A tool known as an ultrasonic thickness (UT) gauge can be utilized to determine the thickness of various solid materials, including metal. In the field of maritime heritage conservation, this device plays a crucial role in assessing the remaining thickness of iron and ship hull structures and plating.
Operating by emitting short pulses of high-frequency sound waves, the UT gauge measures the time taken for these waves to travel through the material, reflect off the back wall, and return. By understanding the speed of sound in the material being tested, the gauge can calculate the thickness of the material accurately.
Fig 1: Displaying the Cygnus DIVE II underwater ultrasonic thickness gauge
There are several advantages to using this method:
- It does not damage the material
- Provides a direct measurement of thickness
- Delivers instantaneous results
- Requires minimal processing and expertise
- Access to only one side of the material is necessary
- Minimal preparation is required
- The method is safe and portable
Disadvantages include the need to clean metal surfaces with concretion, ensuring tight probe coupling, difficulty in measuring rough or thin materials, and the challenge of inspecting coarse-grained materials.
The Corrosion of Iron and Steel
When iron and steel corrode in seawater, a concretion layer forms on the metal surface. This layer slows down the decay process by limiting the amount of oxygen reaching the metal. Once this concretion layer is removed, it can lead to increased localized corrosion. Over time, the metal may corrode, leaving behind a weak residue that could collapse under pressure.
Fig 2: Demonstrating the use of the UT gauge underwater
Fig 3: Showing the use of the UT gauge on a foreshore wreck
The Cygnus DIVE II Ultrasonic Thickness Gauge
The A7 Project, investigating the HM submarine A7, conducted ultrasonic hull thickness measurements using the DIVE Mk2 underwater ultrasonic digital thickness gauge by Cygnus Instruments Ltd. This gauge is user-friendly, operates automatically, and can store measurement data for further analysis.
Furthermore, a software upgrade allows for data storage, display, report generation, and exporting to spreadsheets after uploading the data.
Calibration and Maintenance
Regular calibration of the UT gauge is essential to ensure accurate measurements. Calibration should be performed using reference standards to verify the gauge’s accuracy. In addition, routine maintenance of the UT equipment is important to keep it in optimal working condition.
Data Analysis
After collecting measurements, data analysis is necessary to interpret the results. Utilizing specialized software, such as Cygnus CygLink, allows for in-depth analysis of thickness measurements and identification of any anomalies or inconsistencies in the data.
Training and Certification
Proper training in UT measurement techniques is crucial for obtaining reliable results. Operators should be well-trained in equipment operation, measurement procedures, and data analysis. Certification in UT measurement ensures that operators have the necessary skills and knowledge to conduct accurate measurements.
Fig 7: Demonstration of proper UT gauge calibration
Conclusion
Conducting UT measurements on heritage metal surfaces requires careful preparation, proper equipment, and thorough data analysis. By following the established procedure, using appropriate probe types, and ensuring accurate calibration, reliable thickness measurements can be obtained to assess the condition of heritage structures effectively.
Recommendations
- Utilize the Cygnus DIVE Mk. 2 gauge for underwater cultural heritage work
- Remove all concretion before conducting UT measurements
- The hammer and chisel method is effective for concretion removal
- Use a single crystal probe for good to average quality metal
- Use a twin crystal probe for average to poor quality metal
- Take a minimum of three repeat measurements per sample point
- Take advantage of the logging feature of the Cygnus DIVE and review measurement plots during post-processing
- Calculate the variation in measurements at each sample point and incorporate the value in calculations for changes in thickness over time or across a site
- Choose Milliput epoxy for fixing concretion holes
[1] For in-depth knowledge of iron corrosion, refer to Pearson, 1987, Conservation of Marine Archaeological Objects, p212
When selecting the type and shape of metal required for a project, it is crucial to determine the gauge of the metal. The gauge of a metal indicates its thickness, which in turn affects its strength. Understanding how to gauge the thickness of steel or sheet metal is essential for meeting the structural and functional requirements of a project.
Consider the following factors when determining the metal gauge:
- Sheet gauges range from .010” to .170” (or 7 gauge)
- Plate thickness can start from .188” and higher
- Sheet gauges are typically sold by gauge or decimal equivalent, necessitating the use of a caliper or feeler gauge for thickness determination
In addition to calipers or feeler gauges, reference a sheet metal gauge chart for easy conversion between gauge numbers and corresponding thicknesses in inches or millimeters.
Select a Shape
A significant distinction between flat sheet and plate metal lies in the method of measuring thickness. Sheet metal, thinner in nature, uses a gauge system where smaller gauge numbers indicate thicker sheets, while larger gauge numbers indicate thinner sheets. Plate metal, thicker than gauged measures, is directly measured in thickness values like inches or millimeters.
Additionally, sheet metal is often used for various applications like roofing, car bodies, and ductwork due to its flexibility and ease of manipulation. Plate metal, on the other hand, is commonly utilized for heavy-duty applications such as construction projects, shipbuilding, and industrial machinery.
What Metal Gauge Do I Need?
If uncertain about the required metal gauge, consider the following solutions:
1. Use a Caliper
For accurate measurement of sheet metal or plate metal thickness, utilize a caliper. Calipers, designed for precise distance measurement, are reliable tools for determining thickness. Fit the caliper tips around the metal to gauge its thickness accurately.
Calipers are particularly useful for replacing existing metal, ensuring the new piece matches the previous thickness. Precision in thickness is crucial, as even minor deviations can impact material integrity and performance. Digital calipers offer enhanced accuracy with digital readouts, reducing the potential for human errors in measurements.
