Typical Pressure Vessel Research Articles

A computer program for nonlinear analysis of pressure vessels

This paper describes the nonlinear analysis of pressure vessels necessary for taking into account the large deformations that take place at the junctions of shells of different geometries. Specifically, a computer program has been developed, based on both the linear and nonlinear theories of shells, which obtains numerical solutions for the most commonly used types of pressure vessels, namely those with spherical, ellipsoidal or conical heads and also flat-end pressure vessels. A multisegment integration technique has been used to obtain the solutions of the governing equations. The computed solutions are found to be highly accurate when compared with the known results of simple shells, as no nonlinear analysis is reported in the literature on the shell junctions in pressure vessels.

Design for Buckle-Free Shapes in Pressure Vessels

There are many applications of thin-walled axisymmetric structures as pressure vessels in which buckle-free in-service behavior can only be guaranteed by reinforcements, such as stringers and girths, which not only raise the weight of the structure but also increase its cost. Buckle-free behavior, however, can also be assured by “correcting” the shape of the pressure vessel by a small amount in the area of impending instability. This paper proposes the use of the theory of inflatable membranes to obtain the shape of a pressure vessel subjected to tension only stress state, whereby the possibility of buckling is excluded. Such a shape will be referred to as the “buckle-free” shape. A set of nonlinear differential equations are derived which are valid for any axisymmetric pressure vessel subjected to axisymmetric loadings. The shape obtained from the solution of the equations is an “extremum” to possible stable shapes under the given loading conditions; i.e., there are other stable shapes, for which the circumferential compressive stiffness of the structure has to be relied upon. A closed-form solution for the set of equations was obtained for the constant pressure loading case. For hydrostatic pressure a numerical procedure is applied. Results on “buckle-free” shapes for typical pressure vessel strucures for these two loading conditions are presented. It is established that the deviation of such shapes from the shapes obtained by present design methods and code specifications is small so that this proposed method and the resulting “corrections’ leading to “buckle-free” inservice behavior should not present an aesthetic problem in design.

Neutron diffraction studies of water and aqueous solutions under pressure

2014 A summary is given of data obtained from neutron diffraction experiments on heavy water at elevated pressures and temperatures using three different types of pressure vessel. The pressure vessels were manufactured from (i) hard steel (EN24T), (ii) titanium-zirconium null alloy, and (iii) autofrettaged aluminium alloy (7075-T6). In cases (i) and (ii), hydraulic pressures up to 6 kbar were applied directly to the sample across the oil/aqueous solution interface. In case (iii) the pressurizing medium of argon gas was applied uniformly throughout the sample volume giving pressures up to 2 kbar at temperatures in the range 21 °C to 80 °C. Revue Phys. Appl. 19 (1984) 803-805 SEPTEMBRE 1984,

A Pilot Experiment to Determine the Feasibility of Reconstituting Tested Irradiated Charpy V Specimens

Abstract The role of the Charpy V impact test specimen is well established in irradiation studies of reactor pressure vessel materials and forms the basis for the safety justification of light-water reactor pressure vessels throughout their service life. This report details the experimental work carried out towards determining the feasibility of reconstituting further Charpy V specimens from previously tested Charpy V specimens. In this pilot study each broken half of an A533(B) (Unified Numbering System [UNS] K12539) type plate and a submerged are weld metal Charpy V specimen was electron beam welded between two extension pieces of compatible material (A533(B) plate) with matching cross section. After minimal machining each reconstituted Charpy V specimen was impact tested. To validate this technique, broken halves of three high and three low energy Army Materials and Mechanics Research Center (AMMRC) standardized calibration Charpy V specimens were also reconstituted. In addition, a simple photoelastic study was carried out on a replica Charpy V specimen made from birefringent material. This was an attempt to assess the minimum size of test material that could be reconstituted into a Charpy V specimen. In all instances the results were extremely encouraging, especially in the case of the reconstituted AMMRC specimens, and indicated both the feasibility and validity of reconstituting tested Charpy V specimens of low alloy steel reactor pressure vessel type materials. In addition, it is apparent that as small as a 10-mm “insert” of test material could be successfully reconstituted. The results are discussed and speculation made as to the potential use of this technique with respect to irradiated material.

