Establishing 100-Year Service Life for Corrugated HDPE Drainage Pipe

The design service life of corrugated high density polyethylene (HDPE) drainage pipe has been a subject of considerable debate and research over the past several years. While significant long-term performance data is available for smooth-walled polyethylene pipe, the data for corrugated drainage pipes is somewhat limited. This paper presents 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 plastic pipe industry, while modifying them somewhat to take into account the unique geometry and installation conditions of buried corrugated pipe. The process for long-term service life prediction is two-fold: First, the anticipated service conditions of the drainage pipe must be assessed, including such factors as environmental conditions, soil and traffic loads, and the resulting long-term stresses and strains evident in the pipe. Second, the capacity of the material and the manufactured pipe product must be assessed. The service conditions of the pipe will vary by geographic location, based on temperature and soil and traffic loads. While deep installations may result in large compressive stresses on the pipe, shallow installation are more subject to bending and tensile stresses. Although these stress levels are typically lower in magnitude than the compressive stresses associated with deep burial conditions, they are considered a limiting condition as the material is more prone to failure in tension rather than compression. Recent research performed by Dr. Timothy McGrath for the Florida Department of Transportation on the limiting stress conditions of buried corrugated pipe is presented in this paper. The capacity of the material to resist failure is the second factor that must be addressed. Based on its wide use as a piping material (i.e. gas, water, industrial, oil field, etc...) polyethylene is a highly scrutinized material and its mechanisms of failure are well known. For corrugated drainage pipe, the primary mechanisms of material failure are slow crack growth and oxidation or chemical failure. Some recently proposed methods by Dr. Grace Hsuan for the Florida Department of Transportation to ensure long-term material resistance to these failure modes are presented in this paper.