Norihiko Mukaimachi

Plastic Collapse Assessment Procedure for Vessel with Local Thin Area Simultaneously Subjected to Internal Pressure and External Bending Moment

Assessment of the local thin area should be undertaken for both tension and compression bending. In this paper, simplified reference stresses for a flaw in a cylinder are proposed. By using these results, a newly-developed p-M (internal pressure ratio and external bending moment ratio) diagram which can evaluate the plastic collapse condition for pressure equipment such as vessels, piping and storage tanks with a local thin area simultaneously subjected to internal pressure, p, and external bending moment, M, due to earthquake, etc. is proposed. The p-M line is verified by comparison with the FEA results and the numerous results of experiment for a cylinder with a volumetric flaw obtained through the reference literatures. It was clarified that the differences in plastic collapse limit between the p-M line and DNV guideline under both internal pressure and compression moment became evident where the outer diameter/wall thickness of a cylinder is large and the yield ratio of the material is small.Copyright

Plastic Collapse Assessment Procedure for Vessel With Local Thin Area Simultaneously Subjected to Internal Pressure and External Bending Moment

Assessment of the local thin area should be undertaken for both tension and compression bending. In this paper, simplified reference stresses for a flaw in a cylinder are proposed. By using these results, a newly developed p-M (internal pressure ratio and external bending moment ratio) diagram which can evaluate the collapse condition for pressure equipment such as vessels, piping, and storage tanks with a local thin area simultaneously subjected to internal pressure p and external bending moment M due to earthquake, etc., is proposed. The p-M line is verified by comparison with the finite element analysis results and the numerous results of experiment for a cylinder with a volumetric flaw obtained through the reference literatures. It was clarified that the differences in collapse limit between the p-M line and DNV guideline under both internal pressure and compression moment became evident where the outer diameter/wall thickness of a cylinder is large and the yield ratio of the material is small.

An Advanced Computational Method for Nonlinear Behavior of Piping Systems Subject to Earthquake Load

With regard to piping systems of industrial facilities, sometimes they are subject to large deformation with high local plasticity. This results mainly from the detrimental ground movement due to possible liquefaction near seaside when a strong earthquake occurs. Especially the high local plasticity concentrates on elbows (bends) in piping systems. In this paper, the elbow behaviors of in-plane (closing: deflection to decrease elbow radius of curvature and opening: deflection to increase its radius of curvature) and out-of-plane bending are analyzed in a large plastic range using Nonlinear Finite Element Method (FEM) with the shell elements of material and geometrical nonlinear characteristics. The flexibility factor of elbows depends on flexibility characteristics, angular distortion and yield stress of material. Thus, in order to estimate the behaviors of piping systems with large plasticity at elbow by a simplified method, the modified flexibility factor method is introduced from results of FEM. Calculation results obtained using the simplified method are compared with experimental results, and this method gives an index to assess behaviors of piping systems subject to extremely large movement of supports. It is also possible to estimate local plasticity at elbows in piping systems by this conventional analysis.Copyright

Analysis of stable crack growth across welded fusion line: Japanese round-robin

Abstract Bimaterial CT specimens are numerically analyzed in the elastic-plastic states. By changing the material constants and the distance between the crack tip and the phase boundary, the parametric analyses are conducted. J integral evaluated by the line integration is compared with that obtained by the empirical formula by Merkel-Corten. The effects of the inhomogeneities on the accuracy of the J integral evaluation are discussed. Next the stable crack growth analyses are conducted. Using the relation between a and load-load line displacement obtained experimentally, the generation phase analyses are carried out. J integral, T ∗ integral and CTOA are evaluated and the effects of the fusion line are discussed.

Validity of Assessment Procedure in p-M Method for Multiple Volumetric Flaws

General components such as pressure vessels, piping, storage tanks and so on are designed in accordance with the construction codes based on the assumption that there are no flaws in such components. There are, however, numerous instances in which in-service single or multiple volumetric flaws (local thin areas; volumetric flaws) are found in the equipment concerned. Therefore, it is necessary to establish a Fitness for Service (FFS) rule, which is capable of judging these flaws. The procedure for a single flaw or multiple flaws has recently been proposed by Konosu for assessing the flaws in the p–M (pressure-moment) Diagram, which is an easy way to visualize the status of the component with flaws simultaneously subjected to internal pressure, p and external bending moment, M due to earthquake, etc. If the assessment point (Mr , pr ) lies inside the p–M line, the component with flaws is judged to be safe. In this paper, numerous experiments and FEAs for a cylinder with external multiple volumetric flaws were conducted under (1) pure internal pressure, (2) pure external bending moment, and (3) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic collapse load at volumetric flaws by applying the twice-elastic slope (TES) as recommended by ASME. It has been clarified that the collapse (TES) loads are much the same as those calculated under the proposed p–M line based on the measured yield stress.Copyright

Plastic Collapse Load for Vessel With External Flaw Simultaneously Subjected to Internal Pressure and External Bending Moment: Experimental and FEA Results

The newly-developed p-M diagram provides a means for readily evaluating the collapse load of pressure equipment with external flaws simultaneously subjected to internal pressure, p and external bending moment, M due to earthquake, etc. In this paper, numerous experiments and FEAs for a cylinder with an external flaw were conducted under (1) pure internal pressure, (2) pure external bending moment, and (3) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic initiation load and plastic collapse load by applying the twice-elastic slope (TES) as recommended by ASME. It has been clarified that the collapse (TES) loads are much the same as those calculated under the proposed p-M line based on the measured yield stress. The p-M line adopted in the Ibaraki FFS rule based on the specified minimum yield stress with a safety factor of 1.5 indicates that the safety margin for the plastic initiation loads at LTA is about 1.0–3.0, about 1.5–4.0 for the TES loads at LTA and 2.5–6.5 for the plastic instability (break) loads.Copyright