Valves ratings, pressure-temperature

Fluid designations are convenient letter symbols for the various fluids handled in the process. Lines are numbered from one piece of equipment to another. This system allows recording of various lines on forms for identifying such items as flow rate, pressure, temperature, class and rating of line and fittings, material and labor costs take-offs, etc. Valves can be identified by a suitable code number on both the flow sheet and specification sheets. 

The feed system is composed of a variety of equipment systems, including feed tank, valves, piping, instruments, and pumps. Inside the feed system, the composition of the feedstock is closely monitored. Flow rates, pressures, temperatures, and levels are carefully maintained. 

Valve bodies are also standardized to mate with common piping connections flanged, butt-weld end, socket-weld end, and screwed end. Dimensional information for some of these joints and class pressure-temperature ratings are included in Sec. 10, Process Plant Piping. Control valves have their own standardized face-to-face dimensions that are governed by ISA Standards S75.03, 04, 12, 14, 15, 16, 20, and 22. Butterfly valves are also governed by API 609 and Manufacturers Standardization Society (MSS) SP-67 and 68. 

TABLE 10-45 Pressure-Temperature Ratings for FlangeS/ Flanged FittingS/ and Flanged Valves of Typical Materials/ Ibf/in ... 

The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

G = Gas specific gravity = mol. wt./29 Pi = Valve inlet pressure, psia AP = Pressure drop across valve, psi Q = Gas flow rate, SCFH Qs = Steam or vapor flow rate, Ib/hr T = Absolute temperature of gas at inlet, °R T5I1 = Degrees of superheat, °F... 

Choking, or expansion of gas from a high pressure to a lower pressure, is generally required for control of gas flow rates. Choking is achieved by the use of a choke or a control valve. The pressure drop causes a decrease in the gas temperature, thus hydrates can form at the choke or control valve. The best way to calculate the temperature drop is to use a simulation computer program. The program will perform a flash calculation, internally balancing enthalpy. It will calculate the temperature downstream of the choke, which assures that the enthalpy of the mixture of gas and liquid upstream of the choke equals the enthalpy of the new mixture of more gas and less liquid downstream of the choke. 

The vessel nozzle diameter (inside) or net free area for relief of vapors through a rupture disk for the usual process applications is calculated in the same manner as for a safety relief valve, except that the nozzle coefficient is 0.62 for vapors and liquids. Most applications in this category are derived from predictable situations where the flow rates, pressures and temperatures can be established with a reasonable degree of certainty. 

Pressure/vacuum, 435, 466 Vacuum systems, 343 Absolute pressure conversions, 363 Air inleakage, 366 Calculations, 366-375 Dissolved gases release, 368 Estimated air inleakage, table, 366 Evacuation time, 371 Maximum air leakage, chart, 367 Specific air inleakage rates, 368 Temperature approach, 375 Classifications, 343 Diagrams, 380 Pressure drop, 353 Pressure levels, 343, 352 Pressure terminology, 348 Pump down example, 381 Pump down time, 380 Thermal efficiency, 384 Valve codes, 26... 

Using CONFL03, determine the importance of including the adiabatic work effects in the model, over a range of flow rate, pressure and valve conditions by following the changes in the gas space temperature and pressure. 

When two services that operate at different pressure/ temperature conditions are connected, the valve segregating the two services shall be rated for the more severe service condition. If the valve will operate at a different temperature due to its remoteness from a header or piece of equipment, this valve (and any mating flanges) may be selected on the basis of the different temperature, provided it can withstand the required pressure tests on each side of the valve. For piping on either side of the valve, however, each system shall be designed for the conditions of the service to which it is connected. 

Where Q = Heat-Transfer Rate Fs = Steam Mass Flow AHs = Latent Heat of Vaporization F = Feed Rate Cp = Heat Capacity of Feed T0 = Steam Supply Temperature Pt = Steam Supply Pressure P2 = Steam Valve Outlet Pressure Ps = Condensing Pressure Tj = Inlet Temperature T2 = Outlet Temperature A Tm = Log Mean Temperature Difference Ts = Condensing Steam Temperature... 

SDecification ANSI B16.5 Product Forms All (also valves) Scooe Standard ASTM materials, dimensions, and pressure-temperature ratings... 

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