Cross Country Pipelines - Bonding of Coating to Pipeline
Cross Country Pipelines - Bonding of Coating to Pipeline
(OP)
Good day all!
Recently we carried out a peel test of the asphalt enamel coating on our cross country water pipeline. The coating was observed to be disbonded from the steel pipeline. Our pipeline is protected using an impressed current CP system along with sacrificial Mg anodes at many locations.
As far as my understanding goes, the purpose of a coating is to isolate the steel pipeline from the soil, and to act as a barrier to moisture and other corrosive elements.
As such, can anyone please explain why bonding of the coating to the pipeline is considered to be so vital?
Thanks,
Shaafi
PS: Any literature on pipeline coatings and their types, merits and demerits would be great.
Recently we carried out a peel test of the asphalt enamel coating on our cross country water pipeline. The coating was observed to be disbonded from the steel pipeline. Our pipeline is protected using an impressed current CP system along with sacrificial Mg anodes at many locations.
As far as my understanding goes, the purpose of a coating is to isolate the steel pipeline from the soil, and to act as a barrier to moisture and other corrosive elements.
As such, can anyone please explain why bonding of the coating to the pipeline is considered to be so vital?
Thanks,
Shaafi
PS: Any literature on pipeline coatings and their types, merits and demerits would be great.





RE: Cross Country Pipelines - Bonding of Coating to Pipeline
http://www.crcpress.com/product/isbn/9780849372780
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
Im afraid I dont quite understand the terms "undercut by water and corrodents".
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
Water gets under the coating and has O2 dissolved in it so all the ingredients for corrosion are present - the third requirement is already there - the steel pipe.
'Bonded' in this sense means 'tightly adhered' - that my be slightly confusing the issue.
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
I think you may be confusing 'coating bonding' with 'electrical bonding'.
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
But if it is impermeable, how does whater get under the coating?
Coating bonding would mean the adhesion of the coating to the steel pipeline.
And electrical Bonding would mean?
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
Anyone else wish to explain?
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
RE: Cross Country Pipelines - Bonding of Coating to Pipeline
Brimmer has provided a very good explanation. A coating is only as good as the surface preparation when it was applied and is only of any value when it is well attached to the steel. As soon as it disbonds it allows moisture into the gap through small holes in the coating. Asphalt enamel as it gets old ( > 20 to 30 years) also gets more permeable to the extent that if there is disbondment, water will fill the gap behind it and start corroding your pipeline.
If your line has impressed current and Mg anodes at several locations it sounds like the coating is in very poor condition and if you have disbondment as well then it looks like you'll need a new pipeline quite soon or an extensive re-coating exercise...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way