Allowable stress range for secondary stresses
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I have a question for everyone: According to the relevant provisions in ASME B31.3, the value of the allowable stress is typically related to various parameters such as the material’s ultimate strength values (tensile, bending, shear, yield, etc.), as well as safety factors and size factors associated with its operation. Therefore, we can conclude the following: under the same external conditions (loads, temperature changes, internal and external pressures), the allowable stress for secondary stresses in a tee with a saddle joint configuration will be different from that of a standard tee with identical dimensions and materials. However, according to the formula for calculating the allowable stress due to secondary stresses: f – coefficient that reduces the allowable stress range over the expected service life; allowable stress range, in kPa; allowable stress of the pipe component material at 20°C, in kPa; allowable stress of the pipe component material at the design temperature, in kPa. Since the materials of the two tees are the same and the operating conditions are identical, the calculated allowable stress values due to secondary stresses for both should be equal! Doesn’t this contradict the definition of allowable stress values in ASME B31.3? How to explain this issue?
There is no contradiction; the difference lies in the fact that the stress enhancement factors of the two types of tees are different, which results in different allowable stresses for the two types of tees.
But why isn’t the effect of the stress enhancement factor reflected in the formula? What relationship should be used to represent the effect of the stress enhancement factor on the allowable stresses of the two types of tees?
That formula is for pipes; for fittings, a flexibility factor should be taken into account
That formula is not intended for tees; it is applicable to pipes. To carry out a precise calculation, it is necessary to extract forces and moments from the pipe network stress analysis, and then create a solid model of the tee for calculation
The key lies in the calculation of Se (S1); images are not necessary here. See: http://bbs.hcbbs.com/viewthread.php?tid=424641&extra=page%3D1&frombbs=1
The answer has been found; for the solution to this issue, refer to Chapter 5, Safety Assessment of Pipeline Stress Analysis, in the book Pressure Pipeline Stress Analysis (author: Tang Yongjin) – Section 1, Criteria for Checking Pipeline Stress. Very detailed explanation: victory: This post was last edited by Dongdong on 2009-3-25 at 19:00 ]