Allowable stress for commercial-grade bolts
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When calculating flanges using SW6, the allowable stress of the bolts is required. In SW6, this allowable stress is determined based on the material of the bolts. The values of the allowable stress are mentioned in 150.1 4.4, but it is not specified whether this allowable stress changes at different temperatures or what those values are. 150.2 mentions the allowable stress of studs at different temperatures. Take 8. For grade 8 bolts, only the non-proportional strain strength of 640 MPa is specified. Could someone please explain how to calculate the allowable stress for grade 8.8 bolts?
The last edit to this post was made by the relevant department on 2017-6-12 at 09:41. The properties of 8.8 grade bolts are as follows: tensile strength = 800 MPa, yield strength = 800*0.8 = 640 MPa. In my opinion, there are many different materials used for 8.8 grade bolts, and since their sizes vary, the allowable stress must be determined on a case-by-case basis.
The allowable stress of studs is related to temperature and diameter; the corresponding values can be found in Table 12 of GB150.2. Moreover, SW6 can automatically determine the allowable stress of studs based on design parameters
The allowable stress of studs is related to temperature and diameter; the corresponding values can be found in Table 12 of GB150.2. Moreover, SW6 can automatically determine the allowable stress of studs based on design parameters
Because I’m using grade 8.8 bolts here, and no studs. The medium is water, with a design pressure of 1.0 MPa and a design temperature of 60°C.
In hg/20583, the yield strength of commercial-grade bolts at different temperatures is provided; by dividing this value by the safety factor specified in GB150, the allowable stress can be determined.
Since 150.2 already gives the allowable stress, why do you still need to calculate it?
It should be Appendix A (Materials) of HG/T 20581-2011 \"Specifications for Material Selection of Steel Chemical Process Vessels\" – the mechanical properties of commercial fasteners. This appendix lists only the mechanical properties at room temperature for grades 4.8 and 8.8; other grades follow the same pattern. Treat it at 60°C as normal temperature; there’s no problem with that. If the effect of temperature needs to be taken into account, special-grade bolts should be used. HG/T 20583 is the \"Specifications for Structural Design of Steel Chemical Containers\"; it likely does not list the mechanical properties of materials, and the yield strength of commercial-grade bolts is not specified there.
It is not possible to determine the specific material used for the 8.8 grade bolts. Also, if calculations are done using the allowable stress of SW6 material, then what is the purpose of the stress of 640 MPa corresponding to a 0.2% non-proportional strain for 8.8 bolts? Can the allowable stress for grade 8.8 bolts be obtained by dividing 640 MPa by a safety factor?
Sure. According to Table 2 of GB150.1, fasteners of grade 8.8 are made of low-alloy steel; the safety factor for sizes M24–M48 is 3.0, the yield strength is 640 MPa, and the allowable stress at room temperature is 213 MPa.
I’ve encountered situations where the specification states grade 8.8, while the material column indicates 35. In such cases, how should the allowable stress of the bolts be calculated? Should it be based on the non-proportional elongation strength of grade 8.8 divided by a safety factor, or should it be based on the allowable stress for carbon and low-alloy steel studs listed in Table 12 of standard 150? (This is also data built into sw6)