NACE - National Association of Corrosion Engineers Protective Coatings and Linings Questions and Answers — Questions and Answers
Question 1: According to the joint standard NACE No. 1 / SSPC-SP 5, what is the required condition of a steel surface after 'White Metal Blast Cleaning'?
- The surface must be free of all visible oil, grease, and dirt, but tightly adherent mill scale and rust may remain on up to 5% of the surface.
- The surface, when viewed without magnification, must be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, and other foreign matter. (Correct answer)
- The surface must be cleaned to a near-white metal condition, with no more than 33% of each square inch of surface area containing light shadows, streaks, or minor discolorations.
- The surface must be prepared using high-pressure water jetting to remove all contaminants, exposing the original blasted surface profile.
Correct answer: The surface, when viewed without magnification, must be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, and other foreign matter.
NACE No. 1 / SSPC-SP 5, 'White Metal Blast Cleaning,' is the highest grade of abrasive blast cleaning. It requires the complete removal of all visible contaminants from the steel surface when viewed without magnification. The other options describe different, less stringent surface preparation standards like Near-White (SSPC-SP 10), Commercial (SSPC-SP 6), or methods like water jetting (SSPC-SP 12).
Question 2: An inspector is measuring the dry film thickness (DFT) of a coating on a 500 sq ft steel tank section according to SSPC-PA 2. How are the spot and area measurements correctly performed?
- Take one gage reading per 100 sq ft area, and the average of all readings must meet the specification.
- Take one spot measurement (average of 3 readings) in the center of each 100 sq ft area; all spot measurements must be within specification.
- Take five spot measurements (each an average of at least 3 readings) over each 100 sq ft area, and the average of these five spots constitutes the area measurement. (Correct answer)
- Take three gage readings anywhere within the 500 sq ft section and average them to get the final DFT.
Correct answer: Take five spot measurements (each an average of at least 3 readings) over each 100 sq ft area, and the average of these five spots constitutes the area measurement.
SSPC-PA 2 specifies a clear protocol for DFT measurement. For each 10 m² (~100 ft²) area, an inspector must take five spot measurements. Each spot measurement is itself an average of at least three individual gage readings taken within a 1.5-inch diameter circle. The average of the five spot measurements determines the area measurement.
Question 3: A pipeline operating under impressed current cathodic protection (CP) has its fusion-bonded epoxy (FBE) coating tested. The test involves creating an intentional holiday and applying a negative potential in an electrolyte to measure the coating's resistance to delamination. What is this test called?
- Adhesion Pull-Off Test (ASTM D4541)
- Holiday Detection Test (ASTM G62)
- Abrasion Resistance Test (ASTM D4060)
- Cathodic Disbondment Test (ASTM G8/G42/G95) (Correct answer)
Correct answer: Cathodic Disbondment Test (ASTM G8/G42/G95)
This scenario describes a Cathodic Disbondment (CD) test. This test is specifically designed to evaluate a coating's performance when used in conjunction with a cathodic protection system. It measures the coating's ability to resist delamination or 'disbondment' from the substrate at an intentional defect (holiday) when subjected to the electrical stresses of CP.
Question 4: Which of the following best describes the primary corrosion protection mechanism of an inorganic zinc-rich primer on a steel substrate?
- It forms a non-porous, impermeable barrier that prevents electrolytes from reaching the steel.
- It provides sacrificial (galvanic) protection by corroding preferentially to the steel substrate. (Correct answer)
- It passivates the steel surface by forming a thin, non-reactive oxide layer.
- It releases chemical inhibitors that neutralize corrosive agents at the steel surface.
Correct answer: It provides sacrificial (galvanic) protection by corroding preferentially to the steel substrate.
Inorganic zinc-rich primers protect steel primarily through sacrificial action. The zinc particles in the coating are more electrochemically active than the steel substrate. In the presence of an electrolyte, the zinc becomes the anode and corrodes preferentially, while the steel becomes the cathode and is protected from corrosion.
Question 5: An epoxy coating applied in a cool, humid environment develops a waxy, greasy film on the surface after curing. This defect, which can cause intercoat adhesion failure, is most likely:
- Chalking
- Cratering
- Amine Blush (Correct answer)
- Orange Peel
Correct answer: Amine Blush
The condition described is a classic example of amine blush. It occurs when amine curing agents in the epoxy react with moisture and carbon dioxide from the air, especially in low temperature and high humidity conditions. This reaction forms a carbamate film on the surface that is often waxy or oily and must be removed before recoating to ensure proper adhesion.
Question 6: An inspector needs to perform a holiday test on a 15-mil (380-micron) thick tank lining. Which of the following methods is most appropriate and effective for detecting holidays in a coating of this thickness?
- Low-voltage (wet-sponge) holiday detector set to 67.5V.
- High-voltage (spark) holiday detector set to an appropriate voltage based on the coating thickness. (Correct answer)
- Visual inspection with high-powered magnification.
- Solvent wipe test using a contrasting color solvent.
Correct answer: High-voltage (spark) holiday detector set to an appropriate voltage based on the coating thickness.
Low-voltage (wet-sponge) holiday detectors are generally used for coatings up to 20 mils (500 microns), but are primarily intended for thinner films (typically under 10 mils) and may not reliably detect pinholes without a wetting agent. High-voltage (spark) holiday testing is the standard and more effective method for thicker coatings, like the 15-mil lining described. The voltage must be set correctly (e.g., using NACE SP0188 guidelines) to be effective without damaging the coating.
NACE - National Association of Corrosion Engineers Protective Coatings and Linings Questions and Answers
According to the joint standard NACE No. 1 / SSPC-SP 5, what is the required condition of a steel surface after 'White Metal Blast Cleaning'?