INCRUSTATIONS IN WATER MAINS. WELLINGTON WATER SUPPLY.

Progress, Volume II, Issue 8, 1 June 1907, Page 298

INCRUSTATIONS IN WATER MAINS. WELLINGTON WATER SUPPLY.

By Thomas Ward, H M Inst C.E. ; Member of f the British Association of Waterworks [ Engineers.

The break in the Wainui-o-mata pipes across the Hutt River afforded an opportunity of inspection. Incrustations were numerous throughout the entire length viewed from the end pier that was standing in the stream. Diagram marked No. 1 drawn to scale correctly shows how the water-way is obstructed. Measurements showed the greatest depth of an incrustation to be two inches, and, as they were thickly studded all round the pipe, it will be well within the truth to put down the loss of capacity from 15 to 20°^. This subject is engaging the attention of water engineers in England : and it is being recognised that no water supply scheme can be considered to be complete which does not make adequate provision, by the insertion of hatch boxes and scour pipes along the line of mains, for their periodical scraping and the removal of the mud, filth, and corrosions. It was generally thought that if pipes, both

inside and out, are property coated with Dr. Angus Smith's well known preparation it will effectually prevent corrosion. This, however, is not borne out by experience. The 24 inch pipes from Wainui-o-mata were all coated with this preparation, and the result is clearly seen on inspection of diagram No. 1. With certain waters, pipes would corrode whether coated or not. Watei obtained from upland surfaces is very liable to corrode pipes, while that obtained from wells is not. Pipes may also be well or ill covered with the protecting coat, and in ordinary pipes an engineer is entirely at the mercy of the manufacturer. Cast iron pipes are less liable to this defect than wrought iron ones, and cases have occurred where a wrought iron service pipe would not last 18 months before it was completely blocked up and no water could pass at all. Not only is the scraping of pipes necessary for the removal of adhesions, but for the purpose of seeing that no foreign substances get into them. Pieces of wood, macadam, and even rabbits have been found lodged therein ; also pieces of bone, brick-bats, etc., and a common cause of obstruction is in the overleading of joints, when lead finds its way inside, in large quanti-

titb and lcinains there for many years until the pipes are cut or taken up for some other purpose. At Richmond in Surrey, when the pipes were taken up belonging to a London Water Company a whole brick, a large square piece of flint and an inkstand were found rolling about in a pipe which supplied the water for watering the streets in a very large district. In the same place a 3 -inch pipe on being taken up was found to contain a large leg bone of beef, and the water had had to

pass through the hollow of the bone ! The result was that what was supposed to be an 8 inch main or a 6-inch main proved, from the obstruction at one point, to be perhaps only a 4-inch or even a 3-inch main. Cases have occurred where a service had been stopped most mysteriously, and had become free again, simply through a plank floating in front of the service and afterwards getting away clear ! Although the coating of pipes is not an absolute preventive, too much stress cannot be laid upon their proper coating, as the character of the deposit is very different from that of a pipe uncoated. It should not be overlooked that it is not corrosion alone which forms the carbuncles. Analysis shows that theie is both corrosion, and also the deposition of solid matter, from the water. If the carbuncle is taken off carefully, especially in the case of coated pipes, it will be found that the area of corrosion is very small indeed ; sometimes not larger than a pin's head and consequently easily removed. This is not the case in pipes which are uncoated ; the carbuncles being very hard to remove. In time, however, those formed in a coated pipe will coalesce, and it will be then in the same condition as if it had never been coated. A most interesting description of " The internal Corrosion of Cast Iron Pipes " is given m the paper by Mr M. B. Jamieson, M.1.C.E.; of Aberdeen, printed m volume 65, pages 323-336, in the minutes of the proceedings of the Institution of Civil Engineers in 1881. He shows in this paper that the carbun-

cles round a pipe coated with asphalt usually have a cavity m the under surface, being attached by their edges only ; caused probably by the blistering of the asphalt coating through the collection of air and other gases, thereby preventing the central portion of the carbuncle from touching the iron. He also

shows that the amount of corrosion is proportional to the volume of water passing along a pipe and the commotion existing therein. For example, at the junction with a trunk main, the pipes, where water was constantly flowing, were found to be nearly filled with rust; whereas the hydrant branches through which the water seldom flowed, and at the dead end of the main, where the flow was practically nil. the pipes were comparatively clean, free from corrosion or incrustation, although no doubt full of sediment and deposit. An interesting paper on " The action of water upon metal pipes, and the injurious effect of lead pipes upon water, "appeared in volume 85, page 472 of the minutes of proceedings of Civil Engineers, which is as follows :—: — " Widely different opinions have been published on these subjects by experts and even the official regulations with reference to the employment of various kinds of water pipes are greatly at variance. Thus in Germany, Switzerland, and in other places, galvanized iron piping is used without hesitation, while by government decree, the use of pipes of this kind is forbidden in Austria, and in one instance their employment in Saxony was objected to. Some recent investigations of Mr. Lory, of Grenoble, have shown that water containing organic matter in solution attacks iron pipes very speedily, and after many analyses of water conveyed to Grenoble from difierent sources in iron pipes, and also of water known to have attacked pipes and to have led to the formation of scabs or carbuncles of oxide of iron in other places, Mr. Lory had invariably found that the scabs — consisting mainly of hydrated oxide of iron — contained from 5 to 10

