Steel Tube Handbook - 16. edition january 2021

81 A. GALVANIC PROTECTION OF TUBE SURFACE The outer surface of HPL tubes (or other types of tubes) can be protected by galvanizing. Coatings in addition to corro- sion protection also improve the aesthetic appearance of the product. The coating usually consists of several layers. The first (lower) layer is galvanic excluded zinc (Zn) or zinc alloy. Layer thickness is 5 - 30 µm. The second (eventually middle) layer consits chromium (Cr). In the past were used Cr 6+ salts, which is toxic. Accor- ding to the valence of chromium process is called chroma- ting. Using this type of Cr has been forbidden – European Community Directive Nr. 2000/53/EC ( ELV Directive – End of Life Vehicles) and Directive Nr. 2002/95/EC – so-called RoHS conformity – The Restriction of use of certain Hazar- dous Substances - Pb, Hg, Cr6+, Cd, PBB-polybrominated biphenyls, PBDE-polybrominated diphenylether. This direc- tive restricts the use of hazardous substances in electrical engineering. Procedures, which are not used banned sub- stances are comply with the Directive. Currently used in the process the Cr3+ salts and process is called chromiting or passivation. Last (top) layer increases the resistance and stability of surface and consists of organic matter containing Si. This process is called impregnation or sealing. This layer may not by applied. Depending on changes of used procedures (Cr6+ was replaced with Cr3+) has also changed the applicable stan- dards. In the past were valid the standards DIN 50961 and EN 12 229. The Standard EN ISO 2081 has been in use since year 2008. Not even the procedures according to ISO do not guarantee the conformity with requirements of RoHS. Now is valid new EN ISO 2081, which defines the parame- ters of the surfaces and their marking. In practice are used two types of surfaces: - transparent passivation (thin layer) is colorless to colo- red iridescent. For marking is used code A . - iridescent passivation (thick layer) is colored irides- cent. For marking is used code C . - surface without sealing has not any code, surface with sealing has the code T2 - required thickness of Zn layer in µm (range 5 – 30 µm) - example for marking of the surface: Fe/Zn8/C means: ba- sic material – steel, layer of Zn min. 8 µm, iridescent pas - sivation, without sealing. Dimensional table of Železiarne Podbrezová and Trans- mesa is in Table 34, page 82. B. Protection of the surface of tubeswith plastic layer – with polyolefin. The layer of polyolefin protects the outer surface. It provi- des mechanical protection, anticorrosion, against chemi- cals, thermal - insulation and is used for decorative purpo- ses. Types of tubes coated with polyolefin: 1. HPL tubes non galvanized 2. HPL tubes galvanized with Zn layer 8 – 12 µm - iridescent passivation – Fe/Zn8/C 3. Other types of tubes in the size range: Wall thickness Outside diameter 1 8 - 22 1,5 8 - 22 2 8 - 22 2,5 14 - 22 3 18 - 22 L = 4 000 – 6 000 mm. Material – thin-walled, halogen-free polyolefin according to EN 60684, operating temperature - 40 °C until +105°C (short +150°C), tensile strength min. 10 N/mm2, elongation min. 300 %, nonflammable, resistant tomildew, oil and che- micals. Protection of the outer surface of the HPL tubes