Questions regarding flange bolt torque – Is actual operation carried out strictly in accordance with the data sheet?
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I would like to ask my colleagues in the petrochemical industry in Sichuan: in actual operations, do you use torque wrenches to tighten the flange bolts, and do you follow the torque values specified in the torque tables strictly? What’s the effect of using torque? The reason for raising this topic is that after reviewing numerous documents from equipment manufacturers as well as the official instructions for so-called bolts, it was found that the torque values specified there are actually very low. As shown in the figure below, the operating pressure of the torque meter for a reactor is 2.7 Mpa; yet the torque generated by bolts of the M36 size is only 249 Nm. What does 249 Nm mean? It’s a value that can be achieved even by twisting with one hand using a lever; if a hammer is used, the torque generated will be at least 500 Nm to 800 Nm. So, would you dare to apply such a tightening force as specified in the equipment diagrams? If you work in a manufacturing plant, do you tighten the bolts to the torque values specified in your manufacturing drawings before shipping the products? Of course, this opinion on the torque value is just my personal one; those who strictly follow the values recommended by the manufacturer when operating the equipment are also welcome to share their views. After all, the above guesses are merely my personal opinions; it’s also possible that with strict implementation, the flange will experience even stress distribution, resulting in an exceptionally good sealing effect.
Your value is too low; the standard values are 900#----10\"-----1.5KN.m, 14\"-----2.1KN.m, 24\"------8.5KN.m
That’s the problem: the values provided by the manufacturers are so low that they have no practical value as a reference. Don’t use a torque wrench; they’ll say you’re working in a rough manner. Use a torque wrench, but if you don’t follow the values specified by the manufacturer, they’ll accuse you of not following the design specifications. Use the manufacturer’s values then – although I’ve never tried it, there’s a 90% chance that leaks will occur. Below is the torque table from another heat exchanger manufacturer, and its values are also this low
I have also been puzzled by this issue. Calculated using the methods recommended in mechanical design manuals, the resulting torque is indeed very low. Many manufacturers, including those that produce fasteners and seals as well as torque wrenches, report that the values calculated by these manuals are too low. However, there is no authoritative and relatively accurate method for calculation. It’s such a headache every time I encounter it!
First, you need to follow the design; if it’s not possible to seal it, you can offer suggestions