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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

Testing

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

Procedure:
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.
Results
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).

Conclusions

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.


 

Tuesday, September 30, 2014

Trapped Air Under a Shrink Sleeve

Air Pocket Under Shrink Sleeve

     Occasionally, when an untrained installer is shrinking a heat shrinkable sleeve on a pipeline, it is possible for his shrinking technique to inadvertently cause an air pocket to become trapped underneath the shrink sleeve resulting in a bubble that can be clearly seen by an inspector. 
 
     Does this mean it is time to panic?  Time to call in the cavalry?  Time to tear that darn specification up and begin the coating analysis programs anew?  Should we summon the sand blasting equipment and plan to strip that field joint over the course of the next few hours so we can start fresh with a new installation? (keep in mind - shrink sleeves are not designed to be removable, that's why they do such a good job as a coating!)
 
     Calm down.  Take a deep breath.  Go grab a cup of coffee (maybe a decaf).  We're going to be able to help you fix this.
 
     For starters, make sure you still have the torch and propane tank nearby.  Also, make sure you've got a couple of our silicone rollers on site.  These are going to be what saves the day.
 
     The first thing we've got to do is re-heat the area of the sleeve with the air entrapment.  You will also need to heat a "path" between that air bubble and the edge of the shrink sleeve.  It is important that you aren't overheating the sleeve here.  If you begin to see smoke, or if you begin to see the finish on the shrink sleeve begin to show a rainbow, you are heating too much.  This will require patience and a tender touch, but it shouldn't take more than a minute or two at most.  You will want to be sure it is the yellow portion of the flame that is in contact with the sleeve and you will want to make sure that your torch isn't open full bore.
 
     Now, you will know you've heated the sleeve enough when you touch the sleeve backing with a gloved hand and see that the adhesive sealant underneath the sleeve is soft.  It will be obvious.  Then you will take your silicone roller and slowly push that air pocket toward the edge of the sleeve.  You must be a bit careful, we do not want to displace all of the mastic that is under there.  It will be apparent how much pressure is enough to move the air without displacing the adhesive.
 
     Then you will slowly work that air pocket until it is released back into the atmosphere.  This too will be obvious as you will hear the air popping its way out.  You aren't finished yet though.  We want to go back and roll over all of the area that the air travelled.  We do not want to create any new air pockets and we want to make sure that the adhesive is well bonded to both the bare steel underneath and the polyethylene jacket.  It is possible - if you have a long way for the air pocket to travel (we do make sleeves as wide as 36") that you could have to reheat the sleeve along the way.
 
     In any case, this is actually quite a rare occurrence.  If the installer is moving his torch vertically, and the installer is shrinking the sleeve circumferentially, and the installer is working from the middle toward the edge, something like this should never happen to you.


Wednesday, September 24, 2014

Shrink Sleeve Adhesive Thickness Over Weld Bead

Shrink Sleeve Mastic Thickness and the Girth Weld

      Though not a question that comes up too often these days, during the time when heat shrink sleeves were exploding in the pipeline coatings market (and other markets as well) there was often a contentious debate about mastic adhesive thickness....and what the minimums should be in order to assure proper mastic flow and filling around the weld bead...and at the step down areas from the factory applied coating to the bare steel.  Below is one such analysis completed in 1979. 

     Scope:  This report presents data and observation on the ability of various corrosion preventive products used in joint protection to fill and seal over and around a weld bead.  The results of this analysis will also cross over (based on factory applied pipeline coating thickness) to shed light on the required thickness of adhesive on different pipeline coatings to properly fill at the step down area from factory applied coating to bare steel.

     Test Procedure:  Samples were applied to a 4.5" diameter steel pipe with a circumferential weld bead.  Test samples were applied in accordance with the manufacturer's installation instructions.  After 24 hours, pipeline coating test specimens were examined for voids or leak paths around the are of the weld bead.  During this test, weld bead dimensions were .100" high and .350" wide. 

     Test Samples:
#1: Heat Shrink Tubular Sleeve with total adhesive thickness of 25 mils
#2: Heat Shrinkable Tube Sleeve with total adhesive thickness of 30 mils (<- Covalence)
#3: Heat Shrink Tube Sleeve with total adhesive thickness of 10 mils
#4: Heat Shrinkable Wrap Around sleeve with total adhesive thickness of 70 mils (<- Covalence)
#5 Heat Shrink Wrap Sleeve with total adhesive thickness of 25 mils
#6 Cold Applied Tape with total adhesive thickness of 30 mils
#7 Cold Applied Tape with total adhesive thickness of 40 mils

     Observations After Testing
#1: With a 25 mil supplied adhesive thickness -this shrink sleeve lacked enough flow and volume to fill areas along weld beads leaving a continuous leak path under the shrink sleeve.

#2: (30 mil) The sealant thickness and flow properties were sufficient to obtain complete filling of the weld bead area.

#3: (10 mil) The mastic showed good flow properties but lacked enough sealant thickness to adequately fill around the weld bead area. 

#4: (70 mil) There was sufficient amount of sealant present which flowed well upon heating to give a void-free seal in the weld bead area. 

#5: (25 mil) Insufficient sealant thickness plus low flow properties contributed to a void line along the weld bead. 

#6 & #7: (30 mil and 40 mil) Both of these samples exhibited continuous void lines along the sides of the weld bead.  It has been found that during the application of cold applied tapes, there is a bridging effect which traps air to cause voids along the weld bead.  Most sealants have limited flow when applied at room temperature and do not fill well around the weld bead.

     Conclusions:  The table above lists the various samples tested and gives a comparison of the sealant thicknesses.  Sample 1, 2 and 3 are tubular heat shrinkable sleeves (supplied in the shape of a tube) which, due to their recovery ratio, will have variable sealant thicknesses depending on the degree of recovery.
     Results indicated that an adhesive thickness of 30 to 35 mils is needed to adequately fill around the weld bead on the test fixture. 
     As indicated in several of the observations, a second factor which is equally important is the ability of the sealant to flow during installation.  Samples 1 and 5 both showed low flow characteristics when heated; this contributed to the lack of filling.  Samples 6 and 7 also showed very low flow because of being cold applied.  As noted in the observations, this is a common and known shortcoming of cold applied tapes.
     In general, a product must have a balance of adequate coating thickness (approximately 30 mils or above) and good flow characteristics during installation to deliver a void free corrosion protection coating to the weld bead.