Materials Performance

MAR 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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41 MATERIALS PERFORMANCE: VOL. 57, NO. 3 MARCH 2018 the corroding site. Then, the corrod- ing areas furthest from the anode bed should polarize at least 100 mV from its corroding potential with potentials that are never more nega- tive than –1,000 mV CSE · When the corroding portion of the line is longer and more than one anode bed is anticipated, the poten- tial of the pipe nearest to the anode bed, where the most negative po- tentials are expected, should not be more negative than –1,000 mV (Fig- ure 8). Summary • Prestressed concrete cylinder pipe is inherently corrosion re- s i s t a n t . T h e u s e o f i m p a c t e d mortar coatings passivates the u n d e r l y i n g p re s t re s s i n g w i re and reduces chloride ion pene- tration. • CP is rarely required because of PCCP's inherent corrosion resis- tance. • The minimum CP potential shift criterion is 100 mV polarization or depolarization. • Prestressed wire is susceptible t o H E a t p o t e n t i a l s n e g a t i v e enough to generate hydrogen but required months to years be- fore a failure occurred. The po- larization potential should be maintained more positive than –1,000 mV CSE to avoid HE. More negative potentials can embrit- tle and split prestressing wire. They also can greatly increase the cost of CP and not improve corrosion protection. • T h e d u c t i l i t y o f p re s t re s s i n g wire under excessive CP recov- ered after CP was discontinued, mostly during the first 4 weeks but at least 8 weeks were re- quired for a full recovery. • CP increases the pH around the prestressing wire in carbonated m o r t a r o r a ro u n d c o r ro d i n g wire to initial uncarbonated or noncorroding levels. Limiting potentials do not need to be ad- justed to values more positive than –1,000 mV because of the rapid increase in pH around the wire during CP. • The continuous torsion test in A S T M A 6 4 8 i s a n e x c e l l e n t means to determine the suscep- tibility of prestressing wire to HE. The higher number of turns to break in continuous torsion indicates a less susceptible wire. • Limiting the prestressing wire drawing temperature to 360°F ( 1 8 2 ° C ) g re a t l y i n c re a s e s t h e ductility of the wire and signifi- cantly reduces its susceptibility to HE. • The current from a CP system distributes equally to the pre- stressing wire and steel cylinder in PCCP. References 1. AWWA C301-92, "Standard for Prestressed Con- crete Pressure Pipe, Steel-Cylinder Type, for Water and Other Liquids" (Denver, CO: AWWA, 1992). 2. AWWA C304-92, "Standard for Design of Pre- stressed Concrete Cylinder Pipe" (Denver, CO: AWWA, 1992). 3. Prosser, "Research, Product Improvement, New AWWA Standards, Compliance Certification and Performance Contribute to the Increased Usage of Prestressed Concrete Cylinder Pipe," 1996 ACE Proceedings (Denver, CO: AWWA, 1996). 4. "Review of Water Industry Plastic Pipe Prac- tices," AWWA Research Foundation-Research Re- port, Distribution Systems (Denver, CO: AWWA). 5. ASTM A648, "Standard Specification for Steel Wire, Hard Drawn for Prestressing Concrete Pipe" (West Conshohocken, PA: ASTM). 6. R.L. Benedict, "Corrosion Protection of Concrete Cylinder Pipe," CORROSION/89, paper no. 368 (Houston, TX: NACE, 1989). 7. NACE RP0169-96, "Control of External Corro- sion on Underground or Submerged Metallic Pip- ing Systems" (Houston, TX: NACE, 1996). 8. D.A. Hausmann, MP 8, 10 (1969). 9. NACE RP0290-90, "Cathodic Protection of Rein- forcing Steel in Atmospherically Exposed Concrete Structures" (Houston, TX: NACE, 1990). 10. S.C. Hall, E.J. Carlson, R.G. Stringfellow, MP 33, 10 (1994): p. 29. 11. S.C. Hall, I. Mathew, Q. Sheng, "Prestressed Concrete Pipe Corrosion Research: A Summary of a Decade of Activities," CORROSION/96, paper no. 330 (Houston, TX: NACE, 1996). 12. S.C. Hall, "Analysis of Monitoring Techniques for Prestressed Concrete Cylinder Pipe," CORRO- SION/94, paper no. 510 (Houston, TX: NACE, 1994). 13. S.C. Hall, I. Mathew, "Cathodic Protection Re- quirements of Prestressed Concrete Cylinder Pipe," Second International Conference—Advances in Underground Pipeline Engineering (New York: ASCE, 1995), p. 168. Technical Editor's Note: This is an ab- breviated version of CORROSION/98 paper no. 637, presented in San Diego, California. The essential elements of the text have been retained as well as explanatory portions of the original. Details such as those describing laboratory equipment, procedures, and certain findings have been reduced. Case histories of five field applications and results in various enviromnents may be obtained by contacting NACE Headquarters at phone: 281/228- 6223 to order a copy of the entire original paper. Sylvia C. Hall (now with Sylvia Hall Engineering [SHE]) was a director at Ameron International Corp. She has 35 years of experience in corro- sion and corrosion control of concrete pressure pipe. She has conducted extensive research in HE of prestressing wire used in prestressed concrete pipe. She has masters degrees in chemistry and business administration, is a professional engineer (corrosion) in California, and is a NACE-Certified CP Specialist. She is a 38-year member of NACE. From the Author—Today's Practice This article was based on 13 years of research following a rupture of a PCCP in 1984 sub- jected to CP with polarization potentials in the range of –1,150 to –1,250 mV (CSE). Even though HE of high-strength steels was recog- nized in the corrosion industry, others did not think HE was the cause. This research led to the development of and the CP criteria in NACE RP0100-2000, "Cathodic Protection of Prestressed Concrete Cylinder Pipelines." The RP was expanded in 2008 to NACE SP0100-2008, "CP to Control External Corrosion of Concrete Pressure Pipe- lines and Mortar-Coated Steel Pipelines for Water and Waste Water Service" and included additional concrete and steel pressure pipe. The remaining prestressing wire speci- mens under exposure mentioned in the COR- ROSION/98 Paper no. 637 that this article was based continued to be maintained until the au- thor left the company in 2013. The specimens from wire manufacturers "A", "B," and "C" at –1,000 mV (CSE) and stressed at 60% of its minimum specified tensile strength in a simu- lated mortar environment were cathodically protected at –1,000 mV (CSE) for 23 years without failure. —Sylvia C. Hall, PE Cathodic Protection Criteria for Prestressed Concrete Pipe—An Update

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