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Research Papers: Codes and Standards

J. Pressure Vessel Technol. 2017;139(5):051101-051101-9. doi:10.1115/1.4036919.

The linear matching method (LMM) subroutines and plug-in tools for structural integrity assessment are now in extensive use in industries for the design and routine assessment of power plant components. This paper presents a detailed review and case study of the current state-of-the art LMM direct methods applied to the structural integrity assessment. The focus is on the development and use of the linear matching method framework (LMMF) on a wide range of crucial aspects for the power industry. The LMMF is reviewed to show a wide range of capabilities of the direct methods under this framework, and the basic theory background is also presented. Different structural integrity aspects are covered including the calculation of shakedown, ratchet, and creep rupture limits. Furthermore, the crack initiation assessments of an un-cracked body by the LMM are shown for cases both with and without the presence of a creep dwell during the cyclic loading history. Finally, an overview of the in house developed LMM plug-in is given, presenting the intuitive graphical user interface (GUI) developed. The efficiency and robustness of these direct methods in calculating the aforementioned quantities are confirmed through a numerical case study, which is a semicircular notched (Bridgman notch) bar. A two-dimensional axisymmetric finite element model is adopted, and the notched bar is subjected to both cyclic and constant axial mechanical loads. For the crack initiation assessment, different cyclic loading conditions are evaluated to demonstrate the impact of the different load types on the structural response. The impact of creep dwell is also investigated to show how this parameter is capable of causing in some cases a dangerous phenomenon known as creep ratcheting. All the results in the case study demonstrate the level of simplicity of the LMMs but at the same time accuracy, efficiency, and robustness over the more complicated and inefficient incremental finite element analyses.

Topics: Creep , Stress , Cycles , Rupture
Commentary by Dr. Valentin Fuster

Research Papers: Design and Analysis

J. Pressure Vessel Technol. 2017;139(5):051201-051201-8. doi:10.1115/1.4036853.

In this paper, a cold forming process is used where the connection between a pipe and a flange is created by means of radially expanding tool segments inside the pipe. The method is investigated with two purposes, to set up a robust procedure for the process that allows for connections to be made on site, and to set up finite element (FE) simulations that can capture the forces and deformations when pulling the pipe axially out of the flange. Experimental data and FE simulations are used to describe and understand the forces and deformations during the connection process. The rapid increase in radial stiffness experienced when the pipe comes in full circumferential contact with the flange is identified as the best end-of-process indicator. Also, experimental data and FE simulations are used to predict the axial load capacity of a pipe flange connection, and the FE model is utilized in designing the appropriate ridge height of the tool segments.

Commentary by Dr. Valentin Fuster

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