Maximum expected operating pressure

Pop = Normal expected or maximum expected operating pressure, psia... 

Maximum Expected Operating Pressure (MEOP) The highest pressure that a pressure vessel, pressurized structure, or pressure component is expected to experience during its service life and retain its functionality, in association with its applicable operating environments. It includes the effect of temperature, pressure transients and oscillations, vehicle quasi-steady and dynamic accelerations, and relief valve operating variability. 

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. 

Design Pressure of a Vessel the pressure established as a nominal maximum above the expected process maximum operating pressure. This design pressure can be established by reference to the chart in Chapter 1, which is based on experience/practice and suggests a percentage increase of the vessel design pressure above the expected... 

The pressure at which the valve is expected to open (set pressure) is usually selected as high as possible consistent with the effect of possible high pressure on die process as well as the containing vessel. Some reactions have a rapid increase in temperature when pressure increases, and this may fix the maximum allowable process pressure. In other situations the pressure rise above operating must be kept to some differential, and the safety valve must relieve at the peak value. A set pressure at the maximum value (whether maximum allowable working pressure of vessel, or other, but insuring protection to the weakest part of the system) requires the smallest valve. Consult manufacturers for set pressure compensation (valve related) for temperatures >200°F. 

Table 7-9 summarizes the usual recommended relationship between the operating pressure of a process (should be maximum expected upper range level) and the set pressure of the rupture disk. Recognize that the set pressure of the disk must not exceed the MAWP of the vessel. (See Eigures 7-31A and 31B.) The burst pressure, P, can now be defined. The use of the manufacturing range... 

The guiding principle of all these techniques is that bottomhole pressure is held constant and slightly above the formation pressure at any stage of the process. To choose the most suitable technique one ought to consider (a) complexity of the method, (b) drilling crew experience and training, (c) maximum expected surface and borehole pressures and (d) time needed to reestablish pressure overbalance and resume normal drilling operations. 

Maximum operating pressure (MOP) Maximum pressure expected during normal system operation. 

Appendix A contains a materials selection guide for aerated freshwater systems. As indicated in Note 27 of Appendix A, in freshwater systems, admiralty brass should be limited to a maximum pH value of 7.2 from ammonia and copper-nickel alloys and should not be used in waters containing more sulfides than 0.007 mg/L The materials selection guide is also satisfactory for seawater, although pump cases and impellers should be a suitable duplex stainless steel or nickel-aluminum-bronze (properly heat treated). Neoprene-lined water boxes should be considered. For piping, fiber-reinforced plastic (up to 150 psi [1,035 kPa] operating pressure) and neoprene-lined steel should also be considered. Titanium and high-molybdenum SS tubes should be considered where low maintenance is required or the cost can be justified by life expectancy. 

On the basis of these calcnlations, Karode was able to explain the experimental findings of Bhatfacharjee and Bhatfacharya" for this system. In their experiments and simulations, the maximum wall concentration was always far below the above calculated limit of 340 kg/m. As a consequence, no gel layer was formed on the membrane surface. In addition, it is reasonable to expect the wall concentration to be a function of the operating parameters such as the operating pressure, the stirring speed, etc. In practical applications of PEG ultraflltration, the filtration would be osmotically limited and one could never expect the formation of a gel layer. The formation of such a layer would require application of pressures higher than -30 atm. 

The PV (pressure x velocity) convention is utilized to define the maximum combinations of pressure and velocity at which a given material will operate continuously without lubrication. The values are usually given for operation in air at temperatures of 21°C-27°C. PV limits do not always define the actual combinations of pressure and velocity where the material can be practically used, because wear is not considered in the determination of PV values. In other words, the application must not exceed PV limit and wear limits of a material. Such a limit can be determined by finding the pressure and velocity combination at which wear rate accelerates or exceeds the expected life of a part. 

An easy way to obtain substance data is to look at the organic solvents which are expected to be used. In many cases a selection can be made containing those which cover the operational range by their boiling points under standard pressure and at the maximum relief set pressure. Figure 7-6 shows such a selection for the example used to help understand the presented procedure. 

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