This paper introduces a magnetic field perturbation based on the magnetic response received from a small area of the wall as a solution to measure the internal defects of the pipes. In this method, there is no need for magnetic saturation of the wall, and wall thickness does not affect its performance. To build a magnetic field perturbation receiver, a permanent magnet with Hall Effect sensor was used. Since the arrangement of the sensor, ie. the position of the sensor relative to the magnet is of great importance, so it was simulated using the finite element method and the best position of the sensor was presented by analyzing the software results. Since the wall thickness is reduced, so in the simulations for different depths of the defect, the values of the received magnetic response were recorded and used as a measure to evaluate the amount of thickness reduction or defect depth. Also, an experimental test system was developed to compare the results of theoretical modeling and its results were compared with the results of the proposed model. The results show that the proposed method can be used as an effective tool to identify internal defects.