In total, the Rivelin system supplies approximately 319,000 customers and comprises almost 80 km of large diameter pipe-work, ranging from 12 to 27 inches in diameter. Ian Johnson, with 33 years experience at Yorkshire Water, will head the £11 million project.

The problem

A 20 km, 12 inch diameter unlined cast iron section of the pipeline was laid in the early 1900s and subsequently in situ lined with cement in the mid 1950s. Quality assurance processes and procedures in the 1950s were nowhere near as robust or stringent as today’s highly regulated methods. This led to extremely poor cement lining being applied to the pipe.

Today, many if not all of our existing relining techniques involve the material being ‘sprayed’ onto the pipe wall by a spinning lining head. In the 1950s the technique involved pumping large volumes of cement into the pipe and pulling a cone shaped ‘bung’ through the pipe which, in theory, would spread the cement onto the internal pipe wall surface and displace the remainder of the cement from the length of pipe being lined.

The result of this 1950s process on the Rivelin water supply system resulted in a pipe with little or no lining on the top sections of the pipe, but rather ‘slumps’ of cement at the bottom of the pipe. These ‘slumps’ typically range from 100 mm to 250 mm in height and are extremely dense, well mixed cement.

To overcome the problem, Mr Johnson’s immediate thoughts turned to developing a sliplining solution. This was soon discarded since the pipe needs to retain as much carrying capacity as possible as it will be required to supply large demands to the west of Sheffield when future sections of pipeline are de-commissioned for rehabilitation. Existing technologies and processes

Yorkshire Water's existing mains cleaning technologies are not able to remove the material and had to look for other alternatives. The team recognised very early on that if they were unable to find an alternative cleaning method they would be faced with the probability that the whole 20 km section would have to be renewed using a very costly and disruptive open cut technique.

The team embarked upon a journey to identify options and processes that would remove the cement from the pipe without adversely affecting the structure of the pipe, which could result in increased leakage levels across the Rivelin water supply system.

Various drag scraping and jetting techniques were trialled but proved unsuccessful. Eventually, Mr Johnson discussed the issue with a team of hydro-demolition experts to see if they could help provide a solution to the problem. Hydro-demolition is a process that involves extremely high pressured water being applied to destroy and/or demolish materials such as concrete structures. Following initial discussions, trials began and they worked together to obtain an optimum level of cleaning that would remove the cement and leave the pipe intact to enable application of a polymeric (Pu) lining to the pipe.

The solution After several weeks of trials the team established that pressure of 12,500psi would be effective at removing the cement. Pressures in excess of 17,000psi started to cut the cast iron pipe and would have led to future structural and leakage problems. Production rates onsite are comparable with those that would be expected from similar sized pipe with typical iron tuberculation and manganese deposition using traditional mains cleaning techniques. To date, the team has completed almost 6 km of relining work and is on program to complete the whole 20 km section by the end of December 2009.

Customer service and completion dates

Mr Johnson said “It would be nice if we didn’t have to dig any holes at all. Unfortunately we do. By doing this it means we don’t have to dig as many.”

Without the hydro-demolition process, the Yorkshire Water team would have had to renew 20 km of 12 inch diameter cast iron pipe across the southwest of Sheffield. This technique is extremely disruptive to customers and traffic users and would have resulted in failure to not meet the agreed Regulatory DWI completion date for this phase of work, which is set at 31 December 2009.