Hi all,
I'm calculating an integral-type DN150 PN63 flange, M30-3 bolts, system limits 6 bar and 150degC, in accordance with ASME VIII app.2 in combination with a normal stainless spiral wound gasket. What I've found is that the seating condition fails for this combination. My question regards the change in type of bolt and type of gasket and whether my thoughts are correct:
1. If I lower the diameter of the bolt (from M30 to M27), the corresponding Wm2 value lowers with it;
2. Changing the gasket type from spiral wound to a Grooved metal soft aluminum with graphite also reduces the Wm2;
For question 2 I can understand that the required seating stress lowers based on the minimum design seating stress (at least). For question 1 I'm a bit troubled how a smaller bolt diameter results in a lower required stress. I can see it in the formulas and you don't want to break the bolt so to speak, but doesn't the flange connection still require a good amount of stress to have a proper seating? If you change from M30 to M12, the M12 (probably) won't keep the flanges together besides the question if it fits. I understand that question 1 and 2 influence each other. Please view these questions as separate questions with respect to the calculation. Together they may be a good solution but I'm trying to understand both.
Just trying to wrap my head around the questions and the influence on the calculation. Greatly appreciate your replies.
I'm calculating an integral-type DN150 PN63 flange, M30-3 bolts, system limits 6 bar and 150degC, in accordance with ASME VIII app.2 in combination with a normal stainless spiral wound gasket. What I've found is that the seating condition fails for this combination. My question regards the change in type of bolt and type of gasket and whether my thoughts are correct:
1. If I lower the diameter of the bolt (from M30 to M27), the corresponding Wm2 value lowers with it;
2. Changing the gasket type from spiral wound to a Grooved metal soft aluminum with graphite also reduces the Wm2;
For question 2 I can understand that the required seating stress lowers based on the minimum design seating stress (at least). For question 1 I'm a bit troubled how a smaller bolt diameter results in a lower required stress. I can see it in the formulas and you don't want to break the bolt so to speak, but doesn't the flange connection still require a good amount of stress to have a proper seating? If you change from M30 to M12, the M12 (probably) won't keep the flanges together besides the question if it fits. I understand that question 1 and 2 influence each other. Please view these questions as separate questions with respect to the calculation. Together they may be a good solution but I'm trying to understand both.
Just trying to wrap my head around the questions and the influence on the calculation. Greatly appreciate your replies.
