Inspeção de tubos internos de trocadores de calor bitubulares por ultrassom

Abstract

Bitube heat exchangers are widely used in the petrochemical industry to either cool or heat process fluids. The structure of these heat exchangers comprises of two concentric tubes, with the coolant flowing in the space between the walls and the process fluid circulating inside the inner tube. These heat exchangers operate under significant temperature variations and are susceptible to corrosion caused by the coolant. Ultrasonic thickness measurement can be easily conducted on the outer tube. However, measuring the wall thickness of the inner tube requires inspection through a viewing window, which results in the disadvantage of imprecise measurements of the equipment's integrity. Although the IRIS (Internal Rotary Inspection System) technique can be used, it requires stopping and flooding the exchanger, which leads to production losses and uncertain results due to the difficulty of cleaning the tube based on the process conditions. Alternatively, the thickness can be measured by disassembling the entire exchanger, which is the most disadvantageous method, due to the costs involved. This study proposes a novel methodology for determining the thickness loss in the annular space between tubes from the external wall, using a normal ultrasound transducer. Two specimens were manufactured for this purpose. The first specimen was designed to adjust the inspection procedure and validate the results, while the second specimen was created to reproduce a real condition, using an inner tube that had been in operation for fifteen years. The experimental results demonstrate the feasibility of the proposed methodology and its benefits in ensuring the integrity of this type of equipment.