What should be done if the flange calculation fails after changing the material of the stud?
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First of all, it should be noted that this post is not original; it is being reposted. The original website is: http://url.cn/5r0Co2c, but I think this case is really good, so I’m posting it here so that more forum members can see it and share their opinions. The details are as follows: Initially, the equipment was designed using bolts of 40MnB for its flanges, and those flanges met the required standards. The equipment was manufactured in accordance with the drawings. The owner later discovered that the bolt material specified in the contract should be 35CrMoA, so insisted on changing it to that material. The designers used the 35CrMoA bolts to calculate the strength of the flange; if the bolt pre-tension is too high, the flange needs to be thickened by 3 mm. But the equipment has already been completed; it’s impossible to redo it. What should be done? The owner is too domineering; it’s impossible to persuade them, and one doesn’t dare tell them that it’s not up to standard. The designers believe that although 35CrMoA bolts are used, as long as the same pre-tensioning force as that used with 40MnB is applied, there will be no leakage issues, and it will have no impact on the strength of the flanges. So it’s fine to use bolts made of 35CrMoA; then, change the specification on the drawings to 35CrMoA and manually modify the calculation documents to deceive everyone. Doing this is of course a violation of regulations. But setting aside the issue of violations, is it really dangerous to use this device after its bolts have been modified? If you were the designer, how would you handle this problem?
This post was last edited by tie008 on 2018-1-10 at 17:42. Manufacturing a 5mm thick bolt washer in two matching parts to be placed under the flange~~~ Is this feasible?
After the bolts of this device have been replaced, it should not be dangerous to use it, as long as the original design was sound. However, the designers ran into a really tough opponent – what a pity! It depends on how he tries to trick people.
In the calculations, it is taken into account that when the standard specification is used, the effect of bolts is not considered. But the bolts must be selected according to standards. It has been calculated; it’s best to follow the calculation sheet, otherwise problems may arise with the equipment or in management. You will be fully responsible.
In the calculations, it is taken into account that when the standard specification is used, the effect of bolts is not considered. But the bolts must be selected according to standards. It has been calculated; it’s best to follow the calculation sheet, otherwise problems may arise with the equipment or in management. You will be fully responsible.
The safety factor of the stud material can be increased artificially to reduce the allowable stress, while the preload should be indicated on the drawings. Doing this is compliant.
The 40MnB material is hard to find. I recently needed to use this material in my design, but given its difficulty in acquisition, I changed it to 35CrMoA instead. You can explain to the owner from the perspective of using design and standards as a basis. If one insists on using 35CrMoA material for the equipment, it will actually be less safe.
Haha, what a creative idea! From a computational perspective, this approach is definitely not feasible. Since this gasket ring is not an integral part of the flange, it cannot increase the stiffness and strength of the flange. The reason for the increase in the calculated thickness of the flange after changing the bolt material is not anything other than the fact that, with the change in the material of the studs, their allowable stress increases; this leads to an increase in the flange torque under pre-tensioning conditions. As a result, the checks regarding axial stress, circumferential stress, and radial stress fail to meet the required standards.
So, doing design is not just a matter of knowledge and skills; it also requires a certain degree of persuasion ability. Haha
That’s what they say. Actually, this case is analyzed from the perspective of being overly pedantic or nitpicky based on standards – but is there really a problem? Not necessarily. Because according to the calculation method for flange stresses specified in GB150.3, SW6 is determined by reversing-engineering the thickness based on the maximum stress value in the flange; in other words, it is calculated by working backwards from the maximum stress. However, in practical applications, the bolt preload is several times higher than what is taken into account in these calculations. Therefore, I believe this is also a flaw in the standard (or rather, in the Waters calculation method).
Is 40MnB hard to buy? I really don’t know that. If the design aims to save costs and meet various requirements by using plate-based Type A flanges, wouldn’t 35CrMo be an inappropriate choice? It doesn’t match