Issues with the HG flange pressure-temperature rating table
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I recently started a project and encountered a problem: the client asked why, since the flanges for the equipment in the previous project were of type HG and rated at PN100, they need to be PN160 now I reviewed the standards again and found that the allowable stress values for flanges in version 97 are significantly higher than those in version 2009. For example, for flanges made of 316L material with a stress of 10 MPa, the allowable stress according to version 97 is 9.6 MPa, while it is 7.66 MPa according to version 2009 – the difference is quite substantial. According to the compilation notes, it is stated that the 1997 version was developed with reference to ISO flange standards, while the 2009 version was developed with reference to EN standards. Logically, as smelting technology improves, this allowable stress should increase, so why has it actually decreased? And the reduction is quite significant; experts, please offer some advice~~
I have encountered similar problems with the allowable stresses of some pipes as well; the higher the safety factor, the greater the allowable stress becomes. No one can provide an explanation for this
Standard development is really chaotic; it’s always just copying things from here and there. . .
This post was last edited by Yimi on 2015-7-9 at 17:02. The slight differences in stress arise from different reference points being used or from different values for safety factors; as for the flanges in question, we are not the ones who made the design decisions, so it’s difficult for us to determine which factor is at play. :Q Let me give an example to guess: Regarding the determination of the temperature and pressure ratings for flanges, I’ve heard of a \"stiffness + stress conversion method.\" There is a parameter in this conversion formula called the allowable stress baseline value for the material; could it be that differences in the setting of this baseline value are the cause? Alternatively, in the same conversion formula, different principles can be applied for determining the allowable stress of the flange material: 60% of the yield strength at room temperature ； 1.25 times the tensile strength at room temperature ； Stress value required as determined by high-temperature long-term strength ； Neither the old nor the new standards specify clear principles for determination; they both state something like “mainly refer to XX” or “equivalent but not identical to XX”... There’s nothing left to complain about.
If one isn’t pursuing an academic career, then it’s sufficient to choose based on standard criteria. How many people can really understand the reasons behind these standards? Hold back; complaining is a sign of incompetence: Q: Lol, they are still far more skilled than us, at least they’re familiar with many advanced foreign standards...
The problem is that the old standards were based on ISO, while the new standards are based on EN, and there’s no explanation for this change. . . This standard in the country is really annoying
Others’ standards have been developed through extensive practice and are quite comprehensive. Our standards have a weak foundation, and we simply copy them; if there are any differences, we can’t explain why
It’s just not clear which manufacturing standards for flange materials should be followed; it’s possible that the standards referenced in the older versions were based on ISO standards, while the manufacturing standards cited in the newer standards have since been updated Copied from EN? I haven’t looked at it in detail either, but it should really be a complete system. The foundation was relatively weak to begin with, and a lot was copied.
It’s not that the standard has been lowered; rather, the materials used have become more refined and of higher quality. To reach a higher level, it is necessary to use materials of even better quality. In other words, the standard has been set higher, resulting in better safety
It can’t be put that way; taking 316L as an example, its main property is corrosion resistance. As decarbonization technologies improve, corrosion resistance will inevitably increase, while strength will naturally decrease; the same phenomenon should apply to 304L as well.
Others’ standard is evolution; ours is haha