Pipelines transport invaluable energy resources such as crude oil and natural gas over long distances. The integrity of the piping system in terms of safety of the process is then of high importance. However, pipes are prone by time to defects that may degrade their properties and lead to failures. Particularly, wall thinning is a serious anomaly that threatens aging pipelines. Therefore, their inspection plays a critical role to prevent the collapse of the system. Magnetic Flux Leakage (MFL) is by far the most effective technique of nondestructive evaluation for robotic diagnosis of ferromagnetic pipes. This work follows a novel approach to control such problem and assess the condition of the pipe by measuring with a good precision the wall radial thickness based on calibrated curves of reference and using an MFL diagnostic system tool. The proposed technique is generic and can be applied systematically for pipes with different sizes and material properties. It represents an advancement over the current conventional practices which require multiple physical experiments to generate empirical reference curves. Such procedures are cumbersome, time consuming and in consequence costly. The MFL sensing tool will be placed at the end-effector of a mobile robot platform devoted for external pipe inspection in a desert environment. It is based on permanent magnets producing a strong magnetic field that locally magnetizes and saturates the sample in question. At areas where there is metal loss, the magnetic flux flowing in the pipe leaks from the wall, which is detected by a Hall effect sensor and compared to the reference curve to estimate the wall thickness.