DesignGuidelinesforDoublerPlateRepairsofShipStructures - Design Guidelines for Doubler Plate Repairs of Ship Structures Pradeep K Sensharma,1 Member

DesignGuidelinesforDoublerPlateRepairsofShipStructures -...

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Paper No. 2005-P11 Sensharma 1 Design Guidelines for Doubler Plate Repairs of Ship Structures Pradeep K. Sensharma, 1 Member , Malcolm Willis, 2 Member , Aaron Dinovitzer, 3 Member , Nat Nappi, Jr., 4 Member ABSTRACT The use of doubler plates or ‘doublers’ has become routine for temporary ship repairs. It is the preferred method for ships’ structural repairs for plate corrosion due to its relative ease and low cost of installation over the more costly permanent welded plate insert repair. A lack of performance data and engineering design guidance are the reasons that repairs with doublers are currently considered only temporary. This objective of this study was to develop a set of guidelines for designing and applying doubler plate repairs to ship structures. The guidelines were established using the following criteria: various stress analyses, buckling strength, corrosion types and rates, weld types, and doubler plate fatigue and fracture assessment. Studying and understanding doubler plate repair performance by comparison to that of the primary hull performance allows critical operational decisions to be made with greater ease and confidence. However, the ultimate goal of this study was to establish the design and limitations on the applications of doubler plate repairs for surface ships. KEY WORDS: Buckling; corrosion; doubler; fatigue; fracture; ships. INTRODUCTION The Statistics reveal that corrosion is the number one cause for marine casualties in older ships (Harada et al. 2001). Damage to ships due to corrosion is very common especially in aging ships. The plates and stiffeners suffer corrosion reducing the load bearing capacity of the structure. The consequences of corrosion wastage can be local, but can also be serious in some circumstances. Severe corrosion has resulted in deck cracks across almost the entire ship width and has even resulted in the loss of ships (Wang, 2003). The use of doubler plates or ‘doublers’ has become routine for temporary ship repairs. It is the preferred method for ships’ structural repairs for plate corrosion due to its relative ease and low cost of installation over the more costly permanent welded plate insert repair. A lack of performance data and engineering design guidance are the reasons that repairs with doublers are currently considered only temporary. In numerous cases where doublers were used to cover corroded plate it was later discovered that not only was the original structure corroded, but also the doubler plates used to cover them. Doubler plates have previously not been considered to restore structural strength, only maintain local water tightness. Their use has never been accepted as a permanent repair, by either classification societies or by the U.S. Navy, but only as a temporary one until the ship is dry-docked and permanent repairs can be made. In addition to the questionable structural performance that doubler plates provide, there is also concern about crack initiation in the base metal resulting from the peripheral fillet and ___________________________ 1 Senior Structural Engineer, BMT Designers & Planners, Inc.

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