What happens after the welds have been made? 

The completion of the welding process does not yet mean that the pipeline is ready for operation. Once the joints have been made, the installation is inspected and the results of the assembly work are checked. The type of network, the diameter of the pipes and the specifications in the technical documentation all influence the scope of further activities. These usually include a visual inspection of the welds, preparing the installation for further testing and checking the completed section of the pipeline. 

Records relating to the progress of the work and the results of the tests carried out are then also analysed. Only then can it be determined whether the pipeline is ready for commissioning or handover for further work. 

visual inspection of welds prior to the leak test

Visual inspection of the welds.

The initial assessment is carried out before leak-tightness tests begin. At this stage, the appearance of the joints is checked, paying particular attention to their geometry and compliance with the requirements of the relevant technology. The scope of the visual inspection depends on the type of weld, but the aim remains to identify any irregularities that could affect the future operation of the system. 

Particular attention is paid, amongst other things, to the uniformity of the weld bead, the alignment of the pipe axes and any deformation visible at the point where the materials meet. The surface in the immediate vicinity of the weld is also inspected, as signs of mechanical damage or irregularities arising during installation may indicate the need for a more detailed analysis of the relevant section of the pipeline.  

Before starting the leak test 

Before testing begins, the system must be properly prepared. Checks are carried out to ensure that the joints have had sufficient time to cool and that all components of the pipework have been correctly secured. The pipes are then filled with water and any air that may remain inside the system is removed, as its presence could affect the test results. Before the test begins, time is also allowed for the temperature of the medium and the system to stabilise. Only after these steps have been completed can the actual leak test be carried out. 

How is a pipeline leak test carried out? 

A leak test allows an assessment to be made as to whether a completed section of the installation maintains the required parameters whilst under pressure. In the case of polyethylene pipework, the analysis of the results must take the material’s properties into account, as the pipes may expand slightly under load. For this reason, the interpretation of the results is not based solely on a single reading from the measuring equipment. The course of the entire test and the conformity of the values obtained with the agreed procedure are also taken into account. 

During the test, the behaviour of the section under test is monitored for a specified period of time. The system’s response to the applied pressure is assessed, as well as any signs indicating a loss of tightness. In practice, the analysis covers not only the welded joints but also the other elements of the system, including fittings, connections to other components and sections fitted with additional equipment.  

preparation of the pipeline for pressure testing

The results obtained during the test are used in the subsequent stages of the installation’s technical acceptance. A positive result confirms that the installation meets the requirements specified for the application in question and may proceed to the next stages of the technical acceptance process. 

Documentation of the work carried out 

In many cases, documents confirming the progress of the work and the parameters relating to the fabrication of the joints are also required upon acceptance of the pipeline. The scope of the documentation depends on the type of installation and the requirements applicable to the project in question, but it often includes information on the welds carried out, process parameters and the results of the tests conducted. The compiled documentation facilitates subsequent verification of the work and serves as confirmation that the work has been carried out in accordance with the agreed specifications. 

When is the pipeline ready for use? 

The procedure for carrying out the acceptance test may vary depending on the intended use of the installation and the specific nature of the project in question. Different procedures apply to short sections constructed for local connections, and different ones to extensive networks used in technical infrastructure. Only once all the required activities have been completed can the installation be handed over for operation.  

FAQ: 

1. Is every pipeline subjected to a leak test after welding? 
The scope of the tests depends on the type of installation, its intended use and the regulations applicable to the project in question. In many cases, a leak test is one of the key elements of technical acceptance. Its purpose is to check how the installation behaves under pressure. It also helps to detect any leaks before the pipeline is handed over for further use. 

2. Why is the air removed from the system before the leak test? 
Air trapped inside the pipes may affect the test procedure and make it difficult to interpret the results. For this reason, the system is vented before the test begins. 

3. Does a drop in pressure always indicate a leak? 
Not always. In the case of polyethylene pipelines, the properties of the material must be taken into account, as it may change its dimensions slightly under pressure. For this reason, the assessment of the results is not based solely on a single reading from the measuring equipment. The entire course of the test and the conditions under which it was carried out are also taken into account. 

4. How are the welds inspected before acceptance? 
The first stage involves a visual inspection of the joint locations. Among other things, the appearance of the weld bead, the alignment of the pipes and the condition of the surface near the weld are checked. A check is also carried out to ensure there is no visible deformation or damage within the joint. This enables some non-conformities to be detected even before leak tests and other acceptance tests on the installation begin. 

5. How long does a pipeline leak test take? 
The duration of the leak test depends on the type of installation, the length of the section being tested and the procedure followed. The course of the work is also influenced by preparatory activities, such as filling the pipes with water, venting the system or equalising the temperature. In practice, this means that the time required to carry out the test may vary even for installations with a similar purpose.