Inspection of a cladded pipe

Pipeline Description:

4” wet sour gas flow line in Northern Germany. Pipe dimensions: carrier pipe, (StE 360.7 S) OD 114,3mm, WT=11mm, ID 86,3mm. Liner is Alloy 825 (material no. 2.4858) WT 3mm. Total length is 600m. 

Why is it challenging?

Ultrasonic inspection tools, that could handle the wall thickness, were not available for 4”. Further, limitations were reported whether the surface between carrier pipe and liner will reflect sufficiently. An MFL inspection is not feasible since it does not refer to the liner material. Further the 11mm ferritic wall thickness cannot be magnetized by a 4” MFL tool. 

Target of the inspection:

Perform a high-resolution inspection for liner wall thickness and in particular lift-off of the liner from the internal surface of the carrier pipe.