Pitting Corrosion Rate Calculator
Calculate penetration rates and estimated remaining life of metal structures.
Calculation Results
Understanding Pitting Corrosion Rate
Pitting corrosion is one of the most insidious and damaging forms of corrosion. Unlike uniform corrosion, where the metal degrades evenly across the surface, pitting focuses the attack on small, localized areas. This results in the creation of holes or "pits" that can penetrate deep into the material, leading to catastrophic failure such as leaks in pipes or structural collapse, often with very little total weight loss.
How the Calculator Works
This calculator utilizes the standard linear extrapolation method often used in engineering inspections (based on principles found in ASTM G46). By measuring the deepest pit found during an inspection and knowing the duration of exposure, we can determine the velocity at which the pit is growing.
The core formula for the Pitting Rate (PR) is:
- D_max: The depth of the deepest pit measured (mm).
- T: The time of exposure (years).
Units of Measurement
In the corrosion industry, rates are typically expressed in two formats:
- mm/y: Millimeters per year (Metric standard).
- mpy: Mils per year (Imperial standard), where 1 mil = 0.001 inches. (1 mm/y ≈ 39.37 mpy).
Pitting Factor vs. Uniform Corrosion
It is important to distinguish between the pitting rate and the general corrosion rate. The Pitting Factor is the ratio of the depth of the deepest pit to the average penetration of the metal. A high pitting factor indicates that the corrosion is highly localized, which is significantly more dangerous for pressurized vessels and pipelines than uniform thinning.
Estimating Remaining Life
This tool estimates the remaining life of the equipment by assuming the pitting will continue to grow linearly at the calculated rate until it breaches the wall thickness. The formula used is:
Remaining Life = (Current Thickness – Current Pit Depth) / Pitting Rate