Moorlink develops new steel

By Hans Aronsson, Moorlink materials specialist with 30+ years of specialized steel material experience.

MoorLink and its steel supply partners are continuously improving the steel material properties. There are ongoing projects to improve and optimize the material used in the mooring accessories. This article presents some of the areas of research being explored currently.

The use of accessories is a demanding and critical task; not only for the designer, but also for the engineer specifying the steel material used when manufacturing this highly specialized equipment. The certifying bodies – like DNV and ABS – are emphasizing material knowledge in their updated guidelines. Requirements for materials used in these kinds of applications are increasing, both in terms of engineering values but also in terms of process robustness and quality control. A further design parameter to take into account is the restrictions imposed by the physical size of the components, as heat treatment effects will be dependent on the exposed area and volume of the component being treated. It is thus of utmost importance for the manufacturer of offshore accessories to develop and utilize the steel material in the most efficient and optimal way. MoorLink has since long practiced a close partnership with material suppliers to maximize and optimize the material properties for the use in mooring accessories.

Way forward
There are a number of ways standard grades can be improved and used to achieve improved properties well beyond the requirements in the standards. Some of the ways to improve the material used in the swivels from MoorLink are described below: • Fine tuning the chemical analysis within the limits stipulated by the standard. It can be exemplified by increasing the alloy additions to increase the hardenability and fine grain treatment by micro alloying. • The heat treatment can be performed in a number of ways. There are options to increase both the toughness and tensile properties including quench techniques. • The machining is also important for the properties. The sequences of machining and heat treatment can be optimized to give the best properties of the material used. This development also includes optimizing the shapes being machined. MoorLink is currently actively looking into all of these development paths.

Bright material future
The development described briefly above is creating steel versions that outperform the standardized set of properties. This includes properties given in the national and international standards (as EN, ASTM) as well as accepted industry rules (as DNV, ABS). The end results are successful swivels like the 231M5 and the 177M5, both of which are certified to be included in R5 mooring systems to both DNV and ABS. It is important that the product user and certifying bodies evaluate the improved materials in an open and unbiased manner. The standards and rules should not be seen as given once and for all; more as a set of common rules and understandings for the industry workman-ship at a certain time.
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