Conventional In-Line Inspection (ILI) technology is based on ultrasonic (UT) or magnetic flux leakage (MFL) sensors, both of which are unable to inspect CRA mechanically lined pipelines. UT sensors cannot transmit the sound wave through the interface between the CRA liner and carbon steel base pipe. MFL cannot inspect the carbon steel pipe because of the inability to permeate the magnetic field through the CRA liner. To address this gap in commercial ILI technology, ExxonMobil and Innospection Ltd. are working to develop a new ILI sensor technology based on a combination of MEC (Magnetic Eddy Current) and multi-differential eddy current. Initial feasibility trials were conducted with a prototype ILI MEC tool. Tests were conducted on an 8.625” (219 mm) X65 carbon steel pipe lined with 0.118” (3 mm) of Inconel 825 pipe. Four types of defects were introduced in the pipe to represent natural defects anticipated in service:
- Metal loss of features 3 mm to 24 mm in diameter on the external surface of the carbon steel base pipe
- Erosion on the internal layer of the CRA liner
- Internal girth weld cracks at the interface of the liner and the weld overlay
- Metal loss defects at the interface of the CRA and carbon steel
Over 80 pull tests were conducted to determine the detection capabilities and speed sensitivities of the tool. All defects were detected by the sensors including the very small (<10 mm) pinhole features. No effect of detection performance was observed for speeds up to 0.75 m/s. Since detection capabilities exceeded expectations, future development can continue based on the current prototype.