CEMENT-LINED PIPES

Wairarapa Times-Age, 22 April 1940, Page 2

CEMENT-LINED PIPES

IMPROVING MASTERTON’S WATER SUPPLY PARTICULARS OF PROPOSALS. REMOVAL OF INCRUSTATION. Further information is given below concerning the proposal to concreteline Masterton's water mains. It is generally recognised that a thin coating of cement placed on iron surfaces and exposed to ordinary atmospheric conditions does not protect the iron from corrosion in the same manner as it does when submerged in water. The concrete-lined pipe is therefore -~~- placed under ideal conditions, immediately it is put into use; both from the point of curing (submerging in water being considered the most effective method of curing) and the future life of the pipe. Air being excluded from it, there is no chance of any corrosion taking place. What does take place is this The hydrated Portland cement gives up a calcium hydroxide very rapidly when exposed to water; and produces a solution against the iron surface of the cement-lined pipe that is approximately saturated with lime water when the coating is first applied. The alkalinity is high enough to stop erosion, in a very short time. The surface of the concrete exposed to the air or water does not long remain at its high alkali concentration. If it is exposed to the air, which ia the case for all cement-linings before the pipes are placed into service, some of the high calcium compounds will be carbonated. By carbonated, it is meant that the calcium has been released from its bond with the silicia or alumina and has united carbon droxide. The final product of nearly all calcium in cement exposed to the air, is calcium carbonate; with possibly some lowcalcium compound of silica or alumina. It is claimed that "interior bleeding” caused by intense scraping of the incrusted pipes, is annealed by the application of cement under the process recommended—the Tate process. The most common practice for con-, crete-lining of pipes at present in use is the centrifugal process. The process produces a’ dense film of mortar, and is equally effective; but it has the disadvantage that it is confined to the lining of straight pipes, and that the pipes have to be lifted and re-laid, which naturally increases the cost of treatment considerably. QUESTIONS AND ANSWERS.

7 Q. —Have there been any failures with the cement-lined pipes'? A. —I have no knowledge of any occurring anywhere in New Zealand. Australia or elsewhere: entire satisfaction being expressed in all cases. 8. Q —Will the lining of pipes which are structurally defective make them like new again? A—Definitely no; while it might prolong the life of the pipe for a year or two. the cost involved would not be justified; such a proposal would not be economically sound; replacement with new cement-lined pipes being the solu- ) tion of this problem. 9. Q. —Are the pipe lines proposed to be lined in sufficiently good order to justify lining? A. —Yes. The pipe lines in question are in structurally good order; practically the whole of the defects in the 12in. and 18-inch spiral steel pipes are due to rivets blowing out: and lining will put an end to this trouble. 10. Q—How long would consumers drawing their supply off these mains be without water? A. —Barring accidents; only 24 hours. 11. Q. —Why not tear up the lOin. and 12-inch mains and put. in one 24in. or 30inch new pipe line instead of bothering with cement lining and tackle the major scheme now, even if it is estimated to cost approximately £60,000.

O—Firstly, the cost of lining is only (approx.) one-third of the cost of replacing the mainc with unlined pipes of the same sizes. Secondly, with steadily increasing prices of waterworks materials (including pipes) due to war conditions, it is impossible to give anything like a firm estimate. Thirdly, the indications are that the Loans Board would not consent to such a proposal in adverse times such as we are passing through at present. 12. Q. —Does the present proposal form part of the major scheme? A. —Definitely yes; so that nothing is lost by proceeding with the present lining proposal: on the contrary an improvement in the flow will assuredly result. 13. Q. —Is it proposed to extend the work of concrete-lining in the future? A—Yes. It is proposed to ask the council to provide a sum annually for the extension of this work; the smaller and most heavily incrusted mains to be done first. (To be continued.)