PSI - Issue 16

Valentyn Uchanin et al. / Procedia Structural Integrity 16 (2019) 198–204 Valentyn Uchanin, Giuseppe Nardoni / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 8. (a) ELOTEST SR-1 rotor with developed EC head with calibration reference standard and (b, c) signals from cracks on hole sidewall (b) without signal processing and (c) with 20 Hz cutoff frequency HP filtering. Fig. 8 (right) represents the results obtained in rotating mode at operational frequency 400 kHz with reference standard application without any signal processing (b) and for HP filtering with 20 Hz cutoff frequency (c). In both cases high sensitivity with good noise suppression was achieved.

4.3. Detection of flaws in ferromagnetic steel forgings

Forgings are formed from ingots or billets and shaped applying the hammers or presses by forcing the solid metal into a cavity. In accordance with recommendations for marine industry the surface inspection in forging are to be carried out by visual, magnetic particle or liquid penetrant testing (IACS Rec. № 68 (2000)). Our comparative investigation show that more reliable results can be obtained by EC method when double differential type EC probe is applied (Lutcenko et al. (2012)). Developed array type EC probe (see section 3) in combination with ELOTEST B300 type flaw detector was successfully applied for detection of cracks in ferromagnetic and stainless steel tube forgings. Special reference standard specimen with 0.2; 0.3; 0.5; 1.0 and 2.0 mm depths electrodischarge slots was developed for calibration of the developed array type EC probe before inspection (Fig. 9).

Fig. 9. (left) Ferrous steel reference standard with array type EC probe and (right) signal obtained for 0.2 mm deep electrodischarge slot (upward) and lift-off signal (downward).

In Fig. 9 the signal of array type EC probe from 0.2 mm deep slot in ferromagnetic steel specimen on the screen of ELOTEST B 300 flaw detector on operational frequency 200 kHz are presented to demonstrate the possibility to differentiate the signals created by crack and lift-off due to different direction of these signals in complex plane. Such feature permits to improve the inspection reliability. Array type EC probes were successfully applied for inspection of forgings in connection with ELOTEST B 300 flaw detector. Application of array type EC probes facilitates the 4-5 times increase in inspection productivity.