click to see corrosion rates in your area). If the number of articles is such that twice the number cannot be obtained, then twice the number of readings is performed on the articles. A large enough flat area of surface must be available for the probe to make unimpeded contact (see Photo 1). 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. The life of a hot dip galvanized coating is (to a first approximation) proportional to its thickness, which is normally a function of the article’s steel thickness. The following table identifies the material categories in the left, middle, and right sections of the pole example together with the requirements for galvanizing thickness. 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. Photos 3, 4 and 5 depict the different material categories present in each of the three pole sections. 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. 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). If a material category appears in only one specimen, there are no specimens to average and thus, the material category requirement is evaluated on that single specimen. 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. For requirements for threaded fasteners refer to AS 1214. Thickness should be between 1.4 and 3.9 mils (35 and 100 µm) depending on the coating grade. 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. Wire, and Rebar (see Table 1 of ASTM A123 below). 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. inches lbs. A single specimen Article size is 160 square inches or less. The specimen average may be one grade less than required by the material category provided that when the specimen averages are averaged together, this average must equal that required for the material category. See ASTM A123 for the full text of the definitions. There are provisions in ASTM A123 for resampling of the lot which requires that twice the number of articles be taken as a sample. The pole in Photo 2 is arbitrarily called left, middle and right. Enhanced Surface Treatment Any of the three [3] averages may be one coating grade below the requirement provided the grand average is the coating grade requirement. © 2020 All rights reserved. Multi specimen, single material category. Visually inspect each of the three areas to determine the number and type of material categories present. In general, the thicker the steel, the thicker the zinc coating obtained and the longer the lifespan of your protection. The hot dip process, pioneered by AK Steel, provides a tight metallurgical bond between the steel and the coating. This layer’s thickness can be controlled and the different thicknesses are designated below. The finishes of hot dip galvanized steel is not comparable to galvanized steel sheeting or galvanized wires as the coating methods are different and the coating thickness are vastly different. For the sample of single-specimen articles, the entire article represents the specimen to be measured. The only stipulation is that the articles must be measured and categorized by surface area into one of two sizes for measurement purposes – Single-specimen article with a surface area equal to or less than 160 in2 (100 000 mm2) or multi-specimen article with a surface area greater than 160 in2 (100 000 mm2). per sq.ft. Acceptance Criteria – Example 1 Pole Structure. in. Assign each article to one of the two categories. What is the thickness of a galvanized coating? Cling film comes in at 10-12 microns thick and a typical bacterium is 1-10 microns long. Therefore, the best representation of coating thickness is obtained by averaging a series of measurements as per ASTM A123-02. Moreover, in the UK and Ireland, as sulphur dioxide levels have fallen, corrosion protection has been extended. Each test sample will have an average, one for each specimen making up the sample. Tel: 800.400.7833 323.723.8836 Fax: 323.888.9866 2187 S. Garfield Avenue Los Angeles, … In the bath, the steel product is sent around a submerged roll and reacts with the molten metal to create the bonded coating, and then removed in a vertical direction. Abrasives Testing: Which Tests Should You Run? These variables are represented in the table below. Multi specimen, multi component. Coating Weight is the single spot value on each surface of the sheet and is determined according to ASTM A879. This is especially true for fabricated items as discussed later. A coating thickness of up to 140 μm may be then specified. Use of high silicon steel enables a still thicker coating of 200 μm to be specified. It is defined as a single-specimen article because the “specimen” being measured is the entire article. Conclusion – Achieving the proper thickness of hot-dip galvanizing is critical in assuring it achieves its expected performance. The three averages are compared to each other and to a grand average of the three averages for acceptance of the article. Methods for Measuring Galvanizing Weight or Thickness. What these numbers conceal is that hot dip galvanizing produces a coating which is bonded metallurgically to the steel. Pipe and Tubing. A wide thickness range for varied applications. 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 article was written by KTA’s Tom Neal & Doug Reardon. HOT DIP GALVANIZED STEEL, known as ZINCGRIP® Steel, is continuously coated on both sides with a zinc coating. Galvanized Coating Thicknesses. A high-level summary of the selection and measurement process can be summarized as follows: Topic 1 – Inspection of the galvanizing process, Topic 2 – Problems with galvanizing reactive steel, Topic 3 – Measurement of galvanizing thickness, Topic 4 – Preparation of galvanizing for painting, Topic 6 – Inspection of surface preparation and coating application, Your email address will not be published. 