Design stress factor

This is determined by applying a suitable design stress factor (factor of safety) to the maximum stress that the material could be expected to withstand without failure under standard test conditions. The design stress factor allows for any uncertainty in the design methods, the loading, the quality of the materials, and the workmanship. 

For materials subject to conditions at which the creep is likely to be a consideration, the design stress is based on the creep characteristics of the material the average stress to produce rupture after 105 hours, or the average stress to produce a 1 per cent strain after 105 hours, at the design temperature. Typical design stress factors for pressure components are shown in Table 13.1. 

Sa metals, excluding factor E, or bolt design stress Allowable stress range for MPa Idp/im (ksi)... 

The SE values in Table 10-49 are equal to the basic allowable stresses in tension S multiplied by a quality factor E (see subsection Pressure Design of Metallic Components Wall Tliick-ness"). The design stress values for bolting materials are equal to die basic allowable stresses S. The stress values in shear shall be 0.80 times the allowable stresses in tension derived from tabulated values in Table 10-49 adjusted when applicable in accordance widi Note 13. 8tress values in bearing shall be twice those in shear. 

Part AM This part lists permitted individual constnic tion materials, apphcable specifications, special requirements, design stress-intensity vafues, and other property information. Of particular importance are the ultrasonic-test and tou ness requirements. Among the properties for which data are included are thermal conduc tivity and diffusivity, coefficient of theiTnal expansion, modulus of elasticity, and yield strength. The design stress-intensity values include a safety factor of 3 on ultimate strength at temperature or 1.5 on yield strength at temperature. 

For EPSR design, the stress level to contain an explosion is set at the yield strength, a design factor of 1. Thus, for an alloy, the design stress level would be about 1.5 times the ASME code design stress. So a pressure vessel rated at 6 bar for the ASME code (EPR) would have an EPSR rating of 9 bar. 

Pressure Vessels. Refineries have many pressure vessels, e.g., hydrocracker reactors, cokers, and catalytic cracking regenerators, that operate within the creep range, i.e., above 650°F. However, the phenomenon of creep does not become an important factor until temperatures are over 800°F. Below this temperature, the design stresses are usually based on the short-time, elevated temperature, tensile test. 

The factors Uiat enter into tlie design of vessels include type of material, configuration, inetliod of construction, design stresses, and tliickness of Uie metal. As with any equipment, design pressures and temperatures should take into consideration Uie most severe combination of conditions anticipated. Vessels must be completely drainable. Liners and wear plates may be required to prevent corrosion. 

When bacteria or almost any organism are exposed to high temperatures, the synthesis of a set of HSPs encoded by heat shock genes is rapidly and transiently induced this reaction has been designated as the heat shock response. Later, it was foimd that most heat shock genes are not only induced by heat, but by many other stress regimens (Table 1). The stress factors have been classified into three groups physicochemical factors, metabolically harmful substances and complex metaboHc processes. Therefore, the heat shock is often called the stress shock to comply with these observations. 

The quantity of a material used will depend on the material density and strength (design stress) and these must be taken into account when comparing material costs. Moore (1970) compares costs by calculating a cost rating factor defined by the equation ... 

J = joint factor (if applicable), g = gravitational acceleration, 9.81 m/s2, ft = design stress for tank material, N/mm2,... 

The stress values in Table IX-1A and the design stress values in Table IX-4 are basic allowable stresses in tension in accordance with para. IP-2.2.6(a). For pressure design, the stress values from Table IX-1A are multiplied by the appropriate quality factor, (Ec from Table IX-3 or )from Tables IX-4A and IX-4B). Stress values in shear and bearing are stated in para. IP-2.2.6(b) those in compression in para. IP-2.2.6(c). 

Traditional definitions of safety factors in terms of strength requirements, such as load-resistance factors or allowable stresses, are not applicable in blast resistant design. Safety factors arc more appropriately measured in terms of strain energy demand versus strain energy absorption capacity, Allowable deformations arc a practical method to quantify energy absorption capacity. 

Human Performance. Minimizing tlie stress factor on employees is an important consideration. Stress can be caused by poor enviromiiental conditions, bad equipment design, lack of time, fatigue, and anxiety. 

---