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Find out how to carry out tests on water pipes in accordance with worksheet W 400-2. Fully automated pressure testing using all standard-compliant procedures – from the contraction procedure through the (accelerated) standard procedure to the influence-minimised procedure. Read practical case studies, find out how to meet the stricter requirements, and discover the right system components for your next pipe network inspection.
When carrying out pressure tests in pipework construction, variables arise on a daily basis that can distort the measurement results. These include air bubbles trapped in the pipe without being noticed, the viscoelastic behaviour (relaxation) of PE materials, or unforeseen temperature effects in the pipe trench. In the worst-case scenario, an inaccurate pressure sensor or a purely manual reading can result in a test lasting several hours being classified as ‘failed’, even though the pipe is completely leak-tight, or, conversely, small leaks being overlooked.
Our case studies provide practical insights into the day-to-day work of network operators, utilities and service providers in relation to the commissioning and maintenance of safe drinking water networks.
In Germany, water pipes used for the supply of drinking water must undergo a pressure test prior to being put into service in order to verify that the construction work has been carried out correctly and that the pipework system is leak-free. The requirements regarding the procedures and guidelines for carrying out these tests are set out in DVGW Worksheet W 400-2.
Below, we outline the stages of the water pressure test in accordance with DVGW W 400-2.
The pressure drop test is carried out in every procedure following the preliminary test and prior to the main test. Its purpose is to verify that the pipework system is free of air. An excessive amount of residual air in a pipe during a water pressure test significantly affects the result of the main test.
The current W 400-2 regulations set out strict requirements for the performance and evaluation of the pressure drop test. The volume of water drained must be determined using a digital measuring device, and the measured value must be transferred to the pressure testing device used. The preliminary test shows the greatest differences between the individual procedures, as it is designed to produce different conditions depending on the pipeline material. During the preliminary test of the contraction method, plastic pipes expand under test pressure.
In the preliminary test for the accelerated standard procedure, a cement mortar lining (CML) of a steel or cast iron pipe is to be partially saturated with water under test pressure, whereas in the standard procedure the cement mortar lining must be completely saturated. The procedures are therefore complex and involve numerous different details, which depend on the type of procedure, the pipe material and the nominal diameter.
The main test constitutes the final phase of a procedure and is used as the final assessment of leak-tightness. During the main test, the pressure drop in the pipeline is measured and compared with a permissible pressure drop. The specifications regarding test duration and permissible pressure drop vary significantly between different procedures and depending on the pipeline being tested. To measure the pressure curve, a pressure sensor with a measurement range that complies with the relevant regulations and sufficient accuracy is required.
High-quality measuring equipment that complies with current regulatory requirements should be used to carry out the procedures. A list of the necessary components is provided below. This equipment enables all procedures to be carried out in accordance with document W 400-2.
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The pressure test using the contraction method is designed to reliably assess the leak-tightness of newly laid or replaced drinking water pipes. The procedure takes into account the pressure-dependent behaviour of the pipework and enables an assessment in accordance with DVGW Worksheet W 400-2. Careful execution and clear documentation are crucial to ensuring the quality and operational safety of the drinking water system.
The contraction method places high demands on the preparation and correct execution of the pressure test. In particular, the pipework must be sufficiently free of air, as trapped air can distort the measurement results and mask potential leaks. At the same time, the individual test phases, pressure changes and limit values must be strictly adhered to. External conditions, as well as the specific behaviour of the plastic pipework, can also influence the pressure curve and make it difficult to arrive at a clear evaluation without suitable measurement technology and expert operators.
The contraction method enables a reliable and verifiable evaluation of the leak-tightness of drinking water pipes. Thanks to the defined test procedure, potential leaks can be detected at an early stage, the quality of the installed pipework can be verified, and the test results can be documented in accordance with the relevant standards.
We demonstrate in a practical way how the methodology can be easily implemented using our technologies, despite the challenges.
Enter the pipe data and the required test pressure via the input screen. Set the ‘MPP remotely controlled’ selection parameter to ‘Yes’ so that the MPP is controlled by the smart memo during the pressure build-up and pressure hold phases of the test sequence.
After setting the zero point of the pressure sensor (also set the zero point in the MPP’s main menu), press F2 to switch to the pressure release (relaxation) phase.
