METALLURGY
PLATE
Making Plates for Shipbuilding and Offshore Structures Taking into consideration the existing general trends in the development of heavy plate market in the segments of shipbuilding and offshore constructions, new variants of chemical compositions and production technology for the manufacturing of steel heavy plates with a thickness of up to 55 mm from low-carbon microalloyed D36, D40 steel grades in normalized rolled delivery condition (+NR) were developed at 4200-mm rolling complex of NLMK DanSteel. Such types of steel heavy plates are commonly used for the manufacturing of cruise liners. AUTHOR: E. Goli-Oglu (PhD), Z. Greisen (PhD), NLMK DanSteel A/S, Frederiksvaerk, Denmark CONTACT: EGO@nlmk.com,
ZIB@nlmk.com
S
hipbuilding plays an important role in the development of international, regional tourism and passenger transportation. It remains one of the most metal-intensive segments of the transport industry and the foundation for the development of international trade. Trends in the design and construction of cruise liners (Fig. 1) may serve as a vivid example of the dynamic development of the industry. In the 1970s, the average maximum gross volume of typical cruise liners did not exceed 20,000 GT and the length did not exceed 180 m. With increased interest in this type of vessels, as well as the wish of ship owners to turn a cruise liner into a full-fledged leisure and entertainment centre, the net volume of cruise liners increased at least twice a decade over the past 50 years and as of 2018 the largest launched cruise liner is the 18-deck (70 m in height) Symphony of the Seas, produced by the French shipyard Chantiers de l’Atlantique. Its net volume is exceeding 228,000 GT and its length more than 360 m. According to 2018-2019 Cruise Industry News Annual Report (the major printed magazine of the industry), another 30 new cruise liners with a length over 300 m and a net volume of 130,000 to 230,000 GT will be manufactured in 2019 to 2024. An analysis of shipbuilding steel heavy plate markets shows that, first and foremost, the demand for heavy plates with higher thickness (above 40 mm) is increasing. The strength level requirements are increased by at least one class with respect
MPT International / December 2020
Figure 1. Evolution of cruise liners modern generation design in terms of net volume and dimensions over the past 50 years
to traditional materials. While the temperature requirements for toughness remain the same (0 and -20 °C), impact energy requirements are becoming more stringent with regard to sampling location together with higher demand in resistance to strain aging processes. Surface quality requirements of plates have also become increasingly important and the presence of surface imperfections/imprints, which are formed due to furnace scale, is not allowed in many cases. The above considerations have increased the economic feasibility for development of new chemical compositions and production technology for shipbuilding heavy plates with higher thickness and strength levels compared to those that have already been implemented at NLMK DanSteel.
Requirements of maritime standards The main requirements of DNV-GL, RINA, LR, RMRS, ABS and BV international mari-
time classification societies for the manufacture of steel heavy plates for shipbuilding are similar, since they are based on the requirements of the General Rules of the International Association of Classification Societies (IACS), including acceptance requirements for certification tests in order to confirm the possibility of manufacture of heavy plates of studied steel grades. The existing minor differences are associated with the historical stages of development of regional shipbuilding procedures, as well as with the national or geographical features of each classification society.
Chemical composition The chemical composition and production technology for the manufacturing of shipbuilding heavy plates in normalizing rolling delivery condition (+NR) previously implemented at NLMK DanSteel was based on microalloying of steel with Niobium and enabled the manufacture of heavy plates with a thickness of up to 35 mm
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