ARO Compatible Field Joint CoatingSo you've got a pipeline that is utilizing an ARO (Abrasion Resistant Overcoat) and you're not sure what that means. Don't feel bad! You can't possibly know what you haven't yet learned! Normally an ARO would be factory applied on top of an FBE coating. The abrasion resistant overcoat could be a second layer of FBE or it could be a product like Powercrete (two part epoxy sprayed over the top). In either case though, the important thing to know is: that ARO was selected and paid for....for a very good reason. Oil and gas companies don't generally piss money away for no reason. Most of the time coating decisions are very well thought out and made with great care and attention to detail. So someone, somewhere made the decision to use an ARO. Why would they do that?
|Example of Powercrete being applied as an abrasion resistant overcoat|
So what is the reason? There really can be only one. The engineer is expecting that pipeline (or at least that section of pipeline) to experience tougher than normal conditions once it is installed or once it is in service. This could possibly be very difficult soil conditions (rocks, etc) but more often than not the reason is that this section of pipeline will be involved in a road bore or a directional drill.
Directional drilling subjects a pipeline to tremendous forces and potential damages. Why is that a problem? Because the pipeline can not be visually or externally inspected after it has reached its destination. So what happens if an underground rock or tree root (or other pipeline!) causes a long gash in the factory applied coating that results in bare steel being exposed? You're going to have a large problem! Sure, your CP system will (hopefully) begin to protect that steel when it is activated, but the pipeline is not a world where unnecessary risks are generally accepted by the US government. As a result - extra care is taken during coating selection. Extra expense is undertaken to protect the pipeline as well as can be reasonably expected by the government and by those people who might be living near that pipeline.
So all of that applies to factory applied coating selection. Surely the same care is given to field joint coating selection on ARO coated pipe, right? Unfortunately, the answer is "sometimes yes, sometimes no." On my drive to and from work every single day, I cross a bridge that stretches over a ravine (in The Woodlands, TX) and when that pipeline was constructed (strung up along Kuykendahl) I could clearly see that though the contractor was welding up pipe with an ARO on it...the field joints were being coated with a simple cold applied tape. That terrifies me. There is no way that cold applied tape survived the pull through. That means that the field joints on the pipeline were essentially bare when that line was put into service. It is also possible that since those joints were uncoated; there could have been damages to the steel during the pull through that caused loss of pipe wall thickness to the field joints. Not good.
I wish that were the only time I've seen that, but it isn't. I've seen the same thing along West Rayford when a pipeline was installed (Spring, TX). Cold applied tape on the field joints as the pipe was preparing for the pull through. This is within 200 feet of homes -- where people live.
So why was a lot of money spend on the proper main line pipeline coating....while a contractor was allowed to spend 5$ per field joint on a cold applied tape (not approved by its own manufacturer for this application)? 5$ for the field joint 200 feet from a house?? I wish I could answer that question, but I don't know.
There are many proven and tested products that are specifically designed to withstand the rigors associated with a road bore. These are products that actually offer better protection to the field joints than the mainline has. Field joints are the most critical areas of a coating. They deserve more attention and better coatings than the main line coating, yet they often use cold applied tapes that will never survive a pull through.
Of those options, there is no question in my mind that DIRAX is the best option. A multi layer, incredible peel strength, incredible cathodic disbondment resistance, incredible shear resistance, penetration resistance and abrasion resistance. I am quite confident that field joints protected by DIRAX will be properly protecting those field joints on pipelines long after I have left this earth. These are lifetime coatings we are talking about (as opposed to temporary coatings that will be falling off as soon as the road bore begins).