Transmission pipelines, which are usually subjected to a variety of loads ranging from internal pressure to external pressure ground loading, transport gases and liquids at high pressures. Furthermore, the pipelines exhibit various forms of damage from environmentally induced cracks to manufacture and operation induced cracks. Therefore, it is of great engineering significance to establish acceptable levels for the flaws revealed. The acceptance levels for flaws are based on the concept of fitness for purpose. By this principle, a particular fabrication is considered to be adequate, provided that the conditions to cause failure are not reached. Less severe flaws are accepted without further consideration. Moreover, if flaws are more severe, rejection is not necessarily automatic. Based on fitness for purpose, decisions on whether rejection or repair might be justified, either in the light of previously documented experience with similar material, stress and environmental combinations or on the basis of an engineering critical assessment (ECA). The present paper focuses on two objectives. Firstly, the remaining strength and fracture toughness of the pipeline with defects along the longitudinal direction of the pipeline have been obtained. Secondly, the utilizing reliability of the pipeline, which has been tested to have inner flaws and to what extent this kind of defects may exist in the pipeline purchased from the same manufacturer, has been evaluated. Based upon the description of the defects found in the pipeline, the remaining strength assessment is performed with the application of different codes such as B31G and DNV. Also, an ECA sample for the embedded flaw in plates will be performed according to the existing BS 7910 methodology. The initial crack depth is 2a and the width is 2c. According to the BS7910 standard, the fracture and fatigue assessment is applied to obtain the fracture ratio Kr and the load ratio Lr. A 4th Runge-Kutta method is used to calculate crack growth rate da/dN and the final size of the crack af and cf. Also the Failure Assessment Diagram (FAD) can be changed according to the material stress-strain curve. This work might provide useful reference to safety design and application of pipelines.

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