PSI - Issue 2_A

A. Bastola et al. / Procedia Structural Integrity 2 (2016) 1894–1903 Author name / Structural Integrity Procedia 00 (2016) 000 – 000

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4. Conclusions

Small-scale and full-scale experiments on X80 line pipe specimen containing girth welds have been carried out to determine the strain capacity X80 pipes with girth welds. The observations are as follows: - Small-scale tests have revealed a variation of through-thickness tensile and hardness properties in the X80 pipes. Results of the tensile tests indicate that the yield stress overmatch of approximately 20% for the weld metal, and that the HAZ region is about 7.5% softer compared with BM at 1% applied strain. Both SENB and SENT test results show that the fracture toughness from the WM is lower than that from the HAZ. Hardness measurements on the weld cross-section show that hardness is consistently high in the fusion zone, it decreases on either side of the fusion zone in the HAZ regions. The hardness of the parent material varies significantly with position (distance from the weld root). High hardness in the parent material at the inner diameter of the pipe is also observed which decreases towards the outer diameter. - The full-scale reeling tests have shown that the welded X80 pipes can sustain a nominal strain level of up to 2.5% without any instability for the range of defect sizes considered. - The full-scale bending tests have shown that, for similar levels of applied strain, the CMOD of the HAZ flaw is generally higher than that of the WCL flaw of the same initial size. In addition, tearing of HAZ flaws can be much higher than that of WCL flaws. During pressurised full-scale bending tests, a through thickness crack and unstable crack growth are observed for WCL flaw and HAZ flaw respectively, leading to the conclusion that HAZ softening may limit the acceptable critical size in an ECA for X80 pipes.

Acknowledgements

The authors gratefully acknowledge the significant contribution to this work from the Open University, UK and from DNV GL Høvik Materials Laboratory, Norway. The authors would also like to thank Erling Østby for reviewing and providing feedback on this paper.

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