Sunday, September 7, 2008

Response to Ed Ondak and Roy Bash Comments

I first want to thank these two gentlemen for providing comments to the blog site. I encourage others to provide comments to help us all learn and grow in knowledge of the proper ways to control external corrosion on pipelines.

I do agree with Ed’s assessment of the section 3.2. We do not to write the SP0169 around regulations or regulators from what ever country or entity that may be regulating that industry. All NACE Standard should only be written to provide the industry with the most economically effective ways to prevent corrosion.

I do not agree with all of Ed’s assessment of the remainder of the document, but this is not the first time Ed and I have disagreed! Thanks, Ed.

Roy’s comments are also very good. I do agree with most of it; except for the comments on FBE not have a problem if CP is not available. With few exceptions, if the coating system’s adhesion is good, there cannot be corrosion, because the pipe is isolated from the electrolyte.

I have seen corrosion occur on an FBE coated pipe with no CP. This was not a case of interference problems, etc. Without CP the pipe can corrode at holidays just like any other coating system.

I agree with his comments of the water penetrating and being basically pure water, but there are other conditions that exist that allow corrosion to develop. When contaminants (various salts) remain on the pipe surface before the pipe is coated, the “pure water” that penetrates combines with the salts to form a conductive path for the CP current to provide protection to the pipe surface. Without CP this area would corrode by local cell action or by being anodic to other areas where disbondments and water penetration has occurred.

If Roy’s assumption is correct, the electrochemical reactions taking place would not cause the high pH values recorded under blistered and disbonded FBE. The high pH indicates the electrochemical process is the same as that taking place on bare steel areas exposed to the same electrolyte when adequate CP is available. Therefore the current is being allowed to protect the pipe surface it these areas of disbondment because the FBE is a non-shielding pipeline coating to CP current when disbondments occur and water penetrates between the coating and the pipe surface.

Cathodic protection can be effective if it can get to the pipe surface and is not shielded by coatings or other materials, etc. As long as the coating is adhered, the CP does not need to be effective, because there is no electrolyte to cause corrosion.

There have been many papers written on this topic that explain the processes of shielding by certain types of coating systems. FBE does not have this problem even when protected by using only the -850 mV criterion (without IR drop consideration). We must start understanding this process and putting 2 and 2 together to understand when we do not need to add more CP! We need to educate our engineers and others about shielding and the proper selection of coatings that will not shield CP current if and when disbondments occur.

DO NOT FORGET TO VOTE ON THE SP0169 REVISION. If you have not joined the STG 35 group, you may not be able to vote! If you do not vote the first time, you will not get the chance to vote on other revisions that may take place after the first ballot. I am not sure when it will be voted, but my guess is sometime this year or early 2009.