Lifetime of High-Density Polyethylene Drain Pipe in an Aggressive Environment

The major factors affecting the short term and long-term performances of high and medium density polyethylene (MDPE and HDPE) pipe in various applications such as natural gas transmission, potable water distribution, or drainage include: (1) the chemical makeup (macromolecules, molecular architecture, and additives); (2) the raw material and pipe manufacturing processes employed; and (3) the installation and service conditions, including load, loading rate, temperature, and other environmental conditions. The successful design of MDPE and HDPE pipe for an intended application requires an understanding of the role of the above factors combined with economic considerations that account for the cost of fabrication and installation, as well as the cost of failure. Material characterization and ranking with respect to strength, toughness, and durability provide a basis for the rational design of HDPE pipe. MDPE and HDPE pipe have been successfully employed in various applications for several decades. A number long-term life studies of MDPE and HDPE pipe have been performed in the US and Europe. The three basic modes of PE pipe failure are generally recognized as ductile failure at relatively high stresses (Mode I), brittle fracture at intermediate stress levels (Mode II), and environmental stress cracking (ESC) or stress corrosion cracking (SCC) at low stress levels (Mode III). National and international industrial standards (ASTM D 2837 and ISO 9080) have been adopted to regulate the pressure pipe industry, control durability, and provide a quantitative estimate of expected lifetime for Modes I and II failures. Unfortunately, only qualitative tests exist that rank materials with respect to ESC (and SCC) lifetimes. There is no standard that quantitatively addresses the lifetime of PE pipe under the combined action of mechanical stress and chemical degradation (SCC) even though SCC is the most probable failure mode of the HDPE drain pipe designed for a service life of 100 years. Chemical degradation of polymers is primarily manifested in the breakage of the primary valence bonds (chain scission) resulting in a reduction of molecular weight (MW). This leads to an increase in crystallinity and, consequently, an increase in density, resulting in a build-up of tensile stress within the degraded layer. Chemical degradation is also accompanied by a subtle increase in stiffness and yield strength, as well as a dramatic reduction in toughness. A quantitative model of the above processes, including degradation-induced crack initiation and growth (SCC), as well as guidelines for accelerated testing for material susceptibility to chemical degradation are discussed this work.

• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Wienhold, Paul
  • Chudnovsky, Alexander
• Conference:
  • Transportation Research Board 85th Annual Meeting
  • Location: Washington DC, United States
  • Date: 2006-1-22 to 2006-1-26
• Date: 2006

Language

• English

Media Info

• Media Type: CD-ROM
• Features: Figures; References;
• Pagination: 17p
• Monograph Title: TRB 85th Annual Meeting Compendium of Papers CD-ROM

Subject/Index Terms

• TRT Terms: Corrosion; Corrosion protection; Drain pipe; Drinking water; Natural gas; Stresses
• Uncontrolled Terms: High density polyethylene; Medium
• Subject Areas: Bridges and other structures; Design; Geotechnology; Highways; Materials; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 01024508
• Record Type: Publication
• Report/Paper Numbers: 06-2377
• Files: TRIS, TRB
• Created Date: May 25 2006 7:31AM