Pressure testing of drinking water pipes
Both in new constructions and in rehabilitation, it is important to prevent leaks into and out of drinking water pipes. Water must be clean and safe, out of concern for health, environment and security.
This is especially important when it comes to reducing the leakage percentage in Norwegian pipes. A leakage percentage of 40 is not in line with current environmental concerns.
Flushing and plug cleaning
Water pipes must always be flushed or plug cleaned with new constructions or rehabilitation. When pressure testing is to be carried out, it is important to have a good and correct piping map, where manhole number, length of the test cover and any height profiles of the route is uncovered. It must then stand under operating pressure, normally 24 hours before conditioning. The time varies according to the dimensions and quality of the pipes. After this, the pressure testing may commence.
Methods for pressure testing
The method for pressure testing also depends on the type of pipes to be tested. The most common alternatives for water pipes are ductile iron pipes, PVC or GRP pipes. With these, the pipes are tested according to common standards, while PE pipes are tested according to their own standard (NS-EN 805). Water is pumped into the water pipe to create an operating pressure of 15 bar. The preliminary test, as this is called, lasts for 30 minutes, and is automatically logged by a computer. In this period, the pressure is maintained at a constant of 15 bar, and then a test of the fall in pressure is performed to measure if there is too much air in the pipe. If this is in order, the main test may commence. Before this, our operator uploads any relevant data.
A separate inspection slip has been developed by Rørinspeksjon Norge (RIN). This contains control number, the company performing the control and who the principal employer is. The form gives a full overview of the control process, with pressure, temperature and time. It contains GPS data and control data with results. The inspection slip must always be signed by the operator.
The norm is then entered, and then the program performs the given procedure when the pump starts.
In the main test, which starts on the second day, water is again pumped into the pipe, also this time with a pressure of 15 bar. For the pipe to be approved, it must not fall more than 200 millibar in 60 minutes. This also depends on the pipe type.
After approval of the pressure test, the pipe is to be disinfected immediately with sodium hypochlorite 15%. This is to ensure the drinking water quality according to Food safety requirements. It is mixed automatically at 30 ppm through modern equipment, which also pumps the mixture into the pipe. This is logged and monitored by data equipment to ensure proper use of chlorine. The disinfection lasts minimum 24 hours, so that all bacteria die. During this period, the pipe must be closed off. After 24 hours of disinfection, total chlorine and free chlorine is measured.
Neutralizing the chlorine
The next step is to neutralize the chlorine with sodium thiosulfate or a similar substance. It is added at the time of flushing, through an automatic water measurer, so that the flushing water does not harm the external environment.
Many pipe owners require a minimum pressure of 10 ppm on the second day of pressure testing.
The work of pressure testing and disinfection is finalized with two water samples from the drinking water pipe. There are separate procedures for this, and it is paramount that this is carried out completely sterile.
Accredited laboratories analyse the tests, and check for both E-coli and colony count. If you have doubts about the water in your pipe, it might be a good idea to perform a test at the starting and ending point. All results are documented and sent to the customer.
There is an absolute rule stating that no one should descend into a manhole undergoing a pressure test. Of course, this also entails clean equipment, clean clothes and clean tools.