Assessment of Weep Holes in Cylindrical Shell Based on Elastic-Plastic Stress Analysis Method

2014 ◽  
Author(s):  
Dipak K. Chandiramani ◽  
Suresh K. Nawandar
Keyword(s):  
Carbon Steel ◽  
Stress Analysis ◽  
High Pressures ◽  
Material Selection ◽  
Analysis Method ◽  
Elastic Plastic ◽  
Section Viii ◽  
Vessel Walls ◽  
Division 2 ◽  
Plastic Stress

In urea plant equipment, particularly those operating in the synthesis cycle, anti-corrosive liner plates are usually applied to the pressure retaining carbon steel vessel walls. Even with the correct material selection, controlled fabrication methods and maintenance, the risk of highly corrosive urea-carbamate solution leaking through these liners always exists in these equipment which might eventually damage the carbon steel walls. Existing designs of these equipment utilizes “weep holes” to reveal such leakages. Various designs exist, but in general these weep holes are 15–20mm dia. plain openings in the vessel walls connecting the space between the liner and the vessel wall to the outside atmosphere or the leak-detect apparatus. These equipment operate at high pressures and temperatures and therefore ASME Section VIII Division 2 is normally the preferred design and construction Code. This Code, earlier to the publication of its Edition 2007, had provisions in it to exempt openings not exceeding certain diameters, from any reinforcement calculations. Traditionally, equipment designers have been applying this clause to seek the exemption of these weep holes from any further calculations. However, starting with Edition 2007, this Code did away with such exemptions and has made it mandatory to assess openings of all sizes, particularly if they are in the monobloc vessels. Weep holes are no exception. This paper discusses how the assessment of these weep holes in cylindrical shells can be carried out by applying the “Elastic-Plastic Stress Analysis Method” stipulated in Para. 5.2.4 & 5.3.3 of the ASME Section VIII Division 2 Code. This paper also provides the basis for recommending this method. In the application of this method, the subject is approached as a “shell with opening” and not as conventional “nozzle opening in the shell”.

A Comparison of Design by Analysis Techniques for Evaluating Nozzle-to-Shell Junctions per ASME Section VIII Division 2

2015 ◽  
Author(s):  
Phillip E. Prueter ◽  
Robert G. Brown
Keyword(s):  
Stress Analysis ◽  
Failure Modes ◽  
Elastic Stress ◽  
Limit Load ◽  
Plastic Collapse ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Non Linear ◽  
Section Viii ◽  
Division 2

Part 5 of ASME Section VIII Division 2 offers several design by analysis (DBA) techniques for evaluating pressure retaining equipment for Code compliance using detailed computational stress analysis results. These procedures can be used to check components for protection against multiple failure modes, including plastic collapse, local failure, buckling, and cyclic loading. Furthermore, these procedures provide guidance for establishing consistent loading conditions, selecting material properties, developing post-processing techniques, and comparing analysis results to the appropriate acceptance criteria for a given failure mode. In particular, this study investigates the use of these methods for evaluating nozzle-to-shell junctions subjected to internal pressure and nozzle end loads. Specifically, elastic stress analysis, limit load analysis, and elastic-plastic stress analysis are utilized to check for protection against plastic collapse, and computational results for a given load case are compared. Additionally, the twice elastic slope method for evaluating protection against plastic collapse is utilized as an alternate failure criterion to supplement elastic-plastic analysis results. The goal of these comparisons is to highlight the difference between elastic stress checks and the non-linear analysis methodologies outlined in ASME Section VIII Division 2; particularly, the conservatism associated with employing the elastic stress criterion for nozzle end loads compared to limit load and elastic-plastic analysis methodologies is discussed. Finally, commentary on the applicability of performing the Code-mandated check for protection against ratcheting for vessels that do not operate in cyclic service is provided. The intent of this paper is to provide a broad comparison of the available DBA techniques for evaluating the acceptability of nozzle-to-shell junctions subjected to different types of loading for protection against plastic collapse. Predicted deformations and stresses are quantified for each technique using linear and non-linear, three-dimensional finite element analysis (FEA) methodologies.

