Straw Poll

Comments on Straw Poll concering criteria for SP0169

The recent straw poll sent by the TG 360 committee gives you a chance to provide the committee with your thoughts and potential compromises. They have provided 5 versions to choose. Also, you are to rank each one as to whether you strongly agree to strongly disagree. Then you are asked if you would vote yes or no on each version.

The 100 mV polarization criterion would be common to each version so is not included.

Here is what I think:

Version 1

A cathodic voltage of -850 mV or more negative across the structure to electrolyte boundary as measured with respect to a saturated copper/copper sulfate (CSE) reference electrode.

MY COMMENTS: (Disagree)

The major problem with this version is that there is no “real” way to perform this in the field. Theoretically, this is what we are trying to accomplish, but in the real world, I do not think we can do it with enough consistent accuracy to be viable. The cost of performing these type surveys can be high and the extra cost does not provide much value for amount it could cost. Therefore, I could not agree with this being the only criterion besides the 100 mV.

Interpretation of the way to measure the potentials in this criterion would lead to much confusion and possible problems that could be a major issue for those trying to use such a criterion. The test method committee for TM-0497 would have to come up the ways to measure this version and that may take longer than revising the SP0169!

Version 2

(1) A structure-to-electrolyte potential measured with the cathodic protection current applied. The current-applied potential criterion value shall be established by the owner through sound engineering practice and support by empirical evidence that demonstrates the corrosion control objective of the owner is achieved.

(2) A negative polarized potential of at least 850 mV relative to a saturated copper/copper sulfate reference electrode.

MY COMMENTS: (Has potential, but needs some re-wording)

I like much about this version, but am concerned about the definitions of “empirical evidence” and “objective of the owner”. If these are defined satisfactorily in the document, then possibly I could “strongly agree” with this version. At this time I would say it is a definite “maybe”.

This would leave it up to the owner to determine what “ON” potential they will use at each test site. This could be determined by several methods that should be spelled out in the test method document.

Also, why is it important to establish “by the owner through sound engineering practice and support by empirical evidence that demonstrates the corrosion control objective of the owner is achieved” for the “ON” potential, but if you take an “instant off” you do not have to meet the owner’s objective? Seems like every criterion should meet the owner’s objectives and if we mention it in one we need to mention it in all or make a generic statement as such in the document and not apply it to each separate criterion.

Version 3

(1) A negative (cathodic) voltage of at least 0.85 volt as measured between the structure surface and a saturated copper-copper sulfate half cell contacting the electrolyte. Determination of this voltage is to be made with the protective current applied. The Corrosion Engineer shall consider voltage (IR) drops other than those across the structure-electrolyte boundary for valid interpretation of the voltage drop.
(2) A negative polarized potential of at least 850 mV relative to a saturated copper/copper sulfate reference electrode.

MY COMMENTS (Disagree at this time)

This was almost good. Had they not included the wording “Corrosion Engineer” and “shall consider”. Not sure how we define a corrosion engineer these days. Not even sure we can get a corrosion engineering degree as such in most places around the world. There are “degreed engineers” that work in the discipline of corrosion, but not many who actually have a degree in corrosion. There are also more of us working corrosion that do not have an engineering degree than those with one. So how do we define that?

I know “must” is used in Version 4, but at least they allow for some ways of considering the voltage drops.

Version 4

(1) A negative (cathodic) potential of at least 850 mV with the CP applied. This potential is measured with respect to a saturated copper/copper sulfate reference electrode contacting the electrolyte. Voltage drops other than those across the structure to-electrolyte boundary must be considered for valid interpretation of this voltage measurement.

NOTE: Consideration is understood to mean the application of sound engineering practice in determining the significance of voltage drops by methods such as:

- Measuring or calculating the voltage drop(s);
- Reviewing the historical performance of the CP system;
- Evaluating the physical and electrical characteristics of the pipe and its environment; and
- Determining whether or not there is physical evidence of corrosion.

(2) A negative polarized potential of at least 850 mV relative to a saturated copper/copper sulfate reference electrode.

MY COMMENTS (Agree overall)

These are the same two criterion in the SP-0169 – 2007 and is the same as has been used since 1992 (I believe). We have been able to make this work and I can vote for the document (if a few other areas are corrected) with the criteria as is at present.

I personally could do without the “must” before “be considered” and would prefer “should”, but can live with “must” as a compromise.

Version 5

A cathodic voltage of – 850 mV or more negative as measured with respect to a saturated copper/copper sulfate (CSE) reference electrode. This potential may be either a direct measurement of the instant off potentials, or a current applied potential. Interpretation of a current applied measurement requires correction for voltage drops in the earth or metallic paths.

Note: Correction is understood to mean the application of sound engineering practice in the determination of the magnitude and significance of the voltage drops by methods such as:

- Measuring or calculating the voltage drop(s); or
- Determining whether or not there is physical evidence of corrosion.

MY COMMENTS: (Strongly disagree)

This is the same criterion that was in the most recent revision. The term “correction” concerns many because it means you must determine the “instant off” for each reading when using an “ON” reading. The term “with current applied” is useless, because you have to “correct” for voltage drop by doing an “instant off”. Even though it does give some help with “evidence of corrosion” statement, I could not support this criterion.

FINAL COMMENTS:

Only those on the voting list got the opportunity to vote in this straw poll, but I encourage all those who have interest and want to express their opinion please do so through contacting the TG 360 committee or you can voice it through the blog site. You may have the best wording of the criteria so let us know.

I do hope the committee will take our words and comments as constructive and work to get us a document that gives the industry a valuable tool that can be used reasonably in the field to provide us with the data needed to determine when we have achieved the goal of providing adequate external corrosion control to the industries pipelines around the world. We will never reach 100%, but we can get very close and keep the effort affordable and reasonable. There have been many improvements and updates in the document, now let us compromise and move forward.

Again, I want to thank the committee and everyone else for hard work and effort. Though we may disagree at times, we all want the same thing. This is a critical document to the industry and we all want the best standard possible to provides guidance to the pipeline industry around the world.

I think this is a great opportunity to provide input to the committee. Please respond to best of your knowledge. You do not have to agree or disagree with me or the committee, but we do need to resolve this standard and get it out.

Thanks for your help and time,

Richard Norsworthy