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Wednesday, May 7, 2014

Field Joint Coatings and Pipeline Wall Thickness

Does Pipeline Wall Thickness Affect Field Joint Coating Selection?

pipeline wall thickness chart
A sample of a pipe wall thickness chart, source:  Wikipedia
      The question above is an incredibly common one in my world (almost daily).  When selecting a field joint coating, how important is the wall thickness of the pipeline?  The answer (like all answers seem to be) is complicated.  Wall thickness if both unimportant....and critically important in the field joint coating selection process.  I wish I could just stop there and move on to the next article...but if you're read this blog with any kind of regularity, you probably know that I seem to just like to make every article a few hundred words longer than it really needs to be.  Maybe my wife doesn't listen to me enough at home or something.

     So first things first:  the way this question comes up most often is when someone calls to say they need some basic shrink sleeves for basic 6" OD schedule 40 pipe.  This almost always someone who is a regular customer and has been successfully using our products for years.  In that case, where they essentially "want more of what they've been using for the last five years" - the pipeline wall thickness does not have any bearing.  In my experience, the wall thickness really never has any affect on the actual OD of the pipeline (which is critical for us - SIZE DOES MATTER!) so it is essentially immaterial.

     But let's look at the impact of pipeline wall thickness at the beginning of the specification process rather than at the end (when someone is saying "that worked great....give me more!").  Please keep in mind - I am no pipeline design engineer --- not even on the same planet --- so I will be ignoring all of the factors in their world (pressures / flex / etc). 

     When considering coatings and wall thickness, the first thing we should look at is pipe weight.  Of course, the heavier wall thickness a pipe has, the more pounds per foot a pipe is going to weigh.  This is a pretty important thing.  Even "standard" wall pipe is HEAVY.  Some form of heavy wall pipe is going to be even more - and it might be important to select a field joint coating that is designed to handle extreme weights and extreme conditions.  Possibly something like ROCS or our HTLP60 products; both of which utilize a tough, tough, hot melt adhesive sealant that is capable of supporting immense weight for decades. 

     Another factor to consider or at least be aware of, is that the 'pre-heat' step of shrink sleeve installation will often be a slightly slower process when dealing with heavy wall pipe (this applies to all coatings as all field joint coating materials will require at least some preheat in order to get the pipe temperature up above dew points at the very least).  This is not going to be anything particularly meaningful but you should recognize that getting the pipe to the proper temperature might take just a little bit longer.  This issue also happens to be addressed by using the ROCS or HTLP60 mentioned above.  Both of those products utilize an epoxy as the bonding agent - which allows for a much lower preheat temperature than could otherwise be used for a hot melt adhesive sealant coating.  

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