Wednesday, August 13, 2008

Update on SP0169 and CTW

The NACE International TCC Managing committee has asked us to be sure that everyone knows this is not a NACE sponsored blog. So notice that we have that now posted on the site. Remember also that we are asking for all comments about the proposed revision to NACE SP0169 document to help everyone keep up with the thoughts and comments of others. I am asking anyone who has good data to prove your point (no matter which position you support) to send that to the blog or make an appearance before the committee and present your findings.

The time is approaching for the NACE CORROSION TECHNOLOGY WEEK (CTW) in Salt Lake City this September 14 thorough 18. Please be advised that there will be another all day session concerning the revision discussions around the SP0169-2007 document.

The meeting is set for Wednesday September 17, 2008 from 8:00 am to 5:00 pm in the Sheraton City Centre Hotel. It will be held in the Seasons North room. Hopefully we can have another great meeting with many of you making constructive comments and suggestions to the TG 360 group.

I have not seen the new revision since the CORROSION 2008 meeting, but I do understand they have been working on the document. Hopefully, this information will be posted on the NACE website before CTW so we can digest it and give constructive information to the committee.

If you can not make the meeting, please pass along any information to the committee or to the blog site. I am planning to be there. Hopefully, there will be good attendance.

If there is a way to provide me any more information on FBE coated pipelines and the internal line inspection (ILI) or ECDA results along with CP data this would be very good information to either confirm or deny the theory that we have proposed as to why we do not need to consider IR drop at all test sites as many propose. Again, we question the need for having to consider IR drop (with a few exceptions) when most FBE coated pipelines were only protected using a -850 mV or more negative "ON" potential criterion at least up until 1992 - 96 time frame when RP0169 was changed to say you "must consider IR drop". We did not and still do not see external corrosion on theses pipelines with exceptions mentioned below. Please read the various postings below for more information if you have not.

We do not propose that FBE is the perfect coating system, simply that it does not shield CP currents when you have adequate CP (-850 mV "ON" or more negative or 100 mV of polarization) even if disbondments occur. Why could not this theory be applied to all pipelines that have non-shielding coatings or in areas where the coating is missing (holidays and damage)? Many in the industry are beginning to better understand the relationship between shielding and non-shielding pipeline coatings in relationship to cathodic protection, because disbonded and CP shielding coatings are where we are still seeing external corrosion on most pipelines, not lack of CP.

I have some more questions about IR drops:

1. Does not a large IR drop mean we have an excess of current in that area?
2. If so, where is the current going?
3. Is it not going to the structure where it is not shielded?
4. If current is being picked up by the structure, is not protection occurring? When using conventional current theory, we say where current enters the metal we have protection, so if it is entering the structure metal, how can we have corrosion? I do understand the idea that there may be some very limited sites on the metal that have microscopic areas that are more negative than that shown by the potentials of the reference cell, but again, if there is large "I" in the IR drop there is large current to over come these cells. When the "R" is large, the corrosion rate is less any way. This is where we must better train our technicians the proper techniques to identify and deal with these situations, not force everyone to use only one method to determine protection.
5. It is strange to me, we can protect an uncoated structure at much positive potentials "ON" than a -850 mV "ON". Why do we need more negative potentials to protect a coated pipe?
6. Does IR drop cause corrosion? (NO)
7. Does IR drop protect the pipe? (NO)
8. Is the IR drop in our potential measurement really an "error" or just part of the "ON" potential? (Of course it is only a part of the "ON" potential which is the correct potential for that location of the reference cell placement.)
9. When taking a polarized potential (Instant OFF) measurement over a structure, what does that potential represent? The entire surface of the structure? The top of the structure (assuming we have the reference cell directly over the pipe)? What about the bottom? What about under shielding disbonded coating? What about the sides of the pipe? What about two feet away?

We can go on and on, but I think you get the point. What we do in the field is not an exact science. We must better train those taking these potentials on how to identify problems area that require further testing, not restrict them to a couple of difficult, time consuming and costly criterion that do not solve many of the external corrosion problems in the pipeline (and other) industry today.

Thanks for all the support and interest in this Blog site. Our goal at Polyguard is only to provide a format for information to be distributed in a way that one does not feel intimidated or lacks the presentation skills of others. We really do want information from everyone! We need arguments that define all sides to this argument. This is the way we challenge each other better to know and understand what is the best way to protect our structures from external corrosion. This make us better neighbors, protects the environment, our companies assets and the helps to conserve our resources.

Richard Norsworthy