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).
MAT calculation for a specific corrosion morphology The corrosion morphology factor sets a certain length for which to check the MAT.
The factors for pitting and grooving can be modified by the administrator.
The generic formula to calculate the MAT is:
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 |