Shrink Sleeve Tenting / Wrinkling / Air Entrapment / Bubbles / Edge Lifting

Shrink Sleeve Wrinkling / Air Entrapment / Edge Lifting / Tenting / Bubbles

     Had a recent correspondence with a gentleman abroad.  He was having difficulty finding anyone locally who could answer his questions.  Here was his situation:  He was being encouraged to use shrink sleeves on a project, but he was concerned about some of the "potential issues" that might arise.  As a result, he wanted me to address all of the above on a "what if" sort of basis.  I told him that this was rather unusual, but I would be happy to give him honest answers and do my best to address his concerns.

     In case you're new to this blog; here is my quick background.  I've been with Joint Specialists for 14 years doing nothing but selling and supporting the heat shrink sleeve industry (Raychem/Tyco/Tyco Electronics/Berry/Covalence).  In addition, I have had 14 years as student of one of the most knowledgeable shrink sleeve experts in the world - my father -Stan Simpson.  Stan has been intimately involved with heat shrink dating back to the 1970's.  He has served in R&D, tech service, sales and management for the last 40 years or so.  He knows this product and market inside.  

     Please keep in mind, I'm responding to completely fictional installation issues here.  These are not real problems.  I'm having to answer very generically.  If these were some kind of real issue, I'd be in my car or on a plane heading to a job site right now.  If the job site was inaccessible to me (or if the material was not purchased from me) I'd be asking for photos so that I could determine exactly what was going on.  Our products are proven.  They've been installed successfully tens of thousands of times.  I've never seen a true "failure" of our product.  Installation errors?  Occasionally.  Incorrect product selection?  Rarely, but yet.  True failures?  No.  

     It is always amazing what you can actually find when you get the chance to "see" a "failure" for yourself.  The most memorable was a call that "the sleeves are falling right off the pipe."  It made absolutely no sense, but it was a nice sized job, so there I was on a 4 hour flight to the coast.  I felt like I was on CSI as I studied one of the sleeves that had "fallen off" the pipe....and right there visible to the naked eye were the knife marks and the plier marks where someone had pulled the shrink sleeve from the pipe using brute strength and a lot of sweat (quick side note - hey, thanks for the peel test...it was good to see that the shrink sleeve showed a cohesive failure, just like you'd like to see!).  After the clear evidence of tampering was presented, we quickly learned that there was some kind of a union dispute occurring and as a result, the contractor was being barraged with phantom problems...but I digress.

     So, how about those issues listed above?  Here are my thoughts and experiences.

Shrink Sleeve Wrinkling

     I've seen a lot of shrink sleeves installed and I've shrunk a lot of shrink sleeves.  If I've seen any form of wrinkling at all it has been because of 2 things (or possibly 4 things, depending on how you break these down).

1.  Installing a shrink sleeve on a COLD pipe.  The pipe could be cold because the installers decided on their own to skip the ultra critical "preheat the pipe" step; or - the sleeves are being installed on an active pipeline.  Installing shrink sleeves on an active pipeline can present quite a challenge, I would never recommend it unless I had an opportunity to discuss it with you before hand extensively. 

2.  I have also occasionally seen minor wrinkling when a shrink sleeve is dramatically overheated.  Sometimes this overheating can be caused by the use of a non-approved torch (say a welding torch, rose bud, or extremely high output torch in the hands of an inexperienced crew member). 

     The truth is that I have rarely seen sleeve wrinkling.  It just doesn't happen very often.

Shrink Sleeve Air Entrapment

     When installing a shrink sleeve there are a number of small things that are critically important.  Addressing only those things that could possibly lead to air entrapment underneath the shrink sleeve...here are three:

1.  For pipe sizes 12" and larger, we recommend two installers be working together - one on each side of the pipe - in order to shrink the sleeve together, working in tandem.

2.  An installer working on a horizontal pipeline should always be moving his torch up and down while shrinking the sleeve circumferentially.  An installer cannot have a shotgun blast approach to his shrinking - his movements need to be calculated and logical (common sense).  

3. There are two options for sleeve shrink:  start in the middle then shrink your way (up and down) to one side - then back to the middle and out to the other side.....or.....starting shrinking on one end and shrink with the wind; up and down; all the way across the sleeve.  This way any air is pushed out ahead of you.

