The current generation of High Density Polyethylene (HDPE) pipe materials, classified as PE4710 by U.S. standards and PE100 by ISO standards, has greatly improved toughness characteristics over previous generation materials. Most noteworthy is an increased resistance to slow crack growth and fatigue. In the U.S., PE4710, PE3608, and PE3408 (previous generation material) pipes are used in water mains and forcemain sewers. These pipelines daily experience numerous pressure surges above their standard pumping pressure. For pipes operated at their rated pumping pressure, AWWA C901 and C906 allow recurring pressure surges equal to 0.5 times the pipe's Pressure Class (PC) and occasional surges to equal the pipe's Pressure Class. Thus, the surge allowance results in a total pressure (combined pumping pressure plus surge pressure) equal to 1.5 x PC during recurring surges and 2.0 x PC during occasional surges. While all three materials have the same long-term hydrostatic design basis of 1600 psi, a higher design factor for PE4710 pipe allows it to operate at a pressure 25% higher than either PE3408 or PE3608 pipe. This paper addresses the question, Does the higher surge pressure resulting from operating PE4710 pipe at a higher pressure compromise PE4710 pipe's performance?. This paper gives an overview of design procedures for water and forcemain sewers given in current standards. It discusses considerations for a reasonable safety factor against over-pressurization during transient surge and shows that this factor is met by PE4710 material when designed in accordance with AWWA and ASTM standards. Aside from the pressurization itself, repetitive surge may lead to fatigue. This paper references studies wherein PE4710 material has a fatigue life in the millions of cycles when operated at its pressure rating and subject to recurring surge equal to 0.5 x PC.

Occasional and Recurring Surge Design Considerations for HDPE Pipe

PPI-BoreAid is a free online tool that allows users to perform preliminary pipe design analysis for polyethylene (PE) pipes installed using a horizontal directional drill (HDD). It allows users to determine suitable PE pipe dimension ratios (DR) to satisfy installation and in-service loads required in ASTM F1962 and Chapter 12 of the Handbook of Plastics Pipe Institute (PPI) Polyethylene Pipe Design, 2nd edition. During PPI-Boreaid development, several conservative aspects of the current PE pipe design methodology and PE pipe properties were noted. This paper discusses the requirement for the development of PPI-BoreAid as a preliminary PE pipe design tool, and provides suggested changes to the aforementioned documents. Sample calculations are presented to demonstrate how the new application can be used to select a suitable PE pipe for a site specific HDD project.

PPI-BoreAid: A Preliminary Design Tool for Horizontal Directional Drilling using Polyethylene Pipeline

This paper describes a framework for the design and construction of horizontal directional drilling (HDD) projects implemented in a new HDD software design program BoreAid. The framework consists of six interlinked modules: 1) bore planner; 2) pipe design; 3) drill planner; 4) bore pressure estimator; 5) equipment/tooling selection; and 6) cost estimator. Each module is discussed in detail to demonstrate how this new tool can be used as a design aid to select product pipe that meets the design requirements of the HDD project. This paper also describes PPI-BoreAid, a free online tool - developed by the Plastics Pipe Institute (PPI) in conjunction with eTrenchless Group Incorporated - that allows engineers to perform a preliminary analysis of polyethylene (PE) pipe installed using HDD in accordance with the PPI Handbook of Polyethylene Pipe and ASTM F1962 design methods.

New Generation of Design Tools for Directional Drilling Projects

Horizontal directional drilling is widely used for the installation of Polyethylene (PE) Pipes. The pull distances achievable in these applications are in most cases limited by the PE pipe’s safe pull stress. Historically, the safe pull stress has been established by applying a reduction factor to the tensile yield stress determined by test method ASTM D638, “Test Method for Tensile Properties of Plastics”. The most commonly used reduction factor of 0.4 is based on the observation that little permanent deformation remains when PE is unloaded from 40% of its yield stress. Additional reduction factors to account for material creep under timewise constant stress are estimated from creep tests. Based on successful field experience, this methodology has worked well; nevertheless, a more precise test that accounts for loading conditions similar to the actual field application would provide better engineering values. Additionally, standards allowing the use of PE4710 materials for the manufacture of PE pipe were introduced in 2005 and 2006. Because PE4710 materials have a higher tensile strength than PE3408 materials, they are expected to have higher safe pull strengths than those currently in use. This paper discusses the use of a test procedure that applies a loading history representative of actual field conditions during directional drilling installations. Test results are presented for PE4710 pipe materials and the consequences of loading history on the final post-installation deformation state of PE pipe are discussed. Additionally, the original method employed to determine safe pull stresses did not evaluate fusion joints that are present in directionally drilled applications and subject to the same stress as the PE pipe. This paper presents test results for pipe fusion joints to confirm that the increased pull strength for PE4710 HDPE pipes is suitable for field produced fused pipes. These results and comparisons will be useful in the design of current trenchless projects, as well as setting design requirements for the PE4710 pipe materials in AWWA manuals and other industry guidance.

L. J. Petroff

Papers

A Laboratory Method for Determining the Safe Pull Stress for Directionally Drilled High Density Polyethylene Pipe