ABSTRACT:

Fatigue crack growth behavior in seawater of surface crack on the weld was studied with a structural steel, AH36, manufactured by the thermo-mechanical control process (TMCP). Crack growth rate was measured for the surface cracks located in different regions of weld, such as the heat affected zone, the weld metal and the base metal. Influence of the welding condition was investigated with the variation of heat inputs of 80, 120 and 180 kJ/cm. Electrochemical analysis of each region of the weld was also performed to investigate the corrosion behavior between the weld and the base metal.

INTRODUCTION

Fatigue cracking of structural materials in corrosive environment has been studied with a great importance in the past few decades, especially for offshore structures. When a material is newly applied to the offshore environment, the corrosion fatigue characteristics of the material has to be first considered for safety and lifetime structural integrity of the structure. It is well known that most of the failures of steel structures occur in the weld, not only in atmospheric environment but in corrosive environments. However, the phenomenon of corrosion fatigue of steel welds is too complicated to generalize the effect of corrosive environment on fatigue cracking. Therefore, analysis of reliability and evaluation of lifetime of the structures are carried out based on the experimental data under the similar conditions to those in service. In this study, we measured the fatigue crack growth rate in seawater of surface crack in weld of a steel made by thermo-mechanical control process (TMCP) which offers a great advantage in welding process due to the application of high heat inputs. The crack growth rates in each region of weld were compared and analyzed. The effect of high heat inputs on crack growth rate was also investigated.

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