Development of Methodology for Generating Response Spectra for Decoupled Smallbore Piping

Abstract: In nuclear piping engineering, the response spectrum method of analysis is widely used to analyze piping systems. The matter of combining modal responses is of great interest. Complications may occur with the response spectrum method for large systems. Examples are convergence issues and something called twin-mode effects that may overestimate the effects on the system. This master thesis investigates the possibility of separating small parts of piping systems, thus reducing the original system in size, and analyzing the separated systems independently by loading them with a modified response spectrum based around a dynamic amplification factor. The process of calculating the modified response spectrum is automated by the development of an application using Python. The modeling of the piping systems is done in Pipestress, which is a commonly used computer software for design of pipes at nuclear power plants. Different modal combination methods and certain modeling issues are investigated and finally the stress in the original and the separated system is calculated and compared. There is no experimental data to compare the results to, but the method of separating systems with a modified response spectrum shows some promise, even though further investigation is needed.