During the relaxation phase, you can use the F1 key to open or close the automatic drain valve at the touch of a button. This allows you to vent the EDS2 automatic drain system and the connected EDS2-V flow meter even after the process has started. Furthermore, for pipework without a gradient, you can use an open drain valve to create a pressure-free condition. At the end of the relaxation phase, the valve closes automatically in all cases.
If the MPP is not yet connected to the smart memo or is not yet ready for use, a prompt will appear at the end of the relaxation phase asking you to establish the connection.
In the current version (03/2023) of the automatic system, a prompt appears at the start of the relaxation phase asking whether pressure build-up should be started automatically once the relaxation phase has ended.
If you confirm this prompt with ‘Yes’, the smart memo will automatically switch to the next phase once the 1-hour relaxation phase has ended. If the MPP is already connected to the smart memo via the connection cable, the system will automatically switch to the pressurisation phase and the pressure build-up will commence. Once you have confirmed the prompt with ‘Yes’, the entire test will therefore run automatically without any further user intervention.
The relaxation phase must be ended by pressing the ‘Next’ button. The MPP is now initialised. If the MPP is not yet connected to the smart memo via the connection cable, a corresponding message will appear. As soon as the MPP has been initialised, a prompt will appear asking whether pressure build-up should be started. After confirming with OK (F2), the smart memo switches to the pressurisation phase and the MPP automatically begins operation. Pressurisation is carried out via the MPP’s speed control without overshoot. As soon as the preset test pressure is reached, the smart memo automatically switches to the pressure-holding phase.
This is followed (at the start of the pressure-holding phase) by a message from our air volume measurement system, which was used to determine whether there is too much residual air in the line. We have already compiled further information on air volume measurement for you here on this product page and here in the blog post ‘Checking for air ingress during pressure tests’.
The smart memo continues to control the MPP and ensures that the pressure is maintained at the preset test pressure throughout this phase. Once the 30-minute phase has elapsed, the smart memo automatically switches to the rest phase.
When the system switches to the rest phase, the smart memo automatically finishes the MPP’s pressure control. The MPP is reset to the main menu and, once the cable connection to the smart memo has been disconnected and the ball valve on the test head HANS has been closed (please ensure that you close the correct ball valve), it can be taken out of service, drained and stowed away.
The smart memo monitors the pressure drop during the rest phase. If this exceeds 20%, the testing is automatically terminated, as this usually indicates a leak in the pipe.
Once the one-hour rest phase is complete, the smart memo automatically switches to the pressure drop test.
The EDS2 automatic pressure relief system now begins to perform pressure reduction automatically. The valve opens gradually and regulates the pressure reduction in such a way as to achieve the specified target pressure as accurately as possible. At the same time, the discharge volume is measured by the connected EDS2-V and transmitted digitally to the smart memo. Once the target pressure is reached, the valve of the EDS2 automatic pressure relief system closes completely.
The smart memo automatically switches to the main test as soon as a rise in pressure resulting from the contraction of the test line is detected.
A check of the discharge rate and the pressure drop generated, in accordance with the specifications of the current worksheet W 400-2, takes place in the background. If the check is unsuccessful, a corresponding message appears at the start of the main test; otherwise, the test continues without a message.
The smart memo records the rise in pressure resulting from the contraction and, once the 30-minute main test has finished, provides an evaluation in accordance with the regulations.
If the pressure curve falls within the permitted range, the evaluation is positive.
If an excessive pressure drop occurs during the main test, the smart memo automatically switches to the main test extension phase.
The smart memo records the pressure curve during this phase and, once the 60-minute extension has ended, provides an evaluation in accordance with the regulations.
At the end of the phase, the smart memo automatically switches to the results page or, optionally, to the pressure release phase (if set beforehand, see below).
The pressure release phase can be enabled as an option in the settings under this menu item. If this phase is enabled, the EDS2 automatic drain automatically reduces the pressure to relieve the pipe and terminate the testing.
This ensures that the test pipe is not subjected to the test pressure for an unnecessarily long time once the fully automatic pressure test has been completed.
