Corrosion Rate from Coupon Weight Loss
Converts coupon mass loss to a corrosion rate in mpy and mm/yr, remaining wall life, and life at the deepest pit.
Example
You enter
- Mass lost after cleaning (mg) 125
- Alloy density (g/cm^3) 7.85
- Exposed area (sq in) 6
- Exposure time (hours) 2160
- Current wall thickness (in) 0.25
- Retirement thickness (in) 0.125
- Pitting factor 10
- Alternative mass loss (mg) 2500
You get
- Average corrosion rate 0.6561 mpy (0.0167 mm/yr)
- Corrosion rate mm per year 0.0166652
- Remaining life at the average 190.517
- At the alternative mass loss 13.1222
- Alternative life (yr) 9.52584
- At the deepest pit 6.56 mpy at a pitting factor of 10
- Life at the deepest pit 19.0517
Checked against published worked examples from: EMT.
Details, formula, and sources
ScopeThe worked coupon gives 191 years on the average and 19 at a pitting factor of 10 -- from the same weighing. The pit decides when it leaks.
Formula or tableCR (mpy) = 534 x mass loss (mg) / (density (g/cm^3) x area (sq in) x time (h)); life = (wall - retirement) / rate; pit rate = CR x pitting factor.
Source and editionASTM G1 coupon preparation, cleaning, and weight-loss evaluation. The coupon's own pit-depth measurement governs the pitting factor.
Free accessASTM G1 is a purchased standard; the 534 constant is widely published.
What governsEstimate. AHJ and licensed professional govern.
API field namesmass_loss_mg, density_g_cm3, exposed_area_sqin, exposure_hours, wall_thickness_in, retirement_thickness_in, pitting_factor, alternative_mass_loss_mg, corrosion_rate_mpy, corrosion_rate_mm_per_year, remaining_life_years, alternative_rate_mpy, alternative_life_years, pit_rate_mpy, pit_life_years
- Rate assumed constant; a very long projected life is correct arithmetic and a meaningless forecastspec-v1769 caveat
- Pitting factor deepest pit over average penetration, measured on the couponcoupon inspection