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Pressure Vessel Calculator (ASME VIII) CalQlata's pressure vessel calculator determines the minimum permissible wall thickness(es) or maximum permissible pressure(s) for spherical or cylindrical pressure vessels and their heads ( Fig 1) that. Are subject to internal pressure,. Subject to external pressure, and. Conforms to ASME VIII, Division 1 design code CalQlata's pressure vessel calculator does not include non-circular pressure vessels The minimum required wall thickness of pressurised spheres and cylinders could be determined using classical theory but this is not normally considered appropriate for the safety of pressure vessels, which usually contain considerable levels of stored energy⁽¹⁾ and are frequently in close proximity to operating personnel.

Moreover, physical collapse due to external pressure is always as a result of elastic instability and far too difficult to predict using general mathematical principles. ASME's considerable long-term experience provides far greater confidence in minimising the likelihood of unexpected collapse, given certain design criteria and limitations. Pressure Vessel The cross-section of any internally or externally pressurised vessel (container) should be circular for maximum pressure-carrying capacity and/or stability. Moreover, it should have no irregularities, corners or flat surfaces. A is a container of any size and shape that will maintain its integrity (but not necessarily its size and shape) against an internally or externally pressurised fluid. A properly designed pressure vessel is one that will do so with no risk of damage, and the ASME VIII design code is generally considered to be the most appropriate means of achieving this. Cylinder Any longitudinal container will naturally try to form a cylinder under sufficient internal pressure.

Its length will have no effect on stresses induced in an internally pressurised vessel other than those induced by its support. Pressure Vessels calculates the wall thickness of plain cylinders of same material and equal wall thickness throughout. If you wish to evaluate cylindrical pressure vessels of different diameter and material the wall thickness of each section should be calculated seperately. Conical Head calculations may be used to evaluate conical transitions between each diameter variation, along with any necessary reinforcement. ASME VIII only considers membrane stresses (longitudinal and circumferential) in a cylindrical vessel, i. Ramones Too Tough To Die Blogspot Download Music there. e. Radial stresses are ignored, which is considered reasonable given that the maximum radial stress (equal to the internal pressure) is insignificant compared to membrane stresses in a. Cylindrical vessels will always need a thicker wall than a sphere for any given diameter and design pressure.

Typical Heads Any bulk container will naturally try to form a spherical shape under sufficient internal pressure. Pressure Vessels calculates the wall thickness of plain spheres of same material and equal wall thickness throughout. ASME VIII only considers membrane stresses (circumferential) in a spherical vessel, i.e. Radial stresses are ignored, which is considered reasonable given that the maximum radial stress (equal to the internal pressure) is insignificant compared to membrane stresses in a. Spherical vessels will always need a thinner wall than a cylinder for any given diameter and design pressure, which is why very large pressure vessels tend to be spherical. Heads A cylindrical vessel head is a closure, lid or cap ( Fig 2) of consistent material and wall thickness throughout except as described in Skirt and Knuckle below Skirt is a cylindrical section that forms the interface to the cylinder or connection flange, the wall thickness of which should be at least the same as the vessel to which it is attached.

All head volumetric calculations include a skirt length equal to the minimum value recommended by ASME of; 3 x wall thickness + half an inch. Knuckle is a radiused transition between the head and the skirt of diameter at least 6% of the skirt diameter. Whilst the minimum calculated material thickness for transition knuckles according to the ASME VIII design code is generally less than the calculated minimum wall thickness for the head and cylindrical vessel, Pressure Vessels assumes this wall thickness to be the same as its head for volumetric calculations. Hemispherical is a hemisphere with the same diameter as its skirt. No knuckle is required for these heads. Ellipsoidal is half an ellipse where the head depth (minor axis) is equal to one quarter of the skirt diameter (major axis). No knuckle is required for these heads.

