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Monday, June 17, 2013

Wrap Around Shrink Sleeve

Wrap Around Shrink Sleeve

     A wrap around shrink sleeve is one of two heat shrink sleeve configurations that are available (the other being a tubular sleeve).  A wrap around generally has two components; the sleeve material itself and the closure strip.  To make matters much more complicated than they truly need to be; each component (sleeve and closure) is a multi-layer material.  I'll break each down below.

     First we will look at the shrink sleeve itself.  In this particular case we are looking at the WPCT product, currently manufactured by Covalence Heat Shrinkable Products, underneath the Seal for Life umbrella of corrosion prevention products (WPCT was originally created under the Raychem name).  WPCT is a two layer shrink sleeve, with the outer layer being a radiation crosslinked, high density polyolefin and the inner layer consisting of a mastic sealant (WPCT is supplied with a release paper, but I am ignoring it for the sake of this discussion because it will be discarded during installation).
Shrink Sleeve Backing
Here we see the WPCT backing.  Notice the dimples which will fade away as this product is properly installed
Mastic shrink sleeve
Here we see that once the release paper is peeled back, the stick mastic material is exposed.
     You can't tell from the photo (of course) but the WPCT is coated with an extremely aggressive mastic sealant.  In the Texas summer, this material will stick aggressively to anything it touches.  The beautiful thing is that it retains that same aggressive nature for many years (we know because we have seen pipelines with this product installed many decades after their original installation.

     Next we will take a closer look at the closure strip (internal name 'WPCPIV').  It is typically supplied in the same standard widths as the shrink sleeves are and is available in 3", 4" and 6" widths.  Selecting a width depends primarily on sleeve material type; pipe OD, etc.  The WPCPIV is technically a three layer product; incorporating a radiation crosslinked, HDPE backing; a fiber mesh to give the closure superior integrity and a high shear hot melt adhesive to make sure there is no slipping that occurs during installation (if slipping were to occur, the shrink sleeve might begin to work its way off of the pipe during installation).  
Raychem Closure
The closure backing.  This is the side which will be visible after complete sleeve installation.
Closure Strip
This is the high shear adhesive side (with the fiber mesh visible through it).
     In the picture immediately above this sentence; that checkered pattern is the fiber mesh of the closure and also the side of the closure strip that will no longer be seen once the shrink sleeve is installed (it will be fully pressed and bonded to the PE backing of the shrink sleeve).  

     In our shop, we don't ever sell the closures and shrink sleeves separately; they are always attached to one another to make life easier on the contractors.  The truth is that it makes life easier on us as well as we experience dramatically fewer calls for field service, missing components or field problems.  

     There you have it; all you ever wanted to know about wrap around shrink sleeves!

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