A Procedure for the Assessment of the Structural Integrity of Nuclear Pressure Vessels

This paper presents a simple engineering procedure that the utility industry can use to assess the integrity of typical nuclear-grade pressure vessels. The procedure recognizes both brittle fracture and plastic collapse and is based on a set of proposed failure assessment curves which make up a safety/failure plane. The plane is defined by the stress intensity factor/fracture toughness ratio as the ordinate and the applied stress/reference plastic collapse stress ratio as the abscissa. The failure assessment procedure is based in part on the British Central Electricity Generating Board’s R-6 failure assessment diagram and the deformation plasticity solutions of the General Electric Company. Two parameters, a plastic collapse parameter (Sr′) and linear elastic fracture mechanics parameter (Kr′) are calculated by the user. The point (Sr′, Kr′) is plotted on the appropriate failure assessment diagram. If the point lies inside the respective curve, the structure is safe from failure. Moreover, for a given pressure and a postulated or actual flaw size, the margin of safety of the structure can be simply determined. Consistent with Appendix A of Section XI, (Division 1) of the ASME Boiler and Pressure Vessel Code the procedure presented in this paper is limited to ferritic materials 4 in. (102 mm) and greater in thickness. Details of the derivation of the proposed set of failure assessment curves are provided along with a sample problem illustrating the use of these curves.

Relationships between charpy impact shelf energies and upper shelf [formula omitted] values for reactor pressure vessel steels

Charpy shelf data and lower bound estimates of K Ic shelf data for the same steels and test temperatures have been collated. Included are some typical reactor pressure vessel steels as well as some less tough or degraded steels. The data were evaluated with shelf estimates of K Ic up to and exceeding 550 MPa√m (500 ksi√in). Such high values however must be reduced for analysis applications to preclude failure by some other mode such as ductile tearing. Such reductions are reflected in the conclusions stated below. The conclusions reached for reactor pressure vessel steels are: 1. (1) A Charpy shelf of 47 J (35 ft lbf) indicates K Ic is around 165 MPa√m (150 ksi√in) while 68 J (50 ft lbf) suggests K Ic is near 220 MPa√m (200 ksi√in). 2. (2) A Charpy shelf energy of 102 J (75 ft lbf) indicates 275 MPa√m (250 ksi√in) while a minimum of 357 MPa√m (325 ksi√in) exists for 136 J (100 ft lbf). 3. (3) Shelf energies in excess of 163 J (120 ft lbf) indicate K Ic is very near and/or exceeds 440 MPa√m (400 ksi√in). The high toughness values are based on a thickness of at least 6 in. When linear elastic fracture mechanics is applied using the K Ic estimates, failure by other modes are precluded; however some ductile tearing could occur.

Modeling of Elastoplastic Fracture Behavior Using Acoustic Emission Methods

Using multiple-specimen JIC (R-curve) methods to determine elastoplastic fracture properties is time consuming and costly, and gives limited data about fracture behavior. This paper investigates quantitative acoustic emission analysis methods in modeling elastoplastic fracture in typical pressure vessel steels, and presents the results of a series of compact tension fracture tests, heat treated to exhibit a range of fracture behavior and monitored with acoustic emission. The paper also gives a theoretical formulation relating acoustic-emission parameters with crack length and GIC, and discusses several schemes for acoustic-emission source classification.

Discontinuity stress analysis of pressure vessels using the finite element method

In pressure vessels the centre lines of the cylinder and dome portions often do not coincide thereby leading to a discontinuity at their junction. Structural analysis of such a structure assuming the centrelines of the cylinder and dome portions to be coincident leads to an incorrect estimation of stress and displacement distributions around the discontinuity. To predict accurately the stress and displacement distributions around the discontinuity, an iterative finite element scheme is developed in this paper using a conical shell finite element. The method is applied to two typical pressure vessels, one with hemispherical end domes and the other with ellipsoidal end domes. It is found that the solution converges in a few iterations.

Fracture Toughness of Welded Joints of 9% Ni Steel for the Tank of LNG Carriers

The basic premise of the MOSS-Rosenberg LNG containment system and other spherical LNG tank system is “leak-before-failure”. In other words, the design concept applied to this type of pressure vessel is basically “fail-safe”.Therefore, to evaluate the structural safety of the spherical LNG tank, it is neccesary to obtain the fracture toughness of the tank shell plate and the welded joints, quantitatively. Considering the strength of brittle fracture initiation of 9% Ni steel LNG tank, the fracture toughness in the heat affected zone is the most important problem.Accordingly, the authors carried out the tension test with wide center-notched plate test specimens, notched in the heat affected zone of submerged arc welding with heat input values of about 1050 KJ/cm, in order to evaluate the fracture toughness of welded joints of 9% Ni steel.The following conclusions were obtained.(1) It is reasonable to calculate the critical crack length, using the experimental results obtained from the standard size specimens (about 400 mm wide) on the basis of Linear Elastic Fracture Mechanics.(2) For the butt-welded joints produced with the most practical heat input values of about 1040 KJ/cm, the lowest Kc values at the cryogenic temperature of LNG, -62°C, will be 775500 kg, √mm/mm2, and the critical crack length for brittle fracture initiation of 9% Ni steel LNG tank is satisfactorily long.

