NACE - National Association of Corrosion Engineers Inspection Instruments and Tests Questions and Answers — Questions and Answers
Question 1: An inspector is required to measure the dry film thickness (DFT) of a coating system on a large, flat steel surface totaling 500 square meters (approx. 5,000 sq ft). According to SSPC-PA 2, how should the inspector determine the number of areas to measure?
- Measure three 10 m² areas for the first 100 m², and then one additional 10 m² area for each subsequent 100 m². (Correct answer)
- Take five spot measurements randomly across the entire 500 m² surface.
- Divide the surface into five equal sections and take one area measurement in each.
- Measure one 10 m² area for every 50 m² of the total surface area.
Correct answer: Measure three 10 m² areas for the first 100 m², and then one additional 10 m² area for each subsequent 100 m².
SSPC-PA 2 specifies a clear procedure for determining the number of measurements on large surfaces. For areas over 100 m² (approx. 1,000 ft²), the standard requires the inspector to measure three 10 m² (approx. 100 ft²) areas for the first 100 m², and then arbitrarily select and measure one additional 10 m² area for each additional 100 m² or increment thereof.
Question 2: Which of the following instruments is used to perform a quantitative pull-off adhesion test as described in ASTM D4541?
- A utility knife and pressure-sensitive tape
- A cross-hatch cutter and a dolly
- A portable adhesion tester with a loading fixture (dolly) (Correct answer)
- A Tooke gauge for measuring individual coat thickness
Correct answer: A portable adhesion tester with a loading fixture (dolly)
ASTM D4541, 'Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers', describes a quantitative method for measuring adhesion. This test involves affixing a loading fixture, often called a dolly, to the coating surface with an adhesive and then using a portable adhesion tester to apply a perpendicular force to pull the dolly off, measuring the force required for detachment.
Question 3: A coating inspector is preparing to conduct holiday testing on a new protective coating with a specified dry film thickness of 15 mils (381 microns) on a conductive substrate. Which type of holiday detector is most appropriate for this application?
- A high-voltage AC spark tester
- A low-voltage, wet-sponge holiday detector (Correct answer)
- A high-voltage, pulsed DC spark tester
- An ultrasonic thickness gauge
Correct answer: A low-voltage, wet-sponge holiday detector
NACE SP0188 provides guidance on holiday testing. For coatings less than 20 mils (500 microns) thick on conductive substrates, a low-voltage (typically 67.5V or 90V) wet-sponge holiday detector is the recommended instrument. High-voltage detectors are used for thicker coatings and can damage thinner films if the voltage is not set correctly or is too high.
Question 4: An inspector uses replica tape and a micrometer to measure the surface profile of an abrasive blast-cleaned steel surface, following the procedure in NACE SP0287. What is the primary purpose of this test?
- To determine the level of soluble salt contamination on the surface
- To measure the peak-to-valley depth of the surface anchor pattern (Correct answer)
- To assess the degree of non-visible surface cleanliness
- To quantify the adhesion of the primer coat to the steel
Correct answer: To measure the peak-to-valley depth of the surface anchor pattern
NACE SP0287, 'Field Measurement of Surface Profile of Abrasive Blast-Cleaned Steel Surfaces Using a Replica Tape', describes a method to quantify the surface roughness or anchor profile. The replica tape captures a reverse image of the surface profile, and a micrometer is then used to measure the thickness of the impression, which corresponds to the peak-to-valley height.
Question 5: During a coating application project, the specification requires adhesion testing according to ASTM D3359, Method A. This test is primarily intended for which of the following scenarios?
- Laboratory testing of thin-film coatings under 5 mils (125 µm)
- Field testing of coating systems greater than 5 mils (125 µm) in thickness (Correct answer)
- Determining the pull-off strength of a coating in psi or MPa
- Evaluating the adhesion of coatings on non-metallic substrates like concrete
Correct answer: Field testing of coating systems greater than 5 mils (125 µm) in thickness
ASTM D3359 describes two methods for tape adhesion testing. Method A, the X-cut test, is primarily intended for use at job sites and for coating systems with a total thickness greater than 5 mils (125 µm). Method B, the cross-hatch test, is more suitable for thinner coatings, typically under 5 mils.
Question 6: Which of the following methods would be used to retrieve a sample for assessing the concentration of soluble salts on a steel surface prior to coating?
- Taking a series of dry film thickness readings with a magnetic gauge
- Performing a pull-off adhesion test using a dolly and adhesive
- Using a Bresle patch or adhesive patch to extract surface contaminants (Correct answer)
- Conducting a cross-hatch adhesion test with pressure-sensitive tape
Correct answer: Using a Bresle patch or adhesive patch to extract surface contaminants
SSPC-Guide 15 and ISO 8502-6 describe methods for retrieving soluble salts from a surface for analysis. The Bresle patch method involves attaching an adhesive patch with a reservoir to the surface, injecting a specified amount of deionized water, massaging the water to dissolve the salts, and then extracting the solution for conductivity measurement.
