عنوان مقاله [English]
Polyethylene (PE) pipes are widely used in oil and gas industry. Their joints are prone to various flaws e.g., lack of fusion and cold fusion, and are the most problematic part of the pipeline. So, the infrastructure industry requires effective techniques to evaluate the pipes and joints. Butt-fusion (BF) is the most common method of joining PE pipes. Ultrasonic inspections are usually carried out using pulses of finite bandwidth with different frequency components. PE is viscoelastic and its mechanical response at high frequency differs significantly from that of the low frequency. Therefore, when a broadband ultrasound pulse passes through PE pipe, the waveform of the pulse changes as result of attenuation and dispersion of PE. Previously, attenuation was primarily thought of in terms of the reduction of signal amplitude, ultimately limiting the penetration of ultrasound. Actually, one of the major effects of acoustic absorption through PE is wave form distortion. In the present study, with the aim of investigating the possibility of using ultrasonic waves to evaluate HDPE materials and butt fusion of polyethylene pipes, the characteristics and behavior of ultrasonic waves in HDPE materials are studied and researched. For this purpose, the finite element method is used to simulate the propagation of ultrasonic waves in HDPE butt fusion joints. Changes in the wave velocity, and amplitude of the received waves are measured in order to identify the dispersive behavior and attenuation of the waves in HPDE within the effective ultrasonic frequency range of 1-5MHz. Also, by modeling the lack of fusion (LOF) defects embedded in the BF joint with different lengths, the inspection sensitivity, using a 4MHz transducer, for evaluating the LOF defects is evaluated. The numerical results show that the dispersive behavior of longitudinal wave is decreased, as the frequency of transducer increases. Therefore, higher frequency transducers, in the range of 4-5 MHz, can be used for ultrasonic inspection of HDPE butt fusion joints to increase the inspection sensitivity.