Torispherical has a crown ( of a sphere) radius equal to the skirt diameter and a transition knuckle. Toriconical is a simple cone with a knuckle transition at its skirt. ASME VIII does not limit the included angle of internally pressurised toriconical heads⁽²⁾ Conical is a simple cone that finishes at the vessel with a sharp transition. No knuckle is required for these heads but reinforcement may be required inside the interface. ASME VIII recomends that the included angle of internally pressurised conical heads does not exceed 60°⁽²⁾ Pressure The design pressure of any pressurised container is the difference between the internal and external pressure. For example; if a pressure vessel is exposed to an internal pressure of 100psi and an external pressure of 35psi, the design pressure for the vessel will be an internal pressure of 65psi (65 = 100 - 35) Internal and external pressures should include the effects of head-pressure (pressure due to fluid depth), especially if the pressurising fluid is a liquid, and as head-pressure varies with depth the design pressure at the top of a liquid container need not be as great as that at its base.

For example; if a 500 inch diameter vessel is 90% filled with a fluid of density 0.0362lb/in³ and an over-pressure of 30psi is applied at the surface of the liquid, the maximum pressure at the top of the vessel will be 30psi whilst the maximum pressure at its base will be 46.29psi (46.29 = 90% x 500 x 0.0362 + 30) Internal (pressure) A shell or cylinder of constant material quality and wall thickness exposed to internal pressure will always equalise hoop, radial and longitudinal throughout⁽³⁾, and failure will occur due to the combined effect of these stresses exceeding. Maximum possible pressure without inducing permanent deformation will occur immediately prior to the reaching. Maximum allowable pressure is that which induces an allowable stress (σₐ), which is a specified fraction (. Three I-Beam Stiffening Rings Internal and/or external stiffening rings ( Fig 3) increase elastic stability and are often installed at regular intervals in externally pressurised vessels to minimise wall thickness. You can minimise total vessel weight by optimising stiffener; material, and longitudinal spacing. However, to eliminate and improve weldability the pressure vessel calculator assumes stiffener material to be the same as that of the vessel wall. Stiffeners are added to internally pressurised vessels only to accommodate localised loading due to supports, closures, openings, etc., they will not affect wall thickness.

Reinforcement stiffeners are not included in vessel volume calculations. Welding As all pressure vessels must to be welded using certified materials and coded welders, weld joint factors (WJF) between 0.9 and 1.0 are the norm in their design.

Variable Plate Thickness Whilst there is little to be gained from varying the wall thickness of small pressure vessels and those that contain gas, the weight and cost of large vessels and those that contain liquids can be lessened significantly by reducing the wall thickness with head-pressure (see Pressure above). Moreover, the lower centre of gravity of large pressure vessels with a wall thickness that reduces with height will improve stability during an earthquake. This technique may be applied to both cylindrical and spherical vessels. ASME VIII The world's most recognised design code for pressure vessels comprises two Divisions; Division 1 (mandatory rules): For all pressure vessels including those covered by Division 2, and; Division 2 (alternative rules): For fixed pressure vessels The ASME VIII code provides design, manufacture and inspection rules for all pressure vessels and their head(s) along with the requirements for shape variations, nozzles, closures, openings and reinforcement.

CalQlata's pressure vessel calculator includes cylindrical and spherical shells and heads according to Division 1, Part UG and Appendices 1 & 5. Included in the code is a single plot (Dₒ/t vs L/Dₒ vs A for externally pressurised vessels) used to identify ASME's Factor A, along with about 60 material charts (Appendix 5, Fig 5-UCS-28.1 to UCD-28) that identify ASME's Factor B (and elastic moduli) for various materials at specific temperatures. For maximum accuracy, CalQlata has mathematically modelled each plot on every chart, all of which have been included in the pressure vessel calculator along with interpolation.

