Minimum wall thickness after head forming
Thread Content
Indicate on the drawing the minimum wall thickness after the head is formed; how should this minimum wall thickness be determined? Should it be the wall thickness calculated directly, or the thickness plus corrosion allowance, or rounded to the nominal wall thickness and then minus the negative deviation of the steel plate?
It should be: nominal wall thickness minus the negative deviation of the steel plate, minus the thinning due to head fabrication.
The minimum wall thickness of the head is: calculated thickness + corrosion allowance, which represents the actual minimum wall thickness that meets the operational requirements.
If the thickness, after rounding as a result of calculations, is used in the reinforcement calculations, it should also be taken into account! !
During design, the thickness reduction required for head manufacturing is unknown; otherwise, there would be no need to specify the minimum thickness of the head in the drawings
In other words, it’s the nominal thickness minus the negative deviation of the steel plate, that is, the calculated thickness plus the rounding value plus the corrosion allowance
In other words, it’s the nominal thickness minus the negative deviation of the steel plate; that is, the calculated thickness plus the rounding value plus the corrosion margin. This approach is the most conservative.
The minimum thickness of the head after forming, as indicated on the drawings, should be the calculated thickness plus a corrosion allowance. It is important to note that when calculating the reinforcement for the openings in the pipes connected to the head, the minimum thickness should also be used as a guide; this may sometimes result in the use of thicker pipes or reinforcement rings. Therefore, taking other factors into consideration, we sometimes specify an appropriate minimum thickness as well. I’m not sure what others usually do; I hope everyone can share their thoughts!
JB4746 6.3.10 states that for heads designed in accordance with the relevant rules, the actual minimum thickness of the formed head shall not be less than the nominal thickness of the head minus the negative deviation C1 of the steel plate thickness; however, if the design drawings specify the minimum thickness of the head after it has been formed, then the actual minimum thickness may be accepted as long as it is not less than the minimum thickness specified in the drawings. For heads designed by analysis, the measured minimum thickness shall not be less than the designed thickness of the head.
This is a well-worn topic. The so-called minimum thickness is determined by taking into account the thinning that occurs during processing; the nominal thickness plus this amount gives the required thickness.