Heavy wall – small diameter ILI

 Pipeline Description:

Offshore flowlines 4“, wall thickness ½“, designed as a hair pin loop starting from the Gannet A platform (Central North Sea), passing by two subsea production templates and back to Gannet A. The total length is 11.7 km. There are flexible riser sections at the foot of the platform and bend radius of 5D within the risers. 

Why is it challenging?

½” wall thickness cannot be sufficiently magnetized in a 4” pipeline. Therefore, an MFL inspection is not feasible. Ultrasonic inspection tools, that could handle the wall thickness, were not available for 4”. Further, the permanent pig traps, having a length of only 1100mm, cannot be extended. 

Target of the inspection:

Perform a high-resolution inspection for internal local corrosion. Due to the project circumstances the inspection was to be carried out under urgency.