Minimum wall thickness, pressure

A blow-moulded container, cylindrical in shape but with one spherical end, is prepared from the polysulphone whose creep curves at 20°C are illustrated in Figure 9.9. The cylindrical part of the container has an outside diameter of 200 mm and is required to withstand a constant internal pressure of 7 MPa at 20°C. It is estimated that the required service lifetime of the part will be one year and the maximum allowable strain is 2%. What will be the minimum wall thickness for satisfactory operation ... 

The wall thickness of the pipe or plate used for the shell is normally determined from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. TEMA standards also specify some minimum wall thicknesses for the shell. 

This concept can be especially significant for a low-pressure vessel wl minimum wall thickness is desired. For example, assume the caiv .,.i i.ons for a 50-psig MAWP vessel indicate a wall thickness of 0.20 in., and it is decided to use K-in. plate. This same plate might be used if a MAWP of 83.3 psig were specified. Thus, by specifying the hi MAWP (83.3 psig), additional operating flexibility is available at e dally no increase in cost. Many operators specify the MAWP based on... 

Internal Yield Pressure for Pipe. Internal yield pressure for pipe is calculated from formula 4-133. The factor 0.875 appearing in formula 4-313 allows for minimum wall thickness. 

The analysis of the membrane stresses induced in shells of revolution by internal pressure gives a basis for determining the minimum wall thickness required for vessel shells. The actual thickness required will also depend on the stresses arising from the other loads to which the vessel is subjected. 

The minimum wall thickness required to resist the hydrostatic pressure can be calculated from the equations for the membrane stresses in thin cylinders (Section 13.3.4) ... 

The fluid in a rotating centrifuge exerts pressure on the walls of the bowl or basket. The minimum wall thickness required to contain this pressure load can be determined in a... 

A horizontal, cylindrical, tank, with hemispherical ends, is used to store liquid chlorine at 10 bar. The vessel is 4 m internal diameter and 20 m long. Estimate the minimum wall thickness required to resist this pressure, for the cylindrical section and the heads. Take the design pressure as 12 bar and the allowable design stress for the material as 110 MN/m2. 

A material performance factor, My, shall be applied to the allowable stress, S, in all minimum wall thickness or pressure calculations (see Mandatory Appendix IX, Tables IX-5B and IX-5C, for My). 

Flared, flareless, and compression-type tubing joints may be used. The tubing components and joints shall be suitable for maximum and minimum wall thickness tubing and pressure-temperature limitations designated by the manufacturer or ANSI-approved standards. In addition to the requirements specified by the engineering design, the joints shall be qualified for use under severe cyclic conditions. 

For the design of internal-pressure cylindrical vessels, the API-ASME Code for Unified Pressure Vessels recommends the following equations for determining the minimum wall thickness when extreme operating pressures are not involved ... 

In general, the minimum wall thickness, not including allowances for corrosion, for any plate subject to pressure should not be less than m- f°r welded or brazed construction and not be less than in. for riveted construction except that the thickness of walls for unfired steam boilers should not be less than j in. 

Tube-wall thickness is usually specified by the Birmingham wire gauge, and variations from the nominal thickness may be + 10 percent for average-wall tubes and + 22 percent for minimum-wall tubes. Pressure, temperature, corrosion, and allowances for expanding the individual tubes into the tube sheets must be taken into consideration when the thickness is determined. 

The fluid in a rotating centrifuge exerts pressure on the walls of the bowl or basket. The minimum wall thickness required to contain this pressure load can be determined in a similar manner to that used for determining the wall thickness of a pressure vessel under internal pressure. If the bowl contains a single homogeneous liquid. Figure 13.48a, the fluid pressure is given by ... 

The structure of this formula can quickly be related to the thin-walled pressure vessel cylinder equation. Using the equation that calculates the stress at the center of the vessel wall, ux = P R + 0.5t)/t, and rearranging to solve for the thickness, results m. t = PR/ ux — 0.5P. The addition of the weld joint efficiency, E, and changing the coefficient before P to 0.6 results in the ASME code formula, t = PR/ SE — 0.6P), which they feel best represents the minimum wall thickness required to contain an internal pressure, P, in a cylindrical vessel having a radius, R, and made of a material with an allowable stress, S. 

The experience of the authors after several iterations is that the best system is to use steel cells with the minimum wall thickness permitted for the required temperature and pressure conditions. An off-the-shelf sealing system, such as Conflat flanges with copper gaskets or metal tubes with Swagelok fittings work well. There is also the need to allow the adsorbate access to the sample and all-metal bellows type valves are the best choice. These survive temperature cycling well. A variety of cells that have been used at ISIS are shown in Fig. 3.33. Fig. 3.34 shows a centrestick equipped for gas handling. 

A chemical reactor is a vessel manufactured from metal, often stainless steel or high resistant alloys. A minimum wall thickness is required to resist to different toads, and mainly to internal pressure. Accurate mechanical calculation of process equipment is a matter of mechanical engineering, and out of the scope of this book. Here we present only simple relations that permit the evaluation of weight and cost of vessels in a preliminary economic analysis. More information about mechanical design can be found in Coulson Richardson (1993). 

Beside the resistance to internal pressure, a minimum wall thickness is required to ensure that the vessel resists to deformation due to its own weight, to incidental loads. 

Cold hydro qualification tests, hot functional qualification tests, periodic in-service Inspections, and periodic in-service operation will be performed in situ to verify and assure the functional ability of the valve. These tests will guarantee reliability of the valve for the design life of the plant. The valves will be designed using either stress analyses or the pressure containing minimum wall thickness requirements. On all active valves, an analysis of the extended (e.g., actuator) structure will also be performed for static equivalent SSE loads supplied at the center of gravity of the extended structure. The maximum stress limits allowed in these analyses will assure structural integrity. 

At low pressures, wall thicknesses calculated from Eq. (16.60) may be too small to give sufficient rigidity to vessels. Accordingly, the following minimum wall thicknesses should be used ... 

Treating it as a pressurised thin-walled tube, determine the minimum wall thickness d for an MDPE pipe to meet the specification diameter 104 mm design pressure rating - 400... 

ASME VIII-3 does not give a direct equation for calculating wall thickness. Neither does it give allowable stresses for materials. Instead it gives one simple equation for calculating allowable pressure. By iterative trials, a suitable wall thickness is assumed that will yield a pressure above design. By multiple trials the minimum wall thickness may be determined. 

External insulation permits the use of pressure pipe of a minimum diameter and thus of a minimum wall thickness but requires that the pipe be constructed of cryogenic-rated material, such as stainless steel, 9% nickel steel, or 5083-H113 aluminium. These materials are considerably more expensive than ordinary carbon-steel pipe, ranging from ten times for stainless steel to three times for nickel steel or aluminium. The external insulation, usually urethane foam, is secured to the pipe with a metal or plastic vapour barrier and a protective jacket. Such insulation is relatively weak mechanically and could not impose any significant axial restraint on the pipe. Since such a pipe will be constructed at ambient temperatures, but operate at about 194 K, there will be a considerable range of expansion (0.15% for steel and 0.3% for aluminium), which will have to... 

C-3 Standards for Welding on Thin Walled Steel Cylinders. Standards applicable to DOT welded or brazed compressed gas cylinders designed for 500 psig service pressure or less and having 1,000 lbs. water capacity maximum also minimum wall thickness under 3/8 inch. Covers procedures and operator qualification, radiographic inspection and container repair. Previous edition cited in 49 CFR (27 pages). 

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