Folias Factor

To use Equation (1) above to predict the remaining strength of corroded pipe, two assumptions were made. The Folias factor, M, was defined as:
- M = (1 + .8L2/Dt).5 (2)
- The flow stress, S, was defined as 1.1 x SMYS
To further simplify the analysis and evaluation of corroded pipe, the area of metal loss, A, was defined to be the area of a parabola. This allows the metal loss to be estimated by using only two parameters, the corrosion length, L, and the maximum pit depth, d. The metal loss area then becomes, A = (2/3)Ld, and as defined above.
A0 = Lt

Modified Folias Factor

The two-term Folias factor, Eq(2) above, was replaced in the development of the Modified Criterion by a more exact and less conservative three-term representation.
The percentage differences between the two-term Folias factors and the three-term Folias factors are significant, but the remaining strength of the corroded pipe is not a linear function of the Folias factor.
The three-term Folias factor gives a less conservative, higher, prediction of remaining strength, but only about 3% higher.

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