Desenvolvimento de máquina tracionadora para sonda de inspeção de trocadores de calor

Abstract

The oil and gas industry uses Shell and Tubes heat exchangers in a large amount of production steps, needing this equipment always within the quality requirements. For that is necessary to validate this quality with regular inspections, especially through non-destructing testing. One possibility for this kind of equipment testing is using the Remote Field Testing (RFT). This testing consist of passing an inspection probe equipped with excitation and receiving coils inside a tubular bandle. The induced magnetic field reading has a characteristic signal for tubes within the quality requirements. When the tube under inspection presents out of pattern readings, it is possible to infer the existence of irregularity(s) and/or defect(s), generally material loss due to corrosion. Even more so, the signals show which type of defects and their degrees. For the defect detection success it is necessary to take certain precautions, such as the probe traction in a constant speed. The Acoustics and Vibration Laboratory of the Federal University of Uberlândia does researches involving the RFT, making it necessary to have a traction probe equipment, however commercial equipment has high costs. In this context, the present work aims the development of a low cost traction machine to enable the tests. For this development, the traction machine is divided in three modules: traction, power and control. The first holds a CC motor and incremental encoder to provide movement and angular speed reading. In the power module there is components to convert de alternating current in constant current to supply the machine. Finally, the control module consists of a Human-Machine Interface in a Joystick shape with a microcontroller and FreeRTOS real time operational system for closed loop digital controller implementing to track commanded speed probe motion. Aiming the controller development, a mathematical model was identified for the adopted engine using the frequency response. Then, based on the model achieved, a Proportional-Integral type controller was designed. Results of simulation and experimentation show that the control system developed is able to make the probe move next to the speed set by the operator. Therefore, the traction machine developed throughout the present work achieved the proposed goal. Even more so, adding the costs of material and equipment used, an estimated cost of R$ 1.992,17 was obtained, significantly lower than commercial equipment costs.