Pounds per square inch absolute

FIG. 14-66 Efficiency of FRI reLoiler and space below bottom support plate. To convert pounds per square inch absolute to Idlopascals, multiply by 6.8947 to convert (feet per second) (pounds per cubic foot) " , to (meters per second) (kilograms per cubic meter) " , multiply by 1.2199. Sil-oey and Keller, Cbem. Eng. Prog., 62(1), 6S (1,966).]... 

The vapor pressure of a liquid is the absolute pressure at which the liquid vaporizes or converts into a gas at a specific temperature. Normally, the units are expressed in pounds per square inch absolute (psia). The vapor pressure of a liquid increases with its temperature. For this reason the temperature should be specified for a declared vapor pressure. 

Note To change above values to pressure in pounds per square inch absolute multiply by the following factors ... 

Partial pressure of air in mixture, Ibs/sq in. abs = Absolute intake pressure of pump = Piston displacement, cu ft/min = Partial pressure of non-condensable gas pounds per square inch absolute (or other absolute units)... 

Vapor pressure of condensable vapor, pounds per square inch absolute (or other absolute units)... 

Pj = upsueain relieving pressure, in pounds per square inch absolute. This is the set pressure plus the allowable overpressure plus the atmospheric pressure. 

In calculations that involve gas pressure and volume, absolute pressure or pounds per square inch absolute (psia) must be used. 

Inches of mercury — Absolute (in Hg Abs) Millimeters of mercury — Absolute (mm Hg Abs) Pounds per square inch — Absolute (psia)... 

A different reference level, absolute pressure, is used to obtain the total pressure value. Absolute pressure is the total pressure, i.e., gage and atmospheric, and is expressed as psia or pounds per square inch absolute. To obtain absolute pressure, simply add the value of atmospheric pressure (14.7 psi at sea level) to the gage pressure reading. 

Most steam generating plants operate below the critical pressure of water, and the boiling process therefore involves two-phase, nucleate boiling within the boiler water. At its critical pressure of 3,208.2 pounds per square inch absolute (psia), however, the boiling point of water is 374.15 C (705.47 °F), the latent heat of vaporization declines to zero, and steam bubble formation stops (despite the continued application of heat), to be replaced by a smooth transition of water directly to single-phase gaseous steam. 

These recent tests were conducted at applied stress levels similar to those that might be experienced by ASME Section Vm, Division 2 vessels. Test exposure times exceeded 50,000 hours depending on applied stress and temperature. The test specimens were from weldments of thick section plates and represented base metal, weld metal, and heat-affected zone. Detrimental effects of hydrogen were found down to the Figure 1 limit of 850°F (454°C) at 2000 pounds per square inch absolute (14 megapascals) and 3000 pounds per square inch absolute (21 megapascals) hydrogen partial pressure. 

Figure 2 shows the microstructure of a sample of C-0.5Mo steel damaged by internal decarburization and Assuring. The service conditions were 790°F (421°C) at a hydrogen partial pressure of 425 pounds per square inch absolute (2.9 megapascals) for approximately 65,000 hours in a catalytic reformer. 

Calculated operating stress pounds per square inch absolute... 

The second is conversion of values of pressure measured in atmospheres to pounds per square inch absolute. The conversion factor is a constant, 14.696 psia/atm. 

The third calculation is the conversion of pressure units from pounds per square inch read from a guage (psig) to pounds per square inch absolute (psia). Strictly speaking, the value of barometric pressure in psi read from a barometer at the time the pressure gauge was calibrated should be added to psig to get psia. At sea level, a value of 14.7 psi is usually sufficiently accurate. 

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