Why is the safety factor for equipment bolts higher than that for tower foundation bolts?

According to Table 3-2 of GB150-1998, the safety factor of bolt materials depends on the material used, diameter, and heat treatment condition, and is independent of the location where the bolt is used.

I can think of only one reason: the anchor bolts are affected only by ambient temperature, and not by the operating condition of the equipment.

The bolts of the equipment serve primarily a sealing function, and plastic deformation is not allowed; therefore, a high safety factor must be adopted. Additionally, to ensure sealing, the preload should be slightly higher than the designed value； The bolts may also elongate under operational conditions, leading to loose connections that require repeated tightening; in addition, factors such as thermal stress can arise due to temperature effects.

The safety levels are different. The bolts on the flanges are subjected to compressive forces and serve to ensure a tight seal, while the foundation bolts bear the weight of the equipment itself, as well as loads such as wind and snow loads, in order to meet the requirements regarding stiffness and strength. The safety factor for these foundation bolts should be lower than that of the bolts on the equipment’s flanges. This is just my personal opinion; please feel free to criticize it

It mainly refers to the pressure-bearing parts of the equipment flanges, with each bolt on them being under stress. If one bolt breaks during use, it is very likely that the remaining bolts will also break due to the increased stress. In the case of a tower, only the bolts located on the windward side are under stress; the bolts at the back are not under any stress. Even if those bolts break, the ones at the back can take up the stress, preventing any serious accidents from occurring

Bolts are used in various environments; the conditions surrounding equipment bolts are complex, with significant temperature fluctuations. There is both thermal tightening and cold tightening at the installation site, and the operations involved are subject to large variations and occur frequently. In contrast, foundation bolts experience fewer such changes.

In addition to the tensile forces resulting from pressure, the bolts of equipment must also withstand torque, bending moments, and impact loads. Overloading can easily occur during tightening, so a higher safety factor is required. In contrast, the loads on foundation bolts are much less, hence a lower safety factor for them

This post was published some time ago, and I thank everyone for their participation. The replies given essentially addressed the key points; now I will provide a comprehensive answer: This is because the foundation bolts are used to resist tensile stresses when the tower is at risk of toppling, and the stress distribution on the circular area around the center of these bolts is linear. The bolt under the greatest stress is the one located at the outermost end in the wind and seismic directions, while the stress on the foundation bolts in other areas decreases accordingly. Once the foundation bolt subjected to excessive load yields due to overload, the loads borne by the other foundation bolts are redistributed, preventing the entire tower from toppling over. The stress conditions on flange bolts vary; under compressive loads, the load is not distributed evenly. Once one of the bolts yields, it means that all the bolts enter the yield stage. Therefore, flange bolts should be strictly kept within the elastic range.