A Proposal Procedure to Estimate the Hydrogen Induced Cracking Growth Rate
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The assessment of Hydrogen Induced Crack (HIC) defects have been developed procedures to determine the integrity in terms of Remaining Strength, however, there is not a widely accepted procedure to estimate the Remaining Life of pressurized components with HIC. An equation based on a double exponential, describes adequately the behavior of HIC defects, it was obtained from an experimental array where HIC was reproduced artificially in steel plates with cathodic charging. It was performed an assessment of HIC defects that were founded in a steel pressure vessel, these damages were evaluated with the procedures of Fitness-for-Service Level 1 and Level 2, described in Part 13 of standard API 579-1/ASME FFS-1 (2007). Then with the double exponential equation, the HIC growth rate was calculated for each individual lamination, for this calculation de defect size and service conditions of pressure vessel were considered. The value of individual defect growth rate previously estimated, it was simulated growth defects individually from its initial condition up to 200 hours and phenomena as coalescence, interconnection and emergence of new defects was considered. Then, a new growth rate was estimated and a Fitness-for-Service assessment was performed for the new condition. The simulation was continued to assess growth to every 200 hours to 1200 hours. According to the above procedure, at the first stages of growth of HIC defects values of maximum growth rates of 21 mm2/hr, it occurs when defects have less than 500 mm2 of area. While after of growth of defects and interaction as coalescence and interconnection with its neighbor laminations the growth rate decreases to values of 0.0001 mm2/hr, this phenomenon could explained by the fact of this type of defects growth by inner pressure mechanism in each defect.

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