3. A minimum of 5 spot readings of multiple readings each (generally accepted to be three [3]) are taken spaced evenly over the specimen (article). For galvanized and galvannealed sheet, the relationship between coating weight (mass) and thickness is as follows (based on zinc density of 446 1b/ft 3 or 7140 kg/m 3 ): … Table 1 – Requirements for coating thickness and mass for … If the coating measured does not meet the required minimums for the individual specimen average or for the grand specimen average, then the coating does not pass, and the lot represented by that article does not pass. 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Single specimen, single material component. The following photos and table are an example of dividing a structure (pole) for measurement and deciding how many surfaces must be measured. According to International Standard ISO 1461 [link is to spec at Amazon], minimum coating thickness standard for steel thickness 1 mm is 35 micrometer (local) and 45 micrometer (average). Thickness should be between 1.4 and 3.9 mils (35 and 100 µm) depending on the coating grade. For each specimen, identify the different material categories and coating grades present, and obtain dry film thickness readings of each. The total zinc coating mass applied depends mainly on the mass and thickness of the steel being galvanized. As coating life expectancy figures quoted are based on the minimum coating thickness they are therefore usually very conservative. Coating Thickness vs. The corrosion resistance provided by the zinc coating is in direct proportion to the coating's thickness. There is no set formula except that the areas must be nominally equal. *Single Specimen Articles. ft. heavier or .0037 inch thicker than the weight or thickness of the corresponding U.S. Standard Gauge Number, regardless of coating weights. But how does that microscopic coating translate into performance? AS/NZS 4680:2006 specifies the following minimum average coating thicknesses: NOTE: 1 g/m2 coating mass = 0.14 µm coating thickness. The corrosion rate of a galvanized coating is generally linear. Step 1. This layer’s thickness can be controlled and the different thicknesses are designated below. Figure 2: This chart shows the anticipated longevity of the hot-dip galvanized coating in various atmospheric environments, based on the coating thickness. For the sample of single-specimen articles, the entire article represents the specimen to be measured. Site by Un.titled, Facebook The standard minimum coating thickness depends on the item's steel thickness. © 2020 All rights reserved. AISI Thickness Tolerance Ranges Galvanized Steel Sheets Thinkness. Acceptance Criteria – Example 1 Pole Structure. click to see corrosion rates in your area). A multi specimen article is greater than 160 sq.in. Not only must the thicknesses be measured, but the acceptance criteria must also be established based on the information presented earlier from Tables 1 and 2 of ASTM A123. A minimum of 5 spot readings are obtained in each specimen area. *Multi-Specimen Articles. Abrasives Testing: Which Tests Should You Run? A wide thickness range for varied applications. 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There are two different methods used to measure the coating thickness of hot-dip galvanized steel: a magnetic thickness gauge and optical microscopy. Assign each article to one of the two categories. The readings in each area are averaged to obtain 3 averages per article. Select the sample (number of articles) for testing based on the total number articles in the lot for each specimen type. Service life chart for hot-dip galvanized sheet In addition to The Coating Life Predictor, the books by Zhang10 and Porter11 are excellent sources for additional and more detailed information on the corrosion behaviour of zinc-coated steel, not only in the atmosphere but indoors, in … Therefore, the best representation of coating thickness is obtained by averaging a series of measurements as per ASTM A123-02. Bolting Galvanized Steel Methods for Measuring Galvanizing Weight or Thickness. Use of high silicon steel enables a still thicker coating of 200 μm to be specified. The carbon, sulfur and manganese content of the steel also may have a minor effect on the galvanized coating thickness. Jinan Sino Steel Co., Ltd was one large Steel Holding Company, as a window of foreign trade of Chinese Steel industry, our company has been conducting extensive exchanges and friendly co-operations with domestic and overseas companies on the ba It does indeed pay to know your microns. Contact Us The 5 spot readings are averaged. Hot Dipped Galvanized – sheet or strip steel bathed in a molten solution containing not less than 98% pure zinc to uniformly coat for corrosion resistance. These variables are represented in the table below. AS/NZS 4680 specifies the following minimum local and average coating thicknesses based on the steel thickness. The process of galvanizing bonds a layer of zinc to the steel. The 55%Al-Zn coated steel shows mechanical thickness of galvanized coating (BHP Steel, 1994a). Coating weight or thickness can be measured by one of four methods. Terms & Conditions Introduction – The controls required for the hot-dip galvanizing process are described in Topic 1 of this series. AS/NZS 2312.2 provides recommendations on techniques to minimise distortion and embrittlement, the effect of steel chemistry on the appearance and thickness of coatings. Verify the thickness and chemistry of the applied coatings to ensure product functionality and life-span in harsh environments. For multi-specimen articles, divide each article into thirds to select the specimens for