     Picture this for a moment (I've never seen this).  Picture an installer who wraps the shrink sleeve loosely around the pipe leaving a 'two finger' bag in the bottom (this would be an old-school install technique that is still alive in some corners of the world).  Now picture the installer shrinking one edge of the sleeve.  Then the installer comes back and shrinks just the other edge of the sleeve.  He will have created a ziplock bag!  It wouldn't make any sense and I've never seen it done.

     Now, even with the best installers and the best intentions, it is possible that a small air pocket get trapped under the sleeve.  Have no fear!  That is what the silicone roller is for that you've purchased for your crew.  While the sleeve is hot; that air pocket can be carefully pushed to the side and spit out the edge of the sleeve.  If you were to see an air pocket later after the sleeve has cooled; no problem - get your torch and reheat the sleeve in that area and use the roller to push the air out.  

Shrink Sleeve Edge Lifting

    I've seen this only two times.  

1.  The installer had literally not shrunk the sleeve at the edge.  It was clear because the sleeve backing still had the texture in it!  The crew fired the torch back up; heated up that section of the sleeve and it zipped right down to the pipe surface.  

2.  A sleeve was being installed on a VERY dusty PE coated line.  As the adhesive was pushed out a bit due to the force of the sleeve shrinking; the adhesive was coming into contact with the dusty, dirty PE surface.  Of course, nothing will bond through a thick layer of dirt - so it is impossible for the adhesive to bond to the substrate.  Picture putting a bumper sticker on your incredibly dirty car!  It won't stick -- but it isn't the bumper stickers fault; it is the fault of the dirt. 

Shrink Sleeve Tenting

     The only time I've seen this; I absolutely knew it was going to happen (it was expected).  I've never seen this happen "by accident."  Shrink sleeves are designed to shrink tightly to 'rounded' surfaces.  Rounded is in quotes because it is a bit of a misnomer.  A shrink sleeve will work great on a square, a rectangle, a circle, an oval, a triangle and a myriad of other shapes. 

     But picture a circle with a 'pie piece' cut out (so it looks like pac-man).  What will happen if you install a shrink sleeve on that circle?  It will bridge pac-man's mouth.  It will not flow and fill down into the mouth.  Similarly, take a large square and place it on a circle.  Shrink around that whole contraption and the sleeve will bridge from the top of the square out to the edge of the circle.  

    In other words, the only upsets that a shrink sleeve can truly fill and seal to are upsets whose dimension is at or less than the thickness of the adhesive layer of the shrink sleeve.  That is why when you consider (on a micro level) the 'upset' of the weld bead - or the 'upset- of the step down from factory applied coating to bare steel of the girth weld - those are filled very nicely.  

     So when someone talks about tenting, the first place I am looking is to see what is under that shrink sleeve that is causing this tenting phenomenon.  Rest assured - it is something.  Is the weld bead profile too high?  Weld spatter leave a 'tent pole' so to speak?  Is there a very thick factory applied coating that was not bevelled?  Was the first part of the shrink sleeve set on the pipe folded over to cause an abnormality?  Did someone leave a hunk of duct tape or a weld rod in there?  I've never seen any of these happen; but as we all know - anything is possible on a pipeline spread!

Shrink Sleeve Bubbles

     Well, I left this one for last because I've never heard of it!  I hate to close this article without an answer for every question, but I just don't know what someone might mean by 'bubbles'.  If you'd like to explain - please drop me a note at steve@jsicoatings.com - or better yet - send me a photo!

  

Shrink Sleeve Installation Tools

Shrink Sleeve Installation Tools

Question:  What tools are required for Covalence heat shrink sleeve installation?

Answer:  Ignoring the need to clean the pipe, Covalence heat shrink sleeves do not require

any special tools during installation.  Here is what is needed:

- A means of measuring preheat temperature.  This could range from something as 

sophisticated as a pyrometer with roller probe; to something

as simple as a temp stick.  

An example of temp sticks for different temperatures

 - A broad flamed torch (Covalence shrink sleeves cannot be shrunk

using an acetylene torch or a welding torch).  Our torches are sold as a kit

which includes a torch with a pilot lights; a regulator with a pressure guage

and a thirty foot long hose. 

A JS-2601 Torch Kit - available at JSI

- A long handled silicone roller.  This is used after installation to roll the overlap area

and can be used in the event that any air has become trapped (which could be

caused by poor application).  