per cent, of organic matter. He has been led, therefore, to conclude that the destructive action upon such pipes is due in the first instance to substances of organic origin. This may to some extent explain the reason why in some places cast-iron pipes remain quite free from corrosion, whereas in other cases, even after six months, as happened at Grenoble, they become covered with rust carbuncles." The influence of soft water on lead pipes is considered in the light of a recent report of Dr. White, Medical Officer of Health at Sheffield, and some experiments conducted last year at the Hygienic Institute of Pesth, are quoted in which the water passing through a pipe 39 metres in length, was found to contain from 0.085 to 4.7 milligrams per litre of lead : the latter high percentage only occurred, it is true, after the water had remained in contact with the lead for one month. In view of the destructive action of some kinds of water on cast-iron pipes, information is sought concerning the protection afforded by covering the pipes internally with a coating of magnetic oxide, and the result of any experiments bearing upon this question. The evil effects of corrosion are : Ist, the loss of water carrying space ; secondly, loss of pressure. The space occupied by the carbuncles, etc., is found by filling the pipe full of water, noting the quantity, and

deducting it from what the pipe should contain when clean, the remainder giving the loss. This naturally affects injuriously the discharge. The following Table, No. 1 taken from volume 65, page 333, minutes of proceedings of the Institute, gives the percentage of space occupied by rust, and Table 2 gives the discharge from corroded pipes. This is very marked in small pipes of 3 or 4 inches. The following instance is given on pages 333 and 334, volume 65. "The water in a corroded pipe, three inches in diameter,

registered by gauge a head of 77 feet, and through a two inch outlet, the discharge was only 16 gallons per minute ; while after cleaning, the pipe registered a head of 82 feet, and a discharge of 150 gallons per minute or nearly 9^ times as much." It is now recognised as a mistake to lay down 3-inch mains. The American practice is not to lay down any mains smaller than six inches.

The strength of corroded pipes which have been laid 20 years is a little more than one half that of new pipes, as tested by breaking weight applied at the centre. This is no doubt the cause of many bursts in mains that have been laid for many years, which, on being taken up or bared where a leakage is located, often snap in pieces. Probably more than three-fourths of the total waste of

water is due to defective service pipes, unsuspected by an inspector because it may occur on a disused pipe. In an article entitled " Some causes of failure in service mains and pipes," Mr. John Shaw, C.E., says that the same water will have no effect on one particular part of the main while it attacks another : and further that " The ordinary rusting of iron depends on something more than exposure to an atmosphere containing oxygen. The presence of other substances, notably ammonia and carbonic acid gas, seems also necessary and under certain circumstances, this action is intensified. Iron placed in warm water in a warm position, and carbonic acid gas introduced, is speedily attacked ; so that a small quantity of carbonic acid gas will rust any amount of iron. This process goes on in water mains which leave reservoirs, charged with carbonic acid and free oxygen, travelling swiftly under pressure. When the pressure is reduced the gases rise to the top of the main and are attracted by it ; or, it may be the pipes are laid shallow, so in summer the water is heated and the gases being less soluble in hot than in cold water, they are given off and similarly attracted and the conversion of the iron of the main into ferrous carbonate is commenced. Coating with Angus Smith's solution does not always protect the main ; this composition being soluble with some waters when they attain a temperature over 55° F." These remarks open up the interesting question, viz., whether the mains (the incrustations of which are here shown) on the bridge over the Hutt River are more corroded than those laid beneath the surface of the ground, as during the hot weather there is no doubt the pipes get very much heated on the bridges. Another interesting enquiry would be to ascertain whether the pipes supplied from the Karori Reservoir are more, or less, corroded than those from Wainui-o-mata. The next article on this subject will touch on what has been done in the past in England in the matter of scraping of the pipes, and describing somewhat fully the course followed at Kendal.

The Hon Mrs Assheton Harbord, who within three days, has twice crossed the Channel in a balloon (says "MAP") is a colonial, and hails from Melbourne, Australia. She was a Mrs Arthur Blackwood, and is one of the rare examples of a nch Australian widow who has found a husband m the " Cold Country," as the Australians are pleased to designate Fngland. She married Captain Assheton Harbord two years ago, so is a sister-m-law to Lord Suffield, who, in his younger days, almost held a record for fearlessness. Mrs Harboid upholds all the traditions of the Suffield family, and never seems to be thoroughly happy in her pleasures unless they are accompanied by risk. After having tasted the exhilarations of the air, the earth retains very little attraction for hei The fascination of being above the clouds has made an indelible impiession on the mind of the plucky Australian. " I never saw such a magnificent scene as the sunrise," she says. "It was a fascinating spectacle, which I shall never forget " The time occupied in crossing the Channel on the first occasion was 55 mm. The balloon trailed through the water, and passed through snow and hail storms, but the plucky occupant of the car showed no sign of fear. Mrs Harboid's example will probably be largely followed during the summer

There still lives in London one, Thomas Atkinson, who helped to build the Rocket George Stevenson's woild-iamed locomotive He was born in Northumberland in June 1811, being now 96 years old At the age of thirteen he began as an apprentice to George Stevenson at his workshops. In IS3I he joined the Newcastle branch of the Old Mechanics, and so has been a trade unionist for over "to years He is known as the " father" of the Amalgamated Society of Engineers, and still has in his possession the indentures signed by George Stevenson. The Morning Leader says that a big benefit is shortly to be given to this time-worn " veteran of industry."

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