Operating limits, pressure vessels

Vessels for high-temperature serviee may be beyond the temperature hmits of the stress tables in the ASME Codes. Sec tion TII, Division 1, makes provision for construction of pressure vessels up to 650°C (1200°F) for carbon and low-alloy steel and up to 815°C (1500°F) for stainless steels (300 series). If a vessel is required for temperatures above these values and above 103 kPa (15 Ibf/in"), it would be necessaiy, in a code state, to get permission from the state authorities to build it as a special project. Above 815°C (1500°F), even the 300 series stainless steels are weak, and creep rates increase rapidly. If the metal which resists the pressure operates at these temperatures, the vessel pressure and size will be limited. The vessel must also be expendable because its life will be short. Long exposure to high temperature may cause the metal to deteriorate and become brittle. Sometimes, however, economics favor this type of operation. 

HPR monobloc (Fig. 3.8) For applications at high pressure, the HPR monobloc is available. This tool features six 100 mL PTFE-TFM vessels fixed in a strong casing, serving operation limits of 300 °C and 100 bar. 

Temperature measurement is achieved by means of a remote IR sensor beneath the lower outer surface of the vessels. The operation limit of the IR sensor is 400 °C, but it is regulated by the software safety features to 280 °C as the operation limits of the materials used are around 300 °C. For additional control, temperature measurement in a reference vessel by means of an immersed gas-balloon thermometer is available. The operational limit of this temperature probe is 310 °C, making it suitable for reactions under extreme temperature and pressure conditions. 

The pressure is measured by means of a hydraulic system, either in one reference vessel of the 16-vessel rotor or simultaneously for all vessels of the 8-vessel rotor. The operational limit is 86 bar, sufficient for synthetic applications. In addition, a pressure rate limit is set to 3.0 bar s 1 by the control software provided. Protection against sudden pressure peaks is provided by metal safety disks incorporated into the vessel caps (safety limits of 70 bar or 120 bar, respectively) and by software regulations, depending on the rotor used and the vessel type. 

Similar to its predecessors of the Emrys series, the operation limits for the Initiator system are 60-250 °C at a maximum pressure of 20 bar. Temperature control is achieved in the same way by means of an IR sensor perpendicular to the sample position. Thus, the temperature is measured on the outer surface of the reaction vessels, and no internal temperature measurement is available. Pressure measurement is accomplished by a non-invasive sensor integrated into the cavity lid, which measures the deformation of the Teflon seal of the vessels. Efficient cooling is accomplished by means of a pressurized air supply at a rate of approximately 60 L min-1, which enables cooling from 250 °C to 40 °C within one minute. 

On the other hand, samples can be irradiated at constant microwave power over a certain fixed period, for example at 100 W for 10 min. As there is no control over the resulting temperature or pressure, care has to be taken not to exceed the operational limits of the system and this type of program should only be used for well-known reactions with non-critical limits, or under open-vessel (reflux) conditions. Since in this method only the applied energy and not the resulting temperature is controlled, the quality of reaction control is often superior employing a temperature-controlled program. 

To reduce the risk of container failure, the pressure vessels are equipped with several safety features. These can include an effective self-venting system where unforeseen overpressure is released by a quick open-resealing step, or the use of safety disks which rupture when their pressure limit is reached. The small vials (0.2-20 mL) of some monomode reactors are protected by the pressure limit (20 bar) of the caps used, which is significantly lower than the operating limit of the vials themselves (40-50 bar). 

In the construction of the wet oxidation unit, several areas of safety were considered. Of utmost importance was that of personal safety. Since this type of operation demands the use of high pressures and temperatures, operator contact with the high pressure vessels had to be limited. To accommodate this criterion, a barrier was constructed to shield the operator from any unforeseen releases from the reactor. This barrier was constructed from 1/4 inch steel and is desig ied in a manner that will fully contain any releases. This barrier is also equipped with two explosion vents to direct the force of any explosions away from the main walls and into a safe area. To further maximize personnel safety, all operator assisted controls are mounted on the outside of the unit. 

When pressure vessels will be tested and operated later on in very cold climates the lower limit of the transition temperature zone of the impact strength of the material applied must be considered because the full load pressure during the test or the start up may cause an unsafe situation if the vessel has not been heated up sufficiently. 

First, we need to define generally what we are talking about A pressure relief device is any device that can purge a system from an overpressure condition. More particularly, an SRV is a pressure relief device that is self-actuated, and whose primary purpose is the protection of life and equipment. Through a controlled discharge of a required (rated) amount of fluid at a predetermined pressure, an SRV must prevent overpressure in pressurized vessels and systems, and it operates within limits which are determined by international codes. An SRV is often the final control device in the prevention of accidents or explosions caused by overpressure... 

The PED, as does the ASME VIII, accepts that the SRV is set at the MAP or PS that is the exact equivalent to MAWP in the ASME code. Also in PED, MAP or PS are the design pressure of the weakest component of the equipment used in a pressure vessel, which needs protecting from potential overpressures. This pressure vessel may be an assembly of different components - pipes, flanges, nozzles, shells, and so on - and each may have a different design pressure. It establishes the limit of the pressure vessel for very short and exceptional increases of pressure above MAP, specifically to enable the SRV to operate properly and reach its rated capacity. This exceptional increase is called accumulation. So accumulation is specific to the individual pressure vessel and does not relate to the SRV. The pressure increase of the SRV to nominal flow is called overpressure. 

The maximum operating temperature is 195°F (90°C). The maximum feed pressure is only limited by the mechanical design pressure of the flanges on the pressure vessel. The maximum differential pressure across the membrane... 

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