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Monday, November 16, 2015

Heat Shrink Sleeve Maximum Operating Temperature

Temperature Limitations for Heat Shrinkable Sleeves

     I am often asked about the upper range for temperature limitations on heat shrinkable sleeves.  The most recent cases have been a few different companies inquiring after a coating that is easy to install and able to withstand potential continuous operating temperatures in the 350 to 400F range.  This is a challenge.

     In the world of heat shrinkables, you must really break this question down into two different categories.  Spoiler alert:  in spite of the in depth analysis here - let me offer you an early peak ahead:  there is no shrink sleeve solution for temperatures that high.  I'm sorry!  I wish I had something to offer you.

     So breaking this down into two categories, we must look at the heat shrinkable backing -- and we must look at the adhesive sealant.

     First the Heat Shrinkable Backing:  The backing of our most commonly sold heat shrink sleeves for pipeline coatings are all made from a modified polyethylene (a polyolefin).  The chemistry of that compound by its very nature generally has a crystalline melt point of ~267F.  Now, this means that if the backing had not been radiation crosslinked -- then that backing would essentially melt at 267F.  Because the backing has been radiation crosslinked, however - it does not melt.  But, being crosslinked and then exceeding that 267F temperature rating means that the backing will be 'in a state of shrink' at that temp.  The backing would be soft and malleable; attempting to return to its original shape and size (that is how a shrink sleeve works).  As a result, at or above that 267F temperature, the backing does not have the strength to physically protect the field joint as it is supposed to.  As a result, it can't do what it is supposed to do at that temperature.  As a result, our shrink sleeves would not be recommended for use at or above 267F (or actually even lower; our highest temperature rated heat shrink sleeve is rated for use at up to 251F). 

     The second factor that determined maximum operating temperature of heat shrinkable sleeves is the temperature at which the adhesive is rated with approval.  This means that at 'that' certain temperature, the adhesive behaves as it is supposed to; resulting in the desired and expected physical properties including peel strength, penetration resistance, ring and ball softening point, etc.  There are many characteristics that a pipeline coating is supposed to meet in order to properly offer a protective and corrosion resistant coating to a pipeline or substrate.  Covalence / Seal for Life (formerly Raychem) has patented any number of proprietary adhesives designed for different specific pipeline coating applications.  I'm sorry to say though - that none exceed the 251F mentioned above. 

     I'm afraid that a pipeline operating at 350F quite simply, exceeds the chemical potential of PE based components of a heat shrinkable backing. 

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