engleski

Structural integrity assessment of T-joints in steam pipelines

Structure integrity assessment is issued to failure prediction of cracked structural component regarding to increasing applied load or crack size. In order to ensure safe use of cracked structural component the many standards and procedures are available (e.g. BS7910, API 579, SINTAP, R6), cited as refs. [1-4]. The results obtained by using of these procedures consist always certain portion of conservatism, what leads to underestimation of the real carrying capacity of engineering component. The calculation based on analytical solutions given in such procedures defines in the rule a lower value of critical crack size, which causes the failure of structure. In the other hand the solutions for component carrying capacity or critical crack size determined by numerical model corresponds specific geometry of component and crack’s parameters. The main disadvantage of this approach is that numerical model demands long term and exhausting modelling, especially in the case when the engineering component geometry or crack geometry is complex, e.g. semi-elliptical and spherical crack located out of the model symmetry. In this paper a T-joint of 8 inch RHR nozzle on 29 inch RC hot leg as the part of a high pressured pipeline of the nuclear power plant has been considered as engineering component. The critical part of a T- joint is the transition between two pipes of different diameters, because the difference in the pipes’ shell thicknesses causes higher stress intensity. Some experiences of operators show that a semi-elliptical surface crack can occur at this place during exploitation of steam pipelines.

Integrity assessment; steam pipeline; T-joint; finite element analysis

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