Weld joint coefficient
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Let’s discuss it together. Why is the weld strength reduction factor (weld joint coefficient) not included in the calculation formulas for pressure vessels?
This post was last edited by zhangjuhua on 2020-1-19 at 10:44. External pressure tends to cause the weld to close; the failure resulting from external pressure is usually due to insufficient stiffness, and it has nothing to do with strength. The weld coefficient is introduced mainly to account for strength-related failures. Since failure caused by external pressure is not related to strength, there’s no need to consider Φ in the calculations
Under compressive stress, the presence of defects in the weld does not affect the compressive strength.
For a rigid cylinder, not only the stability issue but also the strength issue is considered.
This post was last edited by zhangjuhua on 2020-1-20 at 10:58. Yes, when the wall thickness is large, strength failure may need to be considered; however, under external pressure, defects seem to tend to close as well. In other words, failure has little to do with welding defects, so Φ is not taken into account
The welds of equipment may have various defects that affect its tensile strength; therefore, when designing pressure vessels, Φ is introduced to keep the maximum tensile stress in the stressed components within the product of the allowable stress and Φ. For externally pressurized vessels, the principle of stability calculation is applied, with graphical methods being used to determine the allowable external pressure or axial allowable stress on the stressed components of such vessels. In externally pressurized vessels, weld defects do not affect the compressive load-bearing cross-sectional area of the components, nor do they cause the defects to lead to cracking and thus pose a risk; therefore, it is not necessary to include Φ when checking the compressive strength.