| tech. |
электроиндуктивный метод дефектоскопии с замером поля в удалённой точке (Remote field testing (RFT) is an electromagnetic method of nondestructive testing whose main application is finding defects in steel pipes and tubes. RFT may also referred to as RFEC (remote field eddy current) or RFET (remote field electromagnetic technique). An RFT probe is moved down the inside of a pipe and is able to detect inside and outside defects with approximately equal sensitivity (although it can not discriminate between the two). Although RFT works in nonferromagnetic materials such as copper and brass, its sister technology eddy-current testing is preferred. The RFEC tool uses a relatively large internal solenoidal exciter coil which is driven with low frequency AC. A detector, or circumferential array of detector coils, is placed near the inside of the pipe wall, but axially displaced from the exciter by about two pipe diameters. Two distinct coupling paths exist between the exciter and the detector coils. The direct path, inside the tube, is attenuated rapidly by circumferential eddy currents induced in the tube's wall. The indirect coupling path originates in the exciter fields which diffuse radially outward through the wall. At the outer wall, the field spreads rapidly along the tube with little further attenuation. These fields re-diffuse back through the pipe wall and are the dominant field inside the tube at remote field spacing. Anomalies anywhere in the indirect path cause changes in the magnitude and phase of the received signal, and can therefore be used to detect defects. ixtra) |
