---
title: "FFS Calculations"
slug: "appendix-1-calculations"
updated: 2026-03-09T10:16:09Z
published: 2026-03-09T11:26:58Z
canonical: "ims-handbook.cenosco.com/appendix-1-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.

# FFS Calculations

## LimitState/MAT

The LimState is the MAT (Minimum Acceptable Thickness) of a corroded pipeline for a specific corrosion morphology and defect assessment code.

The following types of corrosion morphology are distinguished:

- General corrosion.
- Grooving corrosion.
- Pitting corrosion.

Pitting corrosion is characterized by Defects having a length/depth ratio ≤ 20 (pits, short but relatively deep).

Grooving corrosion is characterized by Defects having a length/depth ratio > 20 and ≤ 80 (scars, somewhat longer length, but not that deep).

General corrosion is characterized by losing wall thickness all over the pipeline (length/depth ratio > 80).

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/pl-fit-for-service-image-mfzpvzu1.png?sv=2026-02-06&spr=https&st=2026-10-29T00%3A41%3A25Z&se=2026-10-29T01%3A41%3A25Z&sr=c&sp=r&sig=ZhdghM3QW4syi0nwFTSrIkMVbyatQUrAQoRTPK4sX9s%3D)MAT calculation for a specific corrosion morphology 

The corrosion morphology factor sets a certain length for which to check the MAT.

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/l%20pitting.png?sv=2026-02-06&spr=https&st=2026-10-29T00%3A41%3A25Z&se=2026-10-29T01%3A41%3A25Z&sr=c&sp=r&sig=ZhdghM3QW4syi0nwFTSrIkMVbyatQUrAQoRTPK4sX9s%3D)

The factors for pitting and grooving can be modified by the administrator.

The generic formula to calculate the MAT is:

![](https://cdn.document360.io/e492a0e0-a4ba-4aca-8fc6-76b95f91fdf3/Images/Documentation/Screenshot_152.png?sv=2026-02-06&spr=https&st=2026-10-29T00%3A41%3A25Z&se=2026-10-29T01%3A41%3A25Z&sr=c&sp=r&sig=ZhdghM3QW4syi0nwFTSrIkMVbyatQUrAQoRTPK4sX9s%3D)

The different Assessment codes use different variable assignments for calculating the Remaining Strength Factor (RSF) and bulging factor (M).

## Diameter conversion

There is a conversion from a ‘named’ nominal diameter to the actual outer diameter in mm (which should be used in calculation). A ’10 inch’ line for example has an actual outer diameter of 273.1 mm (and not 254 mm).

Conversion from named nominal diameter to the actual outer diameter:

| **t_pipe_diameter** |
| --- |
| **Name diameter** | **Value delta for OD** |
| 2 | 63.5 |
| 3 | 76.2 |
| 3.5 | 88.9 |
| 4 | 101.6 |
| 4.5 | 114.3 |
| 5 | 127 |
| 5.5 | 141.3 |
| 6 | 168.3 |
| 8 | 219.1 |
| 10 | 273.1 |
| 12 | 323.9 |
| 14 | 355.6 |
| 16 | 406.4 |
| 18 | 457.2 |
| 20 | 508 |
| 22 | 558.8 |
| 24 | 609.6 |
| 26 | 660.4 |
| 28 | 711.2 |
| 30 | 762 |
| 32 | 812.8 |
| 34 | 864 |
| 36 | 914 |
| 38 | 965 |
| 40 | 1016 |
| 42 | 1067 |
| 44 | 1118 |
| 46 | 1168 |
| 48 | 1219 |
| 52 | 1321 |
| 56 | 1422 |
| 60 | 1524 |
| 64 | 1626 |
| 68 | 1727 |
| 72 | 1829 |
| 76 | 1930 |
| 80 | 2032 |
| 100 | 2540 |
| 278 | 7061.2 |
| 300 | 7620 |