Pioneering pigs

A pioneering experiment using ice could prove to be the way forward for removing iron from water mains.

Wessex Water said that a trial by Bristol University researchers along a small stretch of main was so successful that it may have been just the 'tip of the iceberg' for things to come.

Traditionally, polyurethane foam swabs known as solid plugs or pigs were propelled through the main with water, scouring the pipe clean as they went. However, early indications show that 'ice pigs', new products that underwent testing in the Wessex Water region, have eliminated several problems caused by the conventional process.

Ice pigging involves cleaning by injecting ice slush into a rising main before forcing it through the pipe with water. The trial, which took place over a 1.6km stretch of a 150mm-diameter potable raw main in West Lavington, Wiltshire, produced results deemed ideal for pipe cleaning.

Although solid plugs have been used successfully for a number of years to clear and clean pipes in various industries using common methods such as foam swabbing and air scouring, the process has several drawbacks apparent when used in complex pipes.

Matthew Maggs, a production manager for Wessex Water, said: 'Traditional foam swabbing involves installing several access points along a main that can be both costly and time consuming. While extensive flushing can be carried out, it is sometimes to no avail due to the thickness of iron coating, which builds up in the main over time.

'Problems also arise in the complicated internal workings of a pipe that could cause the solid pigs to become intransigent, due to the potential build-up of sediment ahead of the foam,' he added.

A viable solution to the problem was needed and it was Prof Joe Quarini in Bristol University’s Department of Mechanical Engineering who invented ice pigging, which initial tests suggest might just fly.

Researchers in partnership with Wessex Water and Bristol Water were able to develop this method using nine tones of slush during a two-day trial.

During the experiment in the Wessex Water region, ice was treated with a freezing suppressant and was then used to form a soft plug that was pushed along a main, scouring it effectively while adapting its shape to navigate through complex pipe work with ease.

Samples of slush were taken at the exit point and initial analysis proved promising.

'The first pass created a large volume of sludge that was flushed away through the extraction hydrant and removed by tankers,' said Maggs.

'Over the next series of passes, we saw a dramatic drop in the amount of sludge being ejected and, by the final pass, the ice plug was clean at extraction point,' he added.

Bristol University staff and students were monitoring and sampling the resultant waste and will provide a report that will quantify the amount of iron sediment that has been removed.

Maggs said: 'In this instance, by using ice pigs we did not need to install multiple chambers and pigging points, thus saving time and money.

'I’m convinced this technique could be used in other areas of our water-supply network, which spans more than 11,000km,' he added.

Quarini, a professor of process engineering, said: 'We are delighted that the technology is being adopted by the water industry. We all believe that it represents a paradigm shift in pipe cleaning, making difficult, time-consuming and expensive tasks easy and fast to undertake, as well as making some previously impossible jobs doable.'