Coiled tubing is a long (sometimes more than 25000 feet) electrical resistance welded pipes that is uncoiled for the deployment of oil and gas wells to perform a variety of jobs that involve subjecting the pipe to high pressure, axial loads, and contact with acidification, and production environments among others. Since the pipe is coiled and deployed multiple times for different jobs during its lifespan, it is typically plastically deformed and fatigued.
This paper discusses the challenges of improving the performance of this welded pipe base material, as well as its multiple welds, when facing an inhibition failure that could cause exposure to corrosive and/or embrittlement environments.
The product development process resulted in the complete modification of steel chemistry, its welding procedures and heat treatment process. The testing program includes, among other tests, the exposure of the pipe to different environments, followed by fatigue testing to determine the remaining material resistance after such exposure.