A new method for the prediction of the failure pressure of pipelines containing colonies of corrosion defects was proposed in a previous paper. This method, named MTI method, can take into account the length of full wall-thickness pipe that exists between each pair of defects within a colony of arbitrary shape (mixed type of interaction). In this paper the failure pressures of 22 colonies of corrosion defects previously calculated using Finite Element models are compared with those predicted by the MTI method plus other six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects (Part B), the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for interacting defects (Part B).
Traditionally the assessment of a colony of corrosion defects is performed using an interaction rule and a Level-1 assessment method, such as the ASME B31G method (ASME, 1991), the RSTRENG 085dL method (Kiefner and Vieth, 1989), the DNV RP-F101 method for single defects (DNV, 2004) and the RPA method (Benjamin and Andrade, 2003). For longitudinally spaced defects (Type 2 of interaction) an alternative and more accurate approach is to calculate directly the failure pressure of the interacting defects using a Level-2a method, such as the RSTRENG Effective Area method (Kiefner and Vieth, 1989) or a Level-2b method, such as the DNV RP-F101 method for interacting defects(DNV, 2004). For defects that are separated circumferentially whose individual profiles overlap when projected onto the longitudinal plane through the wall thickness (Type 1 of interaction) an alternative approach is to calculate directly the failure pressure of the interacting defects using a Level-2a method, such as the RSTRENG Effective Area method (Kiefner and Vieth, 1989). This approach can be more accurate when the projection of the defects onto the longitudinal plane results in an irregular defect depth profile.
