ASTM D7091 PDF

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ASTM D A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. Scope 1. It includes de? It describes the methods and recommended frequency for verifying the accuracy of gages and for adjusting optimizing the equipment, describes a frequency for measuring the thickness of the coating s and lists the reporting recommendations.

Provisions for measuring on soft or tacky coatings are described in 5. The user should consult the manufacturers instructions regarding the use of coating thickness gages on these types of coatings.

This measured distance is displayed as coating thickness by the gages. Accordingly, these gages cannot distinguish the thickness of individual layers after they have all been applied. The thickness of each layer must be measured after it is applied. Even then, the thickness of the measured layer is the cumulative thickness of that layer and all layers beneath it, down to the base metal.

This practice does not address the use of ultrasonic coating thickness gages. Test Method D should be referenced for this application. As a result, obtaining single-point measurements may not accurately represent the actual coating system thickness. The governing speci?

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. Referenced Documents 2. Current edition approved Aug. Published September Terminology 3. Accuracy statements provide the performance capability across the full functional measurement range of the gage. Accuracy statements frequently include a? For small test panels, it is commonly the average of three spot measurements on each test face one from the top third, one from the middle third and one from the bottom third.

Noncompensation for the base metal effect can result in an overstatement of the true thickness of the coating. The base metal reading is measured, recorded and deducted from the thickness of each coat, in order to correctly state the thickness of the coating over the surface roughness. References should include notations stating the accuracy of the standard. Reference Standards may be coated or plated metal plates, or may be shims with samples of substrate material.

Subject to agreement between the buyer and the seller, a piece of coated substrate may also be used as a project-speci? Traceability may not be required for reference standards used on a day-to-day basis. However, the reference standard should contain the stated value and the degree of accuracy. NOTE 1—This practice addresses only metal substrates. Principles, Advantages, and Limitations of Gages 5. The magnetic force of attraction to the steel substrate beneath the coating is opposed by a spring or coil.

The gage must be placed directly on the coated surface to obtain a measurement. The force holding the permanent magnet to the ferrous base is inversely proportional to the thickness of the coating layer s between the magnet and the ferrous substrate.

For example, a thin coating applied to a ferrous substrate will require greater spring tension to pull the magnet off than will a thicker coating, since the magnet is closer to the ferrous substrate with the thinner coating. This inverse relationship is re? Most Type 1 magnetic pull-off gages do not require a power source for example, batteries.

The manually operated gages may be susceptible to human error caused by inadvertently turning the dial wheel past the point at which the magnet pulls from the surface, yielding a false low measurement.

Type 1 gages should not be used on soft or tacky coatings, as the magnet may adhere to the coating causing false low measurements, or coating materials may dry on the magnet causing false high measurements. The exposed magnet may attract metal? Type 1 gages cannot be used to measure the thickness of coatings applied to non-ferrous metal substrates.

Use of the gage outside of this range may generate false coating thickness measurements and may damage the instrument. The gage probe must be placed directly in a perpendicular position on the coated surface to obtain a measurement. For gages measuring on ferrous substrates, the magnetic induction or Hall-effect principles determine the effect on the magnetic? For gages measuring on non-ferrous metals, the gage probe is energized by alternating current that induces eddy currents in the metal substrate.

The force necessary to pull the magnet from the surface is measured and interpreted as the coating thickness value on a scale or display on the gage. Less force is required to remove the magnet from a thick coating. The scale is nonlinear. Additionally, most manufacturers of high performance coatings will warranty coating systems based upon, in part, achieving the proper thickness of each layer and the total coating system. Even if a project speci? Equipment manufacturers produce non-destructive coating thickness testing gages that are used to measure the cumulative thickness of the coating layers, after they are dry.

The manufacturers provide information for the adjustment and use of these gages, normally in the form of operating instructions. The user of this equipment must be knowledgeable in the proper operation of these devices, including methods for verifying the accuracy of the equipment prior to, during and after use as well as measurement procedures.

The thickness of the coating is displayed digitally. In general, access to tight areas is easier with Type 2 gages, especially those equipped with separate or remote probes. Gage operation should be veri? If necessary, the gage should be adjusted as described in 7. Type 2 gages may be sensitive to some degree to substrate effects including, but not limited to edges, corners and holes in the substrate, as well as substrate thickness, curvature or conductivity, or both.

In general, the user should remain a minimum of 25 mm 1 in. Use of the gage or the probe outside of this range may generate false coating thickness measurements and may damage the instrument. Test Specimen 6. NOTE 3—Coatings should be applied in accordance with Practices D or as agreed upon between the contracting parties. NOTE 4—Test panels may be fabricated from thin gage materials and special consideration for calibration adjustment may be required.

There is no standard time interval for re-calibration, nor is one absolutely required, but a calibration interval can be established based on experience and the work environment. A one-year calibration interval is a typical frequency suggested by many gage manufacturers. The type of reference standard used to verify gage accuracy should be predicated upon the type that provides the best and most appropriate method of veri?

Type 1 and Type 2 gages can be veri? The gage should be veri? Also, the probe should be examined for cleanliness before verifying the accuracy and before obtaining coating thickness measurements. Type 1 coating thickness gages should never be adjusted by the user.

A Certi? If the average thickness measured on a ? The minimum value of ? Otherwise the reliability of the gage is suspect. If the user elects to use shims to verify the accuracy of Type 1 gages, the shim s representing the intended range of use should be placed onto a smooth steel surface zero plate , and a measurement taken.

See 7. The BMR is the effect of substrate roughness on a coating thickness gage. The user obtains a minimum of ten 10 readings on the prepared, uncoated substrate. The arithmetic mean of these values becomes the Base Metal Reading.

The BMR is deducted from the coating thickness values, in order to report the thickness of the coating layer s over the surface pro? See Appendix X1 for more information. Most Type 2 gages can be adjusted using either a one-point or a two-point procedure.

It is recommended that the gage be veri? It is recommended that the gage 5 be veri? The BMR is the effect of substrate roughness on a coating thickness-measuring gage. The shim s representing the intended range of use should be placed onto the prepared, uncoated surface, and a measurement taken.

Frequency for Measurement of Coating Thickness 8. The number of areas to measure is dependent on the size of the structure or part. The following general guidance is provided for measuring coating thickness on larger surfaces. If thickness measurements outside of the speci? For example, the thickness may need to be measured in each 9 m2 ft2 area in accordance with 8. Example: for a structure comprised of m2 25 ft2 , a total of 27 — 9 m2 ft2 areas should be measured. Report 9. Keywords Shim stock typically has an inherent curve.

Various techniques exist to minimize this effect, such as mounting the shim in a holder that maintains tension on the shim to eliminate the tendency of the shim to curve. Special tensioned ring shims are also available.

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ASTM D7091-13

Active view current version of standard. Other Historical Standards. Work Item s - proposed revisions of this standard. More D This practice is intended to supplement the manufacturers' instructions for the manual operation of the gages and is not intended to replace them. It includes definitions of key terms, reference documents, the significance and use of the practice, the advantages and limitations of coating thickness gages, and a description of test specimens.

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ASTM D7091

ASTM D A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. Scope 1. It includes de? It describes the methods and recommended frequency for verifying the accuracy of gages and for adjusting optimizing the equipment, describes a frequency for measuring the thickness of the coating s and lists the reporting recommendations.

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Active view current version of standard. Other Historical Standards. Work Item s - proposed revisions of this standard. More D

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Thank you for interesting in our services. We are a non-profit group that run this website to share documents. We need your help to maintenance this website. Please help us to share our service with your friends. Share Embed Donate. A number in parentheses indicates the year of last reapproval.

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