Flexible Pipe Design

Flexible Pipe Design


The Plastic Pipe Profile Predicament
Resource # e-028
AASHTO’s Load & Resistance Factor Design (LRFD) for thermoplastic pipe requires many inputs from the design engineer ranging from a Deflection Lag Factor to an Installation Factor. Most of the input decisions must be made by the engineer on a project by project basis. One very important design variable, however, has to be provided by the plastic pipe manufacturer; the idealized pipe wall profile for each size of pipe. Pipe wall profiles vary from manufacturer to manufacturer, and potentially region to region from a given manufacturer. This ePipe explains why the idealized pipe wall profile for each size of pipe is critical to the project design calculations and what should be done to obtain correct values.


Plastic Fill Height Table Pitfalls
Resource # e-027
Plastic pipe fill height tables published by the manufacturer are often erroneously used for project design while manufacturers in fact state that the published tables should be used only for general informational purposes, not for design. Critical assumptions must be understood behind the development of these tables including Water Table Impact and Trench Installations. This ePipe explains the reasons why these tables are not to be used for actual project design.


The Importance of the Gradation of Sands With Respect to Structural Backfill Support for Plastic Pipe
Resource # e-024
The engineering community must design their projects with consideration given to gradient control of the backfill envelope. As the AASHTO Section 12 Plastic Pipe Design procedure warns, uniformly graded material with an average particle size smaller than a No. 40 sieve “should not be used as backfill for thermoplastic culverts.” If, however, the design engineer allows the use of such material, that decision requires extra precautions during design and installation.

This ePipe is to be used with YSK 144: A User’s Guide: Adhering to Federal Regulation 23CFR625 in the Design of Buried Culverts.


A User’s Guide: Adhering to Federal Regulation 23CFR625 in the Design of Buried Culverts
(YSK Bulletin #144) October, 2016
YSK 144 summarizes legislation and specifications behind a series of ePipe Design notes that assist the engineer in selected inconclusive areas of the plastic pipe design standard.


Service Life of Aluminized Type 2 Coated Steel Pipe: Predictions vs. Actual
Resource # 07-135

The pipe culverts in question are, at the time of this inspection, approximately 33 years old. This inspection consisted of visual observations of the inside (water side) of the culverts. Usually the water side of metal pipe experience earlier and greater wear than the soil side because of service conditions (including abrasion), oxygen exposure, and replenishment. The lowest water pH and resistivity for those sites as shown in the aforementioned report are 7.0 and 2609 respectively. Most are higher than 7.0 and 5000 and, therefore, not considered harsh conditions by traditional environmental criteria. It is apparent that abrasion is a factor and should be considered as such in any metal pipe durability assessment.

 07-131 Rigid vs. Flexible Material
Resource # 07-131
(Online only; printable using legal size paper)

This document lays out various specification requirements for RCP, CMP, HDPE, and PVC including material requirements, hydraulics, pipe strength or stiffness, installation, soils, corrosion resistance, flammability, flotation, and more.

 e009 New Product, More Concerns – Polypropylene vs. Polyethylene
Resource #e-009
Throughout its history, the plastic pipe industry has developed a startling array of unsuccessful pipe products that have failed to live up to performance expectations. PPI mocks the very real concerns that these risks pose to the public, labeling them “scare tactics.” The ACPA and prudent engineers consider those risks legitimate factors to be weighed in the decision to use or restrict the use of plastic products.
 e006 Flexible Pipe Manufacturers Admit Mistakes
Resource # e-006
For years, the concrete pipe industry has educated owners and engineers regarding the risks of specifying HDPE pipe. However, the statements in this document constitute actual acknowledgments by the manufacturers themselves of the critical weaknesses of conventional HDPE pipe!
 e003 Steel Reinforced High Density Polyethylene Pipe
Resource # e-003
This document provides information specific to SRHDPE pipe and offers insight that should cause designers and owners to question claims about this new product.  How is the pipe designed to support dead and live loads initially and long term? What national specifications are there for installation of SRHDPE pipe?
 e001 Greenbook Changes for Plastic Pipe
Resource # e-001
The “Greenbook” is used throughout southern California for public works construction, and is often referred to by agencies and consulting engineers in other localities as a guide specification. It has been changed significantly in 2009 relative to contractor requirements for installation and deflection testing of plastic pipe. These changes should be carefully reviewed by Engineers and Contractors prior to specifying or using plastic pipe, as the new requirements could have significant cost impacts, as well as affecting considerations whether this flexible pipe is appropriate for the intended application.
 bf7 Plastic Pipe Claims
This publication presents various claims made by the plastic pipe industry, discusses engineering facts which indicate the claims are not justified, and evaluates critical properties of plastic pipe which affect performance, durability and service life.
 ysk101 The Truth Behind the Greenbook Acceptance of HDPE Specifications
(YSK Bulletin 101) March, 1996
Last fall the American Public Works Association’s Joint Cooperative Committee, which publishes the Greenbook, accepted specifications for HDPE pipe. There has been much discussion about why the Greenbook reached that decision. Meanwhile HDPE manufacturers have used this acceptance in their promotional campaigns.