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ASTM Revises 2 Zinc Coating Standards

Monday, November 14, 2011

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ASTM International has revised two zinc coating standards for steel and iron applications: one for measuring coating weight and one for electrodeposited coatings.

A90M: Test Method for Coating Weight

ASTM A90 / A90M - 11 Standard Test Method for Weight [Mass] of Coating on Iron and Steel Articles with Zinc or Zinc-Alloy Coatings provides a standard method for determining the weight, or mass, of coating for comparison with specification requirements.

A coating of zinc on iron or steel articles provides protection against corrosion. As the protection is provided by sacrificial loss of zinc, the degree of protection is proportional to the weight (mass) of zinc coating.

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The standards relate to measuring coating weight and electrodeposited coatings.

Specifications for zinc-coated articles frequently provide for different classes of coating, so that purchasers can select the coating weight (mass) most suitable to their needs.

Standard Scope

This test method covers procedures for determining the weight (mass) of coating on iron or steel sheet, wire, and other articles in which the coating is zinc or a zinc alloy.

The final results determined by this test method shall be expressed in inch-pound units or SI units, depending on the units used in the comparison specification.  For sheet products, the final results are expressed as either total coating weight for both sides, or for individual sides, depending on the specified requirements.

The standard was developed by the subcommittee on Methods of Testing, under Technical Committee A05, Metallic-Coated Iron and Steel Products.

B633: Specs for Electrodeposited Coating Specs

B633-11 Standard Specification for Electrodeposited Coatings of Zinc on Iron and Steel establishes requirements for electrodeposited zinc coatings applied to iron or steel articles for corrosion protection purposes. (The standard does not cover electrodeposited zinc-coated steel wires or sheets.)

The coatings are provided in four standard thickness classes—in the as-plated condition or with one of three types of supplementary finishes. The article surfaces shall undergo pre-plating basis metal cleaning, pre- and post-coating treatment for reducing the risk of hydrogen embrittlement, and reactivation and supplementary treatments.

Coatings should be sampled, prepared, tested and conform accordingly to specified requirements for appearance (luster and workmanship), thickness, adhesion, corrosion resistance, and hydrogen embrittlement.

This standard has been revised to address RoHS requirements that seek to limit the exposure of workers and the public from exposure to toxic metals. Additional types have been added to permit non-chromate passivate treatments to be used in replacement of hexavalent chromium.

The standard was developed by the subcommittee on Soft Metals, under Technical Committee B08 on Metallic and Inorganic Coatings.
 
Like all ASTM standards, neither of these purports to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.