A pipe is not finished when it's assembled — it's finished when it's been tested for leaks, flushed clean and put into operation with tape on. We cover leakage testing of empty pipes before concealment (the new DS 439:2024 requirement), pressure and leakage testing of water, gas and heating systems, flushing through and the certificates that must be in the file.
Introduction
Pressure testing and commissioning is where craftsmanship becomes documentation. It is not enough that the system works on test day — you must be able to prove that it is tight and clean, and that proof is part of the legally required quality documentation (KLS). A careful test catches errors while they are still accessible, and protects both the customer, the building and yourself.
Leakage testing of empty pipe before concealment
With DS 439:2024 came a stricter requirement that changes the workflow on the site: sleeves must be pressure-tested BEFORE they are concealed — bricked in, concreted or closed off. The point is obvious when you have experienced the opposite: a leak first discovered after the wall is closed and tiles are up is expensive and frustrating. By testing whilst the pipes are exposed, you catch the fault where it costs least.
Pressure and tightness testing of water installations
Water installations are tested with water (hydrostatic). The pipe is filled slowly from the lowest point so air can escape at the top — trapped air gives a 'soft', misleading pressure and can hide a small leak. The system must be completely water-filled and de-aerated before the test pressure is applied and read.
DS/EN 806-4 describes several test procedures (method A/B/C), because the materials behave differently: metallic pipes hold the pressure stable, whilst plastic pipes expand elastically under pressure, so the pressure drops a little by itself. For plastic, therefore, a procedure is used with stepwise pressure application and reading of pressure drop over specific time periods, so you can distinguish the normal elastic expansion from a real leakage. Choose the procedure that suits the pipe material, and follow times and steps precisely.
Gas tightness test
Pneumatic testing is more dangerous than hydrostatic
Water is practically incompressible — if a joint breaks during a water pressure test, the pressure drops immediately and not much happens. Air and gas, on the other hand, are compressible and store energy like a spring: if a joint breaks during an air pressure test, the energy is released explosively and can fling parts off. Therefore, the Danish Work Environment Authority states in guidance B.4.2 requirements for pressure testing of pressure vessels and pipelines — seal off the area, keep people away during testing and use pressure relief.
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