When a rising main/pumped sewer was suffering from repeated bursts it drew the attention of the local MP. Replacement tankers were called in to transport sewage to the pumping station, a practice that was expensive, disruptive and time consuming. Gas pockets in the pipe were the suspected cause. If hydrogen sulphide collects in the high points of pipes it can create sulphuric acid, which in turn leads to corrosion and weakening of the pipe. Particular concerns existed about the upstream pipe, where pressures are highest, which is close to a river and a caravan park. Clearly, the presence of any gas pockets needed to be identified, fast.
The water company engaged the service of WRc, which deployed its Sahara® acoustic umbilical system along a suspect 300m-long section of the 250mm diameter pipe.
The survey revealed that a potentially hazardous gas pocket existed on the crown of a bridge as it crossed the river. This allowed the water company to install an air release valve in this location to relieve the gas accumulation and avert any further bursts. As an extra benefit, the Sahara® survey also showed the exact route of the pipe run, thus allowing the water company to update drawings/GIS records. Furthermore, using the conductivity sensor on Sahara®, it was possible to confirm that the pipe was non-metallic (asbestos cement), a fact that was previously unknown.