When forgings are used for takeover, is a negative deviation taken into account?
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When performing the reinforcement calculation for openings in fittings, if standard pipes are used, the negative deviation procedure for those fittings will automatically generate the necessary values based on the standards applicable to them. If the fittings are made of forgings (non-standard items), it is necessary to determine whether to take the negative deviation of the forgings into account in the reinforcement calculation for those openings; if so, how should it be specified? During our last certification review, the evaluation experts pointed out that although the drawings of the non-standard parts of the forged pipe indicated that the machining accuracy should meet the m-grade standard specified in GB1804-2000, the negative deviation of the forged pipe during hole reinforcement calculations did not satisfy the requirements of the m-grade standard as defined in GB1804-2000. In my opinion, the calculation for reinforcing openings using the equal area method is itself an empirical approach, rather than an exact mathematical solution. The m-value specified in the drawings of the connecting parts is intended to control the machining accuracy; indeed, the deviation associated with this m-value should be taken into account during calculations. However, I believe that although this consideration is required (and reasonable), it is essentially meaningless. How did you enter it?
The expert suggested that adjustments should be made according to his recommendations; ultimately, the wall thickness was set with a positive deviation, ensuring that the negative deviation was 0, so as to match the calculations. However, by understanding the practices of some organizations, which ensure a reinforcement margin of over 25%, this aspect is already taken into account; there is no need to consider a one-to-one correspondence with the drawings. Personal opinion
It’s not necessary; the tolerance is too small to worry about, as it’s not a precision instrument.
You should know that many experts are giants in theory but weak in practice; they like to ask how many ways there are to write the character “return”. Theoretically, what they say is absolutely correct. However, pressure vessels are not machined parts and do not require assembly, so such machining tolerances can be completely ignored in the case of pressure vessels. Even if there is a negative deviation in machining, the safety factor of our materials, as well as the various correction factors in the formulas, along with the margins we include in our own calculations, can all offset this negative deviation. But if an expert tells you to make changes, you must do so; otherwise, things like certificate renewal won’t go through for you
I think the same way, so sometimes the questions raised by experts can only be kept as questions.
Yes, one should respond to the questions raised by experts as much as possible, and admit that one is wrong and that the experts are right. Make him feel comfortable. Otherwise, it will be even worse.
First of all, I admire the experts’ pursuit of excellence. But there’s really no need to think like that...
Moreover, the SW6 software doesn’t have an option to enter a negative deviation either; if it really needs to be taken into account, the calculation sheet has to be modified manually. I really don’t understand it – when using the area method for calculation, is it truly necessary to deduct that extra amount?
For SW6, the negative deviation of the default forgings is set to 0, and processing accuracy was never taken into consideration in the calculations. Experts consider issues in a comprehensive manner; you can’t say they’re wrong. Although it doesn’t have much practical significance, it’s still necessary to make the adjustments as suggested by them.
Experts who ask these questions want to show that their level is higher than others’. Once a problem is identified, it’s necessary to make corrections based on the experts’ advice; it’s best to pass the inspection.
This expert, haha, is a fool who started out doing manual labor~~~