Residual stresses in girth welds of carbon steel pipes: neutron diffraction analysis

Abstract

In the oil and gas industry, residual stresses in welded components, such as risers and oil offloading lines, play a key role in determining their fatigue and fracture performance. The focus of this work is on measuring the residual stresses in girth welds of large diameter (508 mm, 20 in. outside diameter) thick walled (25·4 mm, 1 in. wall thickness) pipes. Residual stresses were measured using neutrons on two girth welds on X-65 grade line pipes. One was a carbon steel weld with fully ferritic weld metal, and the second was an Inconel 625 dissimilar weld with fully austenitic weld metal. It was observed that while there were subtle differences, the overall magnitude and distribution of axial and hoop residual stresses were comparable in the two girth welds. These data are consistent with available previous measurements and computer models from the literature.

Keywords:

• Residual stress
• Girth welds
• Carbon steel pipes
• Dissimilar weld
• Neutron diffraction

The authors would like to acknowledge the National Institute of Standards and Technology Center for Neutron Research for beam time and support. NT and RA would like to thank D. Lillig, M. D. Crawford, G. Dunn and G. J. Atkins of ExxonMobil Development Company for their support and for providing the welded pipes used in this investigation.

Certain commercial firms and trade names are identified in this report in order to specify aspects of the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.