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Wednesday, October 1, 2014

Can Shrink Sleeves Hold Internal Pressure?

Heat Shrink Sleeves and Internal Pressure

     Can a heat shrinkable sleeve hold internal pressure?  It doesn't come up often, but it is a phone call that I get a few times per year.  Maybe someone is looking to repair a spot where a water line has been compromised.  Maybe someone is looking to repair significant damage to a PE pipe.  I've even seen someone trying to prevent water ingress at a juncture between a concrete coated line and a pipeline.

     My standard answer is:  well, our heat shrinkable sleeves are not specifically designed to hold internal pressure, they are designed to seal and prevent water or air from getting to the field joint from the outside.  But....there have been cases where one of our sleeves was used to hold internal pressure. 

     First of course, we had to test it.  The industry isn't going to accept a product in an application that hasn't been tested...and tested extensively.  In this case, we tested our DIRAX product (often called ROCS when it is not used in a directional drilling application).  We used an 8" wide DIRAX shrink sleeve and for the sake of this testing, we installed it on a 1.685" OD pipe (smaller than we would normally recommend using a wrap around shrink sleeve on).

Installation procedure:
1.  The pipe was abraded using a wire brush attached to a typical electrical drill.  An area slightly wider than eight inches was abraded to insure good adhesion over the entire width of the sleeve. 
2.  The sleeve was wrapped around the pipe and centered on the pipe joint.  Note: The pipe was not pre-heated.
3.  The preattached closure strip was heated and pressed down to hold the sleeve during the shrink process.
4.  The sleeve was heated in the center and all around the circumference until fully recovered.  As the center area of the sleeve was shrunk, the torch was moved circumferentially and toward one end of the sleeve until one side was fully recovered.  The same process was repeated toward the opposite sleeve end.  Total installation time was approximately five minutes including pipe abrasion.
note: a power wire brush would reduce the abrasion time


Test Fixtures:
Two pipe samples were fitted with an inlet and outlet pipe and valve system along with a pressure gauge.

Test samples were filled with water to a pressure of 11 PSI and held at that pressure for one hour. 
After one hour, the pressure was gradually increased until failure.
Sample One: Held a pressure of 11 PSI for one hour with no leaks.   Sample one eventually failed at 22 PSI.  The failure occurred at the end of the fixture where the end cap was plastic welded to the pipe. 

Sample Two:  Sample two was found to have a small, almost invisible crack as the sample was pressurized.  The area around the crack was abraded.  A small "bicycle tube" repair patch was cut from ROCS material and installed over the crack.  After cooling, the sample was pressurized to 11 PSI and held for one hour.  The sample gradually pressurized until failure at 25 PSI.  Failure occurred at the same area as sample one (the pipe end, away from the sleeve).


An eight inch wide ROCS sleeve is sufficiently wide enough to properly seal the pipe joint at 11 PSI.  An eight inch wide sleeve is easily centered on the joint with no special skill.  The ROCS sleeve appears to be more reliable than plastic welding.  Small "postage stamp" type repairs can be made using rounded patches of ROCS. 

The pipe is a bit subject to overheating with a torch during sleeve installation; therefore, protective blankets would be recommended for use during installation.  The same protective blankets used to protect coating during pipeline welding would be suitable.


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