---
title: "Tank Load Case 3 Calculations"
slug: "tank-load-case-3-calculations"
tags: ["RBI", "PEI"]
updated: 2026-10-27T23:11:45Z
published: 2026-10-27T23:11:45Z
canonical: "ims-handbook.cenosco.com/tank-load-case-3-calculations"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://ims-handbook.cenosco.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Tank Load Case 3 Calculations

LC3 calculations takes place on the [Equipment](/docs/tank-equipment#load-case-calculations). 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:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(26).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)

Where:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(27).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)

*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:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(28).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D) to yield us the so called “Limiting Thickness”. “Current Thickness” = “Initial Thickness” – “That which has Corroded away”. So, *Tt = TInitial* - *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* = *RLLC3*, 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 *Tt* equals the Limiting Thickness. So, we determine time *t*, by entering the known data into:*![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(29).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)**t* is the RL starting at *Tlast*, 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:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(30).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)

*T* = Thickness

#### Automatic Compression Calculation

Constants:

*POL_X_SQR* = 74.173

*POL_X* = -828.93

*POL_C* = 5178*![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(31).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)*

Which gives:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(32).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)

#### Manual Compression Calculation

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(33).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)

Which gives:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pic%201(34).png?sv=2026-02-06&spr=https&st=2026-10-28T13%3A38%3A34Z&se=2026-10-28T14%3A38%3A34Z&sr=c&sp=r&sig=u7miHVb33SOqnXyyAQQR5JWE9K5vQWrW86aDS3Dmw9U%3D)