Why is my culvert rusting out?

Answer: Metal culvert failure, often believed to be due to rocks and gravel washing through the pipe causing the bottom to rust out, actually may be the result of soil and water acidity. Forest Services and Bureau of Land Management engineers in Oregon conducted a field study examining the “pH” value of soil and water contacting metal culverts, and found that even a small amount of acidity or alkalinity of the soil will help in selecting the right kind of pipe to install for maximum cost-effectiveness.

Properly designed, a metal pipe can provide a very long lifespan, but the initial installation may need to include a thicker gauge or a coating on the inside and outside of the pipe to deal with the debris going through the pipe and the soil “ph.” The NYSDOT has a table that can be used to determine the gauge and coating that are needed in their Highway Design Manual Chapter 8: Drainage starting on page 8-52. Most of the southern half of New York State including the Southern Tier need to have thicker pipes or coatings due to the soil conditions.

There are many reasons for culverts to rust out, to read the full review of possible causes please look at the literature review from Kira Glover-Cutter on Factors Affecting the Service Life of Culverts (April, 2020)

Resources:

• National Corrugated Steel Pipe Association (NCSPA) Service life calculator
• NYSDOT HDM Chapter 8 - Highway Drainage