United States Department of Transportation
i
Dent Fatigue Life Assessment: Development of Tools for Assessing the Severity and Life of Dent Features
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2012-01-10
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By Semiga, Vlad
[PDF-1.51 MB]
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TRIS Online Accession Number:01640215
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NTL Classification:NTL-ENERGY AND ENVIRONMENT-Hazardous Materials Transportation
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Abstract:Federal regulatory standards require repair of dents with depths exceeding 6% of the pipeline diameter and for dents exhibiting signs of mechanical damage interacting with secondary features. However, leaks have been known to occur at dents with depths less than 3% of the pipe diameter and dents interacting with secondary features have been known to survive in service for extended periods of time. Engineering tools and empirical and mechanistic (numerical) models currently used for assessing the significance of mechanical damage are not able to accurately predict the strain state or fatigue life of the damage feature, as they are based on a number of assumptions (modeling and experimental data) rather than considering the anisotropy of the material properties, kinematic behavior of the materials, non-linear dent response to pressure and/or treating the dent solely as a geometric imperfection. This lack of accuracy can lead to either overly conservative assessments, promoting unnecessary maintenance, or the lack of required maintenance that could result in unexpected failures, which represent a significant environmental and safety concern and increases pipeline operating costs. The objective of the current project is to develop a detailed dent assessment procedure based on three dimensional non-linear structural and material responses which will then lead to the development of criteria for ranking the severity of dents and develop a simplified methodology for estimating the remaining life of dent features. This project will deliver three related approaches for assessing the fatigue life or cyclic loading dependent failure of pipeline dents (mechanical damage). All three integrity management tools draw upon pipeline operational, design and damage data. The methods provide a range of alternatives for integrity management, where the appropriate method for use is dependent on the desired outcome and the available information. The three methods are: (1) Dent Geometric Severity Ranking; (2) Dent Geometry and Load Severity Ranking; and (3) Dent Fatigue Life Assessment Guidance Note.
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