DOT 2011: Pitting Effect on Ultimate Strength of Aged Offshore Structures

Corrosion can reduce the structural strength of aged marine and offshore structures.

The following is an abstract of a presentation that will be featured at the Deep Offshore Technology International Conference & Exhibition in New Orleans, Oct. 11-13:

Dr. Xiaohong Wang, ABS

Corrosion can reduce the structural strength of aged marine and offshore structures. It is important to properly assess residual structure strength to develop the renewal criteria for the decision of the structural inspection and maintenance plan. There are two types of frequently occurring corrosion, namely general corrosion and pitting corrosion.

In the case of general corrosion, the residual strength of plates and structural members can be readily determined by deducting the corrosion wastage from the as-built values. However, the determination of the strength knockdown due to pitting corrosion is more complicated, and the strength criteria accounting for the pitting corrosion effects on the strength knockdown for the engineering application have not yet been established.

The objective of this study is to evaluate the ultimate strength of steel plate panels with pitting corrosion to develop the prescribed plate panel ultimate strength formulations. In this study, the ultimate strength of the plate panels with a number of local pitting distributions that possibly occur in the marine environments is obtained by using a well-calibrated ANSYS nonlinear FE model considering predefined degree of pitting (DOP) and volume loss ratio (VLR) due to pitting. By introducing a modified plate slenderness ratio, the authors recommend ultimate strength formulations of pitted plate panels under in-plane compressions, taking into account the pitting corrosion effects.

The benchmark study based on more than 300 nonlinear FE simulations indicated that the proposed formulations are appropriate to evaluate the residual strength of pitted plate panels. This study establishes the inspection and maintenance plan of aged offshore structures quantitatively.

This presentation will be featured at the Deep Offshore Technology (DOT) Conference & Exhibition in New Orleans. It is scheduled for 12:00 p.m., Thursday, Oct. 13, in Suite C, Room 15 of the Hilton Riverside.

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