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Preparing Surfaces at Wastewater Plants: An Overview of Substrates, Practices, and Standards

From JPCL, September 2012

More items for Surface Preparation

by Vaughn O’Dea, Tnemec Company, Inc.

The author describes how surface preparation for the use of high-performance protective linings contributes to the sustainability of wastewater infrastructure. Surface preparation for common substrates found within sever wastewater environments is discussed....
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Tagged categories: Carbon Steel; Cast iron; Concrete; Linings; Sewer systems; Stainless steel; Substrates; Wastewater Plants

Comment from Joe Cesarek, (10/4/2012, 3:57 PM)

Groovy stuff here ...... every wastewater engineer specifier should read! Joe at SEH Engineering, Inc.

Comment from Tom Schwerdt, (10/8/2012, 8:45 AM)

I'm surprised there is no discussion of repassivating the stainless.

Comment from Ralph Sabatelli, (10/17/2012, 9:24 AM)

I'll be blasting steel tanks in a wastewater treament facility and found this article very interesting. Thanks

Comment from James Johnson, (10/18/2012, 1:16 PM)

I agree with the author that good surface preparation is key to good coating performance, but I am surprised he did not remark on the need to limit corrosive salts. Due to the chemicals used and the chemical reactions that occur in waste water it is not uncommon for surfaces to be highly contaminated with corrosive salts, such as chloride, sulfate and nitrate. Many otherwise satisfactory coatings have prematurely failed due to these non-visible contaminants and since they are so common I believe a good specification should address them and contractors, who are made to warranty their work, need to be aware of them to limit or reduce rework. In our years as a coating applicator contractor we found it critical that we remove corrosive salts as part of surface preparation if the project was to be successful. In doing this we almost eliminated rework. We still had the occasional application problem, but those were minimal with good supervision and QC. The SSPC offers the Guide 15 document providing testing information and NACE offers the 6G186 document which offers information on how these salts cause coating failures and offers information on various removal methods. Both of those documents are of great value to owners, inspectors and contractors.

Comment from Jerry Trevino, (10/21/2012, 9:15 PM)

Infrastructure in the United States and world wide is in need of rehabilitation. In underground structures such as manholes, pump stations, and piping, the structures along with all other types of materials utilized are not only subjected to corrosive environments, but also to hydrostatic pressures, cyclic loading and unloading, freeze thaw cycles, dry / wet cycles, etc, etc. Thus these structures are subjected to dynamic forces versus just static forces and corrosion. Although, the design life of structures in the waste water infrastructure is 50 to 100 years, little consideration was taken to verify the quality of the construction materials. In addition, as EPA demands less infiltration of clean ground water into these collection systems, the sewer environment is more septic thus more corrosive. Therefore, materials and corrosive protection which may have been sufficient years ago, they may not be effective today or in years for to come. The application of protective coatings in existing infrastructure is extremely difficult due to have to apply coatings in wet conditions, live sewer systems, with active hydrostatic pressures. If the selected coatings require the substrates to be dry and be allowed to cure before immersion, they will probably fail in the rehabilitation of the infrastructure in place. In most cases the structures, pipes, etc have to be coated in place and placed in service immediately. There is a great need to rehabilitate our infrastructure, most municipalities do not have the capital to correct the problems. We must rehabilitate our infrastructure for our health and the health of our future generations.

Comment from André Desestret, (10/23/2012, 6:04 AM)

I agree fully with the comment from Tom Schwerdt, (10/8/2012, 8:45 AM). Stainless steels do not usually need to be coated as they are "self-protecting" by forming spontaneously a protective passive film which slows down corrosion, provided of course the right type of stainless steel has been selected, and also that the surface finish has been correctly carried out, i.e. pickling and passivation.

Comment from Vaughn O'Dea, (4/13/2014, 3:31 PM)

I cannot disagree that the majority of stainless steels generally do not require a protective coating to resist corrosion in water/wastewater treatment environments, provided the correct grade is selected. I’m not a metallurgist so I cannot opine as to why some grades of stainless steel corrodes. What I can say is that as a coatings practitioner I receive 1-2 inquiries a month about topcoat stainless steel in water/wastewater treatment. The majority of the instances involve galvanic coupling with carbon steel, which accelerates the rate of corrosion to the carbon steel. My coauthors and I presented a paper at SSPC GreenCOAT 2014 titled, “Galvanic Corrosion in Water & Wastewater Structures: Coupling Stainless and Carbon Metals Leads to Accelerated Corrosion”. However, I also receive inquiries about topcoating stainless steel, usually Grade 304 that is corroding in sewer headspace environments; occasionally I encounter stainless steel that is corroding in chlorinated water treatment exposures. Regardless, proper surface preparation to achieve cleanliness and profile is required.

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