Mils per Year - MPY - Corrosion Rate

MPY is used to measure the corrosion rate in pipes, pipe systems, or other metallic surfaces by calculating material loss or weight loss of metal surfaces. Based on the type of metal, sample area size, and exposure time, MPY provides a corrosion rate value. One mil equals 0.001 inch or 0.0254 mm in metric terms. In open water systems, a corrosion rate around 1 MPY is normal; rates around 10 MPY warrant action, while 20 MPY and above indicate serious concern as corrosion progresses rapidly. For example, a 24-inch pipeline with 10 MPY corrosion results in nearly half a cubic meter of material loss per kilometer. Pitting corrosion can reach approximately 1000 MPY, which is particularly dangerous as it can rapidly create holes in pipes. MPY calculations are critical for determining pipe lifetime, especially in high-pressure applications like gas pipelines.