Standard and Project Requirements
It seems advisable to split the requirements to the EN 10025-4:2019 S420M/ML structural steel into three complexity classes. The first and simplest class shall include the EN 10025 basic requirements to the chemical composition and basic mechanical properties. The second class shall include customer requirements for lower content of chemical elements in steel. Most sought-after restrictions are restrictions to the maximum permissible content of Carbon (e.g. not more than 0.06%), Manganese (not more than 1.40%), Silicon (not more than 0.25%) and Niobium and Vanadium (not more than 0.030% in total). The carbon equivalents CEQ ≤ 0.34% and Pcm ≤ 0.16% may be restricted additionally.
The third class includes project requirements with additional restrictions to the chemical composition and mechanical properties of the base metal and/ or welded joint. The regulatory requirements to the S420ML heavy plates and additional cumulative project requirements in offshore wind power and bridge construction industries are shown as an example in Tables 1 and 2. It should be noted that project requirements are individual and vary depending on the purpose, economics, specifics of the steel structure manufacturing process, its elements, etc.
Table 1. Project requirements for the chemical composition of S420M/ML steel heavy plates could vary a lot compared to standard requirements and depend on the purpose, economics, specifics of the steel structire manufacturing process etc.
Table 2. Project requirements for the level of mechanical properties of S420M/ML steel heavy plates could be much advanced compared to standard requirements of EN 10025-4 both in strength and in low temperature toughness.
Examples of applications
There are many different common and special applications, where heavy plate products 60 to 100 mm in thickness from S420M and S420ML structural steel grades are used (or could be used). The most advanced applications are related to structural offshore and bridge building segments. For example, transition pieces (Figure 1a) of monopiles, which at present time are the most advanced type of foundation for the construction of offshore wind turbines are commonly manufactured from 50 – 100 mm thick heavy plates. Transition pieces are needed in order to connect the towers of the offshore wind turbines with the respective monopile. Made up of a steel pipe construction, the primary steel part, as well as secondary steel elements like platforms, ladders or boat landing systems, transition pieces are essential construction components of offshore wind turbines. Components of such offshore construction elements like high-load spreader bars, pile followers, crane pedestals (Figure 1c), spud poles, thick-walled tubular sections, dead weight support caissons (Figure 1d) are also produced from thick heavy plate products. Even for more traditional offshore structures like jackets and rigs, a change to higher strength grades can be advantageous due to lower weight and better weldability of these grades. Examples of special application could be centric and eccentric cones (Figure 1b) with various aperture angles and special edge processing, such as crimped edges, which are used to strength construction including ice protection function.
Figure 1. Where heavy plate products 60 to 100 mm in thickness from S420M and S420ML structural steel grades are used (or could be used)
