System pressure

Pressure systems refer to any system of pipes, vessels, valves or other equipment for containing or transferring gases and liquids at high pressure. 

The legislation on pressure equipment, the Pressure Equipment Regulations 1999 (PER), is concerned with the quality of the equipment that is manufactured and supplied and incorporates the requirements of the Pressure Equipment Directive . This Directive is aimed at reducing the barriers to trade in respect of pressme equipment. 

Vessels, piping, safety accessories and pressme accessories where applicable, pressme equipment includes elements attached to pressurised parts, such as flanges, nozzles, couplings, supports, lifting lugs, and similar  

liquids and vapours in pure phase as well as mixtures thereof a fluid may contain a suspension of solids. 

It divides fluids into two groups. Group 1 are those fluids which are in themselves hazardous to health, i.e. explosive, flammable, toxic or oxidising. All other fluids are in Group 2. 

The safety of pressure systems in Great Britain is controlled by the Pressure System and Transportable Gas Containers Regulations 1989. These probably apply if 

All steam systems with a pressure vessel used at work are covered, irrespective of pressure. 

Here the safe operating units are basically the upper limits of pressure and temperature 

The legislation concerning pressure vessels and systems is in 2 parts. The Pressure Equipment Regulations 1999 (PER) dealing with the design and manufacture of pressure equipment, and The Pressure Systems Safety Regulations 2000 (PSSR) dealing with the use of pressure systems. 

PER incorporate the requirements of an EU directive (no 97/23/EC) and comphance with it allows free access to the EU and EEA markets. The main body of the Regulations lays down general requirements to be met and is supported by a series of schedules detailing specific aspects of the design and construction of the equipment. 

Schedule 2 lists the ESRs to be considerd in the design and manufacture of pressure equipment and assemblies. 

The legislative requirements for the safe use of pressure vessels and plant are contained in the Pressure Systems Safety Regulations 2000 with a supporting Approved Code of Practice Safety of pressure systems. Pressure Systems Safety Regulations 2000. Approved Code of Practice . HSC publication no LI 22. 

These Regulations are pragmatic and recognize that differing operating conditions have differing examination requirements. 

The term pressure system refers to the installations found in many workplaces for supplying compressed air, steam for heating and processes, various liquids, oxygen and gases for welding or burning. It includes all pipework, vessels, heat exchangers, calorifiers, boilers, etc. 

Are staff trained in the use of the permit-to-work system and its significance  

Is it clearly laid down who should issue permits and to whom  

Does each permit clearly identify the work to be done and the hazards associated with it  

Does each permit state the precautions which have been taken and those needed while the work is in progress (e.g. isolations, purging, personal protective equipment)  

Is there a system of clear cross-referencing when two or more jobs subject to permits may affect each other  

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Introduction of new technology for example non - invasive testing methods to extend the duration between, or reduce the time taken for, invasive inspections in pressure systems. 

As early as 1966, natural gas was available to all of the lower 48 states in the United States. During the period 1967—1990, the U.S. transmission system grew from 362,700 km to 450,800 km. Over this same time period, the distribution mains increased from 867,800 km to 1,347,000 km. As plastic pipe and reUable joining technology became available, the use of plastic pipe expanded to include the distribution of gas in low pressure systems. By 1990, approximately 24% of the U.S. distribution system was based on plastic pipe (1). 

Molten Salt Distillation. Hafnium tetrachloride is slightly more volatile than zirconium tetrachloride, but a separation process based on this volatility difference is impractical at atmospheric pressures because only soHd and vapor phases exist. The triple point for these systems is at about 2.7 MPa (400 psia) and 400°C so that separation of the Hquids by distillation would necessarily require a massive pressurized system (13). 

C. B. Boyer, HotIsostatie Pressure Systems Failures andMeeidentHistory, BatteUe Memorial Institute, Columbus, Ohio, 1987. 

B. A. Sykes and D. Brown, A Review of the Technology of High Pressure Systems, Institute of Gas Engineers, London, 1975. 

The discovery of chemical N2 fixation under ambient conditions is more compatible with a simple, complementary, low temperature and low pressure system, possibly operated electrochemically and driven by a renewable energy resource (qv), such as solar, wind, or water power, or other off-peak electrical power, located near or in irrigation streams. Such systems might produce and apply ammonia continuously, eg, directly in the rice paddy, or store it as an increasingly concentrated ammoniacal solution for later appHcation. In fact, the Birkeland-Eyde process of N2 oxidation in an electric arc has been... 

