HDGASA

How to specify hot dip galvanizing

Specification SANS 121 (ISO 1461) has been superseded by Hot dip galvanized coatings on fabricated iron and steel articles – Specifications and Test Methods.

The new specification provides for a minimum local coating thickness as well as a minimum mean coating thickness. Table 2 in the specification document provides details of coating thicknesses for galvanized components which are not centrifuged after galvanizing. Table 3 in the specification provides details of coating thicknesses for material which is centrifuged after galvanizing, e.g. fasteners. These requirements are as follows:

Minimum Coating Thickness on Samples that are not Centrifuged SANS121 (ISO1461)
Category & thickness (t) mm	Local coating thickness min. µm*	Mean coating thickness, min. µm*
PROFILES
t >= 6	70	85
3 <= t < 6	55	70
1.5 <= t < 3	45	55
t < 1.5	35	45
CASTINGS
t >= 6	70	80
t < 6	60	70
Thickness Legend 3 <= t < 6 = thickness less than 6mm but greater and equal to 3mm

Minimum Coating Thickness on samples that are Centrifuged SANS121 (ISO1461)
Category & thickness/diameter (t) or (ø) mm	Local coating thickness min, um*	Mean coating thickness min, um*
FASTENERS
ø >= 20	45	55
6 <= ø < 20	35	45
ø < 6	20	25
OTHER ARTICLES (INCLUDING CASTINGS)
t >= 3	45	55
t < 3	35	45
Thickness Legend 6 <= ø < 20 = diameter less than 20mm but greater and equal to 6mm
* Local coating thickness is defined as the mean of the measurements taken within a specified reference area. Mean coating thickness is the control sample number average of the local coating thickness values from each reference area. Where only one reference area is required according to size of the article, the mean coating thickness within that reference area shall be equal to the mean coating thickness given in in the above tables. Deviation from standard coating thickness. A requirement for a thicker coating (25% greater than the standard in table 19 can be requested for components not centrifuged, without affecting specification conformity. Where steel composition does not induce moderate to high reactivity, thicker coatings are not always easily achieved.

*Local coating thickness is defined as the mean of the measurements taken within a specified reference area. Mean coating thickness is the control sample number average of the local coating thickness values from each reference area.

A requirement for a thicker coating (25% greater than the standard in table 2) can be specified, subject to agreement between the specifier and the galvanizer, without affecting specification conformity. Renovation Procedures:

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