There is a standard elliptical head made of Q345R steel plate
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There is a standard elliptical head made of Q345R steel plate with a nominal thickness of 16 mm. The design temperature is –20°C; what should be the allowable stress used in the internal pressure verification calculations? Why?
Its allowable stress should be 163 MPa； Since the allowable stress for low-temperature pressure vessels is taken as the allowable stress of the material at 20°C, and the nominal thickness of the head is 16 mm; considering the thickness reduction due to manufacturing processes, the actual thickness of the material is greater than 16 mm, therefore its allowable stress is set at 163 MPa.
Isn’t choosing it based on temperature and thickness equivalent to 189 MPa? During the verification, I thought there might be an issue with your concept of nominal thickness. Generally, when performing calculations, we take into account the thinning rate of the head and then select the minimum thickness to determine the allowable stress. Your value of 16 mm falls within the lowest range, so the resulting allowable stress is 189 MPa
The allowable stress should be 163 MPa, as the allowable pressure for low-temperature pressure vessels is determined based on the allowable stress of the material at 20°C. The nominal thickness of the head is 16 mm; taking into account the thinning that occurs during manufacturing, the actual thickness of the material is greater than 16 mm. Therefore, the allowable pressure is set at 163 MPa.
When performing internal pressure verification calculations, the allowable stress should be 185 MPa, as the thickness of the material used for the head, after taking into account the thinning due to stamping, is definitely greater than 16 mm.
An allowable stress of 189 at ≤20°C is used; an impact test is required at -20°C
The allowable stress is taken as 163 Mpa, taking into account the wall thickness reduction
When the design temperature is below 20°C, the allowable stress at 20°C shall be used. For Q345R steel plates with a nominal thickness of 16 mm, according to Table 2 in GB150.2-2011, the allowable stress is 189 MPa.
189? When the design temperature is below 20 degrees Celsius, the allowable stress at 20 degrees Celsius is used; within a certain temperature range, the lower the temperature, the better the strength generally is, so it is prudent to use the value corresponding to 20 degrees Celsius.
Its allowable stress is 163 Mpa. Since the allowable stress for low-temperature pressure vessels is taken as the allowable stress of the material at 20°C, the nominal thickness of the head is 16 mm; taking into account the thickness reduction due to manufacturing processes, the initial thickness of the material is greater than 16 mm, hence the allowable stress is set at 163 Mpa.