2. Use our Metal Reference Guide
A gauge chart simplifies understanding sheet metal thickness measurements by converting gauge numbers to equivalent thicknesses in inches or millimeters. Find a gauge chart in our Metal Reference Guide to streamline the measurement process.
3. Visit or Contact Us
Rely on us as your trusted solution for small-quantity metal needs. Unsure about the metal type, grade, or size required for a project? Let us assist in determining the ideal gauge for your specific application, ensuring project success and efficiency.
Contact Metal Supermarkets to learn more about measuring metal gauge and selecting the right gauge and material for your project.
Additional Tips:
– When measuring metal gauge, always ensure the caliper is clean and properly calibrated for accurate results.
– Refer to industry standards or consult with professionals to determine the appropriate metal gauge for specific applications.
– Consider the properties of the metal, such as strength and durability, when choosing the right gauge for your project.
– Keep in mind that thicker gauges are typically used for more heavy-duty applications, while thinner gauges are suitable for lighter projects.
– Regularly check and maintain your measuring tools to ensure consistent and precise measurements.
Remember that selecting the correct metal gauge is crucial for the success of your project, so take the time to measure accurately and choose wisely.
Metal Supermarkets
With 40 years of experience in the industry, Metal Supermarkets is the premier supplier of small-quantity metals, with over 130 physical stores across the US, Canada, and UK. We offer a wide range of metals, including mild steel, stainless steel, aluminum, and more.
We stock various shapes such as bars, tubes, sheets, and plates, and offer custom cutting services.
Traditional coatings are evaluated for dry film thickness and wet film thickness based on specific standards. In the case of thermal sprayed metal coatings, the method for measuring thickness varies in terms of single reading positions, number of readings, and measurement frequency.
When measuring the thickness of thermally sprayed metal coatings, it is important to consider the roughness of the surface. A surface profile gauge can be used in conjunction with the dry film thickness gauge to ensure accurate measurements. Additionally, it is recommended to calibrate the gauges regularly to maintain accuracy.
Calibration of a Dry Film Thickness Gauge
Calibrate the Type II electronic dry film gauge using a plastic sheet of standard thickness for precise measurements. Ensure the substrate surface is clean before and after each measurement to maintain accuracy.
It is recommended to perform regular calibration checks to ensure the accuracy of the dry film thickness gauge. This can be done by comparing the gauge readings with a known reference standard to verify its precision.
Additionally, storing the dry film thickness gauge in a clean and dry environment when not in use can help prolong its accuracy and longevity. Avoid storing it in areas with temperature fluctuations or high humidity levels.
Methods of Measurement
For every 100 to 200 square feet, conduct line and point measurements on the surface of the thermal spray coating:
- Point measurement – Determine thickness by selecting five points within a 1.6 square inch area and averaging the readings
- Line measurement – Recommended for flat surfaces, take five readings on a line, each 1 inch apart, and average the measurements for the line’s thickness
Choose A Reputable Company for Accurate Coding Thicknesses
The experts at A&A Coatings are well-versed in application methods, equipment, products, and measurement techniques. We are certified to work on government projects and ensure the highest quality service across industries.
We offer a variety of coatings for different industries to protect surfaces from abrasion and environmental damage. Contact us to learn more about thermal spray coatings and their benefits for your industry.
Conventional coatings are measured for dry film thickness and wet film thickness according to industry standards. Thermal sprayed metal coatings have a different method for measuring thickness, including readings, frequency, and the type of instrument used.
Thermal Spray Metal Coating Measurement Instrument
An electronic dry film thickness gauge is commonly used for measuring thermally sprayed metal coatings. While a Type 2 gauge is preferred, Type I can also be used for this purpose. However, due to accuracy and calibration issues, Type I is rarely utilized.
It is important to ensure that the dry film thickness gauge is regularly calibrated to maintain accuracy in measurement. Additionally, proper training on the use of the gauge is essential to obtain reliable and consistent results when measuring thermally sprayed metal coatings.
When measuring the thickness of thermally sprayed metal coatings, it is recommended to take multiple readings at different points to ensure an accurate average thickness measurement. This helps to account for any variations in the coating thickness across the surface.
Calibration of a Dry Film Thickness Gauge
Before taking any measurements, make sure to calibrate the Type II gauge using a standard plastic sheet. It is essential to clean the substrate surface thoroughly to guarantee accurate results.
Methods of Measurement
When measuring the thermal spray coating surface, conduct line and point measurements every 100 to 200 square feet:
- Point measurement – Select five points in a 1.6 square inch (10 square centimeter) area to measure coating thickness on complex component surfaces. The thickness is calculated by averaging the readings from these points.
- Line measurement – Take at least five measurement readings along a line, with each point spaced 1 inch (25 mm) apart, for flat component surfaces. The average of these readings provides the measured thickness.
Choose A Reputable Company for Accurate Coding Thicknesses
At A&A Coatings, our experts and technicians are knowledgeable in the latest application methods, equipment, coating products, and measuring specifications. We are certified to work with the United States Navy and the Department of Defense. Our quality system meets compliance with MIL-I-45208 and has been audited by top government agencies. This demonstrates our expertise, reliability, and ability to deliver high-quality service and products to any industry.
We offer coating solutions across various industries. To discover the advantages of thermal spray coatings for your company or how they can be utilized in your industry, get in touch with one of our experienced representatives. Remember, timely protection is crucial as abrasion and environmental factors can cause harm to your parts, components, machinery, and surfaces.