Abstract
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.
Highlights
The continuously growing world energy demand requires access to remote resources. The pipelines to these locations have to traverse through harsh environments and may be subjected to plastic deformation while in service due to imposed displacements
Single edge notch tension testing (SENT) specimens are extracted from an API-5L X70 pipeline steel grade and defects are introduced in the base metal at different locations
Differences in the calculated resistance curves will be compared to the visual information on the fracture surfaces and to a hardness map
Summary
The continuously growing world energy demand requires access to remote resources. The pipelines to these locations have to traverse through harsh environments and may be subjected to plastic deformation while in service due to imposed displacements. An important parameter in this design is the crack growth resistance [1]. The unloading compliance method allows accurate measurement of crack growth and the development of a crack growth resistance using a single specimen [2]. Several analytical equations have been developed to calculate the crack growth based on the measured specimen compliance. SENT specimens are extracted from an API-5L X70 pipeline steel grade and defects are introduced in the base metal at different locations. Differences in the calculated resistance curves will be compared to the visual information on the fracture surfaces and to a hardness map
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