Roy Bash comments

Richard:



The committee’s second reference under “Criteria for Steel and Cast Iron” by S.P. Ewing is considered to be a classic in literature pertaining to valid research projects for field testing CP criteria.

Dr. Ewing explains that all potentials were measured by interrupting the CP current so that the open circuit (instant-off) potential would be free of IR drop. The reference electrode was always placed on the surface of the soil directly above the buried steel pipe specimen being tested.



On page 415 of Dr. Ewing’s paper covering the test results of his field research project at the four locations in Oklahoma in 1948, outlines what he considered to be the most significant findings of his research as follows:

“The most significant findings of the test will be discussed first .The data obtained indicate that corrosion was stopped in each environment at a specific open circuit potential . These potential values varied about 0.1 volt between the different environments. They were 0.05 to 0.15 volt less (more cathodic) than the usually accepted value of -0.85 volt as measured with reference to the copper/copper sulfate electrode.”



From the above Dr. Ewing found that the open circuit (instant-off) potential criterion for CP of steel ranges from -0.70 to -0.80 volt, CSE. Please note that he considered this to be “the most significant finding of the test.



The committee lists this scientifically sound article as their second reference, supposedly in support of their position that the instant-off potential criterion for CP of steel is -850 mV, CSE.



Listing a scientifically sound article as a reference and then ignoring or outright disputing it leaves a lot to be desired concerning the best professional approach for addressing any issue being debated



The-700 to -800mV, CSE instant-off potential CP criterion for steel can easily be supported by use of long standing basic scientific principles from the textbooks. Conversely, the -850 mV, CSE instant-off potential CP criterion for steel can easily be proven to be at least -50 mV, CSE overly stringent.



As A. W. Peabody wrote in his original book, the maximum potential, CSE that can be expected on a buried

steel pipeline in natural soils and waters is –0.8 volt. This is a scientific fact that is as true today as it was when Peabody wrote it. Quoting from the second edition of the A.W. Peabody book on page 69, “Newly laid , coated steel pipelines may have an average potential in the range of -0.5 to -0.7 V, whereas old , bare steel lines may have an average potential more in the range of -0.1 to 0.3 V (CSE)”.



There just can not be any justification for NACE to produce a standards document based on buried steel pipelines reaching potentials even near -0.8 volt, CSE. In 56 years of CP practice this writer has measured only four potentials above -700 mV ,CSE on buried steel pipelines (-705mV, -706mV, -718mV, and -725mV) and all of these were on the same coated steel pipeline in 200 to 250 ohm-cm tropical rainforest soil in Suriname, South America.



Some members of the committee have noted that steel reaches a potential of 0.8 volt ,CSE or more in high pH alkaline environments, but as Peabody has written in his book, steel does not corrode in high pH environments.

Quoting Peabody from page 43 of his book, “When steel is immersed in a sufficiently caustic solution (around pH 11 and higher) it can be made to discharge current without appreciable metal loss”.



All aspects of an overly stringent CP criterion for steel are negative.



1, It offers no more assurance of corrosion control than an adequate CP criterion.

2. It increases the risk of causing corrosion damage on nearby buried or submerged metallic structures

3.It increases the risk of damaging coatings on coated pipelines.

4.It increases the risk of hydrogen damage to the steel being protected.

5. It unnecessarily increases the cost of CP.

6.It would overtly enrich (monetarily) the CP industry and NACE.



Respectfully Submitted,



L.A. (Roy) Bash, P.E.



L.A. (Roy) Bash

Global Cathodic Protection, Inc.

A CerAnode Company

P.O. Box 571507

Houston, TX 77257

5826 Schumacher Lane