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. |