Procedure for Plastic Collapse Assessment of a Local Thin Area Near Vessel and Nozzle Intersections Subjected to Internal Pressure and External Loadings

2015 ◽  
Author(s):  
Shinji Konosu ◽  
Kenta Ogasawara ◽  
Kenji Oyamada
Keyword(s):  
Internal Pressure ◽  
Critical Region ◽  
Pressure Ratio ◽  
Branch Pipe ◽  
Bending Moment ◽  
Plastic Collapse ◽  
Element Analysis ◽  
Diagram Method ◽  
External Moment ◽  
Collapse Assessment

This paper develops a procedure for plastic collapse assessment of vessel (run pipe) - nozzle (branch pipe) intersections with an arbitrarily positioned local thin area (LTA) under different loading conditions, namely internal pressure, external moment on a nozzle applied along various directions with respect to the vessel main axis, and pure bending moment on a vessel. Although simplified procedures for plastic collapse assessment based on the p-M (internal pressure ratio and external bending moment ratio) diagram method have been previously proposed for straight cylindrical vessels and pipe bends with an LTA, very few studies have dealt with the determination of plastic collapse load for an LTA in the critical region of intersecting vessels subjected to internal pressure and external moment loading. This is likely due to the complexity of the stresses caused by the applied loads in the critical region, which arises from geometric discontinuities. In this paper, simple and empirical formulae for predicting conservative plastic collapse loads for an LTA in the critical region of the intersecting vessels are proposed based on the analytical results of stresses at defect-free vessel-nozzle intersections by using linear finite element analysis (FEA). Localized elastic stress retardation factors are taken into account in the evaluation by the results of a non-linear FEA. Consequently, a p-M diagram method is developed for application to vessel-nozzle intersections with an LTA.

Plastic Collapse Assessment Procedure in P-M Diagram Method for Pipe Bends With a Local Thin Area Under Combined Pressure and Out-of-Plane Bending Moment

2012 ◽  
Author(s):  
Kenji Oyamada ◽  
Shinji Konosu ◽  
Takashi Ohno
Keyword(s):  
Internal Pressure ◽  
Pressure Ratio ◽  
Bending Moment ◽  
Piping System ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Diagram Method ◽  
Out Of Plane ◽  
Plane Bending ◽  
Collapse Assessment

Pipe bends are common elements in piping system such as power or process piping, and local thinning are typically occurred on pipe bends due to erosion or corrosion. Therefore, it is important to establish the plastic collapse condition for pipe bends having a local thin area (LTA) under combined internal pressure and external bending moment. In this paper, a simplified plastic collapse assessment procedure in p-M (internal pressure ratio and external bending moment ratio) diagram method for pipe bends with a local thin area simultaneously subjected to internal pressure, p, and external out-of-plane bending moment, M, due to earthquake, etc., is proposed, which is derived from the reference stress. In this paper, only cases of that an LTA is located in the crown of pipe bends are considered. The plastic collapse loads derived from the p-M diagram method are compared with the results of both experiments and FEA for pipe bends of the same size with various configurations of an LTA.

Development of Simplified Plastic Collapse Assessment Procedure for Elbow With an External Surface Flaw Simultaneously Subjected to Internal Pressure and External Bending Moment

2008 ◽  
Author(s):  
Kenji Oyamada ◽  
Shinji Konosu
Keyword(s):  
Internal Pressure ◽  
External Surface ◽  
Pressure Ratio ◽  
Bending Moment ◽  
Cylindrical Part ◽  
Surface Flaw ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Diagram Method ◽  
The Status

A simplified assessment procedure using the p-M (internal pressure ratio and external bending moment ratio) diagram, which can evaluate the plastic collapse load for an elbow with an external surface flaw simultaneously subjected to internal pressure, p, and external bending moment, M, due to earthquake, etc., is derived. The p-M diagram evaluation is an easy way to visualize the status of components with a flaw. For an elbow with an external surface flaw, the already-proposed p-M diagram by one of authors for the cylindrical part of pressure equipment such as vessels, pipes, etc. with a surface flaw can be applied if the parameters proposed in this paper are used. The plastic collapse loads derived from the p-M diagram method are being verified by comparison with existing experimental and FEA results.

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

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Shinji Konosu ◽  
Masato Kano ◽  
Norihiko Mukaimachi ◽  
Hiroyuki Komura ◽  
Hiroyuki Takada
Keyword(s):  
Internal Pressure ◽  
Yield Stress ◽  
Pressure Ratio ◽  
Safety Margin ◽  
Bending Moment ◽  
Plastic Instability ◽  
Plastic Collapse ◽  
Collapse Load ◽  
The Status ◽  
Work Done

This paper is based on work done to establish the validity of a simple engineering approach to assess plastic collapse for a vessel with a local thin area (LTA). The approach is based on a recently developed p-M (internal pressure ratio and external bending moment ratio) diagram, which is an easy way to visualize the status of a vessel with a LTA 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 vessel with the LTA is judged to be safe. Numerous experiments and finite element analyses 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 similar to those calculated under the proposed p-M line based on the measured yield stress. The p-M line adopted in the Ibaraki fitness for service (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.

