Comparison between API and DNV Codes about Fatigue Effects in Tubular Joints of Jackets

One of the important items in offshore structures design is fatigue analysis. Because of existence of periodic loads derived by wave, sea current, wind, etc. This analysis has become one of the major analyses in basic design. Estimate of structures life that is generated from fatigue analysis is more important in operation of the offshore unit. In fatigue analysis, Stress Concentration Factor (SCF) is used a main geometric index for controlling of joints resistant. Fatigue failure in the form of crack will start from details and propagate in structure. In steel structures these cracks will started from welds. Most of methods for failure life assessment in welded connections are based on stress values at critical points, called Hot Spot. The research results that in order to achieve an acceptable and relief pile dimensions, the fatigue of deep pile joints must be controlled using of DNV or API (RP-2A) S-N curves. In these paper fatigue of a jacket connections in south pars phase 12 as sample structure was investigated. The results show that the S-N (F) curve causes less fatigue life in sand in comparison with the S-N (C) in DNV standard. Then it is not fit for pile fatigue analysis. Also joints of pile embedded length is borne greater moment in comparison with leg joints, consequently they have less fatigue life.

کلیدواژه ها:

Jacket ، API code ، DNV code ، S-N curves ، Fatigue damage