Samples Needed For Water-Pipe Survey

Press, Volume C, Issue 29616, 12 September 1961, Page 19

Samples Needed For Water-Pipe Survey

Samples of copper, brass, 1 bronze, or any other copper < ahoy which have been used in water-supply systems are s urgently required by the < Dominion Laboratory. < “The laboratory is survey- < ing the corrosion of copper < by various New Zealand 1 waters, but is hampered ’ greatly by lack of material,” 1 the director (Mr I. K. Walker) 1 said to a statement to “The 1 Press” yesterday. < Christchurch was one of i the areas from which par- 1 ticularly few samples had < been received, he added, i Severe corrosion had been i reported from Ashburton and i some other Canterbury towns. “It does not matter whether the samples have failed, or whether they are still sound ' and have been incidentally i taken out of service for some 1 reason,” said Mr Walker. 1 “Certain information is required. however, if we are to get maximum help from the sample®. We wish to know the address where the pipe was installed: its approximate date of withdrawal from service, -and how tong it was in service; and the type of service-location in the building, whether used for hot or cold water, and whether continuously or only intermittently wet. “All correspondence will be acknowledged, and < all samples reported on.” Small samples should be posted to the Director, Dominion Laboratory, Private Bag. Petone, and large {samples railed c.o.d. Carbon Film “Sometimes, isolated in- ■ stances of green staining of baths and basins, blue water, or premature failure (after 5 to 15 years’ service) of . capper cold-water pipe occur . in districts generally free from such troubles, and ■ where the water may be considered ‘unaggressive,’ ”, said Mr Walker. ’ “Such cases investigated ; by the Dominion Laboratory have been shown to be asso- ■ dated with very thin carbon i films present on the internal surfaces of copper tubes. These films are formed on a small proportion of tubes during manufacture. Their influence on copper water pipe corrosion was first discovered by a British worker, Dr. H. S. Campbell. “The capper metal is completely normal in these defective tubes, only the presence of a carbon film on the , inside service making them so prone to corrosion. I “Carbon films promote cor- ’ rosion partly because car- ’ bon is electrochemically more ‘noble’ than copper. • Galvanic action is therefore i set up at any cracks in the i film, and copper metal i® disi solved. After some time the 5 whole film is undermined, : and eventually pinhole leaks , appear in the tube. Blue i water is caused by unusually : large concentrations of cop- ■ per resulting from rapid cor--5 rosion. ! “At least some British ! manufacturers are now offering copper tube made to a ! British standard specification s and guaranteed free of car- ■ bon film. r “In ‘unaggressive’ waters, t normal copper tube corrodes 1 very slowly (say one teni thousandth of an inch a r year). These small corrosion 1 rates vary for different ‘un- : aggressive’ waters, and it is f hoped that the project will t yield information enabling water composition and cor- > rosion rate to be correlated. - With such information, sert vice lives could be predicted. ‘ Faulty Water _ “In some New, Zealand ‘ waters all copper tube, both " normal and defective, corrodes rapidly, and in such e cases the water is at fault. I Usually, but not always, such 5 supplies are drawn from . artesian bores or wells, the ? water being acid and containing carbon dioxide gas in solution. The Dominion

Laboratory is able to advise on water treatment." In some cases where persons had been sick after drinking water held in domestic piping overnight, the cause had been accelerated corrosion caused by carbon film, Mr Walker added. He was not able to say whether the case reported last week from Mairangi Bay, Auckland. had been caused through carbon film, as the pipes had not yet been examined by his laboratory. The cause could either have been carbon film or "aggressive” water. Another similar case was under investigation. "Dezincification” “In many New Zealand waters brass, which is an alloy of copper and zinc, is prone to a type of deterioration know as ‘dezincification',” he said. “In this type of attack, zinc is preferentially dissolved from the alloy, leaving behind a soft, spongy, porous mass of copper. The rate at which ‘dezincification’ occurs varies enormously in different waters: one of the aims of the corrosion survey is to be able to predict when the use of brass is economic and when more corrosion-resist-ant alloys should be used. "Copper hot-water cylinder failures examined at the Dominion Laboratory have shown that spelter-brazed (bronze welded! cylinders are very unsatisfactory in some waters because of ‘dezincification.’ Cylinders brazed with other alloys are often more satisfactory in such cases. “Some New Zealand waters : (not necessarily the same as ■ the above) are very corrosive ; to any type of copper hot water cylinder, and economic solutions to the problems posed by such waters are under investigation. “The factors influencing valve seat failures are also : being looked at. Important variables include water composition, metal composition, the type of washer and water ; pressure. The number of samples received is still so small that no useful conclusions have been reached.”