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Corps Limits Canal Sheetpile Coating

Wednesday, March 16, 2011

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When the U.S. Army Corps of Engineers agreed last fall to apply protective coating to sheetpile that would be used to shore up a key New Orleans canal, the agency apparently did not mean all of the metal.

Photos show, and the Corps confirms, that it is painting only the top several feet of the steel sheetpiling that is being used to upgrade the London Avenue Canal.

At the request of the Southeast Louisiana Flood Protection Authority-East, USACE said in December that the $17.9 million contract to improve the canal’s floodwalls and levee would include applying protective coating to 6,000 feet of sheetpile.

Time Crunch

Local authorities and the Corps have been locked in a protracted dispute over whether the steel used in the $14.4 billion Hurricane and Storm Damage Risk Reduction System (HSDRRS) for southeast Louisiana should get protective coating. The system includes five parishes, 350 miles of levees and floodwalls, and 73 pumping stations.

The Corps, which built the levee system that failed during Hurricane Katrina, opted last year to forego coatings in favor of oversized pilings with an extra 1/8-inch layer of sacrificial steel on about 23 miles of new levee encircling St. Bernard Parish, which was hit hardest by Katrina.

The Corps said that the system would be difficult to complete on time if it was coated. The Corps declined to discuss the cost of coating vs. sacrificial steel, but said that the difference was negligible and that either option was acceptable.

Corps: ‘Not at Risk’

However, a Corps spokeswoman said in December that the steel on the London Avenue Canal project would get coating, because local authorities had requested it and because there was time to do so.

London Avenue Canal

Photos: Steve Beatty

Photos show partially coated steel to be used in the London Avenue Canal project.

Now, the Corps says that only the top portion of the piling—the part above the water table—requires coating, so that is what the agency is doing. However, the Corps is not using oversized steel or additional steel thickness on the canal project, as it did on the new St. Bernard Parish levee, a spokeswoman said.

Nor is the Corps using cathodic protection or concrete encasement on the sheetpile, she said. The same process is being used on remediation of the Orleans Avenue Canal, the second of three so-called Outfall Canals that drain water from the city into Lake Pontchartrain.

“It is standard to only coat the top portion of the pile with the coal tar epoxy,” Nancy Allen, public affairs officer for the USACE Hurricane Protection Office (HPO) in New Orleans, wrote in an email. “This is being done across the Hurricane and Storm Damage Risk Reduction System in any instance where coated steel (H piles, sheet piles, etc.) is being used.”

Allen said the coal tar epoxy was sufficient to inhibit corrosion. “The local sponsors are well aware that the industry standard only calls for coating the top portion of the piles,” she added. “The portion of the pile that is below the water table is not at risk of corrosion.”    

London Avenue Canal

Coal tar epoxy will provide sufficient corrosion protection, USACE says.

Seepage Remediation

Allen noted that the Outfall Canal remediation and the St. Bernard floodwalls “are vastly different.” Although part of the same system, “the outfall canal work is remediation for seepage and stability issues. We are driving sheetpile to cut off seepage.”

She added:  “There is existing levee or floodwall in place, and the only purpose of the outfall canals at this point is interior drainage.  After Hurricane Katrina, gates and pump stations were installed at the mouths of each of the three canals to block hurricane surge, making the existing levees and floodwalls a secondary line of protection.”

‘An Imprudent Decision’

Members of the SLFPAE did not respond Wednesday (March 16) to a request for comment. Last year, however, local and regional officials demanded that the project steel be coated.

"We have counseled them for months that ... the use of untreated steel in the marine environment was an imprudent decision, and we asked people with more expertise to look at it, and they agreed it was imprudent," levee commissioner Steve Estopinal, an engineer and surveyor, told the local newspaper last summer.

"We want future steel coated, and if the external peer review comes back and agrees with us . . . the federal government should be required to pay for the [monitoring] and maintenance of those walls." Estopinal called the use of untreated pilings "a design flaw."

Estopinal sponsored a successful resolution to fast-track an external peer review of the situation. That review "is being processed by the Army Research Organization's contracting department,” Allen said Wednesday.

Corrosion Control Options

Col. Robert Sinkler, Commander of the USACE HPO, reviewed for the authority the corrosion-inhibiting measures being used on the project. They are, he said:

• Over-sized cross-sections of piles

• Coal tar epoxy or other coating

• Application of a polyethylene sleeve

• Zinc coating

• Electro-chemical (cathodic) protection

• Casting in cement, mortar or concrete

Sinkler said that the system’s design guidelines did not specifically address corrosion.

A USACE official said in September that coating the pilings “would have overwhelmed the coatings industry."

Canal Project

Two of the three major breaches during Katrina occurred on the 15,000-foot-long London Avenue Canal, with much of the problem later traced to seepage, Allen said.

The goal of the six-month canal project is to repair and shore up the weakest sections of floodwall and levee to increase the “safe water” level in both channels to eight feet. The current elevation at London Avenue is capped at five feet.

   

Tagged categories: Corrosion control coatings; Corrosion protection; Protective coatings; U.S. Army Corps of Engineers

Comment from Lubomir Jancovic, (3/17/2011, 7:25 AM)

0,008"coat pure of Zinc, 0,016" coat pure of Aluminum paint sealed top ( use combustion wire flame metal spraying, vacoom blaster for surface preparation ), protecting surface of steel for 50 and more years, with no other maintenance. Pure of Zinc coat never under rusted, covered with barriere coat pure of Aluminum will not spending with oxydation and will protecting surface of steel a Years .


Comment from Tom Schwerdt, (3/18/2011, 9:13 AM)

Judging by the photo, I'm really doubtful they are using coal tar epoxy. If the coating has a meaningful amount of coal tar, it is almost invariably black in color.


Comment from Randy Gordon, (3/21/2011, 12:45 PM)

CTX is very common in sheetpile coatings, and no...you do not coat the entire sheet, only that which is exposed. Use A490 sections and eliminate the coatings all together. Did I just say that?


Comment from Tim Race, (3/24/2011, 8:31 AM)

The definitive study on sheetpile driven in undisturbed soils was performed by NBS (now NIST) in concert with the Corps way back in 1962. Bottom line - no need to coat below the water table. And using thicker steel for corrosion allowance is an accepted practice. The Corps was right all along and the local vocals and their "corrosion experts" are just plain wrong. In any case, most of New Orleans will be under water (global warming) long before this sheetpile fails!


Comment from Michael Beitzel, (3/24/2011, 8:55 AM)

And now for the rest of the story for the "global warmers": The sheet pile being installed in New Orleans is being driven in disturbed, highly corrosive soil in a recently constructed levee that is well above the ground water table. Additionally, the levee is supported on highly organic soils that are going to subside. The concrete cap on top of the sheet pile wall includes a slab to protect in the event of overtopping; however once the levee subsides, oxygen, salt water and a humid marine swamp environment will have direct access to unpainted exposed sheet pile. Sounds like a poorly accessible highly corrosive condition to me. I wonder if all this was accounted for in the 1962 study.


Comment from Tim Race, (3/25/2011, 9:23 AM)

Thanks for your comments Mr. Beitzel. You are right, the conditions you so correctly describe are not undisturbed soil. The 1962 study is available online. For a complete description of what the Corps considered in opting not to coat the sheet pile see http://www.mvn.usace.army.mil/eng/HSDRRSDesignGuidelines_Waiver_SteelPileCorrosionProtection_12162009.pdf I must admit that I was only casually aware of this issue and after reading the Corps memo I see that it is indeed a much more complicated issue. My apologies to the corrosion experts who properly voiced their concerns. Thank you Michael for setting the record straight!


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