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 email@example.com - or better yet - send me a photo!