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API STD 530 ERTA-2009 pdf free download

API STD 530 ERTA-2009 pdf free download.Calculation of Heater-tube Thickness in Petroleum Refineries.
3.6 elastic allowable stress time-independent allowable stress σ el Allowable stress for the elastic range. See 6.2. 3.7 elastic design pressure p el Maximum pressure that the heater coil can sustain for short periods of time. NOTE This pressure is usually related to relief-valve settings, pump shut-in pressures, etc. 3.8 equivalent tube metal temperature T eq Calculated constant metal temperature that in a specified period of time produces the same creep damage as does a changing metal temperature. NOTE The equivalent tube metal temperature concept is described in more detail in 5.8. It provides a procedure to calculate the equivalent tube metal temperature based on a linear change of tube metal temperature from start-of-run to end-of-run. 3.9 inside diameter Inside diameter of a tube with the corrosion allowance removed; used in the design calculations. NOTE The inside diameter of an as-cast tube is the inside diameter of the tube with the porosity and corrosion allowances removed. 3.10 minimum thickness δ min Minimum required thickness of a new tube, taking into account all appropriate allowances. NOTE See 5.4, Equation (5). 3.11 outside diameter D o Outside diameter of a new tube. 3.12 rupture allowable stress time-dependent allowable stress σ r Allowable stress for the creep-rupture range. See 5.4.
4.2 Limitations for Design Procedures 4.2.1 The allowable stresses are based on a consideration of yield strength and rupture strength only; plastic or creep strain has not been considered. Using these allowable stresses can result in small permanent strains in some applications; however, these small strains do not affect the safety or operability of heater tubes. 4.2.2 No considerations are included for adverse environmental effects, such as graphitization, carburization or hydrogen attack. Limitations imposed by hydrogen attack may be developed from the Nelson curves in API 941 [4] . 4.2.3 These design procedures have been developed for seamless tubes. They are not applicable to tubes that have a longitudinal weld. ANSI/API 560 allows only seamless tubes. 4.2.4 These design procedures have been developed for thin tubes (tubes with a thickness-to-outside- diameter ratio, δ min /D o , of less than 0.15). Additional considerations can apply to the design of thicker tubes. 4.2.5 No considerations are included for the effects of cyclic pressure or cyclic thermal loading. 4.2.6 Limits for thermal stresses are provided in Annex C. Stresses imposed by tube/fluid weight, supports, end connections, and so forth are not discussed in this standard. 4.2.7 The relationship between temperature, stress, and time to failure (taken here to mean test, service, or design life) is represented by the Larson-Miller Parameter (LMP) as explained 6.6 and in H.5. The limiting design metal temperature ranges for each material for which the LMP applies are shown in Table 5. 4.2.8 The procedures in this standard have been developed for systems in which the heater tubes are subject to an internal pressure that exceeds the external pressure. There are some cases in which a heater tube can be subject to a greater external pressure than the internal pressure.
The temperature that separates the elastic and creep-rupture ranges of a heater tube is not a single value; it is a range of temperatures that depends on the alloy. For carbon steel, the lower end of this temperature range is about 425 °C (800 °F); for type 347 stainless steel, the lower end of this temperature range is about 590 °C (1100 °F). The considerations that govern the design range also include the elastic design pressure, the rupture design pressure, the design life, and the corrosion allowance. The rupture design pressure is never more than the elastic design pressure. The characteristic that differentiates these two pressures is the relative length of time over which they are sustained. The rupture design pressure is a long-term loading condition over a period of years. The elastic design pressure is usually a short-term loading condition that typically lasts only hours or days. The rupture design pressure is used in the rupture design equation, since creep damage accumulates as a result of the action of the operating, or long-term, stress. The elastic design pressure is used in the elastic design equation to prevent excessive stresses in the tube during periods of operation at the maximum pressure. The tube shall be designed to withstand the rupture design pressure for long periods of operation. If the operating pressure increases during an operating run, the highest pressure shall be taken as the rupture design pressure. In the temperature range near or above the point where the elastic and rupture allowable stress curves cross, both elastic and rupture design equations are to be used. The larger value of δ min shall govern the design (see 5.5). A sample calculation that uses these methods is included in Section 7. Calculation sheets (see Annex D) are available for summarizing the calculations of minimum thickness and equivalent tube metal temperature.

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