Discussion on the calculation of composite panel containers
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A real case I heard about recently – although the situation was simple, it was quite interesting. Such cases must arise frequently in work, so I’m sharing it here for discussion: there was an internal pressure equipment made of a Q345R+S30408 composite plate with a diameter of 3200. The thickness of the steel plates was 3+18. In order to save time, the manufacturer entered Di=3200 and a head depth of h=800 when preparing the strength calculations for the equipment’s cylinder and head for submission to the client (either an engineering company or a design institute). After reviewing these calculations, the design institute issued a correction order, requiring the manufacturer to prepare new strength calculations using Di=3206 and a head depth of h=3206/4=801.5. (Here too, the design institute made a mistake; h=803 would have been more appropriate according to their standards.) Question: A. The manufacturing unit is at fault; it is necessary to prepare a new strength calculation report using the methods specified by the design institute. B. The manufacturing unit is correct; there is no need to prepare a new strength calculation report using the methods of the design institute. C. All of the above are possible.
At present, our company follows the same approach as the manufacturing units; I’m not sure if this is appropriate.
I think so. If the standard diameter DN3200 is directly specified in the design parameters, then composite plate material should be used; the allowable stress for this material shall be that of a composite plate, with the requirement that the condition level be at least B2.
What you say makes sense; it’s safer that way.
Actually, the most conservative approach would be to simply use the base material and increase the inner diameter. Regarding allowable stresses, the allowable stress for S22053+Q245 with 13+16 is much higher than that of Q245R with 19, though this has not been studied systematically.
The design institute’s approach is quite thorough, and I agree with their method.
Generally, the diameter is increased and calculations are done based on the base layer; composite panels are not taken into account in the strength calculations, which makes it safer.
Well, this is also what we use now; when the thickness is too large, we may consider including the cladding material, in accordance with the allowable stress for composite panels
Agree to prepare the strength calculation sheet again using the methods of the design institute, ensuring it corresponds to the actual conditions
For composite plate equipment, the common practice in design institutes is to calculate directly based on the base layer, that is, the inner diameter and allowable stress are taken from the base material, without considering the composite layer. If the inner diameter is considered to have a composite layer during calculation, then the allowable stresses used in such calculations should be determined based on those of a \"composite plate\"; there is a formula that can be used for this purpose, and it’s not difficult at all. If design calculations are carried out based on composite panels, the adhesion rate and non-destructive testing of these panels need to be improved accordingly. The problem is that even with stricter requirements for composite panels, a perfectly ideal situation cannot be achieved. In complex operating conditions, such as large temperature differences, significant temperature gradients, and substantial pressure fluctuations, the risk of delamination in the composite panels increases, which reduces the service life of the equipment and affects its operational safety. Therefore, the common approach adopted by design institutes for composite panel equipment is to base the design on the underlying structure, which is a conservative approach but results in higher safety.
That makes sense; it’s indeed necessary to consider the operating conditions as well. When considering composite panels, the joining condition needs to be taken into account.