W enbin Dong

DNV, Oslo, Norway



In this paper analysis results using finite elements are compared with strain measurements and laboratory fatigue testing of doubling plates used in floating production platforms. Circular and quadratic doubling plates of thickness 10 mm with diameter and length equal to 150 mm fillet welded to a main plate of thickness 20 mm were tested. The doubling plates were fatigue tested to failure and the number of test cycles was compared with design standards. This assessment was also performed by using finite element analyses of the doubling plates using different methods for hot spot stress derivation in combination with relevant S-N curves. The analyses included:

  • The nominal stress method
  • Different hot spot stress methods
  • The notch stress method
  • Crack growth analysis using fracture mechanics.

Analyses were performed using 8-node shell elements and 20-node solid elements. Different methods were used for assessment of hot spot stresses based on calculated surfaces stresses at the weld toe. Also stresses through the thickness of the main plate were used for assessment of the hot spot stress. The main attention was made to the weld toe. However, the main reason for performing the fatigue testing was related to concern for crack growth from the weld root. This failure mode was found to be less critical than fatigue crack growth at the weld toe. The results from this work are being used for developing more reliable analysis methods to be included in design standards.


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