Six-year programme expands knowledge of ageing pvc pipes

Compared with older asbestos cement pipes, the more recently installed pvc pipes experience relatively few failures. But how will this develop over the next fifty years?

Knowledge and implementation programme

To answer this question, the PVC Knowledge Programme has been established within Waterwijs, focusing on building knowledge about pvc piping systems. There is also an Implementation Programme, in which pipe sections are removed and tested to collect data that will form the basis for the research. The programme involves close collaboration with the specialist materials laboratories Kiwa and Normec.

Developing a condition assessment method for pvc

“For asbestos cement and cast iron pipes, we have methods for determining the condition of the material. We use condition assessments that provide an indication of the state of a pipe, even when no failures have occurred,” explains Joren Rombouts, Distribution Asset Management Adviser at Brabant Water, who is responsible for replacement issues relating to distribution and transmission mains. Several factors that may contribute to pvc failure have been identified, but there is still insufficient knowledge about when and under what conditions they actually lead to damage.

Rombouts: “With the PVC Knowledge Programme, I hope that in time we will become better able to identify different groups of pvc pipes and assign them a substantiated probability of failure. I would also like to gain more insight into the conditions that cause certain failure factors to actually result in failure. It would be valuable if we could reach conclusions that contribute to the development of a condition assessment methodology for pvc.”

Intensive preparatory phase

Before the Implementation Programme started this year, an exploratory study was carried out within Waterwijs. Two studies were conducted, examining, among other things, how such a programme should be structured and which testing methods would be most suitable for inclusion. Ralph Beuken, researcher at KWR, explains how this preparatory phase unfolded.

“It was quite an intensive period, during which the drinking water companies immediately indicated that they recognised the need for the knowledge programme. But then questions arise, such as how the removal of pipe sections can be combined with planned work. We want to combine activities wherever possible so that the operational departments are burdened as little as possible.”

The researchers would ideally like to test as many different pipes as possible in order to gain a better understanding of which pipes perform worse than others and when replacement is necessary. This requires a substantial investment from the participating drinking water companies, which have to finance everything themselves.

Testing methods

To arrive at a relevant selection of testing methods, KWR researcher Amitosh Dash carried out a literature review. He also spoke with experts to gain a clearer picture of which tests should be included in the Implementation Programme.

“It is very good that we took the time to investigate this thoroughly first,” says Dash. “It allowed us to make well-founded decisions and to enter the Implementation Programme with confidence.”

As an example, Dash mentions the measurements Kiwa will carry out on the degree of gelation, a method used to assess the quality, impact resistance and service life of a pvc pipe. Testing organisation Normec will also carry out measurements of resistance to slow crack growth.

“One of the ways pvc pipes fail is through the crack-growth mechanism,” Dash explains. “A small crack develops somewhere and, as a result of stresses in the surrounding environment – from water pressure or the soil – the crack grows over time. What you want to know is: how quickly does that happen?”

KWR will also carry out its own tests, including CT scans designed to provide information about inclusions in the pvc. Dash: “We are working with Medispace, a company that has mobile CT scanning equipment intended for healthcare institutions that temporarily do not have access to their own CT equipment. When the mobile equipment is not required for medical applications, we are allowed to use it.”

A CT scan can reveal very small irregularities or foreign particles in the wall of a pipe. Such inclusions could potentially form the starting point for cracks.

Knowledge database

Although the Implementation Programme is the practical and logistical elaboration of the research that preceded it, its results will in turn contribute to the knowledge base on pvc. The researchers are looking not only at the material properties of a pipe, but also at the conditions in which it has operated for many years.

“We want to build up a kind of biography for every pipe section we receive,” Beuken explains. “In what year was the pipe installed? In what type of soil and environment? What is its failure history? This information can then be combined with the test results and with the relationships we identify between them.”

This is important because pvc ageing cannot simply be determined from a single measurable parameter. For metal pipes, for example, corrosion and loss of wall thickness can be measured. With pvc, the relationship between material ageing, environmental conditions and eventual failure is much more complex.

Beuken: “What I hope is that, in six years’ time, we will have a clear understanding of which types of pvc pipes require the most attention. We may even arrive at a new testing method that we can develop further within Waterwijs. That would complete the cycle between the Implementation Programme and the Research Programme.”

Better understanding of failure behaviour

On behalf of the drinking water companies, Rombouts stresses that the objective of the Implementation Programme – gaining a better understanding of the failure behaviour of pvc pipes – is extremely important.

“Pvc has been the most widely used pipe material for the past fifty to sixty years. But its exact service life is still insufficiently understood.” There are also differences between production processes, suppliers and types of pipe.

“You want to build up the complete picture,” says Rombouts. “The more different pipe sections we investigate, the better we can compare groups or cohorts. Ultimately, we want to anticipate failures and replace pipes selectively when necessary.”

The programme will run for six years. During that period, KWR and the partners involved aim to develop an increasingly robust knowledge base for managing pvc pipe networks. In doing so, the research will contribute both to a reliable drinking water supply and to efficient investment in the pipe network of the future.