Tank Load Case 3 Calculations

LC3 calculations takes place on the Equipment. This is the Roof calculations that determines a RL based on an effective Roof pressure. There are two relevant calculations done for the LC3: The RL and the compression values.

Remnant Life

The calculation is a second-degree polynomial function, representing the “Limiting Thickness” of the Shell required to support the weight of the Roof, of which the peak must be found. The generic form for the function being:

Where:

CF = Compression Factor =12411

D = Diameter

CMF = Course Mass Factor=7850

TCH = Top Course Height

TA = Top Angle

G = Gravitation = 9.81 m/s²

SL = Superimposed Load

RP = Roof Plates weight

RF = Roof Framing

This can be solved using:

to yield us the so called “Limiting Thickness”. “Current Thickness” = “Initial Thickness” – “That which has Corroded away”. So, T_t = T_Initial - t x CR, solve for t. This is a line in a plot of (x = time, y = thickness) starting at installation, and finally intersecting with the x axis at time t = RL_LC3, after which there is nothing left.

The Limiting Thickness is a threshold, which cannot be exceeded. So, to determine the RL according to the LC3 calculation, it must be determined when the situation occurs that T_t equals the Limiting Thickness. So, we determine time t, by entering the known data into:t is the RL starting at T_last, which is either the thickness at the last inspection, i.e., Actual Wall Thickness, or installation. So, t is the RL from either the last inspection or installation date.

Compression Values

There are two different calculations for the Axial Compression (AXC): Automatic and Manual. The calculation used, depends if Use Tank Diameter look up for Load weight has been checked. If checked, the automatic calculation is performed, else the manual one. This choice affects the AXC. The Allowable Compression (ALC), for both cases, is:

T = Thickness

Automatic Compression Calculation

Constants:

POL_X_SQR = 74.173

POL_X = -828.93

POL_C = 5178

Which gives:

Manual Compression Calculation

Which gives: