Sylvia Hall Articles and Report Highlights
1994 – Corrosion 94 – Analysis of Monitoring Techniques for Prestressed Concrete Cylinder Pipe
- CTE coated pipe can be monitored because it holds the moisture in the coating. Poly-wrapped pipe could not be monitored because (apparently) the coating dried out and the polywrap did not allow water back into the coating.
- Identifying corrosion on the bottom of the pipe is difficult/impossible until the corrosion shifts the potential of pipe steel farther off the bottom.
- Sensitivity of the pipe-to-soil and cell-to-cell monitoring techniques for the unbonded pipeline decreased approximately 42% to 49% compared to the bonded pipeline.
1994 – Materials Performance – Cathodic Protection Studies on Coal Tar Epoxy-Coated Concrete Pressure Pipe
- Salt water over hole in CTE coating over poor quality mortar, 3 years exposure – chlorides migrated a maximum 3.6 cm from the hole. Similar tests on high quality mortar showed no chloride penetration/spread.
- Similar tests to above, but applied CP to the steel. A white deposit, 83% magnesium, developed at the pinhole; possibly magnesium hydroxide produced by repulsion of hydroxide ions and attraction of magnesium ions to the steel cathode. That or repulsion of Cl- ions may have been the cause of the much lower chloride ion content under the pinhole when compared to the tests in 1) above.
- CP applied to rings around pinhole centerline on similar samples to above tests, and similar samples but with chloride-contaminated mortar. IR drop noted at least 15.2 cm from hole (much farther than chloride ion diffusion). Polarization shift of only 20 mV protected the steel. Within 24 hours of turning off the CP system at the end of the test, the potentials of the specimens depolarized to a range of -192 to -262 mV, which indicates passivation of the steel. CP repelled the chloride ions from the steel and generated additional hydroxide ions at the steel to repassivate the surface.
1995 – ASCE Pipelines – Cathodic Protection Requirements of Prestressed Concrete Cylinder Pipe
- Current density required to achieve or exceed a 100 mV shift of uncoated, CTE-coated and PE-encased PCCP in a non-corrosive environment was approximately 25, 3, and 3 microamps/sf, respectively.
- Polarization potentials more than about -1V CSE will evolve hydrogen.
- Better quality wire (measured by torsion) indicated to have better resistance to failure from hydrogen.
- Even wire exposed to high potentials evolving hydrogen from CP, which does not have reduced physical performance due to hydrogen, may still have high hydrogen content.
1996 – NACE Paper 330 – Prestressed Concrete Pipe Corrosion Research – A Summary of a Decade of Activities
- Increase in chloride content with depth over corroding steel is believed to be due to the attraction of the negatively charged chloride ion to the positively charged corroding surface.
- Higher water content in mortar mix results in lower porosity and greater Cl- resistance.
- Thicker mortar coatings made in one pass with identical water content have higher absorptions and faster Cl- penetration than thinner mortar coatings made in one pass.
- Impacts on mortar coatings can cause greater susceptibility to Cl- induced corrosion.
- Soaking mortar with salt water for 44 wet-dry cycles produced water soluble Cl- contents at wire level of 2400 – 2800 ppm, which still did not depassivate the steel, as indicated by potentials measured with a saturated calomel electrode. This steel passivation may have been extended by drawing lubricant zinc phosphate, a known corrosion inhibitor.
- Less than 1000 ppm water soluble Cl- ion will depassivate ordinary reinforcing steel.
- Low levels of CP can be used to repassivate steel embedded in carbonated mortar or concrete, and then CP voltage can be increased without generating hydrogen around wire.
- Anodic reaction on mortar-coated steel will first consume hydroxide ions, which may occur for a long time before steel is corroded. Potentials more positive than approximately +700 mV (SCE) are required before hydroxide ions are consumed. Large impressed voltages appear necessary to achieve +700 mV (SCE).
1998 – ASCE Pipelines – Corrosion Control of Prestressed Concrete (Embedded) Cylinder Pipe
- Evaluation of soils with resistivity less than 1500 ohm-cm for potentially high chlorides is recommended.
- PCCP lines crossing cathodically protected steel pipelines should be coated (or encased) in dielectric on each side of the crossing; 200 to 400 feet each side is typically specified.
- The potential of steel in concrete normally lies between -50mV and -250mV (CSE), which is approximately 300mV more noble than the potential of bare steel.
- Current density requirements of operating CP systems of unsealed PCCP lines have ranged from 100 to 1000 microampere/m2 (10 to 100 microampere/sf) to achieve 100 mV minimum shift and -1000 mV (CSE) maximum. PCCP lines sealed with a barrier coating require about 1/3 to ¼ that current density.
1998 – Corrosion 98, Paper 637 – Cathodic Protection Criteria for Prestressed Concrete Pipe
- Polarization shifts of only 20 mV have been found to effectively protect corroding steel in mortar.
- Under CP, the pH at the wire surface will increase rapidly in a few hours or days to a value > 12.4 because of the production of hydroxide ions or the consumption of hydrogen ions.
- Pipeline monitoring potentials more negative than –300 mV (CSE) can indicate corrosion, current pickup, or that the line is being cathodically protected.
- The project was to determine the effect of CP on the performance of passivated, corroded, and split prestressing wire immersed in an environment to simulate sound mortar and mortar surrounding severely corroded wire.
- Case studies of successful and unsuccessful applications of CP to PCCP are presented.
1998 – Materials Performance – Cathodic Protection Criteria for Prestressed Concrete Pipe – An Update (2018)
- The 1998 article is updated.
2002 – City of Los Angeles Tests 48 Year Old T-Lock Protected Pipe and 72 Year Old Tile Lined Pipe
- T-Lock PVC liner prevented interior corrosion of sewer pipelines.
2004 – AWWARF – External Corrosion and Corrosion Control of Buried Water Mains, Appendix B-1, Cathodic Protection of Notched Prestressing Wire in PCCP; Ameron International, South Gate, CA
- The objective of the project was to determine the effect of cathodic protection on the performance of notched prestressing wire immersed in solutions simulating sound mortar and mortar surrounding severely corroded wire. The susceptibility of split and non-split prestressing wire to hydrogen embrittlement and the potentials to produce hydrogen embrittlement and eventual wire failure were determined. The data and results are presented.
2011 – ASCE Pipelines – Field Performance of Coatings and Linings for Welded Steel Pipe in the Water Industry
- Compares application processes, cost and performance of mortar and dielectric coatings.
- “Water within the microscopic pores in the mortar inhibits the diffusion of air (oxygen) to the steel surface that is required for corrosion, allowing mortar lining to continue to protect steel even if all excess alkalinity is leached from the lining.”
- Estimated service life for potable water immersion service of liquid epoxy or polyurethane is maximum 16-17 years before first maintenance recoating.
2011 – Journal of Pipeline Systems Engineering and Practice – Discussion of “Pipe Efficiency Analysis at a Water Utility”
- The authors of the original article, through no fault of their own, confused the performance of mortar-coated steel pipe with that of bar-wrapped concrete cylinder pipe.
- The authors of the original article used mathematical manipulations to conclude that concrete pressure pipelines averaging 30” in diameter are less “efficient” than iron or PVC pipelines that averaged 10” in diameter because the larger pipe cost 2.6 times more to install and roughly 3 times more to repair, whenever repairs were required. DUH!
- Average time to first repair of the incorrectly-identified concrete steel cylinder pipe was more than 28 years.
2012 – Coatings Pro Magazine – Linings for Large-Diameter Steel Water Pipelines
- Polyurethanes typically have a substantially greater water vapor transmission rate than epoxies.
- Modifying the polyurethane formulation to tighten molecular structure and reduce water vapor transmission makes the resulting polyurethane less flexible.
- Polyurethanes are relatively susceptible to disbondment due to corrosion under the lining, which can be hard to detect.
2012 – Coatings Pro Magazine – Mortar – The Forgotten Coating
- Abrasive blast cleaning and a surface profile are not required for application of Portland cement mortar, and minor corrosion and mill scale on the steel surface does not affect passivation of the steel.
- Without cathodic protection, the design life of mortar coatings is greater than 50 to 100 years while dielectric coatings typically have a design life of 15 to 30 years.
2013 – ASCE Pipelines – Corrosion Protection Provided by Mortar Lining in Large Diameter Water Pipelines After Many Years of Service
- Test results on mortar linings from 20 pipelines from 20 to 108 years of service carrying various quality waters are presented.
2019 – Letter report to Thompson Pipe Group – Use of PCCP and BWP in AC powerline ROW’s; Effects of AC Powerlines on PCCP & BWP
- The issues with AC interference in the past decade have been on steel pipelines coated with the newer highly-electrically resistive organic coatings on the market. These pipelines are well-coated and have very few small pinholes or flaws in the coating. These small areas of coating imperfections provide a location for extremely high current densities from AC sources (such as AC powerlines) to develop which can initiate and produce corrosion at a rapid rate resulting in pinhole leaks through the pipe wall.
- High AC current densities do not develop on mortar-coated pipe because portland cement mortar and concrete is not a highly-resistive coating relative to the newer organic coatings. The current density on PCCP or BWP from nearby AC sources will be exceedingly lower than that required to cause AC interference concerns.
2020 – ASCE Pipelines – Does My Pressure Pipeline Need Cathodic Protection?
- Cathodic protection is rarely needed on new CPP lines and, if CP is used, it only needs to be used at the location of corrosion or stray current discharge. Non-corroding or stray current pickup locations do not need CP.
- CP is not required on CPP installed near or under AC power lines since the extremely high current densities required to cause DC discharge are not present.
- Ductile iron pipe that has a thinner wall than cast iron pipe will likely have a shorter life without encasement or CP. Even with encasement, DIP could be viewed in the same manner as steel with a dielectric coating, and may need CP.