NACE Corrosion Monitoring Techniques 1 — Questions and Answers
Question 1: What is the primary purpose of a corrosion coupon in a monitoring program?
- To measure pH of the process fluid
- To provide a direct mass-loss measurement of corrosion rate (Correct answer)
- To detect hydrogen embrittlement
- To measure electrical resistance of the pipeline
Correct answer: To provide a direct mass-loss measurement of corrosion rate
Corrosion coupons provide direct measurement of material loss over time, allowing calculation of average corrosion rate in mils per year (mpy) or mm/year.
Question 2: Electrical Resistance (ER) probes measure corrosion by detecting changes in which property?
- The pH of the surrounding electrolyte
- The electrical resistance of a metal element as it loses cross-sectional area (Correct answer)
- The corrosion potential of the structure
- The hydrogen evolution rate at the metal surface
Correct answer: The electrical resistance of a metal element as it loses cross-sectional area
ER probes work on the principle that as a metal element corrodes and loses cross-sectional area, its electrical resistance increases proportionally.
Question 3: Which corrosion monitoring technique provides the fastest real-time corrosion rate measurement in electrochemically active systems?
- Corrosion coupons
- Ultrasonic thickness measurement
- Linear Polarization Resistance (LPR) (Correct answer)
- Electrical Resistance probes
Correct answer: Linear Polarization Resistance (LPR)
LPR techniques can provide instantaneous corrosion rate measurements within minutes, making them the fastest real-time monitoring method for conductive electrolyte systems.
Question 4: A hydrogen probe is primarily used to detect which corrosion-related phenomenon?
- General corrosion rates in pipelines
- Hydrogen permeation associated with hydrogen-induced cracking (HIC) risk (Correct answer)
- CO2 corrosion in gas pipelines
- Microbiologically influenced corrosion (MIC)
Correct answer: Hydrogen permeation associated with hydrogen-induced cracking (HIC) risk
Hydrogen probes detect atomic hydrogen permeating through metal walls, which is a key indicator of hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) susceptibility.
Question 5: Ultrasonic thickness (UT) measurement is used in corrosion monitoring programs primarily to:
- Measure the corrosion rate of sacrificial anodes
- Track wall thickness reduction over time to calculate corrosion rate and remaining life (Correct answer)
- Identify the chemical composition of corrosion products
- Measure the electrochemical potential of a corroding surface
Correct answer: Track wall thickness reduction over time to calculate corrosion rate and remaining life
UT measurement tracks wall thickness reduction across inspection intervals, enabling calculation of corrosion rates and prediction of remaining service life.
Question 6: In corrosion monitoring, what does the unit abbreviation 'mpy' stand for?
- Megapascals per year
- Millivolts per year
- Mils per year (Correct answer)
- Micrograms per year
Correct answer: Mils per year
Mpy stands for mils per year, where one mil equals 0.001 inch; it is the standard US unit for expressing metal penetration rates due to corrosion.
Question 7: Which type of corrosion monitoring probe is best suited for use in non-conductive or low-water-cut hydrocarbon systems?
- Linear Polarization Resistance (LPR) probe
- Electrical Resistance (ER) probe (Correct answer)
- Galvanic probe
- Electrochemical noise probe
Correct answer: Electrical Resistance (ER) probe
ER probes measure resistance change due to metal mass loss and do not require a conductive electrolyte, making them suitable for non-conductive or low-conductivity environments.
NACE Corrosion Monitoring Techniques 1
What is the primary purpose of a corrosion coupon in a monitoring program?