A 74 m section of 300 mm diameter mild steel cement-lined sewer main attached to the Hindmarsh River railway bridge at Victor Harbor was suspected of being in poor condition because of age and the observed amount of cement lining that was being generated during pipe cleaning operations.
A complete survey of the pipe section was completed successfully in October 2010. The inspection identified that a significant portion of the cement lining in the soffit of the pipe was missing or had deteriorated, and some corrosion had occurred in the steel outer casing.
There was concern that further corrosion could result in spillage of sewage into the Hindmarsh River and also weaken the structural integrity of the pipe, impacting its capacity to safely span the 11 m space between supports attached to the railway bridge.
The aim of this project was to eliminate the risk of failure from this section of pipe – and therefore avoid a loss of service and contamination of the river below, which would be a significant environmental incident.Article continues below…
SA Water assessments concluded that a complete replacement of the pipe would be three to four times more expensive than lining, due to the significantly higher environmental and occupational health and safety risks associated with construction work across and above the river.
Given these circumstances, Kembla was one of the companies approached to submit a rehabilitation proposal.
One of the critical aspects of this project was that the pipe had sharp mitre bends at each end of the bridge.
Kembla currently has three structural lining systems suitable for 300 mm diameter, which are the Ex Method (fold and form) PVC lining, SWP DiaFit (spiral-wound pipe) and Enviroliner cured-in-place pipe (CIPP).
Ex Method linings are able to negotiate longer radius bends but not a sharp mitre bend and SWP DiaFit is not able to effectively negotiate anything but small gradual bends. But Kembla’s experienced Enviroliner CIPP crew were confident they could install a lining through these bends with minimum wrinkling.
Therefore the company recommended Enviroliner CIPP lining as the most cost effective option. The proposal included the following activities:
- Impregnation of the lining in Sydney
- Cleaning and pre-lining CCTV survey
- Establishment of equipment, materials and crew to and from Sydney
- Installation of 74 m of 300 mm diameter by 6 mm thick structural CIPP lining
- Traffic control as required
- Bypass of existing sewer flow
- Post-lining CCTV survey.
SA Water accepted the proposal and the project team began planning the work immediately.
After high-pressure water jet cleaning of the pipe, a CCTV survey showed several sharp, protruding and hard deposits still remained on the pipe wall.
Kembla was able to call on one of their robotic cutter truck crews at short notice to travel across the border from Victoria and carefully grind away these deposits.
With the pipe now ready, the resin impregnated lining was brought to site and installation commenced from an access chamber on one side of the bridge using a purpose-built air inversion unit. By maintaining an internal pressure inside the ‘soft’ lining it inverts itself into and along the pipe.
The crew took certain precautions as each bend was approached and once the lining reached the far access chamber, steam was circulated through the lining to cure and harden the lining while it was held in contact with the pipe wall.
After the curing process was complete the ends of the lining at each access chamber were cut and sealed and a final CCTV survey was carried out.
The entire lining process was completed in one day without incident, much to the delight and satisfaction of the SA Water personnel in attendance.