Nozzles In Cylindrical Vessels Research Articles

Shakedown Limits for Hillside Nozzles in Cylindrical Vessels

This research paper is concerned with the mechanical behavior of the cylindrical vessels with hillside nozzles when subjected to both pressure and nozzle bending loads in cyclic forms. The influence of hillside angle on shakedown (SD) limits of the connection under cyclic pressure and combined steady pressure with cyclic nozzle bending is investigated. A shell finite element analysis model is built for the assembly using five different hillside angles ranging from 0 deg to 40 deg. Shakedown limits are determined by a direct technique known as the nonlinear superposition method (NSM). Bree diagrams for cyclic out of plane opening (OPO)/in plane (IP) nozzle moments combined with steady internal pressure are determined. The results show an increase in both OPO and IP shakedown moments as the hillside angle is increased. In addition, the OPO shakedown limit moments for all hillside angles were found to be insensitive to the level of internal pressure; this differs from the IP shakedown moment which starts to decrease with pressure for the high pressures.

Finite Element Analysis and Development of Design Charts for Cylindrical Vessel–Nozzle Junctures Under Internal Pressure

A detailed study for the stresses around internally pressurized cylindrical vessel–cylindrical nozzle junctures is carried out using the finite element method. Based on thin shell theory, two simplified expressions (functions of the vessel–nozzle geometrical ratios) of stress concentration factor (SCF) are obtained: one for the main vessel and the other for the nozzle, respectively. The analysis was also used to study the location of maximum stresses at the juncture as well as provide a more accurate presentation of design charts than the \({\rho}\)-SCF plots. Verification is made using some established models available in the literature.

Shakedown Limit Load Determination of a Cylindrical Vessel–Nozzle Intersection Subjected to Steady Internal Pressures and Cyclic In-Plane Bending Moments

In the current research, the elastic shakedown limit loads for a cylindrical vessel–nozzle intersection is determined via a direct noncyclic simplified technique. The cylindrical vessel–nozzle intersection is subjected to a spectrum of steady internal pressure magnitudes and cyclic in-plane bending moments on the nozzle end. The determined elastic shakedown limit loads are utilized to generate the elastic shakedown boundary (Bree diagram) of the cylindrical vessel–nozzle structure. Additionally, the maximum moment carrying capacity (limit moments) and the elastic limit loads are determined and imposed on the Bree diagram of the structure. The simplified technique outcomes showed excellent correlation with the results of full cyclic loading elastic–plastic finite element simulations.

Elastic shakedown boundary determination of a cylindrical vessel–nozzle intersection subjected to steady internal pressures and cyclic out-of-plane bending moments

In the current research, a non-cyclic simplified technique is utilized to determine the elastic shakedown limit moments of a cylindrical vessel–nozzle intersection. The determined shakedown limit moments are utilized to generate the elastic shakedown boundary and the Bree diagram of the structure. The structure is subjected to a spectrum of steady internal pressure magnitudes and cyclic out-of-plane bending moments on the nozzle. The generated Bree diagram is compared with previously generated Bree diagram of the same structure, but subjected to in-plane bending. Noticeable differences regarding the magnitudes of the generated shakedown boundaries are observed. Moreover, only failure due to reversed plasticity response occurs upon exceeding the generated shakedown boundary unlike cyclic in-plane bending where the structure experienced both reversed plasticity and ratchetting failure responses. The simplified technique outcomes showed excellent correlation with the results of full elastic–plastic cyclic loading finite element simulations.

Plastic limit loads of nozzles in cylindrical vessels under out-of-plane moment loading

The purpose of this paper is to study the plastic limit moment of nozzles in cylindrical vessels with different d/ D ratios under out-of-plane moment loading. Three full size test models were designed and fabricated. A 3D nonlinear finite element numerical simulation was also performed. A twice-elastic-slope plastic moment on the nozzles was obtained approximately by use of load–displacement and load–strain curves. The results show that plastic loads determined by test and numerical simulation methods are in good agreement. The results can serve as a basis for developing an advanced design guideline by limit analysis for cylindrical vessels with a nozzle under external loads.

Development of stress indices for nonradial branch connections

This paper presents a brief summary of the technical basis for the recommended stress indices for 45 degree lateral connections under internal pressure and in-plane moment loadings. Starting with the historical background of the Pressure Vessel Research Committee's (PVRC) long range program on lateral connections, this paper highlights the various aspects intrinsic to this program such as model selection, analysis technique, finite element discretization, loading conditions, material properties and boundary conditions. A discussion of the stress index method and its application to the pressure vessel and piping design is offered as a prelude to the recommended code indices. Proposed changes to Par. NB-3338.2(C) (1) of Subsection NB of the ASME Code pertaining to lateral nozzles in cylindrical vessels and Par. NB-3650 relative to branch connections in piping systems are presented and discussed in detail. Besides, this paper discusses the need to develop additional data in the range of geometric parameters, 0.5 ≤ d/ D ≤ 1.0 and 10 ≤ D/ T ≤ 50, and under other remaining loading conditions to broaden the application of the stress index method.

Stress Analysis of Nozzles in Cylindrical Vessels With External Load

The analysis is carried out for a cylindrical vessel with a nozzle subjected to external loading consisting of longitudinal and circumferential moments and radial force. The Flu¨gge-Conrad solutions with the Sanders-Simmonds concentrated force solution are utilized for a local analysis, to which asymptotic approximations for the effect of the vessel length and continuity around the vessel circumference are added. This is incorporated in a computer code FAST for which set up and run times are minimal for a given case of geometry and load. The comparison with experimental results is about as good as can be expected for eight models, with parameters in the ranges: 50 ≤ D/T ≤ 2530, 0.01 ≤ d/D ≤ 0.5, and 6.5 ≤ d/t ≤ 240. Hence, the calculation should be useful for an improvement in nozzle design. Example curves and tables of stress factors are included.

Assessment of the Plastic Strength of Pressure Vessel Nozzles

Theoretical developments on limit pressures of shells are cited and briefly discussed. Calculated limit pressure from several of the theoretical analyses are compared with numerous tests on radial nozzles in both spherical and cylindrical vessels. Test data on burst pressures of nozzles in cylindrical vessels are presented and compared with limit pressures.

A Study of Nozzles in Pressure Vessels under Pressure Fatigue Loading

Nozzles in cylindrical vessels have been of special interest to designers for some time and have offered a field of activity for many research workers. This paper presents some static and fatigue tests on five designs of full size pressure vessel nozzles manufactured in two materials. Supporting and other published work is reviewed showing that on the basis of the same maximum stress mild steel vessels give the same fatigue life as low alloy vessels. When compared on the basis of current codes it is shown that mild steel vessels may have five to ten times the fatigue life of low alloy vessels unless special precautions are taken.