Application of the Matrix Displacement Method to the Analysis of Pressure Vessels

The matrix displacement approach of the finite element method is applied to the analysis of deformations and stresses in pressure-vessel type structures. Particular reference is made to structures with rotational symmetry, both under axisymmetric and unsymmetric loading and temperature distribution, for which two classes of structural elements for the idealization of solids and membrane shells are described. A survey of some finite elements used for the analysis of more general pressure vessel structures is conducted. Several examples of axisymmetric and nonsymmetric structures are included to demonstrate the versatility and power of the method.

Ductile Creep Rupture of Shells With Strain Hardening and Time-Dependent Loading

This paper presents an analysis of the tensile instability phenomenon in a thin-walled membrane shell of revolution undergoing creep while subjected to a time-dependent internal pressure. Time-independent plastic deformation due to biaxial stress, including strain hardening and biaxial-stress creep, are included. The theory is applied to an example of a typical closed-end cylindrical pressure vessel to emphasize the importance of considering both plastic and creep deformations due to biaxial stress in calculations of ductile creep rupture.

Nonlinear numerical analysis of axisymmetrically loaded arbitrary shells of revolution

The nonlinear interaction between the meridional stress resultant and rotation is significant in discontinuity regions of highly strained, thin-shell structures. The nonlinear equilibrium equations may be linearized for any given axisymmetric-load condition by inserting the meridional stress resultant, obtained from membrane analysis, where it appears in product terms. Forward integration is used to solve the set of linear differential equations that is derived from the linear straindisplacement relations and the linearized equilibrium equations. By introducing artificial boundaries within the shell, the extent of integration is limited to conform with available numerical techniques. Influence coefficients for segments are computed, and standard methods of matrix structural analysis are used to obtain stress resultants and displacements at the segment interfaces. These are used as initial values for a final numerical integration to determine stresses and displacements throughout the shell. The differences between stresses calculated by means of linear and nonlinear equations are represented graphically from the results of the analysis of a typical pressure vessel support joint. The well-known reduction of peak stresses in the vessel wall is verified, but the bending stress in the support skirt is greater with the nonlinear analysis.

Nonmagnetic High-Pressure Vessels

The use of beryllium copper and stainless steel in the construction of pressure vessels to contain 20 000 kg/cm2 is described. Machine drawings are given for the construction of different types of pressure vessels, different types of seal, and methods of introducing electrical leads into the apparatus. Experience in the use of high-pressure vessels and plugs beyond the elastic limit of the construction material is reviewed.

Analysis of Experimental Data Regarding Certain Design Features of Pressure Vessels

Abstract This paper presents an analysis of data obtained by strain-gage experimental stress analysis on drum heads and nozzle openings in drum shells. This analysis, while referred particularly to power boilers, is also applicable to other types of pressure vessels. The data obtained are reduced to dimensionless form so that they may be applied to drums of other size and thickness but geometrically similar, and to illustrate more clearly the action of the drum in resisting pressure. The relationship between operating-stress level and the life of the vessel in service is discussed with particular reference to a drum that has given over 40 years of satisfactory service with an operating-stress range over a considerable area of the vessel of approximately the ultimate strength of the material. The effect of prestress created in the vessel by overpressuring, such as applying the 1½-times working-pressure hydrostatic test, is discussed.

An Alternative Form of Pressure Vessel of Novel Laminar Construction

Although Class 1 welded vessels have been used to an increasing extent for what might be termed moderate-pressure purposes, most of the vessels required for chemical reactions at really high pressures have up to the present been of forged construction—at any rate in this country. There are certain drawbacks and limitations associated with the forging method of construction, and attempts have therefore been made to develop an alternative type of pressure vessel. One such attempt is that of the “multi-layer” vessel developed in the United States by the A. O. Smith Corporation. This consists of a central welded tube on which successive layers of relatively thin plate are wrapped and welded. The present paper describes a vessel of novel laminar design, the main advantages of which are that the vessel can be built up from plate, which is relatively cheap and available from many sources of supply, and the actual construction and assembly does not call for equipment other than that likely to be found in a good engineering construction shop. Furthermore, the present proposed method of construction will allow the manufacture of vessels far larger than can be produced as single forgings, where the limit in regard to ingot size has already been reached. Two of these laminar vessels have been constructed and have given satisfactory service at 350 atmos. pressure for some years. The paper describes the design, construction and testing of these vessels and makes observations on the cost aspect and the future possibilities.