A crucial problem for water pipes
In hospitals, hotels, and other facilities that need to be particularly cautious in regard to the presence of Legionnaires’ disease bacteria in their water pipe systems, chlorine dioxide has become an increasingly common disinfectant. But chlorine dioxide corrodes plastic pipes and this shortens their life spans. This is a crucial problem that Swerea KIMAB now wants to shed light on.
The water that we drink needs to be disinfected to remove harmful bacteria. Chlorine has long been the clear choice in disinfectant due to its long-lasting germicidal action. However, when there is an increased risk of Legionnaires’ disease in the water pipe systems, installing smaller chlorine dioxide generators has become increasingly popular.
“Chlorine oxide is very effective against Legionnaires’ disease – better then chlorine. What no one has considered however, is its effects on plastic pipes. In many systems, the chlorine dioxide has caused the plastic pipes to corrode thus leading to breakdowns. No one knows why this occurs”, Dr. Karin Jakobson tells us, senior researcher at Swerab KIMAB, which is one of the world’s leading institutes for applied materials’ research and problem-resolution.
A growing problem
Water supply companies are responsible for the cleanliness of the water they supply up to the point at which it is delivered to the facility using the water. Once delivered, it is up to the facility to ensure that the water is bacteria-free. Since chlorine dioxide generators are relatively simple and cost-effective to use and maintain, many hospitals, SPA facilities and hotels are now equipped with their own chlorine dioxide generators.
“Chlorine dioxide has long been used in water treatment plants. Moreover, those who conduct research on Legionnaires’ disease consider the use of chlorine dioxide generators to be extremely effective in combating Legionnaires’ disease in particular.
However, plastic pipes are almost always used in water pipe systems. It is only in exceptional cases, for example in the vicinity of petrol stations, or contaminated soil that metal pipes are used. As the use of chlorine dioxide increases, so will the problem of corroding pipes.
“We have been aware of this problem for many years. A considerable amount of research work is being commissioned by the plastic pipe manufactures, but this research is not available to the public.
This is why Dr. Jacobson, in conjunction with the research group from Swerea KIMAB, would like to initiate a research project to find out what mechanisms cause the plastic to corrode when it comes into contact with chlorine dioxide. Dr. Jacobson would like to test plastic pipes that are in actual operation while in conjunction conducting laboratory tests. This has only been done to a limited extent previously and can yield concrete answers as to why certain plastic pipes corrode in contact with chlorine dioxide. Dr Jacobson is currently seeking funding so that the project can get underway.
Breakdowns and accidents
The effects of chlorine dioxide on plastic pipes have already created great problems around the world. In France, the use of chlorine dioxide in conjunction with plastic pipes has been heavily regulated following the occurrence of a number of breakdowns. In the Czech Republic, a number of conflicts are currently ongoing between actors in cases where the chlorine dioxide facilities have destroyed hospitals’ water pipes. But there is still no information available to the public on the number of accidents or the investigations into the causes of the damage.
“The investigation into the effects of chlorine dioxide on plastic pipes is an important issue for all involved actors. Both for those who manufacture the pipes and chlorine dioxide generators and for those who use the chlorine dioxide. Hardly any research is currently being conducted. We in Swerea KIMAB have a tremendous of experience in corrosion and corrosion-protection research. Our involvement in resolving this problem can be immensely beneficial.”
A number of possible causes
Exactly why chlorine dioxide corrodes plastic pipes more quickly than other substances is not currently understood. Possible causes that have been discussed are the residual acid from the production of the chlorine dioxide, poor quality plastic pipes or insufficient maintenance of the chlorine dioxide generators. But at this point these hypotheses are nothing more than speculation.
“An investment in a chlorine dioxide facility can be seen as relatively inexpensive. But if chlorine dioxide causes plastic pipes to corrode to the point that the water pipe system is destroyed, it becomes exceedingly expensive for the hospital or cruise ship using the chlorine dioxide generator. It is important that we shed light on the effects of chlorine dioxide on plastic pipes and avoid accidents with ensuing serious damage to water pipe systems.”
The difference in the corrosion rates also varies widely. Certain plastic pipes resist the corrosive action of chlorine dioxide better than others. Others corrode immediately after a chlorine dioxide facility has been installed.
“Different types of plastic react differently to chlorine dioxide. For example, certain studies show that chlorine dioxide attacks plastic pipes manufactured from polyethylene, polybutene and polypropylene more aggressively than for example PCV. Chlorine dioxide can also be manufactured using different methods. Varying bi-products result depending upon the chemicals used, and it is unclear how these bi-products influence corrosion.”
Standard test insufficient
An accelerated corrosion test is used when testing plastic pipes to see how they react to chlorine dioxide. This involves testing the plastic’s reactions at increasing temperatures and higher concentrations of chlorine dioxide than the pipes would be exposed to in normal operation. This is the same type of test that is used when the reactions of plastic pipes to chlorine are tested.
“The questions is, is this type of test relevant? It is far from certain whether all reactions are accelerated equally, and the tests can yield faulty results.”
Swerea KIMAB and Dr. Jacobson would instead like to focus on pipes in their actual operational environments as opposed to solely conducting laboratory tests. Only by removing and replacing pipes, both those that have become corroded and those that have not, can the mechanisms that affect the corrosion of the pipes be found. This is a research project that will benefit all – both the manufactures of the plastic pipes and the chlorine dioxide generators as well as the end users.
Facts about Legionnaires’ disease
Legionella is the name of a family of bacteria that grows naturally in fresh water and soil. In grows in warm water and steam primarily when the temperature is between 37 and 50 degrees centigrade. As a rule, the bacteria itself is not dangerous. However when water pipe systems are incorrectly designed it can lead to an increase in bacterial growth in the system. This in turn can lead to Legionnaires’ disease or Pontiac fever.
Source: Safe Water (SäkerVatten) and the Swedish Institute for Infectious Disease Control
Contact: Karin Jacobson, karin.jacobson@swerea.se