Elastic-Plastic Design by Analysis for Gross Plastic Collapse

2010 ◽  
Author(s):  
Rory Carmichael ◽  
Donald Mackenzie
Keyword(s):  
Stress Analysis ◽  
Limit Analysis ◽  
Complex Analysis ◽  
Permanent Deformation ◽  
Local Strain ◽  
Plastic Collapse ◽  
Analysis Method ◽  
Membrane Action ◽  
Elastic Plastic ◽  
Plastic Stress

An investigation of the ASME VIII Div 2 elastic-plastic stress analysis method for protection against plastic collapse is presented. Four example configurations are considered and calculated design pressures are compared with values determined by alternative procedures based on limit analysis and bilinear hardening/the twice elastic slope criterion. It is found that the ASME VIII Div 2 procedure does not generally lead to evaluation of higher design pressures than the alternative approaches. In an example configuration demonstrating significant geometric strengthening, the allowable load is limited by the local strain criterion and in practice user-defined service criteria would be applied to limit permanent deformation under design conditions. In two example configurations that failed through membrane action, the evaluated design pressure was found to be less than that based on limit analysis. These initial results indicate that the more complex elastic-plastic stress analysis used in the ASME VIII Div 2 method does not necessarily lead to evaluation of higher design loads than alternative design routes. Further studies are required to determine the general circumstances in which the more complex analysis method is advantageous in design.

Pipeline Valves Technology, Material Selection, Welding, and Stress Analysis (A Case Study of a 30 in Class 1500 Pipeline Ball Valve)

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Karan Sotoodeh
Keyword(s):  
Stress Analysis ◽  
Wall Thickness ◽  
Material Selection ◽  
American Petroleum Institute ◽  
Ball Valve ◽  
The Body ◽  
Hydraulic Actuator ◽  
Pipeline Valve ◽  
Section Viii ◽  
Division 2

Pipeline valves are the largest, heaviest, and most important valves on an offshore platform with long delivery time. A pipeline valve is either a ball type or through conduit gate valve type with a top entry design. The top entry design provides advantages such as a lower risk of leakage, greater mechanical strength against pipeline loads, and ease of maintenance (online maintenance) compared to the side entry design. A 30 in pipeline ball valve in class 1500 and carbon steel body material was chosen for stress analysis in this paper. The valve was connected to the pipeline through pup pieces from both sides. The pup pieces were connected to the body of the valve through transition pieces. The large 30 in valve has an emergency shut down safety function and is equipped with a hydraulic actuator. The valve is designed based on the American Petroleum Institute (API) 6D Specification for Pipeline and Piping valves. The proposed formula of wall thickness calculation in this paper is based on the American Society of Mechanical Engineers (ASME) Section VIII, Division 2, Boiler and Pressure Vessel Code (BPVC) instead of the ASME B16.34 standard. The wall thickness values given in the ASME B16.34 standard of “Valves Flanged, Threaded and Welding End” are very conservative and thick, which makes pipeline valves heavier and more expensive. Noticeably, ASME B16.34 requires an even higher thickness due to assembly loads, actuation (opening and closing) loads, and shapers other than circular that are applicable for pipeline valves. These valves should withstand loads from pipeline systems such as axial, torsion, and bending moments. ASME B16.34 does not specify the body wall thickness of the pipeline valves under the pipeline loads and moments. This paper aims to create a model to prove that the 30 in Class1500 pipeline valve will withstand the loads and moments with the thickness of the valve calculated using ASME Section VIII, Division 2 methods. The criteria and the model used to prove the suitability of the valve against the loads and moments are based on ASME Section VIII, Division 2.

A Comparison Study of Pressure Vessel Design Using Different Standards

2013 ◽  
Author(s):  
Frode Tjelta Askestrand ◽  
Ove Tobias Gudmestad
Keyword(s):  
Stress Analysis ◽  
Elastic Stress ◽  
Limit Load ◽  
Technical Committee ◽  
Pressure Vessels ◽  
Analysis Method ◽  
Elastic Plastic ◽  
Load Analysis ◽  
American Society ◽  
Division 2

