Corrosion rate from coupon mass loss
Average general corrosion rate from the mass loss of a corrosion coupon over the exposure time, in mm/yr and mpy; the corrosivity rating per NACE SP0775.
CR = 87.6 · W / (ρ · A · t) [mm/yr; W mg, ρ g/cm³, A cm², t h]CR [mpy] = CR [mm/yr] / 0.0254The rate is averaged over the exposure and the whole surface; pitting is assessed separately from the pit depth. NACE SP0775 rates general corrosion as low below 0.025 mm/yr, moderate at 0.025–0.12, high at 0.13–0.25 and severe above 0.25 mm/yr.
Source: ASTM G1 (corrosion rate from mass loss, K = 8.76·10⁴); NACE SP0775 (coupons, rate classification)
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Mass before exposure minus mass after cleaning off the corrosion products (ASTM G1).
Carbon steel 7.86 g/cm³.
Usually 30–90 days; the unit can be switched to days.
Unit converter for this formulaDensity and °API · Area · Time
- kg/m³850
- g/cm³0.85
- t/m³0.85
- rel. (water 4 °C)0.850024
- lb/ft³53.0638
- lb/gal (ppg)7.09359
- SG (60/60 °F)0.850837
- °API34.8068
°API and SG refer to the density at 60 °F (15.6 °C) relative to water at 60 °F, relative density to water at 4 °C. The oil's thermal expansion between the measurement temperatures is not included. °API = 141.5 / SG − 131.5.
- CR_mpy — Corrosion rate in mpy–mpy
More in Corrosion protection
Mean protective current from the surface area, the current density and the coating breakdown factor, and the net mass of galvanic anodes for the design life — per DNV-RP-B401; the number of anodes.
Corrosion rate from two wall thickness surveys and the remaining life to the retirement thickness; the longest interval to the next inspection.
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.