Maximum Allowable Pressure

The scope of the directive covers the design, manufacture and conformity assessment of pressure equipment and assemblies with a maximum allowable pressure greater than 0,5 bar. A pressure equipment in the sense of the directive is any vessel, piping, safety accessory or pressure accessory. An assembly means several pieces of pressure equipment assembled by a manufacturer to constitute an integrated and functional whole. It is important to be aware that the directive relates exclusively to the pressure risk and that therefore other directives, such as for machinery, low voltage may be applicable to the equipment concerned. 

It is the rate of temperature inerease (i.e., power output) between the set pressure and the maximum allowable pressure, whieh determines the vent size and not the peak rate. Boiling is attained before potential gaseous deeomposition (i.e., the heat of reaetion is removed by the latent heat of vaporization). The reaetion is tempered, and the total pressure in the reaetor is equal to the vapor pressure. The prineipal parameter determining the vent size is the rate of the temperature rise at the relief set pressure. 

Maximum Allowable Working Pressure (MAWP) The maximum allowed pressure at the top of the vessel in its normal operating position at the operating temperature specified for that pressure. 

Answer Figure 15.5.2-1 shows the "percolator" scheme. At the top of the a reactor vessel, presumably the hottest location, is a diaphragm that blows out if the reactor exceeds the maximum allowable pressure. It is attached by an alloy that melts at that the... 

These devices are generally designed to meet specific pressure-drop limitations. For ordinary installations operating at approximately atmospheric pressure, fan limitations dictate a maximum allowable pressure drop corresponding to a cyclone inlet velocity in the range of 20 to 70 feet per second. Consequently, cyclones are usually designed for an inlet velocity of 50 feet per second. 

For vacuum distillations the maximum allowable pressure drop will be determined by the process requirements, but for satisfactory liquid distribution the pressure drop should not be less than 8 mm water per m. If very low bottom pressures are required special low pressure-drop gauze packings should be considered such as Hyperfil, Multifil or Dixon rings see Volume 2, Chapter 4. 

The design of the network calls for the selection of pipe diameters such that the discharge through each valve attains the maximum (sonic) velocity for an initial transitory period. Since the flare pressure and the process unit pressures are specified, this requirement amounts to the stipulation of a maximum allowable pressure drop over each path Sj (labeled with a roman numeral) from the valve to the flare. The optimal design in this case may be formulated as the following constrained minimization problem ... 

The Poppe plot is a log-log plot of H/uq = t(JN versus the number of plates with different particle sizes and with lines drawn at constant void time, t(). H is the plate height, Vis the number of plates, and u() is the fluid velocity (assumed equal to the void velocity). The quantity H/u() is called the plate time, which is the time for a theoretical plate to develop and is indicative of the speed of the separation, with units of seconds. In the Poppe plot, a number of parameters including the maximum allowable pressure drop, particle diameter, viscosity, flow resistance, and diffusion coefficient are held constant. 

Consider constant flow into protected equipment (blocked outlet). For the steady-state design scenario with a constant flow of fluid Win (kg/s) from a pressure source that is above the maximum allowed pressure in the protected equipment, volume is being generated within the equipment at a rate of Win/pin, where pin (kg/m3) is the incoming fluid density evaluated at the maximum allowed pressure. Denoting pout (kg/m3) as the vent stream fluid density, Eq. (23-89)... 

The properties are evaluated at maximum allowed pressure conditions. For liquids, (3 can typically be evaluated from the specific volume change over a 5°C temperature increment. For ideal gases, Eq. (23-91) becomes... 

Maximum allowable pressure drops (shell or tube side)... 

First, we look at isocratic separations. Let us assume that the analysis can be accomplished within a retention factor of 10. We also suppose that the analysis is carried out with a typical reversed-phase solvent and a sample with a typical molecular weight of a pharmaceutical entity. In order to manipulate the analysis time, we will keep the mobile phase composition the same and vary the flow rate. The maximum backpressure that we will be able to apply is 25MPa (250 bar, 4000psi). In Figure 1, we have plotted the plate count as a function of the analysis time for a 5 J,m 15-cm column. We see that the column plate count is low at short analysis times and reaches a maximum at an analysis time of about 1 h. A further increase in analysis time is not useful, since the column plate count declines again. This is the point where longitudinal diffusion limits the column performance. The graph also stops at an analysis time of just under 5 min. This is the point when the maximum allowable pressure drop has been reached. 

The pressure for which a pressure vessel has been designed, according to a recognised pressure vessel code such as BS 5500. This is the "maximum allowable pressure" in the Pressure Equipment Directive (see Chapter 5). 

The maximum allowed pressure of 100 bar will be reached at approximately 240 °C this temperature will be taken as the maximum temperature for technical reasons (MTT). 

The experiments were conducted in a laboratory scale device. A schematic view of the high pressure fluidized-bed coating apparatus is shown in Fig. 1. The apparatus consists essentially of three subsections the CO2 supply, the extractor (in which the CO2 becomes saturated with coating) and the high pressure reactor (where the coating takes place). The maximum allowable pressure in the device is 30 MPa at... 

The confusion is due to a number of reasons. First is the way ASME does not relate the maximum allowable pressure (MAP) limits to SRV capacity. Throughout the entire document, ASME, Section VIII, Division 1, refers to MAWP when talking about SRV set pressure and allowable overpressure. 

Pressure limiting devices, particularly for pressure vessels The momentary pressure surge referred to in 2.11.2 must be kept to 10% of the maximum allowable pressure. 

API Recommended Practice 520 Part I, Sizing and Selection This API design manual includes basic definitions and information about the operational characteristics and applications of various pressure relief devices. It also includes sizing procedures and methods based on steady state flow of Newtonian fluids. This RP covers equipment that has a maximum allowable pressure of 15 psig (1.03 barg) or greater. 

As a definition for this directive, we can put that it applies to the design, manufacture and conformity assessment of pressure equipment and assemblies with a maximum allowable pressure (MAP or PS) greater than 0.5 barg. 

What the PED does say in its ESR related to SRVs is that pressure-limit- PED categories ing devices must prevent the maximum allowable pressure being permanently exceeded. The safety valve (SV) should be set at PS (= MAP) or lower, with exception of momentary pressure surge (accumulation) which is 10% of PS in all cases (multiple valves also) and except for fire, this can be higher if proven safe. This is much more general but definitely differs with ASME as described in detail in Section 3.6. 

The pressure (P) should be taken as the maximum allowable pressure drop according to the relevant standard. In the case of EN ISO 4126, this would be 10% of the set pressure, and it is at this pressure we determine p. 

In LC (and to a lesser extent also in GC) the limiting factor is the maximum allowable pressure drop over the column. As an example, we will look at the dimensions of packed columns for LC when the operating pressure (Ap) is fixed at the maximum value allowed by the instrumentation [704]. 

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