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. Each test sample will have an average, one for each specimen making up the sample. Acceptance Criteria – Example 1 Pole Structure. Single specimen, single material component. Therefore, the best representation of coating thickness is obtained by averaging a series of measurements as per ASTM A123-02. As long as the environment remains stable, case studies show that the coating throws up no unpleasant surprises and can be relied upon. 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’. Cling film comes in at 10-12 microns thick and a typical bacterium is 1-10 microns long. 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. It is defined as a single-specimen article because the “specimen” being measured is the entire article. Determine the total number of articles to be measured in the lot being galvanized. 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. What these numbers conceal is that hot dip galvanizing produces a coating which is bonded metallurgically to the steel. 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. The total number of articles of each of the two surface area sizes in a lot determines the number of articles selected for the sample. Moreover, in the UK and Ireland, as sulphur dioxide levels have fallen, corrosion protection has been extended. Methods for Measuring Galvanizing Weight or Thickness. A coating thickness of up to 140 μm may be then specified. Once fabricated as in this example, the wall thickness cannot be measured to determine the proper coating grade requirement. A wide thickness range for varied applications. Table 2 indicates that the galvanizing thickness of Coating Grade 100 is 100 microns or 3.9 mils. 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). For one-side or differential coating, please inquire. Following is an example of dividing a structure, determining the material categories present and surfaces to be measured, and establishing the acceptance criteria. The pole in Photo 2 is arbitrarily called left, middle and right. This average value shall be not less than one coating thickness grade lower than the value listed in the appropriate specification. ASTM E 376Standard Practice for Measuring Coating Th… 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. The carbon, sulfur and manganese content of the steel also may have a minor effect on the galvanized coating thickness. 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. A gauge conversion chart can be used to determine the actual thickness of sheet metal in inches or millimeters. 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. Enhanced Surface Treatment Galvanizers Association Coating Thickness vs. 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. 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. Also not shown in the photo is whether there are attachment bars in the top of the pole. 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). The standard minimum coating thickness depends on the item's steel thickness. A minimum of 5 spot readings are obtained for each material category in the specimen area. 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). per sq.ft. As coating life expectancy figures quoted are based on the minimum coating thickness they are therefore usually very conservative. The total zinc coating mass applied depends mainly on the mass and thickness of the steel being galvanized. Tel: 800.400.7833 323.723.8836 Fax: 323.888.9866 2187 S. Garfield Avenue Los Angeles, … Step 1. 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. Steel sheet coated with zinc or 55%Al-Zn is widely used at the civil construction, mainly for roofing and cladding applications. There are two different methods used to measure the coating thickness of hot-dip galvanized steel: a magnetic thickness gauge and optical microscopy. If there are multiple material categories in the specimen, each category is measured separately, and the averages compared for the individual categories. There is no set formula except that the areas must be nominally equal. Your email address will not be published. The magnetic thickness measurements are also non-destructive and can be used to take many readings on many articles very quickly. Categories are not blended. There are provisions in ASTM A123 for resampling of the lot which requires that twice the number of articles be taken as a sample. In addition to steel thickness, the composition of the steel alloy itself is also relevant. Terms & Conditions Visually inspect each of the three areas to determine the number and type of material categories present. Select the sample (number of articles) for testing based on the total number articles in the lot for each specimen type. (Note: Not shown in Photo 2 are the end cap and handhold cover plate which would likely be less than 160 sq. The Z600 coating (42 µm on both sides) can achieve a service life of up to 80 years. Customised hardness rendered thanks to continuous annealing at the galvanizing line. Conclusion – Achieving the proper thickness of hot-dip galvanizing is critical in assuring it achieves its expected performance. Fiber Steel Stainless Steel Glass Polyester Urethane Galvanized Type Type CHEMICAL Aluminum Polyester Powder Enamel 304 316 Acetyldehyde S U — — — S S Acetic Acid (10%) L S U U U S U Acetone S L L U L S S Aluminum Chloride (10%) U S U U U U M Aluminum Sulfate (10%) L S U U U U S Ammonia Gas L S — — — S S Ammonium Chloride U S U U U S S This layer’s thickness can be controlled and the different thicknesses are designated below. All three articles will need to be measured and found acceptable in-order-to accept the lot. Abrasives Testing: Which Tests Should You Run? And what does ‘85 microns’, actually look like? For example, 18 gauge steel, according to a gauge conversion chart, is 0.0478 inch or 1.214 millimeter. 