Safety factors in design

The changing societal, governmental, and industrial perspectives of risk will require that more detailed attention be placed on process safety factors in design and operation of chemical processing plants. 

Possible interference with natural convection currents in tube bundles makes some safety factor in design mandatory. Using a 25% safety factor, the required heating surface is... 

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. 

TABLE 1A Safety Factors in Equipment Design Results of a Questionnaire... 

Roll diameter, D, is calculated from eqn. (1) where a and Ri are determined from Fig. 5.7 and 5.8 for the given 5, 0 and K. Usually the maximum pressure exerted by the press is set equal to the maximum required briquetting pressure, Pb, to provide a safety factor in the design. A lower applied pressure can be used in press operation, if desirable. Note in Fig. 5.8 a correction may be necessary to Rx if the dimensionless roll gap S/D is different from 0.01. Since D is unknown, an iterative procedure is necessary in its determination. 

The design of thickwalled components for pulsating pressure is based on the stress calculation with analytical or numerical methods and the determination of the maximum equivalent stress in relation to the admissible stresses at uniaxial conditions. The latter have to be extracted from Woehler-tests with specimen. If the stresses yield too large at load conditions including a safety factor, the design must be optimized by avoiding the major stress concentrations at bore intersections. The avoidance of T-intersections is reducing stresses by factor 2-3 (Fig. Id). 

As a member of a design group working on the design of a recovery system for SO, you have been asked to estimate the area necessary for a rotary vacuum filter to handle a zinc sulfite filtration. You are also to determine the horsepower of the motor necessary for the vacuum pump. Do not include any safety factors in your results. 

The f -value of a structure determined by analysis assumes that the materials used and the quality of workinansliip meet the standards. Poor workmanship and substandard materials used during construction may result in / -values that deviate from predicted values. Therefore, some engineers use a safety factor in their designs based on experience in critical applications. 

After start of production, analyze complete design (again) to change design/production/safety factors in order to reduce costs... 

In the following sections, the design of flexural and shear strengthening as well as confinement are described. Note that these design methods are still under development and that all equations in these sections are presented without safety factors. In an actual design, safety factors must be applied. 

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