A Comparative Study of Acoustic Emissions from Pencil Lead Breaks on Steel and Aluminum Substrates Using Signal Analysis

Abstract Pipeline infrastructure is crucial in various industries, such as water management, transportation, oil, and gas. Detecting and monitoring potential failures or leaks in pipelines is paramount to ensure safety, prevent environmental damage, and optimize maintenance strategies. Acoustic emission (AE) is a passive non-destructive testing technique commonly used in pipeline monitoring, it detects faults caused by leaks, cracks, and external impacts in various engineering materials. Calibration is an important aspect of any AE monitoring process, and the Pencil-lead break (PLB) technique is highly effective in characterizing acoustic wave speed and calibrating the AE experimental setup. Producing a PLB AE source involves breaking a 0.3mm diameter pencil lead by pressing it against the surface of a test structure and applying a bending moment. This produces energy in the form of elastic stress waves, propagating through the test structure before being recorded and transformed into electrical signals by a transducer mounted on the test surface. In this paper, a comparative study of the behaviour of steel and aluminum substrates based on their time-frequency energy distribution from the burst impact of pencil lead breaks is conducted. This is accomplished by simulating AE PLBs in a controlled laboratory experiment on solid steel and aluminium cylinders (200mm diameter) surfaces to generate acoustic emission signals captured by the Piezoelectric transducer attached to the test objects. The acquired signals were analyzed using MATLAB software to study the differences in spectral behaviour on the test objects. The results indicate that the AE energy and average frequency are lower in the solid steel cylinder than in the aluminium cylinder due to differences in their relative density and strength. The response model will provide a theoretical foundation for future structural AE monitoring of oil and gas pipelines.