Corrosion & Coating Testing
Corrosion Testing with a Potentiostat: Corrosion Rate, Coatings and Inhibitors
Electrochemical methods measure corrosion rates in minutes to hours, far faster than immersion tests. This page covers methods, test workflow, Corrtest models, corrosion cells and equipment packages for a corrosion lab.
- 10¹³ Ωinput impedance, suited to coating EIS
- Floating modefor autoclaves and concrete
- OCP · Tafel · LPR · EISplus CPP, EPR, EN, ZRA
- Official distributorof Corrtest in Indonesia
Why use electrochemical methods?
Corrosion is an electrochemical reaction: metal oxidises at anodic sites while oxygen or hydrogen ions are reduced at cathodic sites. That is why the corrosion rate can be calculated from the corrosion current measured by a potentiostat. Immersion (weight-loss) tests remain a useful reference but take weeks; electrochemical tests deliver results within a working day and can be repeated across many solutions, temperatures or inhibitors.
Corrtest potentiostats were originally designed for corrosion electrochemistry (the first instrument was built in 1995). With 10¹³ Ω input impedance they can run EIS on very high-resistance systems such as paint, concrete and pure water.
Corrosion test methods
| Method | Output | Common reference |
|---|---|---|
| Open circuit potential (OCP) | Corrosion potential Ecorr and surface stability before other tests | First step of every test |
| Potentiodynamic polarisation (Tafel) | icorr, Ecorr, slopes βa and βc, corrosion rate | ASTM G5, ASTM G102 |
| Linear polarisation resistance (LPR) | Polarisation resistance Rp; fast and nearly non-destructive | ASTM G59 |
| EIS | Charge-transfer resistance, film capacitance, coating degradation | ISO 16773 (coatings), ASTM G106 |
| Cyclic potentiodynamic polarisation (CPP) | Pitting potential Epit and repassivation potential Erp | ASTM G61 |
| Electrochemical potentiokinetic reactivation (EPR) | Degree of sensitisation of stainless steel | Stainless steel |
| Electrochemical noise (EN) & ZRA | Localised corrosion without applying a signal; galvanic current between two metals | Galvanic corrosion, monitoring |
| Hydrogen permeation | Hydrogen diffusion through a metal membrane (Devanathan–Stachurski double cell) | ASTM G148; needs a bipotentiostat |
Calculating the corrosion rate
icorr = B / Rp B = (βa · βc) / [2,303 · (βa + βc)]Rp from LPR or EIS; βa and βc from the Tafel plot. When slopes are unknown, B is often assumed to be about 26 mV for actively corroding steel.
CR (mm/tahun) = 3,27 × 10⁻³ · icorr · EW / ρicorr in µA/cm², EW = equivalent weight of the metal, ρ = density (g/cm³). For carbon steel EW ≈ 27.92 and ρ ≈ 7.87.
IE (%) = (1 − icorr,inhibitor / icorr,blanko) × 100It can also be calculated from EIS charge-transfer resistance: IE (%) = (1 − Rct,blank / Rct,inhibitor) × 100.
A typical corrosion test workflow
- Prepare the specimenGrind, clean and define the exposed area (for example 1 cm² in the corrosion cell holder). A wrong area gives a wrong corrosion rate.
- Stabilise the OCPImmerse the specimen and record the OCP until it is stable, typically 30–60 minutes, before polarising.
- Run non-destructive tests firstRun EIS (small amplitude, e.g. 10 mV) and LPR (±10–30 mV around Ecorr) before the Tafel scan.
- Tafel or CPP scanUse a slow scan, e.g. 0.1667 mV/s as in ASTM G5, then fit the Tafel slopes in the software.
- Calculate and compareCalculate icorr, corrosion rate and inhibitor efficiency; repeat on at least three specimens per condition.
