A blast-cleaned steel surface often exhibits random irregularities, making precise profile characterization difficult. Surface profile ranges are frequently specified, and the ideal profile varies based on the coating type. Replica tape has become a popular field method for measuring surface profiles.
What is Testex Press-O-Film Replica Tape?
Testex Press-O-Film Replica Tape is a specialized film composed of a compressible foam layer bonded to an incompressible polyester film. When pressed onto a surface, the foam conforms to the surface's contours, creating an accurate replica. Available in various grades to accommodate different surface roughness ranges, replica tape offers a non-destructive method for measuring surface profiles.
Conventional Testex Press-O-Film Tape Grades
Testex Press-O-Film replica tape is available in a variety of thickness ranges for measuring substrate roughness from 0.5 - 6 mils (12 - 150 µm).
|
Grade |
Range |
Measurement Tool |
|
Coarse Minus |
0.5 to 1.0 mils (12 to 25 µm) |
Testex Digital Micrometer Testex Analog Micrometer PosiTector RTR H |
|
Coarse |
0.8 to 2.0 mils (20 to 50 µm) |
|
|
X-Coarse |
1.5 to 4.5 mils (38 to 115 µm) |
|
|
X-Coarse Plus |
4.0 to 6.0 mils (100 to 150 µm) |
Optical Grade Testex Press-O-Film Tape Grades
Testex Press-O-Film Optical Grade replica tape, when used with PosiTector RTR 3D models, provides higher quality surface data files (.SDF) than conventional replica tape. Optical Grade Replica Tape is available in Coarse or X-Coarse.
|
Grade |
Range |
Measurement Tool |
|
Optical Grade Coarse |
0.8 to 2.5 mils (20 to 64 µm) |
PosiTector RTR 3D |
|
Optical Grade X-Coarse |
1.5 to 4.5 mils (38 to 115 µm) |
Legacy Testex Press-O-Film Tape Grades
All tape grades are available in the legacy roll format. Instructions and Standards will continue to support both methods and burnishing tools.
Why Measuring Surface Profile is Important?
Industrial steel structures, such as bridges, ships, and railcars, are typically coated to prevent corrosion. Before applying coatings, these metal surfaces must be cleaned and roughened to ensure proper adhesion. This is often achieved through abrasive blasting. The height of the surface profile significantly influences coating adhesion and corrosion resistance.
How Does Testex Press-O-Film Work?
1. Prepare
Use cleaning putty to remove dust, debris, or residual blast media from the measurement site by firmly pressing the putty onto the surface to be tested using your fingers and remove.
2. Burnish
Select the appropriate grade of replica tape, then Place the replica tape (Testex Tape) on the substrate and burnish; the compressible foam within the tape forms a reverse replica of the surface.
3. Measure
Insert the compressed replica tape between the PosiTector RTR's measurement anvils and take a reading. Ensure the tape is properly positioned so that the burnished region is centered in the anvils with the adhesive side down.
How Accurate is Testex Press-O-Film Replica Tape?
In 2024, a comprehensive study was performed to determine an accuracy statement for replica tape. That study determined the following accuracy and precision statements:
|
Replica Tape Grade |
Precision |
Accuracy |
|
Coarse |
±2 µm (± 0.1 mils) |
±8 µm (± 0.3 mils) |
|
X-Coarse |
±6 µm (± 0.2 mils) |
±8 µm (± 0.3 mils) |
|
X-Coarse Plus |
±8 µm (± 0.3 mils) |
±10 µm (± 0.4 mils) |
Advantages and Disadvantages of Replica Tape
Replica tape has been a reliable method for measuring surface profiles of abrasive-blasted steel since the late 1960s. Compared to other techniques, it offers several advantages:
- Ruggedness: Ideal for field conditions and harsh environments.
- Low startup cost: Relatively inexpensive compared to other methods.
- Good repeatability: Provides consistent results.
- Physical replica: Allows for visual inspection and analysis.
A significant advantage of replica tape is its ability to sample a larger area of the surface compared to point-probe methods, providing more robust statistical data. However, replica tape also has some limitations:
- Analog nature: Measurements are based on physical properties, which can introduce potential inaccuracies.
- Limited range: Each grade of tape is accurate within a specific range of surface profiles.
- Non-linearity: Measurements can be less accurate at the extremes of each grade's range due to compression effects in the replica foam.
To address these limitations, multiple grades of replica tape are typically used, including Coarse Minus, Coarse, X-Coarse, and X-Coarse Plus. This allows for accurate measurements across a wider range of surface profiles.