Pre-coating Pipe Weld Inspection

Key details

  • Extra wide scanning width of the area to be coated is obtained

  • Height of features are measured to assess for coatability

  • Images are taken to provide two views of any feature – visual and 3-D

  • Assessment against the pass/fail criteria allows immediate remedial action

  • Rapid assessment of potential problems saves many days of pipelay vessel downtime if the problem is discovered early

  • Removal of coating problems saves many $100k's of costs should a pipe fail in service

  • The OMS systems have been used on multiple projects and more than 40,000 pipe joints

  • All systems are set-up, calibrated and verified using calibration artefacts

  • Improved pipeline integrity

Why?

Internal corrosion is a major issue in many pipelines. A first level of defence against corrosion is to paint the inside of the pipe to prevent it from starting. However, while it is relatively easy to coat the pipe as it is manufactured it is more difficult to coat the area around where the pipes will be welded together. Pipes are usually uncoated from approximately 50 mm at each end. This is because prior to welding, there will be some cleaning and grinding in this area, which is then followed by the welding process. There may be molten balls of weld spatter from the welding process which will adhere to the pipe wall. The coating process is a spray where each paint particle will generally follow a straight line from the source. What happens with any protrusion such as a weld or spatter is the spray may not completely cover the feature. When this happens the uncoated area is then likely to become a corrosion site. Any such site might eventually lead to the failure of the pipe as corrosion tends to accelerate around any weak areas. Weld spatter is not the only source of problems, sometimes the weld itself may not lend itself to coating.

Solution

In order to identify and prevent problems to the coating it is possible to review the coating area for spatter or a weld profile that does not meet the specification. Typically a camera might be used but as there is no depth information the image is only an aid to interpretation. The scheme used by OMS is to use a stripe laser to measure the height of any feature. This information coordinated with an image provides the means to easily identify and quantify problems that might occur in the coating process.

How?

The system uses the latest in camera and laser technology to collect the synchronised set of images and laser scans to provide the basic information for the pass/fail test. The laser beam is wider than for a typical weld scan in that it must encompass the both sides of the painted regions of the pipe.

The system has to operate on-board a pipelay vessel at sea close to the time of welding such that the weld itself is still very hot. Any delay in the inspection process will delay the entire vessel production as only when the weld area has been passed for coating can the pipelay process continue.

The system must be able to find the weld by traversing up and down the pipe because the system is connected to the internal line-up clamp (ILUC). The ILUC ensures that the pipes are aligned properly during the first pass of welding before it is released and withdrawn to bring the laser and camera system into operation. All of the information from the scan is rapidly sent from the device in the pipe to the qualified weld/coating inspectors who visually and dimensionally check for any problems. If everything is acceptable the pipe can continue to be welded but if a problem is found it will be necessary to manually remove the weld spatter or grind the weld back. In the worst case the pipe will be cut and the process of welding the pipe together started again.