Recommended models
Corrtest's brochure recommends the CS310M, CS350M, CS2350M and CS310X for corrosion.
| Product | Best for | Price | Purchase |
|---|---|---|---|
| Corrtest CS300M (no EIS) | Tafel, LPR and CPP without EIS; a budget option for corrosion teaching labs. | Rp 99.144.000 | Buy online |
| Corrtest CS310M (EIS, ±2 A) | Tafel, LPR and EIS in one instrument. | Rp 129.438.000 | Buy online |
| Corrtest CS350M (EIS to 1 MHz, ±2 A) | High-impedance coating EIS, EN/ZRA and booster option. | Rp 167.884.000 | Buy online |
| Corrtest CS2350M bipotentiostat (2 channels) | Two-cell hydrogen permeation and two simultaneous working electrodes. | Rp 190.026.000 | Buy online |
| Corrtest CS310X multichannel (option A, 4 channels) | Screening many inhibitors or specimens in parallel. | Rp 240.700.000 | Buy online |
Store catalogue prices before 11% VAT and shipping; subject to change. Stock and delivery time are confirmed in the quotation.
Corrosion cells and accessories
| Accessory | Purpose | Price | Purchase |
|---|---|---|---|
| CS9305 5-port 500 mL corrosion cell, electrodes included | Ready-to-use cell with a 1 cm² specimen holder | Rp 20.655.000 | Buy online |
| CS936 flat corrosion cell | Plate and sheet specimens without cutting them small | Rp 20.022.000 | Buy online |
| CS934 coating evaluation (paint test) cell | EIS of paints and protective coatings | Rp 5.784.000 | Buy online |
| CS900 saturated calomel electrode (SCE) | Standard reference for chloride solutions | Rp 2.066.000 | Buy online |
| CS901 Ag/AgCl reference electrode | Mercury-free reference | Rp 2.149.000 | Buy online |
| CS915 graphite rod | Economical counter electrode | Rp 1.653.000 | Buy online |
| CS946 specimen holder | Only one face of the sample touches the solution | Rp 6.335.000 | Buy online |
| CS942 Faraday cage | Reduces noise for very low currents and coating EIS | Rp 4.131.000 | Buy online |
Store catalogue prices before 11% VAT and shipping; subject to change. Stock and delivery time are confirmed in the quotation.
Corrosion lab packages
Basic Corrosion Testing Package
Tafel, LPR and EIS for metals in salt or acid solutions.
- Corrtest CS310MPotentiostat with EISRp 129.438.000
- CS9305 corrosion cell 500 mL5-port cell with electrodesRp 20.655.000
- CS942 Faraday cageNoise shieldingRp 4.131.000
Coating & Inhibitor Testing Package
High-impedance coating EIS and inhibitor screening on plates.
- Corrtest CS350MEIS to 1 MHz, 10¹³ Ω input impedanceRp 167.884.000
- CS936 flat corrosion cellPlate specimensRp 20.022.000
- CS934 coating cellPaint test cellRp 5.784.000
- CS900 SCEReference electrodeRp 2.066.000
- CS942 Faraday cageEssential for high-impedance coatingsRp 4.131.000
Estimate = sum of store catalogue prices per component, before 11% VAT and shipping. Components can be swapped to suit your methods and budget; the final price is in the formal quotation.
Common mistakes
- Starting polarisation before the OCP is stable, so Ecorr drifts during the test.
- Scanning too fast, which flattens the Tafel curve and overestimates icorr.
- Undefined specimen area because of crevices around the holder.
- Running EIS after a Tafel scan, when the surface has already changed.
- Measuring coatings without a Faraday cage, giving noisy low-frequency data.
- Fitting Tafel lines too close to Ecorr instead of in a clearly linear region.
Frequently asked questions
How long does an electrochemical corrosion test take?
Usually 1–3 hours per specimen: OCP stabilisation, EIS, LPR, then Tafel. Long-term coating tests are repeated over days or weeks.
Can I test corrosion in reinforced concrete?
Yes. Corrtest potentiostats have a floating mode for systems whose working electrode is grounded, such as concrete structures and autoclaves.
Which model for hydrogen permeation testing?
Use the CS2350M bipotentiostat, which the Corrtest brochure describes as designed for RRDE and hydrogen permeation tests.
Do I need EIS for inhibitor testing?
Not strictly; inhibitor efficiency can be calculated from Tafel data. EIS adds information on adsorption mechanisms and gives Rct as a cross-check.
Need help choosing?
Tell us about your samples, methods and budget. Our team will put together the equipment and supplies with a formal quotation.
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