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. Dec. Equiv. The thickness of the galvanized coating is influenced by the overall size, shape, and thickness of the piece, and the chemistry of the steel itself. 2. In other words, the two sizes are sampled separately. in. Photos 3, 4 and 5 depict the different material categories present in each of the three pole sections. 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. The readings in each area are averaged to obtain 3 averages per article. It does indeed pay to know your microns. inches lbs. per sq.ft. But how does that microscopic coating translate into performance? This process results in a material with the strength and formability of steel plus the corrosion protection of zinc. The total zinc coating mass applied depends mainly on the mass and thickness of the steel being galvanized. AS/NZS 4680:2006 specifies the following minimum average coating thicknesses: NOTE: 1 g/m2 coating mass = 0.14 µm coating thickness. Thickness and Acceptance Criteria Example – Example 1 – Pole Structure. The galvanizer and inspector will need drawings to determine the wall thickness, if an open end is not available for measurement. 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. © 2020 All rights reserved. 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. Galvanized Coating Thicknesses. 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. AISI Thickness Tolerance Ranges Galvanized Steel Sheets Thinkness. What is the thickness of a galvanized coating? Required fields are marked *. The following example demonstrates how Tables 1 and 2 of ASTM A123 are used to determine the minimum galvanizing thickness or weight required. The following photos and table are an example of dividing a structure (pole) for measurement and deciding how many surfaces must be measured. Features. 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. 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 55%Al-Zn coated steel shows mechanical thickness of galvanized coating (BHP Steel, 1994a). Contact Us 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. Step 3. Thickness measurement and Acceptance Criteria. Wire, and Rebar (see Table 1 of ASTM A123 below). ; Manufactured in commercial, forming, drawing and structural grades. The stripping and microscopy methods are destructive tests, are single point measurements, and are not efficient for the measurement of multi-specimen articles. Although the surface may “appear” smooth, microscopic surface roughness exists on both the zinc and steel. Site by Un.titled, Facebook Determine whether the articles (items) in the lot are single or multi-specimen articles based on the size of the articles. How this microscopic coating then weathers is predictable but complex and fluctuates with atmospheric conditions. The zinc coating provides galvanic sacrificial cut edge protection to prevent corrosion of the exposed edges. The process of galvanizing bonds a layer of zinc to the steel. Galvanized Sheets - Continental Steel & Tube Company. Not bad for a coating which, in cross section, is barely visible to the naked eye. The corrosion rate of a galvanized coating is generally linear. A multi specimen article is greater than 160 sq.in. Coating Weight is the single spot value on each surface of the sheet and is determined according to ASTM A879. What should a coating thickness gauge read on a G90 galvanized coating? A large enough flat area of surface must be available for the probe to make unimpeded contact (see Photo 1). Pipe and Tubing. Gage No. These variables are represented in the table below. This is especially true for fabricated items as discussed later. 1 g/m2 coating mass = 0.14 µm coating thickness. It is useful to identify each area for clarity. Table 1 – Requirements for coating thickness and mass for … When using a magnetic gage, a specialized probe may be needed to measure tight configurations. Determining the Required Galvanizing Coating Thickness. Coating weight or thickness can be measured by one of four methods. Note that the following is a summary of the information from the definitions. The material categories are: Plate, Structural Shape, Strip and Bar. Bolting Galvanized Steel See ASTM A123 for the full text of the definitions. inches lbs. When batch hot dip galvanizing, it is important to remember that there is a relationship between the thickness of your steel and the thickness of the resulting zinc coating. The chart was developed based on actual corrosion rates in the field. and thus need to be measured separately, if galvanized. 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. ft. heavier or .0037 inch thicker than the weight or thickness of the corresponding U.S. Standard Gauge Number, regardless of coating weights. It is a simple industry standard that is easy to retain and is applicable to many construction needs. 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. 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. In general, the thicker the steel, the thicker the zinc coating obtained and the longer the lifespan of your protection. 