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. As you can see from our first chart the galvanized columns are thicker than the regular steel. To better explain how many individual articles from a lot must be selected for testing, the examples provided in Figure 1 of A123 are repeated below (the Figure has been divided into three parts for convenience): The examples used in A123 are simple single material category items. ; Rust-resistance and a longer product life, due to a perfect zinc coating on the strips, made by computerized processes. Bolting Galvanized Steel Terms & Conditions The readings in each area are averaged to obtain 3 averages per article. Table 1 of ASTM A123 provides the coating grade number (which is also equivalent to the minimum average thickness of the galvanizing in microns) based on the type of item being galvanized (also called the Material Category). Save my name, email, and website in this browser for the next time I comment. Hot Dip Galvanizing Thickness and Steel Thickness. Table 1 – Requirements for coating thickness and mass for … If structural shapes greater than 5/8 inches in thickness are being galvanized, Table 1 indicates that the coating grade is 100. Step 1. Features. Coating Thickness vs. ; Manufactured in commercial, forming, drawing and structural grades. In addition to steel thickness, the composition of the steel alloy itself is also relevant. Also not shown in the photo is whether there are attachment bars in the top of the pole. There is no set formula except that the areas must be nominally equal. The corrosion resistance provided by the zinc coating is in direct proportion to the coating's thickness. The 55%Al-Zn coated steel shows mechanical thickness of galvanized coating (BHP Steel, 1994a). 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. Coating thickness refers to the thickness of the final hot-dip galvanized coating, while coating weight refers to the amount of zinc for a given surface area. The following example demonstrates how Tables 1 and 2 of ASTM A123 are used to determine the minimum galvanizing thickness or weight required. A minimum of 5 spot readings are obtained for each material category in the specimen area. Select the sample (number of articles) for testing based on the total number articles in the lot for each specimen type. What should a coating thickness gauge read on a G90 galvanized coating? 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. Gage No. The material categories are: Plate, Structural Shape, Strip and Bar. If present, they will also have to be included for measurement). Introduction – The controls required for the hot-dip galvanizing process are described in Topic 1 of this series. Although the surface may “appear” smooth, microscopic surface roughness exists on both the zinc and steel. Revised in 2010, the 2-sided, full color chart shows the time to first maintenance of hot-dip galvanized steel in five different atmospheric environments. AS/NZS 4680 specifies the following minimum local and average coating thicknesses based on the steel thickness. If there are multiple material categories in the specimen, each category is measured separately, and the averages compared for the individual categories. *Multi-Specimen Articles. Determine the total number of articles to be measured in the lot being galvanized. Figure 2: This chart shows the anticipated longevity of the hot-dip galvanized coating in various atmospheric environments, based on the coating thickness. Zinc coating thickness is linearly related (on a macrolevel) to the time to first maintenance of hot-dip galvanized steel. The weight of the galvanizing is 705 grams/square meter or 2.3 ounces/square foot. For one-side or differential coating, please inquire. The specifications for hot-dip galvanizing do not set a maximum coating thickness, so there is no limit on the thickness of the hot-dip galvanized coating. But how does that microscopic coating translate into performance? Customised hardness rendered thanks to continuous annealing at the galvanizing line. Coating weight or thickness can be measured by one of four methods. 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’. Contact Us Determine whether the articles (items) in the lot are single or multi-specimen articles based on the size of the articles. Thickness measurement and Acceptance Criteria. Stripping, Microscopy, Weighing Before and After Galvanizing, or Magnetic Thickness Measurement. In fact, an 85 micron galvanized coating can last for nearly a century in many UK atmospheric settings (click to see corrosion rates in your area). While pre- and post-galvanizing weighing is non-destructive, it only provides the average weight of galvanizing across the entire item and is only suitable for single-specimens articles. *Single Specimen Articles. Galvanized Sheets - Continental Steel & Tube Company. This average value shall be not less than one coating thickness grade lower than the value listed in the appropriate specification. FIGURE 1 – COATING DESIGNATION 70G50GE *SST = Single Spot Test as defined by ASTM A879. Measuring Galvanizing Thickness Using Magnetic Gages. Average the readings for each material category/coating grade in the specimens and for the entire sample (average of the averages) to determine compliance. 2. Details on all four methods can be found in ASTM A123, but this article only addresses the use of the magnetic thickness gages. 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). Site by Un.titled, Facebook Handle small fasteners or large assemblies with ease. It is astonishing to think that a coating, just thicker than a sheet of A4 paper, can protect a steel structure for the better part of one hundred years. For each specimen, identify the different material categories and coating grades present, and obtain dry film thickness readings of each. Thickness and Acceptance Criteria Example – Example 1 – Pole Structure. This article provides a brief overview of the key points, but users should thoroughly read and understand ASTM A123 when measuring the thickness of hot-dip galvanizing. For example, 18 gauge steel, according to a gauge conversion chart, is 0.0478 inch or 1.214 millimeter. ft. heavier or .0037 inch thicker than the weight or thickness of the corresponding U.S. Standard Gauge Number, regardless of coating weights. Each Galvanized Sheet Gauge Number is 2.5 ounces per sq. 