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API 650 - Allowable External Loads on Tank Shell Openings

API 650 - Allowable External Loads on Tank Shell Openings

(OP)
Hi, I am trying to figure out how to extract the data from the P.2a to P.2l graphs. There is an example problem on P.2.9.1 and in the solution it gets a value of 3.1 x 10-4 for KR/E(2a) on Figure P.2a. I enter that figure and dont understand how to get that value. Is there a tabulated graph or equation to do it?

RE: API 650 - Allowable External Loads on Tank Shell Openings

No There is no tabulated graph i think. This is a logarithmic scale and you can interpolate between the values graphically. I have used same example values to interpolate graphically.

RE: API 650 - Allowable External Loads on Tank Shell Openings

(OP)

The two additional lines you are adding to the graph, how do you interpolate them? Linearly on the graph or do you have to consider it is a logarithmic scale?

I did get the equations for the three original lines from a/R (they are approximate)

a/R = 0.005
KR/(E * 2 * a) = 41285 * (R / t)^-2.566

a/R = 0.02
KR/(E * 2 * a) = 66.762 * (R / t)^-1.975

a/R = 0.04
KR/(E * 2 * a) = 13.971 * (R / t)^-1.823

RE: API 650 - Allowable External Loads on Tank Shell Openings

Yes, interpolation should also have been on logarithmic scale. I have mistakenly done linear interpolation in above figure. Using graph it can only be performed through approximation i guess.

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