, protected from shock or impact with moving objects, and a circulation of sufficient velocity maintained within them to prevent freezing.
There are places where it is impossible to give pipes a cover of more than two or three feet of earth or pavement. The situations I have in mind are where distribution mains and laterals pass over large conduits, sewers or subways.
An Excellent Insulating Compound
As a rule, the length of pipe thus exposed does not exceed 35 or 40 feet. In such cases we use with satisfactory results an insulating compound consisting of granulated cork mixed with hot pitch. The cold storage people use the same mixture around their brine pipes to keep them cold or more properly to prevent the brine from absorbing the heat of the ground.
A roughly made form is placed around the pipe, on the bottom and two sides, providing a space of about six inches all around, to be filled with the mixture. About six gallons of pitch are mixed with two bushels of medium sized granulated cork. Two kettles are used, one in which the pitch is melted and the other, in which the hot pitch is mixed with the cork. Pour from the melting kettle into the mixing kettle. Keep a slow fire under the mixing kettle. After mixing and while in a fluid state ladle out into the form and fill same until the pipe is completely covered. The compound will harden when cold.
The cold storage people place the mixture around our service pipes where they lie in proximity to their brine pipes. They do this at their own expense as we charge them for thawing should a service pipe freeze near one of their conduits.
It has served us to good purpose in several localities where our service pipes were laid shallow, upon rock, and covered with a loose stone back-fill. Winter after winter these pipes would freeze with provoking regularity until finally we enclosed them in boxes, 4″ x 4″ inside dimensions, filled with cork and pitch. Since then we have forgotten they exist.
The Protection of Hydrants
We have also used this compound to protect post hydrant pots where they set close to an area, or catch basin. With regard to the protection of hydrants, there are two dangers to guard against — frost and automobiles.
Frost, of course, comes first. As we all know the preventive of a frozen hydrant is to keep water out of the barrel. This is sometimes a difficult matter for various reasons. Sometimes the waste does not work. It may be clogged, or perhaps the operator does not sufficiently vent the hydrant after using. Sometimes the ground around the hydrant is saturated and will not take any more water. Sometimes the ground around the hydrant contains water to the extent that it enters through the waste and partially fills the hydrant barrel. Sometimes the valve leaks. Pebbles are caught in the closing and embedded in the leather or rubber packing thus preventing a tight shut-off. Sometimes because of a poor quality of rubber or leather, pieces of the same breakoff. Sometimes the stem becomes warped or strained, and so on.
It is an old story, but nevertheless true, that hydrant troubles are largely attributable to the mis-use and abuse of the hydrant. Originally a hydrant was an exclusively fire-fighting adjunct, now it is an appurtenance for public convenience. Tom, Dick and Harry use it for the most trivial purposes. It is used by boys to flood vacant lots for skating purposes. It is used by the owners of automobiles to wash their machines. One case I have in mind is where on a Sunday morning, no less than six or eight cars, mostly flivvers, were lined up waiting their turn at a hydrant to receive their weekly wash. Some one in the neighborhood had a reducing cap and a garden hose. As for the wrench, it was a Stillson. I have seen the eye of a pick used to turn the operating nut of a hydrant. I have seen a junk collector descend from his team and open a hydrant on the public highway, fill a pail and water his horse. I have been informed of a teamster who stopped along a main thoroughfare and opened a hydrant, filled his pail repeatedly and with a sponge washed his wagon and so on.
The Thawing of Frozen Hydrants
I cannot see why a hydrant is not just as much a pan of the Fire Department equipment as the hose, the pump, or the ladders, and should not be respected as such.
However, it is a condition we are up against and not a theory, and if water will get into hydrant barrels in cold weather, it is our work to remove it, if possible, before it turns to ice.
