Introduction of High-Tensile Steel in Shipbuilding

Field of research: Fatigue Strength; Carrying Behaviour; Ship Structural Design

Duration: 01.01.2001 – 30.06.2003

Project leader: Prof. Dr.-Ing. W. Fricke

Funded by: Stiftung Stahlanwendungsforschung (FKZ AVIF A 164)

stress curve

Summary

Several investigations have been performed regarding the possible application of high-tensile steel with yield strength of up to 690 MPa in thick-walled structural members in ships. The experimental investigations had the focus on the fatigue strength of those structural details, which are practically unavoidable in the longitudinal hull structures and, therefore, determine the structural design: free plate edges, butt joints without and with change in plate thickness and joints of longitudinals with cut-outs (scallops) for welds. Compared with the normal and higher-tensile steels used up to now, having a yield strength of up to 355 MPa, partly the same and partly a somewhat increased fatigue strength were observed for the high-strength steel used. Investigations of the roughness and residual stresses at plate edges and of the weld profile at butt joints could explain the fatigue strength behaviour. However, some detrimental fabrication effects were identified, i. e. small hot cracks in the butt joints at thicker plates and cracks initiating from removed auxiliary welds for fabrication purposes. The first mentioned problems are less related to the high-tensile steel but more to the usage of rutil filler wires. A comparison of the midship sections of medium-sized container ships, which were designed with different steel strengths in the upper flange of the hull girder, shows that in usually welded ship structures made of high-tensile steel, the permissible stress should not be more than about twice of that for normal strength steel for fatigue reasons, whereby in this case the notch effect has to be reduced by structural or fabrication-related measures at several details. Almost 5 % of the total steel weight compared to higher-tensile steel may then be saved.

Final Report

W. Fricke, C. Weißenborn, L. Eggert, G. Huismann: Erschließung des hochfesten Stahls für den Schiffbau. CMT-Bericht 1/2004, Center of Maritime Technologies, Hamburg 2004

Further Publications:

C. Weißenborn: Einsatz von hochfestem Stahl in den oberen Längsverbänden großer Containerschiffe. Schiffbautag der Dillinger Hütte, Stralsund, Sept. 2003.

W. Fricke; H. Paetzold und C. Weißenborn: Zum Einsatz hochfester Stähle im Schiffbau. Jahrb. der Schiffbautechn. Ges., 98. Bd. (2004), Springer-Verlag, Berlin Heidelberg New York.

H. von Selle und W. Fricke: Festigkeitsgesichtspunkte beim Einsatz von hochfestem Stahl in der Schiffskonstruktion. In: Festigkeit gefügter Bauteile, DVS-Berichte Bd. 236, S. 125-129, DVS-Verlag Düsseldorf 2005.