In the construction phase, a lot of human activities are taking place around the pipeline. During the construction therefore, damages in the external coating system can easily occur. Employees walking over the pipes, construction tools can fall at the coating, during pipe laying in the ditch. You could think of many different scenarios that will harm the future integrity of the pipeline. We will sumarize the most common damages during the construction phase.
The application of coating at the circumferential welds
As a circumferential weld is present every 12 or 16 m in a pipeline, proper application of the coating system at the weld is very important.
The pre-treatment of the steel surface and the factory coated area around the weld should be performed according the recommendations of the supplier of the weld coating system.
Poorly coated areas may lead to damage of the coating in the near future. Such areas are the overlaps of the coating on itself (wrapping systems) and the overlap on to the factory coating. In case of poor application, this may lead to disbonding in a relative short period of time.
Please note that spark testing of the weld area in the field, the poor overlap at wrapping coating systems may not be detected.
Damage of the coating after the application of the CP cables
In order to apply cathodic protection by ICCP systems, cables need to be connected to the steel surface. This is usually done by pin bracing the cable on the pipe surface. In order for this welding procedure to take place, removing of a small area of factory applied coating is unavoidable. It is most important that this area is recoated in a proper way. When performing a coating survey on a pipeline, many indications of coating damage are detected around these pin brace connections; in most cases the coating defect is related to a wrong recoating after applying the CP cables.
Damages in the external coating during backfilling
Damages may occur during the backfilling of the pipeline ditch. Stones and other sharp objects in the backfilling soil may damage the external coating even before the pipeline will be operated. The use of fine grained sand at the bottom of the ditch is recommended. Another possibility is to seeve the original sand and to gently fill back this filtraded sand in the ditch.