Practical Guidelines for the Inspection and Repair of Hot Dip Galvanized Coatings
Information courtesy of: HOT DIP GALVANIZERS ASSOCIATION SOUTHERN AFRICA
Reference Areas
The number of reference areas, dependant upon the size of the individual articles in the control sample, shall be as follows:
| a) |
For articles with significant surfaceB area greater than 2m2, at least three reference areas shall be taken on each control sample. B A significant surface can be defined as a surface which impacts on the performance of that article. |
| b) |
For articles with a total significant surface area greater than
2m2, manufactured from material of several different thickness', at least three reference areas shall be taken on each specific material thickness. |
| c) |
For articles with significant surface area between
1000mm2 and up to and including 2m2 inclusive, each article in the control sample shall have at least one reference area. |
| d) |
For articles with a total significant surface area between 1000mm2 and up to and including
2m2 inclusive, manufactured from material of several different thickness, each different material thickness, representing the control sample shall have at least one reference area, per material thickness. |
| e) |
For articles with less than 1000mm2 of significant surface area, enough articles shall be grouped together to
provide at least 1000mm2 surface for an individual reference area. The number of reference areas shall be as given in the last column of
table 1. Hence, the total number of articles tested equals the number of articles required to provide one reference area multiplied by the appropriate number from the last column of
table 1 related to the size of the lot (or the total number of articles galvanized if that is less). Alternatively, sampling procedures selected from ISO 2859 shall be used. |
Note: 2m2 is typically 200 cm x 100 cm and 1 000 mm2 is typically 10cm x 1 cm. For case a) and b) on each article taken separately in the control sample, the local coating thickness within the reference area shall be equal to or greater than the mean coating thickness values given in table 2 or 3 or the local coating thickness values given in table 4.
In cases c) to e) the coating thickness on each reference area shall be equal to or greater than the local coating thickness values given in table 2, 3 or 4 as appropriate. The mean coating thickness on all reference areas on material of equal thickness in a sample shall be equal to or greater than the mean coating thickness values given in table 2 or 3 as appropriate.
When more than five articles have to be taken to make up a reference area of at least 1000 mm2, a single magnetic measurement shall be taken on each article if a suitable area of significant surface exists: if not, the gravimetric test shall be used.
Within each reference area, which should be at least 1000 mm2, a minimum of five magnetic test readings shall be taken. If any of the individual readings is lower than the values in table 2 or 3, this is irrelevant as only the mean value over the whole of each reference area is required to be equal to or greater than the local thickness given in the table.
Thickness measurements shall not be taken on cut surfaces or areas less than 10mm from edges, flame cut surfaces or corners.