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Thursday, August 8, 2013

Can a Heat Shrink Sleeve be used to coat a 90 degree bend?

Question:  Can I use a Covalence heat shrink sleeve to coat a 90 degree bend?

Shrink sleeve a bend
An example of a 90 degree bend
Answer:  Yes and No.  A standard tubular or wrap around shrink sleeve cannot be used to coat a 90 degree bend in one fell swoop.  Picture in your mind the bend above.  Now picture that there is a more-or-less straight line pipe welded to each end.  Also, for the sake of this discussion, let's imagine that the bend above is 3 feet long (along the outer radius). 

Both wrap around shrink sleeves and tubular sleeves are manufactured from sheet material.  This means that both; when/if laid out flat (say you cut a slit down the length of the but) would leave you with a rectangular shaped heat shrinkable PE (plus the adhesive sealant).  The way shrink sleeves work (read more here) is that that plastic sheet; when properly heated is going to attempt to return to its original rectangular shape (obviously smaller than it is in the current shape).  Picture a rectangle that is 24" x 11" and after you shrink it; it becomes 18" x 11". 

All of that is explained so that I can say:  Sleeves do not conform to the shape of the substrate to which they are applied - unless that substrates' shape is conducive to a rectangle.  So - on straight line pipe where a shrink sleeve is installed to seal a girth weld; the shrink sleeve can easily wrap around the bare steel and weld (sealing tightly) and then shrink to and seal tightly to the adjacent factory applied coating.  Picture a scenario where you have a factory applied coating that is 1" thick.  As long as the installer shrinks the area of the steel first; the shrink sleeve will bond to both the bare steel and the factory applied coating and will assume the 'stair step' at each end of the girth weld. 

At the same time; picture a large flange welded to a pipe.  A shrink sleeve will seal to the flange (which is the area that would be shrunk first) and then will shrink down to the pipe forming an extremely noticeable step down to the pipe.  I give those examples to show that a heat shrink sleeve can be used in multiple scenarios where its rectangular shape work and work well.

But!  Try to install a shrink sleeve on a bend as you see above (picture a very wide shrink sleeve that attempts to coat that entire bend in one fell swoop); and you are likely to see the shrink sleeve "bridge" the bottom of that bend rather than perfectly conform to it.  This would (obviously) be a big problem! 

So - we can't coat that bend with one, very wide, shrink sleeve.  But we do still have options.  We could use smaller shrink sleeves to install one after; essentially breaking that 'bend' up into multiple small, essentially straight line sections of pipe.  That would work; but can be a little bit more complicated.

The other (and best) alternative is to simply use our Flexclad tape.  It is available in 2", 3" or 4" widths and rolls are a standard 50 feet long.  It is designed for exactly this application and has a long, successful use history. 

Ninety degree bends can pose quite a challenge when it comes to properly coating them and protecting them from corrosion.  That challenge is easily faced with our Flexclad heat shrinkable tape

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