Utilizing Circumferential MFL for the Detection of Linear and Axially Oriented Metal Loss Anomalies in Pipelines

In-line inspection (ILI) technologies have advanced quite significantly since their first usage over 30 years ago. This has been even more evident over the last 5–10 years. Technological developments in electronics, computing power, combined with an increased and better understanding of complex physical applications have lead to the latest generation of in-line inspection technologies which have been commercially available over this same time period. The owner / operators of the liquid and gas pipeline systems are faced with an increased awareness of their aging infrastructures and they are looking to the experts and providers of the latest technological developments to assist them in their efforts to manage and maintain pipeline integrity. ILI has proven time- and time again to be the most useful and cost effective tool that pipeline operators have to ensure safe, reliable and economic operation of their pipeline system(s). One of the main challenges that the industry is currently facing is the early detection of long narrow, axially oriented defects in pipelines. There have been various efforts within the industry to accomplish the goal of producing an efficient system that is economically feasible as well as reliable. In an effort to meet the demand for an in-line inspection tool that can meet the challenge, ILI companies have developed different applications. Ultra-sonic tools have been researched, developed, and used commercially in an effort to detect axially oriented anomalies affecting both pipe body and longitudinal weld seam. However, a tool utilizing UT technology is highly dependant upon the pipe’s functionality and medium (gas / liquid), and thus, is prone to incomplete and/or unacceptable survey data. Taking this into account, the utilization of UT technology for these purposes can be very costly with limited results. Because of the limitations and issues that UT tools experiences, ILI providers also researched the feasibility of utilizing proven MFL technology in this application. After proper development and testing, Circumferential Magnetic Flux Leakage technology was released for the inspection of pipelines — specifically, pipeline systems that were in need of longitudinal seam weld inspection. ROSEN’s solution to this challenge is the Axial Flaw Detection (AFD) tool. The AFD tool utilizes Magnetic Flux Leakage (MFL) technology by applying a circumferential magnetic field (CMFL), as opposed to the traditional axial oriented application of the field, to the pipe wall in order to detect and characterize anomalies which are linear and/or axially oriented that a typical MFL tool would under grade or not even detect. This article is meant to give the reader a better understanding of the technology as well as the development process of complex in-line inspection in today’s comprehensive and demanding pipeline industry. It will also provide historical findings within controlled environments and statistics from dig verifications from actual surveys.