In the field of defects assessment, mechanical damage severity analysis is an issue of interest for many pipelines operators [1]. Indeed, common literature fatigue criteria [2] [3] [4] [5] often give underestimated dent lifetimes compared with experimental results. This causes repairs which could be avoided, therefore more predictive criteria would generate a significant maintenance costs saving.
This paper presents an improved method developed at CRIGEN (GDF SUEZ research center dedicated to gas and new energies) to assess dent defects subject to fatigue loadings. A realistic computational model based on the finite elements method has thus been developed. An analytic formulation of the stress concentration factor (SCF) giving more realistic results has then been set, allowing a classical fatigue analysis with S-N curves to be performed.
A specific software plug-in has been developed to automate the creation of the finite elements models. In these models dents are created at a realistic pressure with regard to the pipe characteristics. Then damaged pipe is exposed to a pressure variation to determine the maximal SCF.
After validation based on tests results, a simulated experimental design which covers diameters from 8 inches to 36 inches and steels from A37 to X70 has been set. Different indentation tools and different strokes have also been defined, resulting in 1080 simulations.
As a conclusion, this paper shows the method leading to the analytic formulation of the SCF allowing the fatigue assessment.
Experimental design, validation and computational modeling uncover DNA damage sensing by DNA-PK and ATM
