Bend it like Beckham
Written by Tim Clarke FInstPhys
David Beckham was a master of the curved ball caused by spin and the difference in pressure of one side of the ball compared to the other. Technip and Subsea7, and a small select group of companies, are the masters of taking seemingly rigid and straight pipes and bending them onto a bobbin, then deploying them offshore and unwinding the bobbin into the sea via a straightening device. While Beckham’s aim in life was to sneak a ball into a part of the goal mouth the goalkeeper could not cover, the other benders aim is to get the largest oil companies in the world to accept that this method is as good as any other for putting their pipes in the water.
I got involved in the process of helping these major league contracting companies to convince the Shell’s, Chevron’s, Petrobras’s of the world in about 2002. This was when Technip asked me to produce an instrument for them that could measure changes in ovality and the residual ovality during simulated reeling trials. The reeling trial involved bending a pipe against a former to simulate the bending onto the reel onboard a pipelay vessel. Then unbending the pipe against another former to simulate the unreeling process from the reel to the sea. During this process the pipe, just like a drinking straw, can change shape and ultimately collapse. The trick is to know that this is not happening and will not happen. As the pipe is bent and unbent it will go from being more or less round to an egg shape. When it is straightened it will return to the original shape but some residual ovality will remain. To the expert this change of shape can be tied to the model the engineer had of the process and if the two things tie up the pipe can be deemed to be capable to being bent without fear of a collapse.
The tool I delivered to Technip, who were pioneering this method, is shown in Figure 2.
I had hoped that having developed this equipment my fortunes were going to be made by selling tools like this to queues of willing buyers. Unfortunately after a comprehensive publicity round I found that the number of clients beating a path to my door was precisely zero. This is often the problem for those who are too far in advance of the needs of the time. I had my early adopter but would need to wait a while for the rest of the pack to catch up with Technip and myself.
Figure 3 illustrates a typical bending rig where the bending has taken place for this particular pipe.
In order to understand the extent of the ovality of the pipe during this process it was necessary that the pipe measurement tool was inside the pipe during the bending and unbending process. Figure 4 illustrates an operator moving the tool within the pipe using pushrods.
Figure 3. Bending Trial Rig with pipe bent against the former Figure 4. Operator moving tool inside pipe using pushrods
At any location along the pipe, required by the client, it became possible to provide the client with a detailed understanding of the pipe shape. Figure 5 illustrates a typical unwrapped and exaggerated profile of the pipe during the simulated reeling process.
While a small amount of ovality is good, excessive ovality is not. By taking over 2,000 measurements around the pipe a very clear and accurate understanding of the geometry of the pipe was obtained. The end goal is demonstrated in Figure 6 which shows how pipes of several kilometres long can be reeled onto a vessel for subsequent pipelay.
There are huge benefits to the client in being able to lay many kilometres of pipe in one go. For myself, the satisfaction of being involved in this process is part of the story and the eventual development from a one off sale to a complete world beating pipe measurement service was the other part.
Figure 5. Unwrapped ovality plot (blue) and exaggerated plot (black) Figure 6. Spooling onto a pipelay vessel