Relationship between design thickness and effective thickness
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This post was last edited by zjq1962 on 2019-3-22 at 13:57. Design thickness = calculated thickness + C2. Effective thickness = nominal thickness – C1 – C2 = (calculated thickness + C1 + C2 + Δ1) – C1 – C2 = calculated thickness + Δ1. Therefore, the comparison between the calculated thickness and the effective thickness is essentially a comparison between the corrosion margin and Δ1 (the rounded value). The relationship between the sizes of C2 and Δ1 is uncertain. Therefore, there is no fixed size relationship between the design thickness and the effective thickness.
The effective thickness must be greater than or equal to the design thickness.
Design thickness: equal to strength + lifespan；
Effective thickness: equal to material thickness minus allowance! >Greater than calculated thickness
Yes, the calculated thickness meets the basic strength requirements, while the corrosion margin is determined based on the design service life of the container.
It is not compared to the calculated thickness, but to the designed thickness
The design thickness is the sum of the calculated thickness and the corrosion allowance, that is, the thickness which meets the requirements for strength and design life; the effective thickness is the nominal thickness minus the corrosion allowance and the negative deviation of the material thickness； A comparison is provided in Figure SY3-2 on page 29 of the interpretation of standard GB/T150.1-2011.
In this diagram, the line representing the effective thickness + (C1+C2) is a dashed line; the dashed line indicates that the position of this line is uncertain (the reason being that the relationship between the integer value and C2 is not clear)
The dashed line indicates that the position of this line is uncertain, but its position below the design thickness is definite.
Assume the design thickness is 5.7, C1=0.3, C2=3. Nominal thickness = 5.7 + 0.3 + 3 + 1 = 10. Effective thickness = 10 – 3.3 = 6.7. Design thickness = 5.7 + 3 = 8.7. Since the design thickness is greater than the effective thickness, is there anything unreasonable about this result?