Pressure-temperature operating limits

Operating hmit curves for normal plant operation are developed using approximately the same deterministic methodology in all countries. Key features that must be dehned are  

The basic relationships utilized in the deterministic methodology can be simpHfied as follows (using the US reference curve) to calculate the allowable pressure (P) as an explicit function of temperature (T)  

SI method Methodology Reference flaw Safety factor(s) Fracture toughness curve Comments 

USA ASME Code, Vi-t depth, length 2 on dp, 1 on j, 1 on Kio curve (or K i, curve for New risk-informed 

Russia PNAE-G-7-008-89 Vi-t depth, length of %-f 1 on dp, 1 on dj 1 on fracture toughness Specific Kjc curve for normal operation Safety factor on included in curve itself 

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Minimum pressurization-temperature (MPT) curves specify the temperature and pressure limitations for reactor plant operation. They are based on reactor vessel and head stress limitations and the need to preclude reactor vessel and head brittle fracture. Figure 4 shows some pressure-temperature operating curves for a pressurized water reactor (PWR) Primary Coolant System (PCS). 

Irradiation embrittlement in RPVs mainly results in two consequences. First, it narrows the pressure-temperature operation window for normal operating conditions. Second, it limits RPV lifetime as the transition temperature of RPV materials cannot be higher than that determined from the pressurized thermal shock (PTS) calculations. Several mitigation measures can be applied to decrease radiation embrittlement of RPV beltline materials ... 

An extraction plant should operate at steady state in accordance with the flow-sheet design for the process. However, fluctuation in feed streams can cause changes in product quaUty unless a sophisticated system of feed-forward control is used (103). Upsets of operation caused by flooding in the column always force shutdowns. Therefore, interface control could be of utmost importance. The plant design should be based on (/) process control (qv) decisions made by trained technical personnel, (2) off-line analysis or limited on-line automatic analysis, and (J) control panels equipped with manual and automatic control for motor speed, flow, interface level, pressure, temperature, etc. 

The operating variables for a dmm or roHer dryer iaclude coadeasatioa of incoming product ia an evaporator, temperature of incoming product, steam pressure (temperature) ia dmm, speed of dmm, and height of product over dmm. The capacity of the dryer is iacreased by increa sing the steam pressure, the temperature of the milk feed, the height of milk over the dmms, the gap between dmms (double), and the speed of rotation of the dmms. Increasing the capacity is limited by the effect on the product quaHty. 

The oxygen release rate is directly proportional to the cross-sectional area of the candle for a specific composition and also depends on the linear bum rate. Lower fuel contents decrease the bum rate slightly, eg, ca 2 wt % iron is the lower limit for rehable room temperature operation. Low temperature starts require at least 3.5 wt % iron. Another factor is direction of flow of the evolved gas. If the hot oxygen flows over the unbumed portion of the candle, as much as 15% rate iacreases can be produced. The bum time is halved for each 3.4 MPa (500 psi) pressure rise. The highest pressure that can be produced is ca 138 MPa (20,000 psi). 

FIG. 28-1 Operating limits for steels in hydrogen service, Each steel is suitable for use under hydrogen-partial-pressure-temperature conditions below and to the left of its respective curve, (Coutiesy of National Association of Conosion Engineers)... 

Use of materials sensitive to shock, high temperature or high pressure. If the material is inadvertently exposed to an unsuitable condition, or if the process moves out of the safe operating limits, it could result in a loss of containment. 

The maximum attainable production was sought that did not cause thermal runaway. By gradually increasing the temperature of the water, boiling under pressure in the reactor jacket, the condition was found for the incipient onset of thermal instability. Runaway set in at 485.2 to 485.5 K for the 12 m reactor and at 435.0 to 435.5 K for the shorter, 1.2 m reactor. The smaller reactor reached its maximum operation limit at 50 K lower than the larger reactor. The large reactor produced 33 times more methanol, instead of the 10 times more expected from the sizes. This... 

Common operating limits for turboexpanders are an enthalpy drop of 40-50 Btu/lb/stage of expansion and a rotor tip speed of 1,000 ft/s or higher. Turboexpanders are available with inlet pressures up to 2,500 psig and inlet temperatures over 1,000°F. Allowable liquid production can be as high as 20% of the discharge weight. 

Selection and care of the hydraulic fluid for a machine will have an important effect on how it performs and on the life of the hydraulic components. During the design of equipment that requires fluid power, many factors are considered in selecting the type of system to be used-hydraulic, pneumatic, or a combination of the two. Some of the factors required are speed and accuracy of operation, surrounding atmospheric conditions, economic conditions, availability of replacement fluid, required pressure level, operating temperature range, contamination possibilities, cost of transmission lines, limitations of the equipment, lubricity, safety to the operators, and expected service life of the equipment. 

This recommended practice summarizes the results of experimental tests and actual data acquired from operating plants to establish practical operating limits for carbon and low alloy steels in hydrogen service at elevated temperatures and pressures. The effects on the resistance of steels to hydrogen at elevated temperature and pressure that result from high stress, heat treating, chemical composition, and cladding are discussed. 

In cases where surface decarburization predominates over internal attack, the actual values of pressure-temperature combinations have not been extensively studied but the limits deAned by Naumann8 probably give the most accurate trends. Naumann s work, which is based on 100-hour tests, indicates decarburization tendencies however, long-time exposures have indicated lower operating limits. 

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. 

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. 

Microwave heating is often applied to already known conventional thermal reactions in order to accelerate the reaction and therefore to reduce the overall process time. When developing completely new reactions, the initial experiments should preferably be performed only on a small scale applying moderately enhanced temperatures to avoid exceeding the operational limits of the instrument (temperature, pressure). Thus, single-mode reactors are highly applicable for method development and reaction optimization. 

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. 

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