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Tuesday, April 21, 2015

Pipe Doughnuts on Polypropylene Coated Pipe

Bore Bumpers for PP Coated Pipelines

     Had a recent phone call from a contractor who had a large problem.  He had been awarded a project to complete a directional drilling bundle where the pipe was factory coated with polypropylene...and company he was working for had commissioned him to find a a spacer system to insure that the two pipelines did not damage one another during the pull through process.  We seem to get a lot of telephone calls where someone out in the pipeline world is asking us to engineer a solution for them.  We love it when that happens because it is one of the most exciting aspects of our jobs.
Here you see one of our BBS Bundled Bore Bumper sleeves installed in the field (not on PP).
     In this case, things were a little bit different, because we have the product (BBS - Bundled Bumper System) and it has been thoroughly evaluated.  In fact, we had the amazing opportunity to evaluate our product in true "before" and worse than "after" fashion when the pipe bundle entered the bore and then had to be pulled back out after a malfunction (and amazingly, in that case, how did they pull the pipe out?  by strapping onto our bumpers and pulling...which we would never recommend...but hey, they had to get that pipe out of there and it actually held up very well).  

     So what was the problem then?  If you're reading this blog, you almost certainly know that polypropylene is notoriously difficult to bond to unless you are using a stick, aggressive mastic sealant.  At the same time, a sticky aggressive mastic sealant does not offer great shear properties (when evaluated in light of a 20+" multi pipeline directional drill).  This left the question:  Would our shrink sleeve material that has successfully been used numerous times in bundle bore applications bond well enough to a PP coating to complete its mission?  (The mission being to hold that bumper in place until the pipelines reach their final resting places). A good question. 

     One of the challenges with polypropylene in my experience (and some polyethylenes to a lesser degree) is that there are many different types of polypropylene and not all polypropylenes interact with our adhesives in the same manner.  This was going to present a problem.  Fortunately, the contractor was able to send us a small sample of the exact PP that was coated on his line (by stripping it from an unneeded section of pipe).  Great!  No need to speculate...we can evaluate this ourselves without even needing to leave our own warehouse!

     But first, let's take a closer look at the function of our BBS bundled bore sleeve system.  The purpose of the system is to hold our special formulated bumper in place, so that bumper can prevent two or more pipelines from colliding during the pull through.  Sounds fairly simple:
- Put bumper on
- Lock bumper in place
- Survive

     That is important to keep in mind.  Beyond that, it is important to fully understand what types of forces will be exerted on this system.  Let's look at and evaluate some of the different material properties associated with our product and determine whether they are or are not going to come into play in this particular application.
  1. Peel Strength - based on our experience with the product, we don't believe peel is any factor here at all.  For the system to be put into peel would require a set of circumstances that are pretty much unimaginable. 
  2. Impact Resistance - the system has excellent impact resistance of course, but we don't believe this characteristic will come into play here.
  3. Penetration Resistance - again, not a factor.  This system has excellent penetration resistance (I would say unmatched) but the chance that a penetration occurs that is somehow eventually able to dislodge and/or move the bumper is very difficult to imagine.  
  4. Cathodic Disbondment Resistance - again, not a factor.  This material is not acting as a coating (but when it does act as a coating it exhibits excellent CD resistance). 
  5. Shear Resistance - Bingo.  We have a winner.  The forces exhibited on the profile of the bumper will put front edge of the sleeve under shear forces.  The front of the sleeve will see shear forces and the weight of the other pipelines along with the force of the pull will exhibit shear forces.  
     So going through all of that, we arrived at the conclusion that the single largest factor when determining (in this particular case) whether our system would properly hold the bumper in place through the duration of the pull through is shear resistance.  Now we have a road map toward proper product evaluation.

     The samples came in and we began determining the best way to evaluate shear strength.  The contractor already had a system in place that required abrading and heat treating the polypropylene for his field joint coating procedures, so the first simple step was to expect that same treatment for the areas where our BBS sleeves would be bonding to the factory applied polypropylene.  Clearly step one was going to be: prepare the PP samples with abrasion and heat treating.

     Next we bonded stamps of our material onto the PP samples.  Our base bonding product exhibits shear values that pass at 80 pounds per square inch when installed on epoxies and dual layer FBE.  DIRAX (the product in question) has been used successfully hundreds of thousands of times, there is no question that the shear resistance values of DIRAX are more than sufficient to survive the forces associated with a directional drill. 

     Using a testing system that we developed here, we were able to determine that our material samples installed directly on the PP samples held up at 80 pounds per inch without failure.  The bond could have taken more than 80 pounds, but we saw no real reason to test to failure.  In any case, given that the single most important technical value in this application is shear resistance, and given that our product exhibits exemplary shear resistance; as high as has been successfully used many, many times in directional drilling applications, we felt incredibly comfortable to approve the use of our product for this specific application.  I am hoping we will be able to get photos from the field of the project which is going on as we speak.  If I can - check back in as they will be posted here.

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