A long handled roller; used during heat shrink sleeve installation

(Keep in mind that the contractor or end user will need to supply their own propane tanks for installation) 

Installing Shrink Sleeves: How Important Is Pre-Heat?

     Another common question:  How Important is Pre-Heat?

     Short answer:  ABSOLUTELY CRUCIAL

     Long answer:  When installing a heat shrinkable sleeve as a field joint coating, you are doing so for one reason and one reason only.  You are protecting that field joint (girth weld) from corrosion.  Of course, the idea is, that if you can seal that field joint in a way that prevents water and oxygen from reaching the bare steel; then it will be impossible for corrosion to occur.


     We do this by installing a heat shrinkable sleeve that is coated with a sealant or adhesive of some kind.  If we can install that sleeve so that we get the best possible bond between sealant and bare steel (and factory applied coating) then we begin the life of that field joint from the very best possible position:  properly coated and protected.

     Of course the first step of installation is making sure we've achieved the proper cleanliness standard on the bare steel.  Different adhesives will have different requirements there and I won't discuss them here (but I did touch on surface prep for WPCT here).  The next step however is preheating the steel (and adjacent factory applied line coating) to the proper temperature.  Why is this necessary?

     Any hot melt adhesive or mastic coated shrink sleeve will have an optimum temperature at which the adhesive bonds to the substrate.  When we look at it very closely, we must create an environment where the bond-line reaches a temperature sufficient for ideal bonding.  The bond-line is that area where the hot melt adhesive of the mastic come into contact with the substrate (pipeline).  That interface is critical.

      Even though there is a significant amount of heat put into a heat shrink sleeve during the installation process; when you consider the heat insulation properties of the heat shrink sleeve and when you consider that the steel pipe will act as a heat sink (carrying temperature away from the girth weld as it acts to spread any elevated temperature through the steel in the immediate area) it isn't possible to actually achieve the necessary bond-line temperature exclusively using heat from the sleeve shrinking itself.

     As a result, the steel must be preheated.  This assures that the bond line temperature is met and that the adhesive/steel interface will be properly prepared for the bond to occur.  All Covalence heat shrink sleeves will be supplied with an installation sheet in each box.  No matter the product; there will be a 'minimum recommended preheat temperature' listed on that installation sheet.  It will certainly cause no problem to heat higher than that; with two exceptions.

- When installing a shrink sleeve system that utilizes a liquid epoxy (DIRAX, HTLP60, HTLP80, etc) it is important to keep the preheat temperature down below 200F.  Installing S1301M epoxy on a pipe that is heated above 200F will result in some smoke - and result in the epoxy more or less flash curing (which we want to avoid since we want the epoxy chemically bonding with the sleeve adhesive; and that can't happen in the epoxy cures "early")

- Most all shrink sleeves (all PE shrink sleeves anyway) shrink at ~267F.  We would not want to preheat (most of the time) to a higher temperature than that, as it could result in the sleeve shrinking before the installer is ready (as an example, before the closure has been secured). 

How Important Is Surface Preparation?

Question:  How important is surface preparation when installing a shrink sleeve?

Answer: It is VERY important!  The simple fact is that when considering the cleanliness of the bare steel field joint (and the adjacent factory applied coating), the cleaner it is; the better your bond will be (generally speaking).  When considering the strength of a bond between a coating of some type and a substrate of some type; we can illustrate this point simply using real world examples.

How well will a bumper sticker stick to this car?

     Imagine slapping a bumper sticker on this car.  How long do you think it would stay put?  My guess is that it would fall off just about the second your hand stopped holding it up!  In any bond scenario; a bond is only as strong as its weakest link.  In a case like this (pictured above) no matter what you put on the outside of the dirt; the weakest bond will always be the bond between the dirt and the car.  How strong it that bond?  So weak that you can destroy it with something as weak as a wet finger or a squirt gun.

     Another factor in determining surface preparation requirements is the specific adhesive type involved in the coating.  In general, an aggressive mastic will require minimal surface prep (though it will still need to be free of dust, dirt, grease, etc).  The higher performance the adhesive, the higher the required surface prep is likely to be.  

     Keep in mind when considering minimum surface preparation requirement, these are the cleanliness levels that have been determined to meet or exceed the data as reported on data sheets or manufacturing specifications. 

 

Shrink Sleeve Overheating: What is the Effect?

Question:  My crews have overheated a shrink sleeve.  What do I do now?

