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A variety of techniques are available for monitoring metal corrosion in electrolytes. However, only some of them can be applied in the atmosphere, in which case a thin discontinuous electrolyte film forms on a surface. Traditional and state-of-the-art real-time corrosion monitoring techniques include atmospheric corrosion monitor (ACM), electrochemical impedance spectroscopy (EIS), electrochemical noise (EN), electrical resistance (ER) probes, quartz crystal microbalance (QCM), radio-frequency identification sensors (RFID), fibre optic corrosion sensors (FOCS) and respirometry.
Technique | Environment * | Sensing Metal ** | Range of Measured Corrosion Rates ***, [µm·a−1] | References | Localised Corrosion Detection |
---|---|---|---|---|---|
ACM 1 | Outdoor exposures | Fe | 1 × 10−1–1 × 102 | [4][5][6][7][8][9][10][11][12] | – |
Zn | Not calculated | [13] | |||
ACTs | Fe | 1 × 102 | [14] | ||
Laboratory tests | Fe | 1 × 101–1 × 103 | [15][16] | ||
Zn | 1 × 101–1 × 103 | [15][16] | |||
Cu | 1 × 101–1 × 103 | [15] | |||
Al | 1 × 101–1 × 103 | [15] | |||
ER | Outdoor exposures | Fe | 1 × 10−1–1 × 103 | [17][18][19] | [3][20][21] |
Zn | 1 × 10−1–1 × 101 | [18] | |||
Cu | 1 × 10−1–1 × 100 | [22] | |||
ACTs | Fe | 1 × 101–1 × 103 | [2][23][24][18][25][26][27] | ||
Zn | 1 × 100–1 × 103 | [2][23][24] | |||
Cu | 1 × 103 | [2] | |||
Al | 1 × 10−1–1 × 101 | [20] | |||
Laboratory tests | Fe | 1 × 10−3–1 × 101 | [2][3][28] | ||
Cu | 1 × 10−3–1 × 10−1 | [2][29][30][28] | |||
Ag | 1 × 10−3–1 × 101 | [29][30][31] | |||
Zn | 1 × 100–1 × 102 | [2] | |||
Pb | 1 × 10−3–1 × 102 | [32][33][34] | |||
Indoor exposures | Cu | 1 × 10−3–1 × 10−1 | [29][35][36][37][38][39] | ||
Ag | 1 × 10−3–1 × 10−1 | [29][35][36][38][40] | |||
Pb | 1 × 10−2–1 × 101 | [36][38][41] | |||
EIS 2 | Outdoor exposures | Fe | 1 × 10−1–1 × 101 | [42][43] | [44][45] |
Cu | 1 × 102–1 × 103 | [22] | |||
ACTs | Fe | 1 × 102–1 × 103 | [46] | ||
Laboratory tests | Fe | 1 × 10−1–1 × 104 | [47][48][49][50][51] | ||
Zn-coated steel | 1 × 100–1 × 103 | [52][53][54][55] | |||
Zn | 1 × 101 | [56] | |||
Cu | 1 × 10−1–1 × 101 | [57][58][22] | |||
EN 3 | Outdoor exposures | Fe | 1 × 10−1–1 × 101 | [44][59] | [44][59][45][60] |
Cu | 1 × 10−2–1 × 102 | [61][60] | |||
QCM 4 | Laboratory tests | Cu | 1 × 10−1–1 × 100 | [62] | – |
Ag | 1 × 10−3–1 × 10−2 | [63][64][65][66][67][68] | |||
Indoor exposures | Cu | 1 × 10−3–1 × 10−1 | [36][69] | ||
Ag | 1 × 10−2–1 × 10−1 | [36][40][69] | |||
Co | 1 × 10−2–1 × 10−1 | [69] | |||
RFID | ACTs | Fe | 1 × 102–1 × 103 | [70][71] | [72][73] |
Laboratory tests | Zn | 1 × 101 | [72][74][73] | ||
FOCS | Fe | No data for atmospheric corrosion | – | ||
Respirometry 5 | Laboratory tests | Fe | 1 × 10−1–1 × 102 | [75][76] | [77][78] |
Cu | 1 × 10−2–1 × 10−1 | [75] | |||
Al | 1 × 10−1–1 × 100 | [77] | |||
Mg | 1 × 101–1 × 103 | [77][78] |
Technique | Current Applications | Potential Fields of Application | Sensitivity * | Commercial Suppliers | Main Advantages | Main Drawbacks |
---|---|---|---|---|---|---|
Coupons | Indoor and outdoor corrosivity classification according to standards Verification of other techniques |
Applicable in any environment | High at long exposure times, otherwise medium | Several | Standardised technique Easy data interpretation |
No real-time data Time-consuming |
ACM | Outdoor monitoring TOW assessment |
Outdoor and indoor at higher RH | Medium | 1 | Not sensitive to temperature fluctuations Suitable for harsh outdoor environments |
Corrosion acceleration due to galvanic coupling Unclear data interpretation during rainfall Electrolyte presence required |
EIS | Laboratory tests at higher RH and under thin electrolyte layers Assessment of protective coatings |
Outdoor and indoor at higher RH | Medium | 0 | Information about corrosion mechanism Non-destructive assessment of coatings |
Knowledge about investigated system needed for correct data interpretation Electrolyte presence required Unclear results under very thin electrolyte layers and in presence of thick corrosion products |
EN | Outdoor corrosion monitoring | Outdoor and indoor at higher RH | Medium | 0 | Localised corrosion detection Corrosion mechanism determination |
Complex and unclear interpretation Electrolyte presence required |
ER | Indoor and outdoor corrosion monitoring, laboratory studies Corrosivity classification |
Applicable in any environment | High | 4 | Universal technique High sensitivity Easy operation and data interpretation Optimal for uniform corrosion monitoring |
Sensitive to temperature fluctuations Limited possibilities in monitoring of non-uniform corrosion |
QCM | Indoor corrosivity classification Laboratory tests |
Indoor at lower corrosivity | High | 2 | High sensitivity and short response time Electrolyte presence not required |
Sensitive to temperature fluctuations, moisture and pollutants presence Not suitable for harsh environments |
RFID | Laboratory tests | Outdoor and indoor at higher corrosivity | Low | 0 | Compact and wireless Electrolyte presence not required |
Further development needed |
FOCS | None for atmospheric corrosion | Not clear yet, as the technique is at the development stage | Not available | 0 | Not known for atmospheric corrosion yet | |
Respirometry | Laboratory tests | Not clear yet, as the technique is at the development stage | High | 0 | High sensitivity Information about corrosion mechanism Electrolyte presence not required |
Sensitivity to RH, temperature and pressure fluctuations Further development needed |