AMLoCor® Increases Design Life of Marine Structures

Introduction

ArcelorMittal’s ‘low corrosion’ steel grade will undoubtedly revolutionize the design of maritime infrastructure. As a matter of fact, steel sheet piles have been used for over 100 years to build reliable and cost-effective temporary and permanent structures worldwide. Countless quay walls of major European ports have been constructed with steel sheet piles. One concern of the designers and port authorities was the durability of these marine structures. Corrosion of steel is a natural phenomenon that occurs whenever steel is in contact with humidity or water. However, it has not prevented investors and engineers from using steel in marine applications.

Advantages of AMLoCor

The main advantage of AMLoCor is a significant reduction of the corrosion rates in the Low Water Zone (LWZ) and in the Permanent Immersion Zone (PIZ).

For the verification of the structure, the designer considers average homogeneous corrosion, assuming that the loss of thickness is uniform all over the surface, as opposed to ‘pitting’ corrosion, which might have more local influence on the serviceability state.

In general, the maximum bending moments, and consequently the steel stresses, are in an area where corrosion rates are relatively low: permanent immersion zone or embedded zone (see Fig. 4). Yet the Low Water Zone sometimes governs the design, because in the permanent immersion zone the reduction of the section properties is offset by the lower thickness loss.

Fabrication, connections, maintenance

The intrinsic properties of AMLoCor make it a ‘special’ steel grade with respect to welding. Specific welding procedures have been worked out to ensure state-of-the-art welding. Welders also have to be certified accordingly. The choice of the electrodes is important. Please contact us for more information on the different welding procedures.

Splicing and special piles can be based on EN 12063, except for the welding procedures. Welding procedures are referenced in the German General Technical Approval Z-30.10-55. 

Installation

It is common practice to analyse the driveability of new steel grades during the development stage. Having a good toughness, it was never really an issue, but nevertheless, a driving test in very hard soil conditions was performed in Denmark, in order to compare the behaviour of one section rolled in a ‘standard’ S 355 GP vs. AMLoCor steel grades. The whole test programme was done under the supervision of an independent body to certify the results of the test. Piles were driven with an impact hammer and a vibratory hammer, and then pulled out for visual inspection and measurement of the section geometry. Additionally, a PDA analysis of the piles was done during the driving. The test confirmed that AMLoCor performed as well as equivalent carbon steel in hard driving conditions.