Time-dependent residual ultimate longitudinal strength - grounding damage index (R-D) diagram

Abstract

In this study, the development of the R–D diagram taking into account the time-dependent corrosion wastage effect is presented to identify the necessity of applying the time-dependent corrosion wastage on R–D diagram. The R–D (Residual strength–Damage index) diagram was proposed by Paik et al. (2012) and is an innovative method relating to safety assessment for damaged structures; its feasibility has been confirmed by a previous study concerning double hull oil tankers under grounding damage. Generally, as a result of corrosion, the structural capacity of ships and offshore structures should be decreased in parallel with the operational period. Therefore, an Aframax class double hull oil tanker that has sustained grounding damages and also corrosion with a time-dependent corrosion wastage model (13 years, 19 years and 25 years (net scantlings specified by CSR)) applied to gross (new-built) scantlings is analyzed by the ALPS/HULL progressive hull girder collapse analysis program. Based on the obtained results, the time-dependent R–D diagram is produced and compared with the original R–D diagram. Finally, for practical purposes, empirical formulas based on time-dependent R–D diagrams are proposed to evaluate the residual ultimate longitudinal strength of the corroded Aframax class double hull oil tanker under grounding damage. The proposed time-dependent R–D diagrams will be useful for assessing the first-cut safety evaluation for a ship that has sustained grounding damages under different operational periods.