Chlorine blamed for damage to cylinders
Chlorination is to blame for damaged hot water cylinders in Christchurch and could cause further problems to pipes and foundations, according to a University of Canterbury study.
More than 2000 cylinders have been replaced since June and a 45-page report by the department of mechanical engineering concluded chlorination was to blame.
‘‘In the absence of a creditable alternative proposition, the chlorination of the Christchurch water supply by the Christchurch City Council has caused the failure of copper hot water cylinders.’’
The investigation was commissioned by Woolston manufacturer Superheat and headed by Professor
Milo Kral to establish the cause of a sudden spike in cylinder failures.
Copper tanks are prone to pitting, a form of corrosion which causes tiny holes. If pitting occurs, cylinders usually cannot be fixed and have to be replaced at a cost of around $2000.
After analysing four defective cylinders, experts found multiple corrosion pits and concluded each unit failed due to leaks caused by pitting.
Evidence of chlorine was identified in the corrosion products of all pitting sites but was not detected on surfaces other than pits.
In his report, Kral said: ‘‘Although a small population of exemplar cylinders were examined, the pitting observed was most likely due to the presence of chlorine and was influenced by the presence of iron in the sediments that settled to the bottom of the cylinders.
Due to changes in chlorination, corrosion of copper hot water cylinders was likely to become more common in Christchurch, with a reduction in the life of cylinders, Kral said.
‘‘Each cylinder installation is at least slightly different from every other, so patterns of failure may be difficult to determine.’’ Superheat managing director Trevor Edwards supplied the University with four damaged hot water cylinders from three different manufacturers; Superheat, Peter Cocks and Rheem.
The cylinders were either 180 or 225 litre capacity and between three and 10 years old. They were removed from homes in Linwood Ave, Westmont St, Showgate Ave and Perth St.
They were from different manufacturers, different locations, and different ages and they all had the same problem, Edwards said.
‘‘The combination of the chlorination and iron oxide has accelerated the corrosion on cylinders that would usually have a life of about 10 more years.’’
Christchurch City Council head of three waters and waste John Mackie said council was working with cylinder manufacturers and researchers to find the cause of the problem.
They hoped to have a ‘‘clearer picture’’ in a few weeks, he said.