Flaw assessment according to Fitness-For-Service (FFS) codes is usually based on equations describing the impact of a single flaw in piping or pressure vessels components. However, when multiple flaws are detected, combination rules are to be taken into account to evaluate whether these flaws should be combined into a larger flaw or should be evaluated as separate ones. In recent years, numerous works have been done to evaluate the conservatism of the combination rules required by FFS codes and, if needed, establish new characterization rules. These new characterization rules are based on the distance between flaws, their depths, their lengths or a combination of these three parameters in order to reflect the level of interaction between adjacent flaws. A comparison, focusing on multiple surface planar flaws, between ASME B&PV Section XI current combination rules, other Fitness-For-Service codes and other combination rules established by fellow authors is presented in this paper.

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