Gb2013 frank goodwin_ international zinc association


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  • This table shows the typical duplex (HDG + organic coating) systems that have been used.
    Revisiting these coatings shows that there is little difference (in terms of the ISO 12944 recommendation) in the probable performance of the coatings except that 9.01 could not be recommended. In theory, the longevity of the duplex coatings chosen could be questioned. However, can we test this theory?
  • Gb2013 frank goodwin_ international zinc association

    1. 1. The use of Galvanizing in the Mining sector in the World by Frank Goodwin William Marques Rob White International Zinc Association
    2. 2. Underground facilities • Mining projects require much steel-based infrastructure • The environments can be severe (water and air) • Maintenance of structural components can be difficult (limited and difficult access) • A robust corrosion protection system is required
    3. 3. The mine environment can include: • • • • • Full water immersion Long-term surface wetness, high humidity Elevated temperatures Acidity and alkalinity Impact and abrasion
    4. 4. Corrosion in South African mine shaft, uncoated, 20 years service
    5. 5. Blasting effect of sharp stones on galvanized structure
    6. 6. Effect of pH on the rate of corrosion of zinc: (a)rapid corrosion (b) stable film – low corrosion rate (c) rapid corrosion Otherwise pure H2O !
    7. 7. Corrosion in Mine Waters Mine water can vary in pH from 2.8 to 9.0, depending on origin and possible pretreatment Mine water can be very hard, then it can contain salts that help create a stable protective film on Zn In: normal waters: ZnO +H2O Zn(OH)2 (both slightly insoluble) 5Zn(OH)2 + 2CO2 Zn5(OH)6(CO3)2 + 2H2O (highly insoluble) 5Zn2+ + 2HCO3- + 8(OH) Zn5(OH)6(CO3)2 + 2H2O (highly stable) Fe + water = rust Fe + Zn + water Fe + Zn(OH)2 (cathodic protection and precipitation))
    8. 8. With Cl- contamination With SO4-2 contamination
    9. 9. Other reactions are present A galvanized coating will be attacked fairly rapidly at 1000 ppm Cl- levels in soft water But, similar levels of Cl- may be tolerated on galvanized surfaces in hard water (>100mg CaCO3). Hard water, including water high in SO4-2, can precipitate a deposit of protective Ca salt, such as carbonate or sulphate, on to the galvanized surface. Such deposits retard the dissolution of underlying Zn as soluble ZnCl2 or ZnSO4
    10. 10. The mine environment Rate of corrosion observed on a galvanized coating fully immersed for 100 days in South African mine water having a pH of 5.7 (chloride 986 p.p.m., sulphate 270 p.p.m., total dissolved solids 2689 p.p.m.).
    11. 11. The mine environment In high humidity, pH of condensed moisture on Zn is influenced by contamination from acidic gases (e.g. CO2 and NO2), also deposited dust contamination.
    12. 12. Example from Black Mt., S. Africa Pb/Zn mine, HDGASA inspection
    13. 13. Flowing water can cause erosion/corrosion (Black Mt. HDGASA inspection) Use of cover to prevent flow contact is effective
    14. 14. In many cases very satisfactory performance is seen 238 µm of Zn remaining 165 µm of Zn remaining
    15. 15. Hot dip galvanized shaft guides before installation
    16. 16. Surface Facilities In many cases mine surface facilities are viewed as “chemical” environments (SO2, Cl-) where galvanized steel would not be applied, but many are benign as, apart from some acidic and alkaline reagents, generally in small quantities, their processing streams are at near to neutral pH values
    17. 17. Atmospheric Corrosion Corrosivity Categories
    18. 18. Life of galvanized coatings
    19. 19. Life of galvanized coatings to first maintenance
    20. 20. 6500 tons of superstructure hot dip galvanized steel at BafokengRasimone Platinium Concentrator Plant, S. Africa
    21. 21. Galvanized steel, Marula Platinum Smelter, S. Africa
    22. 22. Douglas Middelburg Opimisation (BHP Billiton) Primary Crusher 26 km of Conveyors
    23. 23. Sishen Iron Ore Beneficiation Plant, S. Africa
    24. 24. Anglo Platinum’s Spud shaft 193µm of galvanized coating being indicated on horizontal hand railing. 101µm of galvanized coating being indicated on the “ball” of the stanchion.
    25. 25. Alcoa Pinjarra Alumina Refinery, Western Australia
    26. 26. Teck Red Dog, Alaska 54 tons of galvanized structurals
    27. 27. Actual costings ESTIMATE OF TOTAL COSTS FOR STRUCTURAL STEEL PROJECT (ACTUAL PROJECT – 30 YEAR LIFE EXPECTANCY) South African Rand (R) Amount of Steel to be protected = 6300 tonnes Hot Dip Galvanizing 1 Heavy Duty Coating 2 Initial Cost of Application R9 072 000 R11 340 000 3 Total Initial Cost R9 072 000 R11 340 000 Future Maintenance Costs 4 Years 5 - 30 Nil R250 000 pa Total Maintenance Costs Nil R8 250 000 Total Lifetime Cost R9 072 000 R19 590 000 Notes: 1. Actual Cost 2. Based upon – vinyl primer, vinyl intermediate, vinyl enamel finishing coat to total DFT 200µm 3. Includes scaffolding, abrasive blast cleaning and all inspection 4. Based on experience at similar sites by consultant mining engineer and all estimates at current prices including scaffolding and inspection
    28. 28. Typical duplex coating specifications for SA mining industry Environment Underground corrosive conditions Primer coat (um) Epoxy (40) Intermediate coat (um) Epoxy tar (90) Top coat (um) Epoxy tar (90) ISO 12944-5 Surface plant corrosive conditions Epoxy (100) Surface plant moderate conditions Epoxy (75) Epoxy (40) Epoxy (75) Vinyl (15) Vinyl (80) Epoxy (75) PU (50) Epoxy (125) HB vinyl (100) S9.11 S9.09 S9.01 Phenolic (100) PU acrylic (30) S9.10 Vinyl (40)
    29. 29. Remarks • Mining industry applications can be severe, but many successful applications are realized • Success depends upon: -Understanding the environment of application: use test samples when situation uncertain -Understanding of how to design steelwork for galvanizing -Work with fabricators on correct practices for galvanizing -Good coordination between galvanizer and contractors