measurement (3 specimens for each article). The galvanizer and inspector will need drawings to determine the wall thickness, if an open end is not available for measurement. The chart was developed based on actual corrosion rates in the field. The number of articles to be sampled, the number of thickness measurements to be taken and the acceptance criteria are discussed. It is useful to identify each area for clarity. Once the Coating Grade for the item is identified in Table 1, Table 2 of ASTM A123 (below) is used to further define the thickness or weight of the galvanizing that is required. The definition of a lot is flexible in that it can be a shift’s production, a day’s production, or a truck load, but it generally consists of articles of the same size and shape. Twitter This article is based on the use of magnetic gages to measure galvanizing thickness according to ASTM-A123, including the number of galvanized articles to be sampled, the number of thickness measurements to be taken, and the acceptance criteria. Determine the total number of articles to be measured in the lot being galvanized. HOT DIP GALVANIZED STEEL, known as ZINCGRIP® Steel, is continuously coated on both sides with a zinc coating. The weight of the galvanizing is 705 grams/square meter or 2.3 ounces/square foot. It is defined as a multi specimen article because multiple “specimens” within the article are measured – the article is too large for a single set of measurements. 2. Coating Weight Coating Thickness to reach 1 oz/ft2 Hot-dip galvanizing (batch or continuous), electroplating, zinc plating 1.7 mils (43 µm) Metallizing (zinc spraying) 1.9 mils (48 µm) Mechanical plating 2.2 mils (55 µm) Zinc-rich paint 3-6 mils (75-150 µm) For these applications, as steel thickness is increased, heavier galvanize coating should be used to insure sufficient galvanic edge protection for the increased cut edge surface area. Stripping, Microscopy, Weighing Before and After Galvanizing, or Magnetic Thickness Measurement. Under the international system of units (SI) the micron is represented by the Greek symbol μm, which signifies one thousandth of a millimetre. Gage No. In the example in A123 above, the three averages are compared to the dry film thickness requirement for compliance and are averaged together to verify compliance to the required thickness. A coating thickness of up to 140 μm may be then specified. Thickness measurement and Acceptance Criteria. To put that in perspective, it is often cited that the human eye can perceive objects no smaller than 40 microns and that the average human hair is a mere 50 microns in diameter. How this microscopic coating then weathers is predictable but complex and fluctuates with atmospheric conditions. After the various articles have been classified as a single or multi-specimen article, the number of test articles selected for the sample for each specimen type shall be based on the chart in Section 7.3. For requirements for threaded fasteners refer to AS 1214. The specimen average may be one grade less than required by the material category provided that, when the specimen averages for the articles are averaged together, this average must meet or exceed that for the material category requirements. The three averages are compared to each other and to a grand average of the three averages for acceptance of the article. The definitions are provided in a logical order in which the terms are used, rather than alphabetical. Galvanized Sheets - Continental Steel & Tube Company. Determine whether the articles (items) in the lot are single or multi-specimen articles based on the size of the articles. Th en the steel is cooled For one-side or differential coating, please inquire. The chart shows that steel with an initial coating thickness of 85µm in a C4 corrosivity zone will have an expected life to first maintenance of 20 – 40 years. This average value shall be not less than one coating thickness grade lower than the value listed in the appropriate specification. When it comes to the specification of hot dip galvanizing, most contractors know that to be standards compliant, 7mm steel requires an average coating thickness of ‘85 microns’. Photos 3, 4 and 5 depict the different material categories present in each of the three pole sections. The selection of articles (items) to be measured and the surfaces to be measured can be very complex, requiring careful analysis of the size and type of materials used in the fabrication. Multi specimen, multi component. The Galvanized Sheet Gauge is based on the U.S. Standard Gauge. Hot-dip galvanization is a form of galvanization.It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 449 °C (840 °F). Cling film comes in at 10-12 microns thick and a typical bacterium is 1-10 microns long. FIGURE 1 – COATING DESIGNATION 70G50GE *SST = Single Spot Test as defined by ASTM A879. The magnetic thickness measurements are also non-destructive and can be used to take many readings on many articles very quickly. We updated our privacy and cookie policy to improve the functionality of this website. Questions Average the readings for each material category/coating grade in the specimens and for the entire sample (average of the averages) to determine compliance. Following is an example of dividing a structure, determining the material categories present and surfaces to be measured, and establishing the acceptance criteria. In addition to steel thickness, the composition of the steel alloy itself is also relevant. Measured in the lot being galvanized, divide each article to one of the articles lower than the galvanized steel coating thickness chart! 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