Ultrasonic testing of railheads using the electromagnetic-acoustic method

Abstract

Theoretical and experimental studies of the mirror-shadow ultrasonic testing of railheads using the electromagnetic-acoustic (EMA) method have been performed, and schemes and facilities for this technique have been developed. The main factors affecting the results of tests are determined. The tolerable limits of the changes in the tested parameters are established. It has been shown experimentally that the EMA method is highly sensitive in detecting flaws of technological origin in the railhead bulk, which do not produce echo signals with sufficiently high amplitudes.The surfaces of many industrial products have intricate shapes. This leads to significant difficulties in developing the facilities and techniques for ultrasonic (US) tests. Rails are such objects. Semenov and Karpushenko [1] have reported that "In accordance with the information from the Russian Ministry of Railways, 100000 to 150000 defective rails, including 20000 to 42000 highly defective ones, are removed from railway tracks every year. The considerable number of fatigue-type defects is due to the presence of flaws of metallurgical origin in rails." Let us consider an example of flaw detection in a railhead as one of the most important and intricate forms of rail elements. A large number of schemes for performing the US testing of a railhead are known, according to which its bulk is sounded using differently-oriented transducers [2,3]. Piezoelectric transducers that were used to perform tests in well-known studies possess substantial shortcomings inherent to them [4]. The situation can be improved by using the automatic electromagnetic-acoustic (EMA) "dry" US testing technique, which has substantial advantages over the "wet" method of US flaw detection in articles [5], especially in the case of automatic and automated inspection. The pioneering studies in this field were carried out using the mirror-shadow method at the Research Institute of Bridges at the Leningrad Institute of Railway-Transport Engineers under the supervision of A.K. Gurvich. The results of studies and development of facilities for US testing of railhead bulks using the EMA method accompanied by the echo technique were considered by us earlier in [6]. At the same time, papers [7,8] show theoretically and experimentally the advantages of applying the mirror-shadow testing method using linearly-polarized bulk shear waves for detecting internal flaws that appear during manufacture and do not produce echo signals with sufficiently high amplitudes. Therefore, this study is devoted to the study and development of the techniques and facilities for mirror-shadow testing of railheads using the EMA method.Let us model a railhead by an object with two surfaces tilted relative to each other. When an US beam propagates in this object, zones are formed in which the metal surfaces vibrate with different phases. The path length passed by the US beam determines the phase of elastic vibrations. It can be easily shown that, for ∆ l = n λ , where ∆ l is the path difference of beams, λ is the wave...

Sensitivity Of Ultrasonic Testing By Electromagnetoacoustic Technique At Detection Of Natural Internal Defects Of Metal Products. Possibilities Of Thickness Measurement. (review P. 3)

“…В результате, например, в железнодорожные пути попадают рельсы с дефектами, которые приводят к авариям поездов (рис. [8]. Параметры контроля: частота заполнения зондирующего импульса -1,9 МГц; индукция постоянного магнитного поля в зазоре между ЭМАП и головкой рельса -0,9 Тл; зазор между ЭМАП и рельсом -0,5 мм; соотношение амплитуды донного сигнала и помех на контрольном образце не менее 21 дБ.…”

“…7. Дефекты макроструктуры в головке рельсов в виде белых пятен (а) и скоплений НВ (б) [8] ПРОИЗВОДСТВЕННЫЙ РАЗДЕЛ вучивание дефекта выполняли со стороны поверхности катания головки рельса (расстояние от индуктора ЭМАП к вершине трещины около 150 мм). Установлено, что отношение амплитуд эхо-сигнал/шум по длине рельсовой пробы менялось от 0 до 4,5 раз.…”

State-of-the-art capabilities of EMA flaw detection

“…The further service of this facility yields an economic effect of ~105 million rubles a year owing to an increase in both the quality of products and the inspection rate and exclusion of the procedure of conditioning the articles' surfaces, which costs approximately 550 rubles/t. In addition, the introduction of overall inspection leads to a sharp increase in the processing discipline.FEASIBILITIES OF THE EMA TECHNIQUE DURING NONDESTRUCTIVE TESTING As in the case of contact acoustics, the flaw detection with the use of the EMA technique predominantly utilizes two inspection techniques: pulsed and resonant [1,5,20]. The pulsed method is implemented by using mainly the same electronic units [32] as those in conventional ultrasonic instruments, in which sound is excited and received by piezoelectric transducers [33].…”

“…FEASIBILITIES OF THE EMA TECHNIQUE DURING NONDESTRUCTIVE TESTING As in the case of contact acoustics, the flaw detection with the use of the EMA technique predominantly utilizes two inspection techniques: pulsed and resonant [1,5,20]. The pulsed method is implemented by using mainly the same electronic units [32] as those in conventional ultrasonic instruments, in which sound is excited and received by piezoelectric transducers [33].…”

“…Since 1983, all rails produced at the OAO Kuznetsk Iron and Steel Works, OAO Nizhni Tagil Iron and Steel Works, and OAO Azovstal' Mariupol Iron and Steel Works have been subjected to nondestructive testing by the mirror through-transmission method in the cross section restricted to the rail-neck thickness [4,5,27] and in the railhead cross section (OAO Kuznetsk Iron and Steel Works) [20,96]. Attempts to test ferromagnetic rods [55]; tubes [12,28,56,57]; separators of bearings [25]; rolled sheets [58]; billets of round cross sections [26]; and other articles [1] produced from steel [4,9,26,28,39,42,57], cast iron [9], aluminum [9,36], copper-and titanium-based alloys [1,9,59], composite materials [60], etc., have been undertaken.…”