HDPE vs. RCP, Round 2
By Dr. Patricia D. Galloway
Dr. Patricia D. Galloway, PE, is CEO of the Seattle-based Nielsen-Wurster Group. In June she was appointed by President Bush to serve a six-year term as a director of the 24-member National Science Board, the National Science Foundation's governing body.
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| Patricia D. Galloway |
I have received a surprising number of comments about the recent blog on manufacturer's warranties and specifically, the differences between HDPE pipe and concrete pipe.� As a professional, I thought I'd revisit the issue in light of those comments, which rightly pointed out that I may have over-simplified the matter regarding some of the opinions I gave.
I said, in the context of discussing pipe failures, that some states had banned the use of HDPE pipe.� In fact, no state has banned HDPE pipe in its entirety, and I stand corrected if any of my readers made this interpretation.� However, several states and municipalities have investigated it, limited its use, are studying the issue, or have implemented testing regimens designed to ensure they get what they pay for.� The Kentucky Transportation Cabinet has formed a task force to evaluate specifications and use of HDPE pipe on its future projects, based on the dismal results of performance inspections carried out in Kentucky in 2002 and July 2005. �Knoxville, Tenn., now mandates the exclusive use of concrete pipe within city right-of-ways.� Pueblo, Colo., no longer allows HDPE to be placed in any of the City's public rights of way.� Georgia now requires a minimum of 25 percent of a pipe system to be mandrel tested and any pipe over 5 percent deflection be removed and replaced. Kentucky now pays half the full rate, after mandrel testing, it finds if inferior installation causes pipe to deflect beyond the 5 percent deflection limit. �Wisconsin requires a minimum of 10 percent of the system be mandrel tested and any pipe over 5 percent deflection be removed and either reinstalled if not damaged, or replaced at no cost. Illinois requires mandrel testing of a piping system after 30 days of installation with pipe limited to 5 percent deflection. The State of Nevada does not allow pipe to exceed 5 percent vertical deflection after 30 days of installation and does not allow rerounding of the pipe that does not meet the test.� Admittedly, these are not outright bans, but do reflect concern regarding the appropriate use of HDPE.
I also stated that, unlike HDPE, concrete pipe does not depend on the surrounding soils to support it.� Again, I stand corrected--To a point.� HDPE pipe requires the activation of soil's internal friction to develop the passive pressure necessary to develop its strength, whereas RCP does not require this activation for its structural integrity.� Hence, the soil envelope that needs to be evaluated around an HDPE pipe is much wider, and thus, a larger area of the surrounding soil must be evaluated and properly placed, than is the case with RCP.� �
Finally, I made a comment that loss of life had occurred. As this was a matter that is confidential and has settled, I would retract the statement in that the evidence was not conclusive as to whether the accident was the result of poor installation, design, and/or material properties.
I appreciate readers keeping me on my toes.� My aim in the original blog, as it is now, is to ensure that engineers understand that use of different materials require different considerations, and carry with them different risks.� It behooves careful engineers, living up to their full ethical, legal and moral responsibility, to take those risks into account when designing a project.
Who is Really Responsible for Design Coordination?
By Dr. Patricia D. Galloway
I increasingly see more and more projects facing multi-million dollar claims as a result of lack of design coordination, primarily in public-works construction. More and more often, the lack of design coordination appears to be the result of the need to get bid documents on the street to meet referendums on the ballot, federal funding requests and/or commitments made with third party utilities in memoranda of understanding. The rush to get the design finalized and out to bid results in a high probability that the design has not been fully coordinated, especially when there are multiple design firms involved.
When things go bad on the project because things "just don't work", who bears the responsibility for the incomplete and/or uncoordinated design? I have seen attempts by owners to include contract clauses attempting to shift the risk to the contractor with the requirement to identify any glaring errors and omissions. Other risk-shifting clauses include the requirement to perform constructability reviews, thus appearing to indicate that if it is not constructable then the contractor is somehow responsible. However, as more and more cases are demonstrating, these clauses cannot protect the owner, in a design-bid-build project, from issuing a complete set of coordinated and accurate plans.
This is the key question: when a set of drawings contains sheets that conflict with each other, or information that may be correct on one sheet in one discipline, but incorrect on another sheet in another discipline depicting the same design, who bears the ultimate responsibility when the design was rushed to bid? Is it the owner or is it the designer? Or is it a combination? It surely is not the contractor's responsibility!
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Related Links: The answer lies in the engineer's role and responsibility under his or her license. The engineer must assure that the design is complete, accurate and constructability--simple as that. If an engineer is aware that there are errors or omissions in the documents, the engineer cannot simply hide behind the guise of limited or depleted funds available to it, or the owner's directive to do so. The engineer must recognize that by stamping a set of drawings, that he or she is telling the contractor that he or she has checked the drawings and to the extent of what is reasonably known or could have been known, that the drawings are complete, accurate and constructable-and thus have been coordinated with the various disciplines. The initial claims will of course be made by the contractor against the owner due to the contract being between the two parties, but ultimately the owner will look to the engineer for whatever final action was taken.
