The fuzzy logic in corrosion under insulation pipelines CUI is an estimating method of corrosion rate for pipe material based on the API data. The fuzzy model has five inputs;
operating temperature
type of environment
type of insulation
pipe complexity
insulation condition
The resulted outputs of this estimation model will be in terms of CUI corrosion rate. more details in the reference;
Regarding the (more general) question from the top, according to Czabanski, Jezewski, and Leski (2017):
"Fuzzy systems are structures based on fuzzy techniques oriented towards information processing, where the usage of classical sets theory and binary logic is impossible or difficult".
Chapter Introduction to Fuzzy Systems
Czabanski, R., Jezewski, M., & Leski, J. (2017). Introduction to fuzzy systems. In Theory and Applications of Ordered Fuzzy Numbers (pp. 23-43). Springer, Cham.
Fuzzy logic is an extension of Boolean logic by based on the mathematical theory of fuzzy sets, which is a generalization of the classical set theory. By introducing the notion of degree in the verification of a condition, thus enabling a condition to be in a state other than true or false, fuzzy logic provides a very valuable flexibility for reasoning, which makes it possible to take into account inaccuracies and uncertainties.
One advantage of fuzzy logic in order to formalize human reasoning is that the rules are set.