Answer:  I wish the answer were a little simpler!  There are many different levels and degrees of overheating.  I will try to address three below.

    First of all; as seen here - a shrink sleeve is supplied with a cross hatch pattern in the backing.  As the sleeve is properly heated (the backing temperature must reach 267F in order for the cross linked PE to reach its crystalline melt point and revert back to its original size), those cross hatches disappear and are replaced by a smooth PE backing. 

    For the purposes of this discussion, I will limit the possible extent of overheating to three different groups:  surface crazing; crazing with smoke and/or flame; and splitting.

     Surface crazing can occur when an area of the shrink sleeve gets too hot.  This is most often caused by the installer failing to keep his torch continually moving in a circumferential motion.  Keep in mind, a propane torch might operate at several thousand degrees.  In order to shrink a shrink sleeve, we are trying to get the temperature of the backing up to 267F.  Installers MUST keep their torches moving!  In a case where a sleeve has cooled, and there is an area with light surface crazing (often accompanied by a dull area lacking in shine) this is not a problem.  Crazing does not effect the integrity of the sleeves (in fact some studies would actually indicate the crazing increases the fracture toughness of a polymer! That doesn't mean we recommend intentionally creating crazing in your shrink sleeve).  In a case where crazing has or is occurring; simply STOP heating that area and move on to the other sections of the shrink sleeve; always moving the torch in a circumferential motion. 

      Sometimes, this surface crazing can be accompanied by smoke or even flame.  The fact that the PE backing of our shrink sleeves have been cross linked means that the backing will no longer melt as a typical PE will.  The backing can still burn, however, and will burn if the installer is not continually keeping his torch moving.  In a case where a sleeve begins to smoke; the installer should simply stop heating that section of the sleeve!  In a case where a sleeve begins to flame; the installer should immediately put the fire out (this can be done by simply removing the torch and quickly patting the flame out with a gloved hand).  As long as this has been caught soon enough; again - this causes no serious damage to the shrink sleeve and no repair needs to take place.

     Finally, there are times that an installer seriously, seriously overheats a shrink sleeve.  I have seen hundreds of shrink sleeves installed and I've never actually seen this happen in person.  To actually burn completely through one of our shrink sleeves; an installer would have to be incredibly distracted by something; leaving his torch open full bore while concentrating the flame on a small portion of the sleeve.  Even then; the sleeve itself would give him many warnings as it crazed; smoked; caught fire; and ultimately burned through.  Once the backing has been compromised, it will be obvious as the mastic material will begin to flow freely through the backing and the backing will continue to split wide open.  This is the kind of thing that could not possibly escape the attention of even the most inexperienced inspector.  In a case like this; there would absolutely have to be repairs made.  Repairs are discussed in depth here.  

     One other thing I would mention.  Every wrap around shrink sleeve requires a closure strip to hold the sleeve in the shape of a tube during the installation process.  That is the closures only job; it has no corrosion prevention or sealing duties.  At times, particularly when it is dog eared; or slightly raised; the closure strip can flame up when overheated.  In such a case, the torch would simply be moved away; the installer would 'pat out' the flame (patting down the closure in the process) and then installation would resume.  This would not be a problem at all and would require no repair.  

     As always, we are available for consultation.  Any time someone might have a question about overheating; my first bit of advice would be to take some photos and email them right away to steve@jsicoatings.com - I will get back to you quickly. 

DIRAX Installation Video

     DIRAX is the toughest shrink sleeve on the market.  With a successful history of use on pipelines with outside diameters between 2" and 48", this product is unmatched in the industry.  Effectively a five layer sleeve system (two layers of PE surrounding a layer of fiber mesh installed on a high shear adhesive, installed over a two part liquid epoxy).  On the leading edge of this sleeve - it is a ten layer system!

   The installation steps (as shown in the video above) are simple:

1. Clean the pipe
2. Preheat the pipe to a temperature between 140F and 200F
3. Mix and apply the S1301M liquid epoxy in a very thin quote
4. Wrap DIRAX sleeve and secure closure
5. Shrink sleeve always moving torch circumferentially
6. Wrap 3" wide leader strip and secure closure
7. Shrink leader strip
8. Roll overlap areas with a silicone roller
9. Be sure sleeve conforms to pipe surface; adhesive flow is evident at all sleeve edges; and there are no cold spots in the sleeve.