Training sessions offered by the insurance companies providing error and omission coverage provide guidance on these issues. It would be wise for more engineering firms to take advantage of this training and to assure that its engineers who are stamping drawings in their firms are aware of the risks and liabilities that he or she may face (as well as the firm) regardless of what "directives" may have been issued by the owner. A little more prevention may save everyone millions of dollars and litigation time.
Art and Engineering:
Leonardo, Where Art Thou?
By Dr. Patricia D. Galloway
Art and Engineering-whoever heard of such a thing!! After all, we know that artists think with the left side of their brain and engineers with the right side--or is it the other way around? For centuries, people have thought that artists are technically inclined become Architects. And we all know the battle between architects and engineers! Most people tend to think of engineers as people with lab coats, dark thick glasses and solitary individuals working behind closed doors devising solutions to problems based on math and physics. Architects, on the other hand, portray the beauty in what they do on paper and transform that art into physical buildings hoping for artistic awards. What aren't we getting?
Engineers are just as much artists as architects and have been using their full brains for centuries. The best example of one of the greatest artists and engineers of all times was Leonardo DaVinci. I was watching a PBS special the other night on DeVinci and two plans of his work that never got off the ground in his lifetime (No pun intended). One was a hang-glider and the other was a weapons slingshot for use in battle in lieu of cannons. The story was about how two groups of researchers were able to take his original plans and recreate them using the original intent of Leonardo, and to demonstrate that they indeed worked. Over months of design review and construction, the two inventions were born.
How is it that such a great artist could also create some of the world's greatest engineering inventions long before they were actually put into application? Creativity--it all goes to what we tell our kids about careers and what they do. Somehow we have forgotten that work is "fun" and that the best part of working is creative thought and dreams of inventing new means and methods and/or new inventions of machinery or other objects which make life easier. When one is told to dream and told to transorm the impossible into reality, it removes certain barriers from one's internal mind and allows a more free flowing thought process. This thought process can actually result in greater efficiency if one is able to "think out of the box" and recognize that it does not always have to be done the same way it has been done for 100 years.
We have examples of engineers who are just as much artists today as Leonardo was then. Look at some of the greatest bridges around the world--the Tsing Ma in Hong Kong, The Brooklyn Bridge in NYC or the Fred Hartman Bridge in Baytown, Texas, near Houston--all designed by structural engineers and examples of art and beauty that the public admires. Having just attended my first National Science Board meeting, I was able to see scientific engineering projects being built around the world that look more like "art" than research. Nanotechnology produces some of the most magnificent forms of molecular art that anyone has ever seen. When the new NSF Strategic Plan is released in September, I urge my readers to look at the cover and to guess what it is. I guarantee you are in for a surprise.
Manufacturer's Warranties:
Just Another Pipe Dream?
By Dr. Patricia D. Galloway
Recently, I have been researching the difference between the use of High Density Polyethylene (HDPE) plastic pipe versus Reinforced Concrete Pipe (RCP) for drainage and sewer work. In interviewing several engineers who design pipe, as well as contractors who install pipe, I asked them what they believed the difference to be. The answer: it is merely a material substitution. The primary reason in specifying HDPE pipe over RCP pipe appears to be primarily cost and ease of installation. Some also indicated that they relied on the manufacturers’ warranties in their decisions. Benefits claimed life expectancies of between 50-100 years. If the manufacturer says it is true-it must be so. But is it?
The answers seemed too easy. I began to investigate what the manufacturer’s warranties actually said. True to form, what some of the engineers told me was indeed true. Manufacturers, as well as the Plastic Pipe Institute have made claims that HDPE pipe is lighter, easier to install and in the end-results in thousands of dollars of savings. (Note that the fine print, however, disavows any responsibility if anything goes wrong). Thus, with such great assertions, why go anywhere else?
The answers however, seemed too easy and simple. Further research indicated significant failures in HDPE pipe resulting in significant monetary damages from both property losses as well as life in some cases. Failures in some states have resulted in some DOTs digging out and replacing pipe and several indicated they had now banned its use. Seemed a little extreme to me as well. Thus, more research.
What I discovered was that HDPE plastic pipe is simply NOT a material substitution. While RCP is a rigid structure and does not depend on the surrounding soils to support it, HDPE pipe is merely a material which requires the soil envelope around the pipe to act as part of the actual design. Thus, the drainage (or sewer) system is not truly designed until the pipe is actually placed in the field, requiring the Engineer to oversee the installation as the Engineer of record takes full responsibility for the pipe design.
Does this mean that HDPE pipe cannot be used at all? Absolutely not! However, what it does mean is that the engineer has the responsibility to review the criteria set forth by the Client and to fully evaluate whether HDPE pipe is the most suitable alterative for a project. Further, the engineer must assure that it has fully designed the pipe in consideration of the soil envelope around it. Merely accepting the manufacturer’s assertions as shown on the packaging will not exonerate the engineer nor relieve the engineer of its full responsibility to assure the health, safety and welfare of the public. When the pipe fails, it will not simply be the contractor on the hook for recovery. The engineer could also be liable. Is it worth the risk of losing one’s license or the cost of fighting a lawsuit? Engineers need to understand the risks and liabilities before proceeding with any design and to recognize the appropriate standard of care. Nothing, including warranties, will ever substitute for hard work.
