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Thursday, February 6, 2014

Epoxies and PE (Part 2)

Do Epoxies Bond Well to PE?

     I received a comment from yesterdays post (do epoxies bond well to PE) and I realized that I'd failed to address one very important aspect of that discussion.  Here was the message I received:

"If epoxies don't bond well to polyethylenes, how do you properly coat field joints on 
three layer PE coated pipelines??"

     Oops!  In my mind, yesterday's article was all about stand alone epoxies being used with PE coated lines (in my mind, I was picturing epoxy with a two layer PE; or with a solid film PE backed tape).  

     Thank you my friend for asking this question!  When coating the girth weld of pipe with a plant applied three layer coating -- of course you are going to utilize an epoxy as the primary corrosion protection on that field joint.  Anytime an end user has spent the money to put a high performance coating like TLPE on their pipeline; it makes absolutely sense to recreate a similar three layer PE coating on the field joints (a la` HTLP60 and HTLP80). So please understand, there is a difference here between an epoxy being used as one component of a three layer system; and an epoxy being used as a stand along coating where it is expected to bond/seal to a polyethylene directly.

     In many cases, on three layer PE coated pipe, there are two cutbacks to consider (three if this is an offshore pipeline as there will likely be a concrete cutback as well); the FBE cutback and the PE cutback.  In many cases, the TLPE line will have a "toe" of FBE sticking out.  This is perfect as liquid epoxies generally bond quite well to FBE.  This also allows the field joint to be coated bonding epoxy to epoxy; shrink sleeve adhesive to PE and shrink sleeve adhesive to epoxy.  All proven; all reliable, all cohesively bonded.  

     Please note - nothing I've written here says that epoxies will bond to PE.  So please be aware that there is a world of difference between the two scenarios presented here in the last 24 hours.

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