What causes this type of corrosion?

Corrosion is an electrochemical process requiring three conditions: an anode (oxidising metal), a cathode (noble metal or cathodic site), and an electrolyte (conducting liquid such as water, seawater, or process fluid). Removing any one of these three conditions stops the corrosion process. The specific morphology depends on the local electrochemical environment, chloride concentration, pH, temperature, and material composition.

How is corrosion rate measured?

The standard weight-loss method (ASTM G1/G31) measures mass loss from standardised coupons exposed to the corrosive environment for a defined period. Corrosion rate (mm/year) = 87.6 × W / (D × A × T), where W = weight loss (mg), D = density (g/cm³), A = exposed area (cm²), T = exposure time (hours). Use our free Corrosion Rate Calculator for instant results.

What material provides the best corrosion resistance?

Material selection depends on the specific corrosive environment. For chloride-containing media: duplex stainless steel (2205, PREN ≈35) or super duplex (SAF 2507, PREN ≈42) for ambient seawater; titanium alloys or nickel alloys (Alloy 625, Hastelloy C-276) for aggressive hot seawater and acids. Use our PREN Calculator to compare grades for chloride resistance.

Corrosion Rate Calculator — Weight Loss

Calculate metal corrosion rate from gravimetric weight loss coupon data — the most reliable and widely used method for monitoring corrosion in process plant, pipelines, and test programmes. Outputs corrosion rate in mm/year, mils per year (mpy), µm/year, and g/m²/day per ASTM G1 / ASTM G31 standard formula.

Corrosion Rate Calculator (Weight Loss Method)

Weight loss — W (mg)

Exposure time — T (hours)

Exposed surface area — A (cm²)

Metal density — D (g/cm³)

Custom density (g/cm³) — if selected above

Corrosion Rate (mm/year)—

Corrosion Rate (mils per year — mpy)—

Corrosion Rate (µm/year)—

Mass loss rate (g/m²/day)—

Corrosion Severity—

ASTM G1 formula: CR (mm/year) = 87.6 × W / (D × A × T)
where W = weight loss (mg), D = density (g/cm³), A = area (cm²), T = exposure time (h)
1 mm/year = 39.37 mpy = 1,000 µm/year

Figure: The eight forms of corrosion (Fontana classification) with schematic cross-sections showing characteristic damage morphologies. © metallurgyzone.com/

References

ASTM G1-03(2017) Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens.
ASTM G31-21 Standard Guide for Laboratory Immersion Corrosion Testing of Metals.

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