Several codes are currently available for design and analysis of pressure vessels. Two of the main contributors are the American Society of Mechanical Engineers providing the ASME VIII code, Ref /4/ and the Technical Committee for standardization in Brussels providing the European Standard, Ref /2/. Methods written in bold letters will be considered in the discussion presented in this paper. The ASME VIII code, Ref /4/, contains three divisions covering different pressure ranges: Division 1: up to 200 bar (3000 psi) Division 2: in general Division 3: for pressure above 690 bar (10000 psi) In this paper the ASME division 2, Part 5, “design by analysis” will be considered. This part is also referred to in the DNV-OS-F101, Ref /3/, for offshore pressure containing components. Here different analysis methods are described, such as: Elastic Stress Analysis Limit Load Analysis Elastic Plastic Analysis The Elastic Stress Analysis method with stress categorization has been introduced to the industry for many years and has been widely used in design of pressure vessels. However, in the latest issue (2007/2010) of ASME VIII div. 2, this method is not recommended for heavy wall constructions as it might generate non-conservative analysis results. Heavy wall constructions are defined by: (R/t ≤ 4) with dimensions as illustrated in Figure 1. In the case of heavy wall constructions the Limit Load Analysis or the Elastic-plastic method shall be used. In this paper focus will be on the Elastic-plastic method while the Limit Load Analysis will not be considered. Experience from recent projects at IKM Ocean Design indicates that the industry has not been fully aware of the new analysis philosophy mentioned in the 2007 issue of ASME VIII div.2. The Elastic Stress Analysis method is still (2012) being used for heavy wall constructions. The NS-EN 13445-3; 2009, Ref /2/, provides two different methodologies for design by analysis: Direct Route Method based on stress categories. The method based on stress categories is similar to the Elastic Stress Analysis method from ASME VIII div. 2 and it will therefore not be considered in this paper.

Applicability of Design Rules for Openings in Shells, ASME B&PV Code, Section VIII, Division 2 - A Case Study

2021 ◽  
Author(s):  
Gurumurthy Kagita ◽  
Krishnakant V. Pudipeddi ◽  
Subramanyam V. R. Sripada
Keyword(s):  
Stress Analysis ◽  
Failure Modes ◽  
Element Analysis ◽  
Design Rules ◽  
Area Method ◽  
Replacement Method ◽  
Local Stresses ◽  
Pressure Area ◽  
Section Viii ◽  
Division 2

Abstract The Pressure-Area method is recently introduced in the ASME Boiler and Pressure Vessel (B&PV) Code, Section VIII, Division 2 to reduce the excessive conservatism of the traditional area-replacement method. The Pressure-Area method is based on ensuring that the resistive internal force provided by the material is greater than or equal to the reactive load from the applied internal pressure. A comparative study is undertaken to study the applicability of design rules for certain nozzles in shells using finite element analysis (FEA). From the results of linear elastic FEA, it is found that in some cases the local stresses at the nozzle to shell junctions exceed the allowable stress limits even though the code requirements of Pressure-Area method are met. It is also found that there is reduction in local stresses when the requirement of nozzle to shell thickness ratio is maintained as per EN 13445 Part 3. The study also suggests that the reinforcement of nozzles satisfy the requirements of elastic-plastic stress analysis procedures even though it fails to satisfy the requirements of elastic stress analysis procedures. However, the reinforcement should be chosen judiciously to reduce the local stresses at the nozzle to shell junction and to satisfy other governing failure modes such as fatigue.

scholarly journals Assessment of DBA-L Pressure Vessel Design Method by a Cylindrical Vessel with Hemispherical Ends

2019 ◽  
Vol 256 ◽  
pp. 02001
Author(s):  
Ren Xincheng ◽  
Hongjun Li ◽  
Xun Huang
Keyword(s):  
Stress Analysis ◽  
Pressure Vessel ◽  
Design Method ◽  
Design Methods ◽  
Cylindrical Vessel ◽  
Elastic Analysis ◽  
Explicit Method ◽  
Elastic Plastic ◽  
Cylindrical Pressure Vessel ◽  
Plastic Stress

Stress categorization is an essential procedure in Design by Analysis (DBA) pressure vessel design methods based on elastic analysis in ASME and EN code. It was difficult to implement especially around structural discontinuities. A new elastic analysis, DBA-L, was proposed recently to avoid stress categorization. A model of the cylindrical pressure vessel with spherical end is used to check the validity of this method by comparing with other design methods based on stress categorization procedures and elastic-plastic stress analysis from ASME and EN code. The results indicate that the DBA-L is an economic and explicit method, and can be used an alternative method to stress categorization.

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