Let’s all try to understand this sentence
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HG20592 specifies that the operating conditions for commercial-grade hex bolts should meet the following requirements: 1) PN≤1.6MPa; 2) applications without severe cycling; 3) use of non-metallic gaskets; 4) environments where the medium is not flammable, explosive, or highly toxic. The operating conditions for commercial-grade double-headed studs and nuts shall meet the following requirements: 1) PN ≤ 4.0 MPa; 2) In applications without severe cycling, special-grade studs and nuts should be used in addition to those mentioned above. It mentions that in the cases specified in point four where the toxicity level is high, “moderate hazard” represents a situation with a high level of hazard, right? How should we understand situations that are not intense cycles? Please ask the experts to explain. :lol
The simplest way to understand it is that it cannot be used in environments with extremely high levels of hazard, nor can it be used in designs based on fatigue considerations.
So it seems that bolts have a wide range of applications. It appears I misunderstood before; thank you
Commercial-grade bolts have the narrowest range of applications, followed by commercial-grade double-headed studs, while specialty-grade double-headed studs have a wider range of applications.
“The statement “the degree of toxic hazard is high” is relative, and this definition is not precise. Intense cycling and stress alternation can easily lead to fatigue damage, meaning it cannot withstand fatigue loads
In situations where the degree of toxic hazard is high, I consider situations with high or extreme levels of hazard to be those with a significant degree of risk. In cases where there is no intense cycling, that is, in designs that are not subject to fatigue, there is no variation in stress
I believe that moderate levels of hazard should be treated differently; for example, when the type of equipment is reaction or storage equipment, its category should be upgraded by one level (compared to separation and heat exchange equipment). In such cases, taking into account factors such as pressure and whether there is cyclic loading, it is advisable to choose equipment designed for specific purposes if available. And components like fasteners may seem unimportant for the entire device, but a leak from them can pose serious safety risks and lead to major accidents; don’t be cheap! Additionally, for determining cyclic and non-cyclic loads, reference can be made to JB4732 (the section on exemptions from fatigue analysis); pressure variations and temperature differences are the main factors to consider. In general, it is better to choose fasteners with higher specifications rather than lower ones
Severe cycling refers to situations where the displacement stress in the pipeline is greater than or equal to 0.8 times the allowable displacement stress, or when the equivalent number of cycles is greater than or equal to 7000. By \"high toxicity,\" I also understand it to mean extremely high toxicity, i.e., a level of danger that is very severe.
Personally, I think substances with high toxicity should include those with moderate hazard