Cyclohexylamine is miscible with water, with which it forms an azeotrope (55.8% H2O) at 96.4°C, making it especially suitable for low pressure steam systems in which it acts as a protective film-former in addition to being a neutralizing amine. Nearly two-thirds of 1989 U.S. production of 5000 —6000 t/yr cyclohexylamine serviced this appHcation (69). Carbon dioxide corrosion is inhibited by deposition of nonwettable film on metal (70). In high pressure systems CHA is chemically more stable than morpholine [110-91-8] (71). A primary amine, CHA does not directiy generate nitrosamine upon nitrite exposure as does morpholine. CHA is used for corrosion inhibitor radiator alcohol solutions, also in paper- and metal-coating industries for moisture and oxidation protection. 

Selection of the high pressure steam conditions is an economic optimisation based on energy savings and equipment costs. Heat recovery iato the high pressure system is usually available from the process ia the secondary reformer and ammonia converter effluents, and the flue gas ia the reformer convection section. Recovery is ia the form of latent, superheat, or high pressure boiler feedwater sensible heat. Low level heat recovery is limited by the operating conditions of the deaerator. 

In other designs, a diffused siUcon sensor is mounted in a meter body that is designed to permit caUbration, convenient installation in pressure systems and electrical circuits, protection against overload, protection from weather, isolation from corrosive or conductive process fluids, and in some cases to meet standards requirements, eg, of Factory Mutual. A typical process pressure meter body is shown in Figure 10. Pressure measurement from 0—746 Pa (0—3 in. H2O) to 0—69 MPa (0—10,000 psi) is available for process temperatures in the range —40 to 125°C. Differential pressure- and absolute pressure-measuring meter bodies are also available. As transmitters, the output of these devices is typically 4—20 m A dc with 25-V-dc supply voltage. 

Pure zirconium tetrachloride is obtained by the fractional distillation of the anhydrous tetrachlorides in a high pressure system (58). Commercial operation of the fractional distillation process in a batch mode was proposed by Ishizuka Research Institute (59). The mixed tetrachlorides are heated above 437°C, the triple point of zirconium tetrachloride. AH of the hafnium tetrachloride and some of the zirconium tetrachloride are distiUed, leaving pure zirconium tetrachloride. The innovative aspect of this operation is the use of a double-sheU reactor. The autogenous pressure of 3—4.5 MPa (30—45 atm) inside the heated reactor is balanced by the nitrogen pressure contained in the cold outer reactor (60). However, previous evaluation in the former USSR of the binary distiUation process (61) has cast doubt on the feasibHity of also producing zirconium-free hafnium tetrachloride by this method because of the limited range of operating temperature imposed by the smaH difference in temperature between the triple point, 433°C, and critical temperature, 453°C, a hafnium tetrachloride. 

Because of tank heating, fuel volatiUty is also more critical in supersonic aircraft. For example, the Concorde tank is pressurized to prevent vapor losses which could be significant at high altitude where fuel vapor pressure may equal atmospheric pressure. The tank can reach 6.9 kPa (1 psi) at the end of a flight. The need to deoxygenate fuel for thermal stabiUty in the HSCT will doubdess require a similar pressurized system. 

Dilute Phase Conveying. Dilute conveying systems, sometimes called disperse conveying or stream conveying, operate as positive pressure systems at pressures up to 100 kPa (14.5 psig), or as negative pressure systems (vacuum conveying) at pressures up to —50 kPa (—500 mbar). 

In pressure systems (Fig. 21-12 ), material is dropped into an air stream (at above atmospheric pressure) by a rotaiy air-lock feeder. The velocitv of the stream maintains the bulk material in suspension until it reaches the receiving vessel, where it is separated from the air by means of an air filter or cyclone separator. 

Pressure systems are used for free-flowing materials of almost any particle size, up to 6.35-mm (J/i-in) pellets, where flow rates over... 

Table 21-28 gives dimensions of hopper cars and other cars typically used in the chemical industiy. Vacuum-pressure systems are used most frequently for unloading covered hopper cars. For certain free-flowing materials, in both covered and open-top hopper cars, shakeout devices are useful. 

For flammable and/or toxic materials all of the precautions for a pressurized system should be considered. For example, when a centrifuge is pressurized, overpressure protection is required, even if the pressurization is an inert gas. Relieving of the pressure to a closed system or safe location must be considered. 

Figure 31.10 Typical layout illustrating pressurization system for an IPB bus system...

Grayson, H. G. and Streed, G. W., Vapor-Liquid Equilibria for High Temperature, High Pressure Systems, 6th World Petroleum Congress, Germany, June 1963. 

There is usually some descent (subsidence) of air above surface high-pressure systems. This air warms dry adiabatically as it descends, decreasing the relative humidity and dissipating any clouds in the layer. A subsidence inversion forms as a result of this sinking. Since the descending air compresses as it encounters the increased pressures lower in the atmo-... 

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