To All,
I am in the process of writing a paper for NACE 2009. The paper will be about the relationship of FBE and cathodic protection criteria. As I mentioned in my speech before the TG 360 group (changes to SP0169) the industry rarely sees external corrosion on FBE coated pipelines even though most of the pipelines have been protected by using the "ON" -850 mV criterion, especially for the first 30 + years that FBE has been used.
I need to find as many case histories as possible for showing that this is true. We can do this generically, but it will hold more weight if we can actually show the company, etc. Preferably, we will have case histories where we can show no or otherwise explained external corrosion on FBE coated pipelines over the period of time when the only criterion used was an "ON" -850 mV.
Since FBE allows CP to be effective should there be disbondment we do not normally see external corrosion on FBE coated pipelines. Most of the times we have seen external corrosion was in areas where the CP was shielded or there was an interference problem. In most cases, companies used only an "ON" -850 mV, yet we did not and do not see external corrosion on FBE coated pipelines.
So what I need are case histories that show (as much as possible):
1. What criterion (criteria) was (were) being used?
2. What potentials ranges were in the area inspected? (with or without IR drop consideration if possible to give this information)
3. Did ILI or ECDA show external corrosion? (PHOTOS where possible)
a. If so, was it under the FBE or other coatings?
b. If so, were there other reasons why the corrosion existed? (shielding, AC or DC interference, etc)
c. Were pH readings taken?
d. Was it evaluated to see if it occurred during times CP was not applied or effective? (if data is available, etc.)
e. Was it active or old corrosion?
4. Age of the system.
5. Thickness of the FBE.
6. Soil or environment in which the pipe is in service.
7. Service temperature of the product.
8. Type of girth weld coating used.
9. If you have examples of surveys (CIS, DCVG, ACVG) showing protected levels (especially with the polarized -850 mV), yet you still had external corrosion (caused from coatings that shielded, etc.) when the line was inspected, this is valuable information also to prove the point that nothing is 100%. Once again case histories and photos are valuable!
10. Any thing else that will help!
If any one would like to co-author the paper, you are more than welcome to work with me on this project. This information is critical to demonstrating why an "ON" -850 mV is an acceptable level of cathodic protection, even when not considering IR drop. Now is the time for all good women and men to step up give the industry something to help us solve this problem. We all know field data is more accurate and valuable than the lab and test data being quoted by some on the committee.
As we know if these folks get their way they will force us to all go to a polarized -850 mV or the 100 mV of polarization. Please help those of us who know from field experience what we are doing is working without having to consider IR drop except in very unusual areas and circumstances that can be given.
Since the PCRI report is quoted often in the defense of the polarized -850 mV criterion, I need a copy if anyone has one. If not let me know how to get a copy and I will buy it. From some of the data that has been shown, I do not think it show any definite conclusions.
This will also be posted on the SP0169.com blog site. If you have not visited it there are some good comments and information. We will be glad to add yours to it. It can be anonymous if you wish, but I would at least like to know who you are and I decide what goes on, etc. I also welcome comments and case histories from each side of this issue, because that is the way we all learn and make our industry better.
Thanks for your help and we must pull this information together to head off the proposed changes. We can make this a very good document if we work together with a united effort.
Richard Norsworthy
Polyguard Products, Inc.
214-912-9072
Thursday, May 22, 2008
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1 comment:
Solid film back pipeline coatings such as coal tar have the property to keep the pipeline perfectly dry. This is the reason that steel never corrodes under these coatings. Dry steel at normal operating temperatures never corrodes. These coatings are supplemented with cathodic protection for protecting the bare steel at places where the coating is not intact. The steel under the intact coating does not receive any cathodic protection current and it does not need any to prevent it from corroding.
Hydroscopic pipeline coatings such as FBE allow water molecules to pass through them, by the process of osmosis, to the pipe surface. This water is pure and pure water is non-corrosive to steel; hence no corrosion, cathodic protection or no cathodic protection.
From basic theory, the hydrogen ion consists of a single hydrogen atom minus its single valence electron embedded in a single water molecule. It is designated in electrochemistry text books as (H+.1H2O) or (H3O+).
When cathodic protection is applied, the FBE coating allows hydrogen ions to pass through it, by the process of electro-endo-osmosis, to the pipe surface. At the pipe surface the ion accepts one electron from the pipe and forms one atom of hydrogen which leaves one molecule of water at the pipe surface. Again, this water is pure and non-corrosive to steel, hence again no corrosion.
The water underneath a hydroscopic coating resulting through the process of osmosis is always pure and non-corrosive to steel. This is the reason that no significant corrosion is ever found under these coatings even in the water with hydrogen bubbles that are often observed under these coatings on cathodically protected pipelines when they are excavated and inspected. Just beware of the overly stringent -0.850v, CSE instant off cp criterion. History has proven the adequacy of the much less stringent -0.850v, CSE CP criterion measured with the CP applied (IR drop ignored) on steel pipelines with FBE coatings, and it reduces considerably the risk of forming the water bubbles compared to the overly stringent -0.850v, CSE instant off CP criterion which has the potential to completely disbond FBE coatings on buried or submerged pipelines over a period of time.
Respectfully submitted,
L.A.(Roy) Bash, P.E.
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