EXAMPLES OF CORROSION RESOLUTIONS CORROSION MONITORING METHODS
METHOD |
TYPE OF DATA PRODUCED |
BASIC LIMITATION OF THE METHOD |
| Visual/Mechanical Measurements | Total penetration to date | 1. Can only be used during shutdown/partial
outage or when, e.g. a spoolpiece can be provided 2. Does not reflect the present corrosion rate and may not reflect the present corrosion mechanism |
| Coupon Immersion and/or Spoolpiece Analysis | Long term performance data on uniform corrosion and some forms of localized corrosion | 1. Provides time weighted average corrosion
rate. 2. Cannot be used as an early warning system. 3. Substantial intermittent manpower required. |
| Destructive Analysis, e.g. Metallography, EDS, etc. | * Corrosion mechanism * Corrosion rate |
Intermittently labor intensive |
| Ultrasonic Testing | Total uniform and localized corrosive penetration. | 1. Provides time weighted average corrosion
rate. 2. Surface preparation may be required. 3. Substantial intermittent manpower required. |
| Eddy Current Testing - Lift Off Technique | Total pitting penetration and location of corrosion | Substantial intermittent manpower required. |
| Electrical Resistance Technique | Time weighted average corrosion rate with an indication of trends in corrosion rate. | 1. Does not necessarily reflect the present-day
corrosion rate. 2. Useful data produced only when uniform corrosion or erosion-corrosion predominates. 3. Only fair performance as an early warning device |
| Hydrogen Penetration | Hydrogen penetration through metal lattice, indication of embrittlement failure susceptibility and uniform corrosion rate. | Limited usefulness, except where potential hydrogen embrittlement is a concern. |
| AC Impedence | * Corrosion mechanism * Corrosion rate |
Intermittently labor intensive. |
| Bioassay & Spectroscopic or Other Analyses | * Identification of microorganisms involved in
microbiologically influenced corrosion & confirmation of activity by spectroscopic
& other analytical methods which identify the necessary presence of by-products,
metabolites, etc. * Chemical analysis of coolant and/or corrosion product for various analytical reasons. |
Intermittently labor intensive. |
| Linear Polarization Resistance or Tafel Slope Extrapolation | Operational uniform corrosion rates | Not applicable to demineralized water systems - electrolyte required. |
| Open Circuit Corrosion Potential Monitoring | Indication of susceptibility to localized corrosion | Not quantitative |
| Full Polarization & Cyclic Potentiodynamic Hysteresis Analysis | * Corrosion Mechanism * Corrosion Rate |
Must be used infrequently; therefore, cannot be used as an early warning device. |