Session: 03-02-01 Fatigue Performance and Testing

Paper Number: 127160

127160 - Fatigue Performance of Riser Quality Girth Welds: Fracture Mechanics Study of the Slope Transition Point Using Dnv’s Girth Weld Database. 

The fatigue design S-N curves for welded joints include a change in slope to enable fatigue life under variable amplitude loading to be calculated. In in DNV-RP-C203 and BS7608 the slope changes from m to m+2, for most of the fatigue Classes for welded joints, this is a change from a slope of m = 3 to m = 5. The slope transition point (STP) is located at 1x107 cycles in DNV RP C203 but at 5 x 107 cycles in BS7608.    

A method was proposed which uses fracture mechanics analysis and a variable amplitude loading spectrum to understand the most suitable location for the STP for girth welds in risers and pipelines. The crack growth assessment is evaluating the failures occurring at 10 million region of the girth weld database Different positions of the slope transition point (STP) were used in conjunction with two-slope S-N curves in the Miner’s damage sum. By comparing the number of blocks of the histogram applied in both analyses, a suitable position for the slope transition point (STP) in the bilinear S-N curves can be suggested, for the particular VA stress histogram applied. This paper describes the findings related to STP for VA loading for different VA stresses, including recommendations for further work        

Presenting Author: Agnes Marie Horn DNV

Presenting Author Biography: Agnes Marie Horn has a M.Sc. from NTNU in Trondheim 1996. She has more than 25 years of experience within Offshore and Energy related topics with focus on design and fatigue analyses of jackets, steel catenary risers, flexible risers and umbilicals. She is currently involved in several H2 related project. She has carried out both research and project work related to arctic and cold climate issues with focus on arctic pipelines, arctic materials and marine icing, fatigue of girth welds. She has been chairing the 2009 and 2012 ISSC working group “Fatigue and Fracture” and Subsea Technology committee ISSC2022, a member of the 2015 Committee and ISSC 2018 working group for Material and Fabrication Technology. She is currently a chairing the Material and Fabrication Technology ISSC2025. She is part of the technical material program of the OMAE conference. Her main interest and skills are within fatigue and fracture related topics, environmental impact of materials, Hydrogen transportation and technology qualification.

Authors:

Agnes Marie Horn DNV
Carol Johnston TWI