Fig 5 (Appendix 5) This sub-section (Fig 5) applies only to pressure vessels exposed to external pressure. Refer to Mandatory Appendix 5, Fig 5 (material charts) below for material chart titles. ASME VIII Fig 5 UCS-28.6 @ 300°F Fig 5 titles refer to the following materials: UCD: Sub-section C, Ductile Cast Iron UCI: Sub-section C, Cast Iron UCS: Sub-section C, UHA: Sub-section C, UHT: Sub-section C, UNF: Sub-section C, The plots included in this group of ASME figures are interpretations of a modified version of the for each metal concerned. The horizontal axis (A) is and the vertical axis is a Logarithmic and non-logarithmic versions of the plot for UCS-28.6 @ 300°F are provided in Fig 4 for comparison purposes, where it can be seen that above a relatively low stress (B) a minor increase is expected to induce a significantly greater strain (A) than would otherwise be expected for the same material in tension or linear compression. ASME expects the maximum permissible stress in an externally pressurised vessel manufactured from this metal to be approximately a ¼ of that for an internally pressurised vessel. 'A' is nominally defined by ASME as; 0.125÷(Dₒ/t)⁽⁶⁾.

The relationship 'Dₒ/t' is the reciprocal of strain in a curved vessel wall (e = y/R), where 'Dₒ' is the outside diameter of the vessel, 'R' is its radius, 't' is its wall thickness and 'y' represents half the wall thickness or the distance from the to the outer fibre of the vessel wall. Therefore, 'A' represents ⅛ᵗʰ the expected strain. Twice the value of Factor 'B' is used in the allowable stress calculations⁽⁶⁾. Therefore applying one eighth of the strain with twice the stress means that ASME expect elastic instability to occur at one quarter of the material's tensile yield stress. You are permitted to use any portion of each plot. The maximum value indicated for 'B' on any plot is regarded by ASME as the yield stress associated with elastic instability. Any further increase in 'B' and you can expect elastic instability to increase the risk of localised with little increase in stress (see Fig 4) The maximum allowable stresses are similarly reduced for all ASME VIII-Fig 5 metals used in the manufacture of externally pressurised vessels.

UCS-28.6 @ 300°F You can verify CalQlata's mathematical modelling of ASME's plots for factor 'B' (Division 1, Appendix 5, Figs UCS-28.1 to UCD-28) using the co-ordinates provided below the 'Output Data' in the Data Listing window ( Fig 5). One plot is provided where interpolation has been unnecessary, otherwise two plots are provided; one at the temperature above that entered and one below. Verification using your preferred spreadsheet (e.g. Plate Arc length Liquid depth Total pressure Plate thickness level (L) ins (d) ins (p) psi (t) ins top 8 1256.64 -50 # 29.4 0.087 7 1120 -26.89 # 29.4 0.087 6 960 55.04 31.389 0.093 5 800 183.54 36.031 0.107 4 640 338.32 41.624 0.123 3 480 494.94 47.282 0.140 2 320 628.68 52.114 0.154 bottom 1 160 718.42 55.357 0.164 # Overpressure (pₒ) only apply to these plates as the surface of the liquid falls below the bottom of the plates concerned. You could alter the plate thickness for each stratum or multiples thereof. However, the thickness selected for each level must be suitable for the bottom of its lowest plate. The above table also shows that if the vessel were to be manufactured from a single plate thickness it must be no less than 0.164inches (4.2mm).

Whilst the above calculation procedure may also be applied to externally pressurised vessels, plate thickness variations may exacerbate elastic instability. Example Calculation 2 A typical practical use for externally pressurised vessels is mid-water support buoys. These use their buoyancy to support a weight, e.g.

Risers, cables, measuring equipment, etc. Above the seabed.

Question: A cylindrical buoy of minimal mass is required to lift 4000lbf (total capacity) and operate in seawater at a depth of 325ft. What would be the dimensions of a suitable steel buoy (ignore the effect of vessel heads for this example calculation)? Assuming the buoy is manufactured from the same material as used in Example 1 (above), the maximum allowable stress will be 12,700psi. The external pressure at this depth would be 144.4psi, which is also the differential pressure as it is assumed that atmospheric pressure (1 bar) is inside the vessel.