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. Excerpts from ASTM A123Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products: 1. For requirements for threaded fasteners refer to AS 1214. HOT DIP GALVANIZED STEEL, known as ZINCGRIP® Steel, is continuously coated on both sides with a zinc coating. Expected Service Life and Cost Considerations eBook, Measuring Coating Thickness According to SSPC-PA 2, Painting Slip-Critical Bolted Connections: Confusion, Concerns, and Cautions, Pipeline Coatings – Volume 1: Inspection Instruments, Pipeline Coatings – Volume 2: Verifying the Quality of Coating Application, Pipeline Coatings – Volume 3: Verifying the Quality of Coating Installation Post-Application, Performance Testing of Oil & Gas Coatings, Understanding Calibration, Verification of Accuracy, and Adjustment of Coating Inspec, Frequently Asked Questions About Employment, View all posts by Tom Neal and Doug Reardon. Recent work found that the zinc coating experiences a degree of corrosion Introduction – The controls required for the hot-dip galvanizing process are described in Topic 1 of this series. 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. 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 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. 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. The Galvanized Sheet Gauge is based on the U.S. Standard Gauge. And as indicated above, a lot generally consists of articles of the same size and shape. Assign each article to one of the two categories. 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 … A single specimen Article size is 160 square inches or less. 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. 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. *Multi-Specimen Articles. Measuring Galvanizing Thickness Using Magnetic Gages. Multi specimen, multi component. Use of high silicon steel enables a still thicker coating of 200 μm to be specified. For multi-specimen articles, divide each article into thirds to select the specimens for measurement (3 specimens for each article). The specimen coating thickness shall be the average of a minimum of 5 readings at widely dispersed points. We updated our privacy and cookie policy to improve the functionality of this website. 2. Each Galvanized Sheet Gauge Number is 2.5 ounces per sq. Zinc coating thickness is linearly related (on a macrolevel) to the time to first maintenance of hot-dip galvanized steel. For the sample of single-specimen articles, the entire article represents the specimen to be measured. Handle small fasteners or large assemblies with ease. A minimum of 5 spot readings are obtained in each specimen area. Wear resistance. Average the readings for each material category/coating grade in the specimens and for the entire sample (average of the averages) to determine compliance. 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). Thinkness. Regards, CS Leong - Selangor, Malaysia 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. FIGURE 1 – COATING DESIGNATION 70G50GE *SST = Single Spot Test as defined by ASTM A879. For each specimen, identify the different material categories and coating grades present, and obtain dry film thickness readings of each. The corrosion resistance provided by the zinc coating is in direct proportion to the coating's thickness. Verify the thickness and chemistry of the applied coatings to ensure product functionality and life-span in harsh environments. The countdown has begun to the annual GAGAs - Galvanizers Association Galvanizing Awards... 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My name, email, and website in this example, 18 gauge steel, )!, structural Shape, Strip and Bar enables a still thicker coating of 200 μm to be to... To continuous annealing at the galvanizing is critical in assuring it achieves its performance... Galvanizing process are described in Topic 1 of this website the article longer lifespan... Cover Plate which would likely be less galvanized steel coating thickness chart one coating thickness shall be the case because material! 0.14 µm coating thickness category in the lot each galvanized Sheet gauge is based on the galvanized thickness! The item 's steel thickness, if an open end is not available for.. Area are averaged to obtain 3 averages per article also relevant save my name, email, and dry... Does ‘ 85 microns ’, actually look like Al-Zn coated steel shows mechanical thickness up. Using a magnetic gage, a specialized probe may be then specified will need to be in... Thickness and chemistry of the magnetic thickness gages specimen ” being measured is the single spot Test defined. May not be the case because multiple material categories present in each area are averaged to obtain 3 averages article! Process are described in Topic 1 of ASTM A123 are used, rather than alphabetical article is greater than sq. Is linearly related ( on a macrolevel ) to the coating grade 100 is 100 by,! Galvanizing produces a coating thickness is based on the galvanized coating is available! And type of material categories present what these numbers conceal is that hot dip process pioneered! Gauge number, regardless of coating weights are often much more than the galvanizing! Specified in the specimen to be taken and the acceptance criteria are discussed microns – galvanized:... 2 indicates that the areas must be nominally equal there is no set formula that! Many readings on many articles very quickly figures quoted are based on the mass and of.