A Service Life Assessment of Corrugated HDPE Drainage Pipe

The service life of our nation’s infrastructure has become a topic of increasing focus in recent years. While above-ground infrastructure deterioration is readily apparent, the infrastructure beneath the surface can be much worse and yet is often largely ignored until it is too late. Since culverts and other buried structures typically aren’t inspected as frequently as above-ground structures such as bridges, the proper assessment and determination of their service life becomes very important. Some states now require 75-year or greater service life for culverts and other drainage pipes, though a recent survey conducted by the Kansas Department of Transportation (Kansas DOT 2009) showed just 19 states with a Design Service Life requirement for pipes (most typically 50 years for all pipe types), with a majority of states showing no requirements. The design service life of corrugated high density polyethylene (HDPE) drainage pipe has been a subject of considerable research over the past several years. This paper discusses a method for determination of long-term service life of corrugated HDPE pipe by utilizing some of the current widely-accepted methods employed by the smooth-walled plastic pipe industry while modifying them somewhat to take into account the unique geometry and installation conditions of buried corrugated pipe. For corrugated HDPE drainage pipe, the primary mechanisms of material failure are slow crack growth and oxidation (chemical failure). The service conditions of the pipe will vary by geographic location, based on temperature and soil and traffic loads. Recent research performed by the Florida Department of Transportation (FDOT) details the limiting stress conditions of buried corrugated pipe which will be used to predict the service life of pipe in this paper. After identifying the failure modes and long-term stresses on the pipe, the capacity of the material and the pipe system to resist failure is assessed. Some recently proposed methods by FDOT to ensure long-term material resistance to these failure modes are reviewed in this paper. FDOT has a 100-year service life requirement for pipe, which will be the focus of this paper. In addition to the pipe material, one also must consider the joints, gaskets, and installed pipe system in assessing service life. Since a pipe system is only as strong as its weakest link, the entire installed system for all pipe types should be assessed.