Pipe defect assessment made by strain based design

Strain-based design is preferred for situations where the loadings of the pipelines are due to forces other than the internal pressure and produce large stress and strain in the pipe wall. Such loadings can be generated by either permanent or transient ground deformation caused by seismic activity, soil subsidence, slope instability, frost heave, thermal expansion and contraction, landslides, pipe reeling, pipe laying, and other types of environmental loading. Therefore strain-based design is appropriate where the stresses and strains exceed the proportional limit and where the peak design loads will be reduced when the material strains. When strain and stress are not proportional, stress-based methods become very sensitive to details of the material stress strain behaviour and to any safety factors. Strain-based design avoids these problems. The methodology of strain-based design is developed in connection with the limit states: tensile rupture (material limit state) and compressive buckling (material and serviceability limit states). This paper presents an extensive review of strain-based design methods used for pipe defect assessment as: critical global strain as a criterion for pipe defect assessment; critical local strain as a criterion for pipe defect assessment; strain intensity factor as a criterion for pipe defect assessment; notch ductility factor; strain based design based on J-integral; strain based design based on crack tip opening displacement.