News>Pigging Raw Water Line
Trenchless Australasia | December 2009
Dawson River case study – pigging raw water line
The 150 mm diameter pipeline is ten kilometres in length, pumping raw water from the Dawson River to the treatment plant to service parts the Duaringa Shire, Queensland.
Mission
To remove the internal debris and weed growth built up in the pipeline over a period of ten years.
Due to the location of the site and the urgency of the program, Clearflow Australia worked purely on telephone communication and faxed documents in order to fabricate a pig launcher to suit the conditions onsite. After some difficulties it was made to fit and is now a permanent fixture of the pipe at the river end.
Managing Director David Elderfield said “On inspection of the pipeline at the river and pumping end we adapted the existing fittings, removed a flanged section of the existing pipe and made our pig launcher fit.
“The best location for the discharge was at the water plant. A section of pipe was exposed and removed with the excavation of pit leaving the open end of the pipe discharging into the settling pit.”
There was no confident local knowledge of the pipeline and the only map available was a longitudinal section map, said Mr Elderfield. “It is difficult to know what to expect when launching a pig that is required to travel ten kilometres and at the same time achieve the desired results.”
Most of the pipeline is located in bush terrain with difficult access, with a number breaks in certain sections and unknown debris in the pipe.
As the pipeline had no offshoot sections or designed breaks it was necessary for the pig to travel the entire ten kilometres and achieve the desired result. If the wrong type of pig is used and too much debris is dislodged too early the pig could jam up in the pipe. On the other hand, if the pig is too soft it may break up during the run. Or if the pig travels too quickly we may not get a true idea on the condition of the pipe or the type and amount of debris that is in the pipe to be removed.
At the time of fitting the launcher the pipeline showed signs of encrustation with a large amount of weed slime and sludge – the aftermath of pumping raw water.
Clearflow’s normal procedure on the first run is to try and determine the condition of the pipe. The first run took approximately four hours to travel the pipe, removing large amounts of sludge and slime.
This initial run was not without complications. The pig did jam up with the amount of debris in the pipe and it was decided to release the pressure in the pipe.
In doing so, Clearflow drained some of the pipe to get another run with the pig and to try and dislodge the debris.
Under normal conditions the first-run pigs or proving pigs will float, however, in this case, when they were finally discharged from the pipe they were so full of sludge and slime that they just settled on the bottom of the discharge pond. They were stuck in the sludge and at the bottom of the pit.
It is necessary when refurbishing pipelines to try and control the speed of the pigs through the pipeline. After two proving runs the company was confident the pipeline was reasonably true and launched the working pig; a harder compound, poly-foam pig.
This purpose of running this pig was to remove all of the debris of weed sludge and slime as well as any harder encrustation.
The results achieved were very good. Clearflow not only removed large amounts of raw water slime sludge and weed growth, but also the heavy scale evident in the bottom of the discharge pit. There were also signs of manganese mixed up with the weed growth.
The final analysis
Improved water quality delivery with increased flow rate to the dam of 60 per cent. This alone decreased the operating costs of pumping water.