Stress assessment in piping under synthetic thermal loads emulating turbulent fluid mixing

• Published in: Nuclear engineering and design 2015-03, Vol.283, p.114-130
• Main Authors: Costa Garrido, Oriol, El Shawish, Samir, Cizelj, Leon
• Format: Article
• Language: English
• Subjects: Assessments; Fluid dynamics; Fluid flow; Fluids; Piping; Stresses; Three dimensional; Turbulence; Turbulent flow
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2014.10.016

•Generation of complex space-continuous and time-dependent temperature fields.•1D and 3D thermo-mechanical analyses of pipes under complex surface thermal loads.•Surface temperatures and stress fluctuations are highly linearly correlated.•1D and 3D results agree for a wide range of Fourier and Biot numbers.•Global thermo-mechanical loading promotes non-equibiaxial stress state. Thermal fatigue assessment of pipes due to turbulent fluid mixing in T-junctions is a rather difficult task because of the existing uncertainties and variability of induced thermal stresses. In these cases, thermal stresses arise on three-dimensional pipe structures due to complex thermal loads, known as thermal striping, acting at the fluid-wall interface. A recently developed approach for the generation of space-continuous and time-dependent temperature fields has been employed in this paper to reproduce fluid temperature fields of a case study from the literature. The paper aims to deliver a detailed study of the three-dimensional structural response of piping under the complex thermal loads arising in fluid mixing in T-junctions. Results of three-dimensional thermo-mechanical analyses show that fluctuations of surface temperatures and stresses are highly linearly correlated. Also, surface stress fluctuations, in axial and hoop directions, are almost equi-biaxial. These findings, representative on cross sections away from system boundaries, are moreover supported by the sensitivity analysis of Fourier and Biot numbers and by the comparison with standard one-dimensional analyses. Agreement between one- and three-dimensional results is found for a wide range of studied parameters. The study also comprises the effects of global thermo-mechanical loading on the surface stress state. Implemented mechanical boundary conditions develop more realistic overall system deformation and promote non-equibiaxial stresses.