Discussion on Plastic Collapse Criterion at High Temperatures in FFS Assessment Rules

2010 ◽  
Author(s):  
Kenji Oyamada ◽  
Shinji Konosu ◽  
Hikaru Miyata ◽  
Takashi Ohno
Keyword(s):  
Comparative Study ◽  
High Temperatures ◽  
Bending Moment ◽  
Flaw Size ◽  
Metal Loss ◽  
Plastic Collapse ◽  
Loss Assessment ◽  
Element Analysis ◽  
Diagram Method ◽  
The Difference

There are several Fitness-For-Service (FFS) standards with evaluation rules in terms of plastic collapse for a pressure vessel or piping component possessing a local metal loss area simultaneously subjected to internal pressure and bending moment. The authors have already reported the results of a comparative study of FFS rules, including the remaining strength factor (RSF) approach in Part 5 of API 579-1/ASME FFS-1 and the p-M diagram method, which pointed out that there could be significant differences in allowable flaw sizes. This paper describes an additional comparative study on the difference of allowable flaw size for local metal loss assessment between the RSF approach in Part 5 of API 579-1/ASME FFS-1 and the p-M diagram method, focusing on the effect of decreasing yield strength of the material at high temperatures, such as 350 degrees C. The allowable flaw depth at high temperatures derived from API579-1/ASME FFS-1 is larger than that derived by means of the p-M diagram method. However, it is verified by the finite element analysis that the allowable flaw size of the p-M diagram method is set on the stress state of general yielding near a local metal loss area if safety factor is not considered and it is possible to evade ratcheting due to cyclic bending moment in service, such as that caused by earthquake, etc.

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

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Shinji Konosu ◽  
Norihiko Mukaimachi
Keyword(s):  
Internal Pressure ◽  
Pressure Ratio ◽  
Bending Moment ◽  
Outer Diameter ◽  
Assessment Procedure ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Tension And Compression ◽  
And Storage ◽  
Moment Ratio Diagram

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.

Validity of Procedure for Plastic Collapse Assessment of a Local Thin Area Near Vessel and Nozzle Intersections Subjected to Internal Pressure and External Loadings

2015 ◽  
Author(s):  
Kenji Oyamada ◽  
Shinji Konosu ◽  
Tetsuji Miyashita ◽  
Takashi Ohno ◽  
Hideyuki Suzuki
Keyword(s):  
Numerical Analysis ◽  
Internal Pressure ◽  
Branch Pipe ◽  
Plastic Collapse ◽  
Collapse Assessment

There are numerous cases in which a volumetric flaw such as a local thin area (LTA) is found in pressure equipment such as vessels, piping, tanks, and so on. Sometimes it is found near vessel and nozzle intersection. A fitness for service (FFS) rule of such cases was desired, because plastic collapse assessment of LTA near vessel and nozzle intersection usually needed to conduct by numerical analysis such as FEA. Recently, an FFS assessment rule of plastic collapse assessment of LTA near vessel (run-pipe) and nozzle (branch pipe) intersection subjected to internal pressure and external loadings has been developed and proposed by one of authors of this paper. In this paper, the proposed plastic collapse assessment rule was verified with results of experiments and FEA for cylindrical vessels with an LTA near vessel and nozzle intersections subjected to internal pressure and external loadings.

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

2006 ◽  
Author(s):  
Shinji Konosu ◽  
Norihiko Mukaimachi
Keyword(s):  
Internal Pressure ◽  
Pressure Ratio ◽  
Bending Moment ◽  
Outer Diameter ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Moment Ratio ◽  
Tension And Compression ◽  
And Storage ◽  
Moment Ratio Diagram

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.

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

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Shinji Konosu ◽  
Masato Kano ◽  
Norihiko Mukaimachi ◽  
Shinichiro Kanamaru
Keyword(s):  
Internal Pressure ◽  
Bending Moment ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Storage Tanks ◽  
Collapse Load ◽  
Element Analysis ◽  
The Status ◽  
Single Flaw

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 such as local thin areas are found in the equipment concerned. Therefore, it is necessary to establish a fitness for service rule, which is capable of evaluating these flaws. The procedure for a single flaw or multiple flaws has recently been proposed 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 finite element analysis 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.

Development of Simplified Plastic Collapse Assessment Procedure for Vessel With Internal Surface Flaw

2007 ◽  
Author(s):  
Shinji Konosu ◽  
Kenji Oyamada
Keyword(s):  
Internal Pressure ◽  
Bending Moment ◽  
Internal Surface ◽  
Outer Radius ◽  
Surface Flaw ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Diagram Method ◽  
Surface Flaws ◽  
And Storage

A simplified assessment procedure using the p-M diagram, which can evaluate the plastic collapse load for pressure equipment such as vessels, piping and storage tanks with an internal surface flaw simultaneously subjected to internal pressure, p, and external bending moment, M, due to earthquake, etc., is derived by taking into account the influence of internal pressure acting on the flaw surface. For an internal surface flaw subjected to pressure, the already-proposed p-M diagram for an external flaw can be applied if the parameters for an internal surface flaw proposed in this paper are used. And the plastic collapse loads derived from the p-M diagram method are being verified by comparison with experimental results. It has been clarified that the parameters for internal surface flaws are also the same as those for external surface flaws where the ratio of thickness to outer radius of a vessel is significantly smaller than unity and internal pressure is small.

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