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Internal corrosion to cast iron water supply causes a water leak on a pressurised fire main.

Author: Graham Mann, Water Audit Expert. 

Unilever Plc needed urgent site attendance for a water leak detection and water leak repair team due to a large water leak on a fire main distribution system, it is a pressurised main which means large pumps maintain pressure or 10bar through the fire main distribution system. The jockey pumps were cutting in and out having to make up pressure losses in the system loosing 1bar per second.

The site was in danger of losing the fire main which was crucial to site operations.

Because of the noise the pumps generate using sounding techniques  to trace the water leak noise was out of the question so the system was isolated and the tracer gas injection method was used to locate the water leak. Inert gas was injected into the water supply main in the jockey pump house, when a certain measure of gas has been injected an ultra-sensitive gas detection device is slowly passed over the ground above the water pipe and when the strongest amount of gas is recorded above ground the jockey pumps are re-started pressurising the water pipe and then turned off.

Then leak noise equipment was used to verify the water leak and when the leak position was verified the water pipe was excavated with the 30 year old cast iron water pipe exposed, it was evident that it was suffering from internal corrosion as you can see the leak in a pin hole in the pipe which would get substantially worse over time.

 Photo 1: – Water leaking out under pressure from a pin hole.

Photo 2: – Pin hole in water pipe.