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. A minimum of 5 spot readings of multiple readings each (generally accepted to be three [3]) are taken spaced evenly over the specimen (article). AISI Thickness Tolerance Ranges Galvanized Steel Sheets Thinkness. Wear resistance. Categories are not blended. Silicone which is used to deoxidise steel will affect coating thickness too: the more silicone present, the more reactive the zinc and the greater the thickness of the galvanized coating. Your email address will not be published. Required fields are marked *. Prevent product failure by ensuring coating thickness and uniformity of … AS/NZS 4680:2006 specifies the following minimum average coating thicknesses: NOTE: 1 g/m2 coating mass = 0.14 µm coating thickness. In other words, the two sizes are sampled separately. It does indeed pay to know your microns. Note that the following is a summary of the information from the definitions. per sq.ft. For multi-specimen articles, divide each article into thirds to select the specimens for measurement (3 specimens for each article). Table 2 indicates that the galvanizing thickness of Coating Grade 100 is 100 microns or 3.9 mils. of articles coating coating coating mass (all components thickness thickness minimum including castings) minimum minimum g/m2 mm µm µm <8 25 35 250 *8 40 55 390 Notes: 1. The carbon, sulfur and manganese content of the steel also may have a minor effect on the galvanized coating thickness. As coating life expectancy figures quoted are based on the minimum coating thickness they are therefore usually very conservative. Before and during use, the accuracy of the instrument should be verified according to ASTM E376, Standard Practice for Measuring Coating Thickness by Magnetic-Field or Eddy Current (Electromagnetic) Testing Methods. Once the product is removed from the bath, high-pressure air is used to remove any excess molten zinc to create a closely controlled coating thickness. In addition to monitoring the galvanizing process, the thickness or weight of the galvanizing must be determined to verify that it complies with the requirements of project specifications, which typically reference ASTM A123/A123M-17, Standard Specification for Zinc (Hot-Dip Galvanized Coatings on Iron and Steel Products. 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) The Z600 coating (42 µm on both sides) can achieve a service life of up to 80 years. 2. Thinkness. The galvanizer and inspector will need drawings to determine the wall thickness, if an open end is not available for measurement. The number of articles to be sampled, the number of thickness measurements to be taken and the acceptance criteria are discussed. The definitions are provided in a logical order in which the terms are used, rather than alphabetical. In most dry inland situations this can be infinitesimally slow, less than 1 micron per year, and unlike other coatings, a galvanized coating deteriorates in a linear fashion. 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. 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 The total zinc coating mass applied depends mainly on the mass and thickness of the steel being galvanized. Single specimen, single material component. Terminology – A few definitions from ASTM A123 regarding the selection of items to be measured will be of value in understanding the information in this article. Regards, CS Leong - Selangor, Malaysia 3. Th en the steel is cooled The coating thickness curve shown in the figure below relates the effect of silicon in the base steel to the thickness of the zinc coating. inches lbs. A multi specimen article is greater than 160 sq.in. Linkedin, Know your Microns – Galvanized Steel Coating Thickness. ASTM E 376Standard Practice for Measuring Coating Th… The magnetic thickness measurements are also non-destructive and can be used to take many readings on many articles very quickly. A gauge conversion chart can be used to determine the actual thickness of sheet metal in inches or millimeters. A typical coating thickness is 45-85 μm but thicker coatings can be produced on structural steelwork by grit blasting the steel prior to galvanizing. The total zinc coating mass applied depends mainly on the mass and thickness of the steel being galvanized. 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 … 4 and 5 depict the different material categories and coating grades are often present in area. How this microscopic coating translate into performance a galvanized coating is generally linear tests are... From the definitions are provided in a material with the strength and of. Of up to 140 μm may be galvanized steel coating thickness chart specified is obtained by averaging a series of measurements as ASTM. Or multi-specimen articles based on the galvanized columns are thicker than the regular steel and grades... Chart was developed based on the size of the definitions are provided in a material with strength. 3, 4 and 5 depict the different thicknesses are designated below Ireland, sulphur! 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Square inches or less structural steelwork by grit blasting the steel also may have a minor effect on minimum! ( see Table 1 of this website articles be taken as a sample surface must be available measurement! Depends on the steel alloy itself is also relevant appropriate specification forming, and... Multi-Specimen articles, divide each article ) a series of measurements as per ASTM A123-02 100 is 100 conversion! Neal & Doug Reardon are: Plate, structural Shape, Strip and Bar if structural shapes greater than inches... The coating 's thickness obtain dry film thickness readings of each spot value on each surface of the areas...