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Using the ISO 9223 Table, estimate the thickness of a coating required on an aircraft hangar to provide a coating service life of twenty years. The coating on this steel structure is to be produced by the hot-dip galvanizing process. The following data shows the measured time of wetness at the hangar location. The average chloride deposition rate in this atmosphere was estimated to be 314 mg m-2 day-1 and the average SO2 deposition rate to be approximately 42 mg m-2 day-1. Use a conservative engineering approach in your estimation (use the maximum value) and short term corrosion rate data to produce your estimates.
Month | Average daily TOW (h) |
January | 5.8 |
February | 4.1 |
March | 5.5 |
April | 6.0 |
May | 8.9 |
June | 11.6 |
July | 12.2 |
August | 13.5 |
September | 11.3 |
October | 9.5 |
November | 7.3 |
December | 4.8 |
You should find all the information required to answer these problems by consulting the ISO 9223 standard.
Convert the chloride deposition rate to an ISO salt category (S)
Do the same for the ISO pollutant or sulfur dioxide category (P)
Now you should convert the data of your average daily TOW above into units compatible with the ISO TOW category (T) (how many hours in a given month? how many hours per year?)
With these three categories you are now in a position to estimate the ISO corrosivity category (C)
Knowing that the galvanized coating is made of zinc convert the ISO corrosivity category into a corrosion rate (CR) expressed in g m-2 year-1
Also knowing that the density of zinc is 7.14 g cm-3 convert the mass loss you just estimated into a penetration rate for one year (how many days in a given year?)
What maximum thickness of this zinc coating would be required for a minimum life of twenty years?
