Safety factor of pressure vessels

It seems that’s not the case; in clause 3.6 of GB150, when determining the allowable stress values for pressure vessel materials, safety factors such as 3.0, 1.6, and 1.5 are to be used.

Let me explain: The safety factor for pressure vessels is a coefficient that relates the strength parameters of the material to the pressure-bearing components. It is a constant value that takes into account various factors such as the material, design, manufacturing, inspection, and usage, in order to ensure an adequate and reasonable safety margin for the pressure vessel. It represents the balance point between the safety and economic efficiency of pressure vessels. For Q235 steel at room temperature, σb is 339 Mpa; this value is reduced to 113 Mpa according to a certain ratio, and this ratio is 3 – which is the safety factor. Of course, it can also be derived from σs, endurance strength, and the creep limit; the safety factor values vary in different cases, being 1.6, 1.5 (average), and 1 respectively. Depending on **the category, the values of the safety factor also vary; they are not listed here one by one. To summarize, the main factors affecting the safety factor are: 1. The impact of material quality stability; 2. Differences between the designed loads and metal temperatures and actual values; 3. Variations in the correction factors used in design calculations; 4. Differences in manufacturing and inspection requirements; 5. Differences in operating conditions.

Minimum tensile strength at room temperature, σb; Yield strength at room temperature or the design temperature, σs or σst; Endurance strength after 100,000 hours at the design temperature, σD’; Creep limit with a 1% creep rate after 100,000 hours at the design temperature, σn. Materials: Carbon steel, low-alloy steel, ferritic high-alloy steel – ≥3.0, ≥1.6, ≥1.5, ≥1.0; Austenitic high-alloy steel – ≥3.0, ≥1.5, 1) ≥1.5, ≥1.0. 1) When the design temperature of a component is below the creep temperature range and minor permanent deformation is acceptable, the allowable stress can be increased appropriately, but not beyond 0.9σst. This requirement does not apply to flanges or other components where leakage or failure may occur due to even minor deformation.

The safety factor of pressure vessels is closely related to material parameters. When determining the allowable stress value of a material, both its tensile strength and yield strength, as well as their ratio, must be taken into account; in other words, the lower the yield-to-tensile strength ratio, the better； The selection of the safety factor for pressure vessels is based on experience; by reducing this safety factor, while still ensuring the safety of the vessels, it is possible to save materials and reduce costs.