Pressure vessels shell

Openings are always required in pressure-vessel shells and heads. Stress intensification is created by the existence of a hole in an other-... 

Larger clean-steam generator designs typically employ a pressure vessel (shell) containing a U-shaped tube bundle. The heat source is primary steam supplied to the shell side (which may be amine treated), and secondary clean steam is generated within the tubes. 

Openings are always required in pressure-vessel shells and heads. Stress intensification is created by the existence of a hole in an otherwise symmetrical section. The code compensates for this by an area-replacement method. It takes a cross section through the opening, and it measures the area of the metal of the required shell that is removed and replaces it in the cross section by additional material (shell wall, nozzle wall, reinforcing plate, or weld) within certain distances of the opening centerline. These rules and formulas for calculation are included in Subsec. A. 

Heat transfer area per unit volume is greatly increased by placing a large number of small-diameter tubes inside a shell, that is, a pressure vessel. Shell-and-tube heat exchangers, whose design is standardized by the Tubular Exchanger Manufacturers Association (TEMA)... 

In case of heat exchangers where both shell and tube sides are connected by uninterrupted pipelines and other equipment where isolation of one side by valves or blind is not possible, the tube sheets may be designed for differential pressure only. Also, internals provided with insulation to prevent contact of hot process media with the pressure wall of the equipment can be designed for a differential pressure only and save money for the pressure vessel shell as it can be designed for a lower temperature, whereas the internals must be designed for the high temperatures but for lower pressures. 

The experimental activity was carried out on a cylindrical pressure vessel whose capacity is 50 litres and made from steel 3 mm thick. Fig. 2 shows the layout of the pressure vessel considered. The pressure vessel was connected to an oil hydraulics apparatus providing a cyclical pressure change of arbitrary amplitude and frequency (fig.3). Furthermore the vessel was equipped with a pressure transducer and some rosetta strain gauges to measure the stresses on the shell and heads. A layout of the rosetta strain gauges locations is shown in fig.4. 

The calculation was carried out using the ANSYS F.E.M. code. The pressure vessel was meshed with a 4 nodes shell element. Fig. 18 shows a view of the results of calculation of the sum of principal stresses on the vessel surface represented on the undeformed shape. For the calculation it was assumed an internal pressure equal to 5 bar and the same mechanical characteristics for the test material. 

A horizontal belt filter has been used in place of the small dmm filter in filtration studies (17). The entire filter was placed in a large pressure vessel with no moving parts passing through the filter shell. There is no commercial filter based on this principle the utilization of the space inside the pressure vessel would be poor and the filtration areas limited. 

The axial filter (Oak Ridge National Laboratory) (30) is remarkably similar to the dynamic filter in that both the rotating filter element and the outer shell are also cylindrical. An ultrafiltration module based on the same principle has also been described (31). Unlike the disk-type European dynamic filters described above, the cylindrical element models are not so suitable for scale-up because they utilize the space inside the pressure vessel poorly. 

Construction Codes Rules for Construction of Pressure Vessels, Division 1, which is part of Section T11 of the ASME Boiler and Pressure Vessel Code (American Society of Mechanical Engineers), sei ves as a construction code by providing minimum standards. New editions of the code are usually issued every 3 years. Interim revisions are made semiannually in the form of addenda. Compliance with ASME Code requirements is mandatoiy in much of the United States and Canada. Originally these rules were not prepared for heat exchangers. However, the welded joint between tube sheet and shell of the fixed-tube-sheet heat exchanger is now included. A nonmandatoi y... 

Shell and Tube Heat Exchangers for General Piefineiy Seivices, API Standard 660, 4th ed., 1982, is published by the American Petroleum Institute to supplement both the TEMA Standards and the ASME Code. Many companies in the chemical and petroleum processing fields have their own standards to supplement these various requirements. The Jnterrelation.ships between Codes, Standards, and Customer Specifications for Proce.ss Heat Tran.sfer Equipment is a symposium volume which was edited by F. L. Rubin and pubhshed by ASME in December 1979. (See discussion of pressure-vessel codes in Sec. 6.)... 

Tube material includes any that can be formed into a coil, but usually copper, copper alloys, and stainless steel are most common. The casing or shell material can be cast iron, cast steel, cast bronze, fabri-catea steel, stainless, and other high-alloy materials. Units are available with pressure vessel code conformance. 

The shell is usually a steel design and, like the graphite units before, can obtain pressure-vessel certification. 

Figure 16.1 shows part of a steel tank which came from a road tank vehicle. The tank consisted of a cylindrical shell about 6 m long. A hemispherical cap was welded to each end of the shell with a circumferential weld. The tank was used to transport liquid ammonia. In order to contain the liquid ammonia the pressure had to be equal to the saturation pressure (the pressure at which a mixture of liquid and vapour is in equilibrium). The saturation pressure increases rapidly with temperature at 20°C the absolute pressure is 8.57 bar at 50°C it is 20.33 bar. The gauge pressure at 50°C is 19.33 bar, or 1.9MN m . Because of this the tank had to function as a pressure vessel. The maximum operating pressure was 2.07 MN m" gauge. This allowed the tank to be used safely to 50°C, above the maximum temperature expected in even a hot climate. 

Fig. 16.1. The weld between the shell and the end cap of the pressure vessel. Dimensions in mm.

The ASME code provides the basic requirements for over-pressure protection. Section I, Power Boilers, covers fired and unfired steam boilers. All other vessels including exchanger shells and similar pressure containing equipment fall under Section VIII, Pressure Vessels. API RP 520 and lesser API documents supplement the ASME code. These codes specify allowable accumulation, which is the difference between relieving pressure at which the valve reaches full rated flow and set pressure at which the valve starts to open. Accumulation is expressed as percentage of set pressure in Table 1. The articles by Rearick and Isqacs are used throughout this section. 

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. 

Type S is a floating head type. As the tubes heat up, they expand. As they expand, the floating head moves back and forth, but the pressure seal is not at the sliding joint. The pressure seal is at the fixed shell Joint in the outer head, which contains the pressure. The floating head floats free inside the pressure vessel as the tubes move. Types P and W are floating heads where the movement of the head effects the seal between either the shell-side or tube-side fluid and atmosphere. 

Often, a slightly higher MAWP than that calculated from Tabl possible at almost no additional cost. Once a preliminary MAWP is cted from Table 12-1, it is necessary to calculate a wall thicl r shell and heads of the pressure vessel. The procedure for doii s... 

The vessel shell wall thickness shall be the greater of Equations 7-2 or 7-4, or the pressure shall be the lower of Equation 7-1 or 7-3 [1]. 

Chilling of brines for pre-cooling will generally be in shell-and-tube evaporators. The Baudelot cooler within the pressure vessel may be cooled by flooded or dry expansion refrigerant, or by brine. 

Typically, modern, vertical boilers are of tubeless design. They contain a suspended, dry-back, two- or four-pass, circular water jacket, of pressure vessel construction, about 5/16th inch (7.94 mm) in thickness. The inner tube of the water jacket is in reality the furnace tube, whereas the outer tube is the boiler shell. 

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