In our day-to-day work at Esders, we regularly assist our clients with the evaluation and interpretation of pressure tests. Recently, a sales representative from one of our clients approached us regarding a pressure test carried out in accordance with the Accelerated Standard Procedure (ASP) – a test whose result he simply could not explain.
In fact, the behaviour we observed in the measurement data was, at first glance, new and puzzling even to us. However, after an in-depth investigation into the cause, we were able to solve the mystery. As this was not a classic user error but rather an unfortunate combination of circumstances, we would like to share our findings with you in this article to help prevent similar cases in future.
The client carried out a pressure test on a steel pipe with a cement mortar lining (CML) in accordance with the Accelerated Standard Procedure (ASP). To fill the pipe, he used water to which the approved disinfectant Sanosil had been added (Sanosil was fed into the system correctly via an Esders EDK20).
A notable feature of the pressure test procedure: During the rest phase, the measurement data showed a sharp and continuous rise in pressure within the pipe. In the Accelerated Standard Procedure, no pressure rise is normally expected during the rest phase. The test pump is switched off during this phase and the pipe is at rest. Normally, the pressure should fall steadily during this phase due to the typical saturation behaviour of the CML. Instead, the pressure shot up. How was this possible?
The Sanosil disinfectant used is a common and approved product based on the active ingredient hydrogen peroxide (H₂O₂). This is the key to understanding the phenomenon: a decomposition process took place within the pipe. Over time, hydrogen peroxide decomposes into water (H₂O) and gaseous oxygen (O₂).
If gas suddenly forms in a pipe that is completely filled with water and sealed, this inevitably leads to a rise in pressure. But why did this happen so rapidly and to such an extreme degree in this case?
The decomposition of H₂O₂ in the pipe was massively accelerated by various factors. High pressure, such as that present during a pressure test, promotes decomposition. Furthermore, heavy contamination, metallic surfaces, rust and high temperatures can act as so-called catalysts, which significantly accelerate the chemical process.
However, the decisive factor in this particular case was the pipework material itself: the CML.
Hydrogen peroxide is stable in an acidic environment (at a pH < 5). At higher pH values, however, this stability decreases drastically. From a pH value > 5, decomposition is already greatly accelerated (the higher the pH value, the more rapid the decomposition).
The cement mortar lining creates an extremely alkaline environment inside the pipe with a pH value of over 10. The CML therefore acted as a powerful catalyst here.
There is also a mechanical aspect: the cement mortar lining is porous and forms a vast (internal) surface area. The greater the surface area available to the H₂O₂-laced water, the more decomposition reactions can take place simultaneously. As saturation progresses slowly, the water molecules penetrate ever deeper into the small pores of the cement mortar lining. The reactive surface area therefore continues to increase as saturation progresses, leading to further, intensifying decomposition processes. The result is the observed, seemingly unstoppable rise in pressure.
Once the cause was clear, the question arose: had the client done something wrong? The clear answer is: no.
According to DVGW Worksheet W 400-2 (Section 7.4), this procedure is not only permitted but is even explicitly mentioned:
“The pipework must be filled with drinking water and, if necessary, flushed; where required, a disinfectant must be added (see also DVGW W 291 (A).”
The standard does not, as far as is immediately apparent, restrict the type of disinfectant to be used in relation to the pipe material.
Following the analysis and investigation into the causes of the pressure curve described above, we have noted numerous other pressure tests on steel and cast iron pipes using CML which show a rise in pressure during the stabilisation phase of the process, for example as in this pressure test.
This “phenomenon” is therefore not an isolated case, but occurs frequently, partly because the use of disinfectants is becoming increasingly common practice even during pressure testing.
Based on our findings from this case, we offer the following detailed recommendations for the use of disinfectants during pressure testing:
If the addition of a disinfectant to the drinking water is absolutely essential for carrying out the pressure test, we strongly recommend, in the case of metal pipes containing CML, the use of a disinfectant that does not react with the strongly alkaline CML (e.g. based on sodium hypochlorite NaOCl or chlorine dioxide ClO₂).
Pressure tests are complex procedures in which physical, material-specific and – as we have seen in this case – chemical properties interact. If you encounter unexplained phenomena or anomalous readings during your tests, please do not hesitate to contact us. Our experts will be happy to help you identify the causes and test your pipes safely and in accordance with regulations.
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