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Friday, March 14, 2014

Shrink Sleeves on a Bumper

Installing a Shrink Sleeve Over a Bumper

bundled road bore
This is a properly selected shrink sleeve holding a bumper in place pre-bore.
     There is a lot that can go WRONG when installing a shrink sleeve over a bumper of some kind.  Fortunately, all of those pitfalls are easily avoided if you are talking to a knowledgeable shrink sleeve expert prior to actually ordering material.  There are many cases where a shrink sleeve over a bumper or cable makes a great deal of sense - examples could be a bundled road bore system or securing a cable to a pipe.  But if the shrink sleeve is improperly sized - or if you are expecting a sleeve to do something that a shrink sleeve is not intended to do.  

     First, lets talk about sizing.  A wrap around shrink sleeve must be manufactured for a specific pipe size.  A shrink sleeve made for a 4.500 inch OD pipeline will not work on a pipe with a 6.625 inch OD pipe.  It is really about the substrate circumference at that point.  It works the same way when considering installing a shrink sleeve over a bumper.  If your using a 1" bumper on a 6" pipe; your sleeves really need to be designed for an 8.625" OD substrate (6.625" pipe + two inches of bumper).  If you are putting a 2" bumper on a 6" pipe; your shrink sleeves really need to be designed for a 10.625" OD substrate.  

     Next, lets consider heat shrink sleeve capabilities.  Heat shrinkable sleeves are manufactured with a certain amount of 'shrink' build into the backing.  For many of our products, that shrink percentage is 28% plus or minus 3%.  To say that another way; most of our products shrink somewhere in the range of 25% to 31%.  Because anything in that range is within the variance accounted for in the manufacturer's specification, we really have to assume that material will have only a 25% shrink built in. 

     So, will a standard heat shrink sleeve be able to shrink between a 10.625" substrate and a 6.625" OD pipe?  Let's do the math:

Circumference of a 10.625" circle:  33.36"
Take away 3" because the area underneath a closure strip is restricted from shrinking:
33.36 - 3.0 = 30.36
30.36 * .75 = 22.77" (since it shrunk 25%; it is now 75% the size it was)
22.77 + 3.0 = 25.77 (add back in the closure dimension)
25.77 / 3.14 = 8.20" (with a 25% shrink product; a 10.625" will only shrink to 8.2")

     Mathematical proof that a shrink sleeve with a 25% shrink ratio will not shrink from 10.625" down to 6.625" -- not even close! 

     What happens when a contractor orders sleeves like this without consulting a heat shrink sleeve expert?  They get the sleeves -- they install the sleeves -- and then one of two things happens:  1)  They call us saying that they were supplied faulty sleeves (they weren't) or 2) More likely, they recognize that they goofed.  They think 'darn it!' I should have called first.  Then they think "how are we going to make these work?" And ultimately they do something that is largely insane:  they throw on some metal banding to hold the sleeve ends tightly to the pipe.

     Yes, you read that right.  Metal banding outside of an improperly ordered shrink sleeve.  An actual band of metal introduced and buried right next to your pipeline.  Not good. 

    Please, please, please, please.  If you are going to use a shrink sleeve for something a little bit 'unusual' - talk to us first!  It costs nothing!  It takes only a few minutes to pick up the phone or shoot off an email. 


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