In response to the request of Viakon Technologies LLC to the profile Institute in the field of metal science about the possibility of interchangeability of S315MC STB EN 10149-2-2009 «Flat hot-rolled steel with a high yield point for changing the shape in a cold state» on steel grades* according to GOST 1050 (similar in both mechanical properties and chemical composition), taking into account the long-term reliability of the main anti-corrosion protective coating applied by hot-dip galvanizing, as well as the degree of compliance of steel grade 09G2S according to GOST 19281 with the S315MC grade (for the manufacture of elements of prefabricated metal corrugated galvanized structures with backfill as a superstructure on transport structures with an estimated service life of 75-100 years), the following explanation was received:
«It is known from the literature that hot-dip galvanizing is suitable for the protection of low-carbon steels (carbon content of no more than 0.25%) and with a silicon content of up to 0.37% with a relatively low content of elements that are commonly referred to as alloying. These requirements for chemical composition are met by carbon steels of ordinary quality according to GOST 380-2005 (from sto to St4sp), rolled products of high-quality carbon structural steel according to GOST 1050-88 (up to steel 25 inclusive) and rolled products of construction steels according to GOST 27772-88 (steel C235, 245, 255, 275, 285). The coating of the smallest thickness with good adhesion, smooth and shiny is obtained on boiling steels (steels with a silicon content of less than 0.05 %). A matte coating with a thickness of 120 to 180-200 microns with satisfactory adhesion is obtained on calm steels with a silicon content in the range of 0.15-0.25%.
The most unpredictable coating is obtained on semi-quiet steels. When hot-dip galvanizing low-carbon steels with a higher silicon content (more than 0.37 %), the coating turns out to be thicker, uneven, more brittle and prone to peeling (the higher the silicon content, the thicker and more brittle the coating turns out). The silicon content in steel grade 09G2S — from 0.50% to 0.80 % (GOST 19281-2014), which does not meet the requirements of STB EN 10149-2 (according to Table 1, the silicon content should not exceed 0.50%).»
Regarding prefabricated structures under the brand name «ViaCon», please note that in order to ensure the design life of 75 – 100 years, the manufacturer orders steel with an even lower silicon content (up to 0.25%) for the production of structures such as «MultiPlate MP200» (MP200), «SuperCor» (SC) and «UltraCor» (UC). This choice of steel grade corresponds to the approaches to hot-dip galvanizing according to STB ISO 14713-2-2012 » Zinc coatings. Guidelines and recommendations for corrosion protection of cast iron and steel structures. Part 2. Hot-dip galvanizing» and the requirements of TKP 45-2. 01-111-2008 » Protection of building structures from corrosion. Building design standards » Table Vol. 1 Notes p. 5:
«For hot-dip galvanizing of low-alloy steels, it is necessary to use steel of a separate supply with a regulated content of carbon (up to 0.25 %) and silicon (up to 0.30 %), which should be specified in the project documentation.»
In the production of «Helcor» (HC) and «HelCor Pipe Arch» (HC PA) spiral corrugated pipe links, steel with a chemical composition that meets the requirements of STB EN 10346-2009 «Flat steel products with hot coating. Technical conditions» (the silicon content should not exceed 0.60 %). The production of spiral pipes involves the use of steel with a thickness of up to 3.9 mm in rolls, respectively, high-quality hot-dip galvanizing of an anticorrosive coating on such relatively thin metal sheets is technologically possible with a thickness of up to 50-55 microns. In this regard, in order to ensure an estimated service life of at least 75 years, the manufacturer of spiral pipes orders for the production of steel not only with a low silicon content (the actual values are 0.01%), but also with a double-sided anticorrosive coating formed in the factory by two layers:
— 1 coating layer: zinc (hot dip galvanizing method) with an average thickness of at least 42 microns);
— 2 layer of coating: polymer material » trenchcoat «(high — density polyethylene-HDPE) with a thickness of at least 250 microns.
* steel grade – an indicator of the quality of steel, reflecting its mechanical properties, chemical composition, degree of deoxidation, cold resistance (Large construction Terminology Dictionary-reference. Official and unofficial terms and definitions in construction, Architecture, urban planning and construction equipment, Minsk: Minsktipproekt, 2008).