NACE Corrosion Monitoring Techniques 2 — Questions and Answers
Question 1: Electrochemical Noise (EN) monitoring detects corrosion by measuring:
- Acoustic noise generated by vibrating corroding metal
- Spontaneous fluctuations in potential and current that reveal corrosion mechanisms (Correct answer)
- Electrical interference caused by cathodic protection systems
- Ultrasonic reflections from corrosion pits
Correct answer: Spontaneous fluctuations in potential and current that reveal corrosion mechanisms
EN monitoring captures natural, low-level fluctuations in electrochemical potential and current that serve as fingerprints for corrosion mechanisms including pitting and stress corrosion cracking.
Question 2: A Zero Resistance Ammeter (ZRA) is used in corrosion monitoring to measure:
- Corrosion potential against a reference electrode
- Galvanic current flowing between two dissimilar metals coupled together (Correct answer)
- Electrical resistance of a corroding pipeline segment
- Soil resistivity around a buried structure
Correct answer: Galvanic current flowing between two dissimilar metals coupled together
A ZRA measures the galvanic current between two coupled metal electrodes while maintaining zero resistance in the coupling circuit, accurately simulating real galvanic couple behavior.
Question 3: The Field Signature Method (FSM) monitors corrosion by:
- Mapping wall thickness changes using an array of pin electrodes that measure resistance patterns across a pipe section (Correct answer)
- Using electromagnetic fields to detect coating defects from the pipe exterior
- Monitoring cathodic protection current distribution along the pipeline
- Tracking inhibitor film coverage on pipe walls using fluorescent tracers
Correct answer: Mapping wall thickness changes using an array of pin electrodes that measure resistance patterns across a pipe section
FSM uses an array of pins welded to the pipe and measures electrical resistance patterns between them, creating a 'signature' that reveals localized wall thickness changes and corrosion distribution.
Question 4: What is the main advantage of online corrosion monitoring over offline inspection methods?
- Online monitoring is always less expensive to install and maintain
- Online monitoring provides continuous data without removing equipment from service (Correct answer)
- Online monitoring requires no calibration or maintenance
- Online monitoring can identify specific corrosion product chemistry
Correct answer: Online monitoring provides continuous data without removing equipment from service
Online monitoring enables continuous, real-time data collection while the system remains in service, allowing early detection of corrosion upsets and trend analysis without production interruption.
Question 5: When calculating corrosion rate from a corrosion coupon, which piece of data is NOT required for the standard calculation?
- Initial weight of the coupon before exposure
- Final weight of the coupon after cleaning
- Exposure time in the corrosive environment
- Ambient temperature during the exposure period (Correct answer)
Correct answer: Ambient temperature during the exposure period
The standard coupon corrosion rate formula uses mass loss, surface area, metal density, and exposure time; ambient temperature affects corrosion but is not a variable in the rate calculation equation itself.
Question 6: What is a key limitation of Linear Polarization Resistance (LPR) probes that restricts their application?
- They can only measure cathodic half-reactions
- They require a conductive electrolyte and are unreliable in low-conductivity environments (Correct answer)
- They cannot detect any form of localized corrosion
- They must be physically removed from service for data download
Correct answer: They require a conductive electrolyte and are unreliable in low-conductivity environments
LPR is an electrochemical technique that requires ionic conductivity in the surrounding medium; in low-conductivity, dry, or predominantly hydrocarbon environments, LPR measurements become inaccurate.
Question 7: Sand/erosion monitoring probes are deployed in corrosion monitoring programs primarily to detect:
- Microbiological activity and SRB populations in pipelines
- Mechanical metal loss caused by particle impingement distinct from electrochemical corrosion (Correct answer)
- Scale and mineral deposit formation on pipeline walls
- Hydrogen blistering damage from sour service conditions
Correct answer: Mechanical metal loss caused by particle impingement distinct from electrochemical corrosion
Sand/erosion probes detect metal loss caused by mechanical abrasion from entrained sand, proppants, or other solids, which is a distinct failure mechanism from electrochemical corrosion.
NACE Corrosion Monitoring Techniques 2
Electrochemical Noise (EN) monitoring detects corrosion by measuring: