One of the most widely used sectors in the industry is energy, which has been given many devices with the advancement of science and its emergence in the industry. In the discussion of energy, exchange is very important, the equipment used for this purpose is heat exchangers, and the heart of the heat exchanger is its tubes, which are responsible for this important. Due to high operating temperatures and proximity to the fluid, heat exchanger tubes become corroded or have various other defects over time and must be inspected periodically. One of the non-destructive inspection methods is magnetic flux leakage, which is based on magnetic testing, which is much less expensive than other methods due to the widespread use of ferromagnetic tubes in exchangers. According to research, an exchanger that is widely used in the industry has similar specifications to the heat exchangers of Pakman Company, a 3-pass horizontal steam boiler, model PSBHN-3500, ferromagnetic, with a small diameter and thick wall. Specifically, the tubes in question have an outer diameter of 50 mm and a wall thickness of 3 mm, seamless fire-resistant steel Mn417, which poses a challenge to other non-destructive testing methods. Given the conditions of the heat exchanger tubes, including the need to access both sides, the fastest and least expensive option for identifying corrosion defects is to use the magnetic flux leakage method. In this thesis, a simulation based on studies has been carried out first, then, according to the simulation results, a real device has been built and experimental tests have also been conducted. The result of these measures has been the detection of groove and hole defects with very low depth percentages on the control tube. With increasing the current applied to the electromagnetic generator, the signal voltage received from the sensor has increased, and with increasing the air gap of the sensor, the received voltage has decreased, and with increasing the air gap between the yoke legs and the surface of the inspected part, the peak value has decreased.