We might utilize the method we take to prevent freezing of our automobile radiators and use some nonfreezing compound like denatured alcohol, calcium chloride, kerosene, glycerine, etc. Certain queries with reference to the use of those substances enter our minds. How shall we confine it to the barrel? What is to prevent its running out through the waste? What effect will it have on the leather or rubber packing? What proportion shall we use, not knowing how much water will accumulate in the barrel?
There are some things we can do with a certainty of results however. If ground water backs into the hydrant we can connect the waste with a sewer. If there is no sewer nearby we can plug the waste hole and visit the hydrant frequently, test it for water or ice and remove either one or the other.
Use Rock Salt for Underground Hydrants
In Boston, we have a number of underground hydrants, called Lowrys. To use one a cover is removed and a chuck screwed on the barrel. The top of the barrel is open and is a little below the level of the street. Surface water frequently flows into it, especially during a thaw. This water will then freeze and the hydrant cannot be opened by the firemen. Our hydrant men prevent the freezing in many cases by dropping a handful of rock salt into the barrel.
Whether that method would function successfully in a post hydrant is a question worth considering. The reason for using it in our lowrys and not in our posts is that we can watch its action in the Lowry barrel, but not in the Post. Of course, the salt is efficacious only where there is little water in the bottom of the barrel. If the barrel should fill up, the handful of salt would either dissolve or remain at the bottom and the water would freeze at the top of the barrel.
There is really no panacea for frozen hydrants. The one dependable method is frequent inspection — eternal vigilance; keeping in touch with the Fire Department and having some arrangement with the Sewer and Street Cleaning Departments to the end that immediately after the use of a hydrant it will be examined and put in condition for use. The aid of the Police should also be enlisted to the extent of their reporting the use of any hydrant that comes under their observation.
The Automobile Menace to Hydrants
As for protection of hydrants from automobiles, nothing can be done except to relocate those that are placed in obviously exposed locations. In extremely dangerous situations, posts may be set to act as buffers on either side of or in front of the hydrant. These posts may be made of old iron pipe filled with concrete and painted black and white or yellow.
It may readily be understood that there cannot be too many of these buffers placed throughout the city. There would be objection to them as obstructions and as being unsightly.
It is impossible to foretell where and when the next hydrant will be struck and broken by an automobile.
The Care of Valves
Underground valves do not as a rule, suffer from frost or other danger. Their position underground in brick or concrete vaults, serves as a protection. Occasionally if exposed in an excavation during cold weather, it is necessary to cover them. Manure, straw, salt, hay, felt or heavy bogging will afford protection. It is quite necessary to keep valve boxes clear of mud and water especially so when the boxes are small. If the mud or water remains in the boxes during cold weather it freezes and the operation of the valve is delayed. Sometimes this is a serious matter.
Another trouble that has developed in recent years as a by-product of the use of cement grout to fill the joints of granite block pavement is the seeping down through the valve box cover of the liquid grout, filling or partially filling the box and later setting into a rock hard substance that required drills to break up and remove. As a prevention, we fill the spaces in the cover through which the grout may flow, with paper or jute or clay or sand. A little attention to this matter during the pouring of the grout will save trouble later on.
The Laying and Up-keep of Services
With regard to Service Pipes, care should he exercised to see that they are laid at proper depth with reference to frost and where the Department lays only to the property line the owner should be made to continue it on his property with the same amount of cover into his cellar.
There is a tendency among builders to dig shallow trenches inside the property line. To avoid removal or rock, they will sometimes lay the pipe with only a foot or two of cover. This, of course, is a starting point for a freeze that will run out towards the main in the street and before water is made to flow in the pipe, the Water Service will have performed a job of thawing. It is often a difficult matter to convince the owner that the ice began to form on his property.
The foregoing is only a bare outline of the measures to he taken in self-defence against some of the accidents and untoward incidents due to the exposed conditions of water pipes and their appurtenances.
Possibly it may stimulate a little constructive thought that will develop into more efficient and economical ways and means of treating the conditions mentioned.
(Excerpts from paper read before the March Meeting of the New England Water Works Association.)
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