Imaging a weld cross-section using a novel frequency feature in multi-frequency eddy current testing

In this paper, a novel frequency feature (the frequency at which the real part of the inductance reaches a specified value) is proposed for imaging an X70 welding cross-section. It is derived that this frequency feature is related to the permeability of the sample and therefore the imaging results obtained from this feature are a reflection of the electromagnetic properties (in particular permeability) map of the sample. The resulting images are then compared with the weld macrograph and the hardness map. The shape and contour of three weld zones (fusion zone, heat-affected zone and base metal) can be identified. This novel imaging method has a high sensitivity to changes in microstructure and, by adjusting the inductance value it crosses, the frequency range can be adjusted to suit the capability of a particular instrument.

Evaluation of ductile tearing for API-5L X70 pipeline grade steel using SENT specimens

Pipelines in harsh environments may be subjected to large deformations. Classic stress-based design needs to be complemented with strain-based design. An important parameter in the design is the crack growth resistance. SENT testing (Single Edge Notch Tension) allows to determine the so-called material’s tearing resistance curve. Very recently the first standard on SENT testing, BS 8571:2014, has been published. SENT testing is however still subject to extensive research and different approaches with respect to eg. notch placement, crack extension measurement and analysis exist. In this paper two methods for calculating crack extension based on the unloading compliance procedure are used and compared, proving that they show little difference. This is performed on an API-5L X70 steel grade and this for different configurations, namely an inner diameter notch and a through thickness notch. The results showed little difference between the different configurations, although the inner diameter showed higher crack growth resistance. Furthermore, the results are compared to visual observations of the fracture surfaces and a hardness map. The fracture surfaces corresponded to the obtained resistance curves. However, no real correlation between the hardness map and the other results could be seen.