TPS and WPCT Shrink Sleeve (Covalence / Raychem)

 TPS and WPCT Shrink Sleeve 

(Covalence / Raychem)

A roll of WPCT material

     One of the very first, original shrink sleeves was an early form of TPS.  It was a tubular sleeve, bonded into the form of a tube in the plant.  It was originally offered for pipe sizes 2" through 12".  The sleeves did revolutionize the market taking business away from cold applied tapes, from coal tar joint applications and from granny ragging the field joints.  Suddenly with TPS on the market, field joint applications were faster, more consistent, simpler and technically superior.

     Having seen the success of the TPS product, Raychem created the WPC sleeve (wraparound pipe coating).  After a few iterations, WPC eventually became WPCT (when the Thermal indicator was added into the backing).  Now, WPCT was able to be wrapped and shrunk around any size pipe which product a LOT more flexibility to the industry. 

     Now here we are nearly 50 years later, and WPCT and TPS are still cornerstones of the Seal for Life corrosion prevention catalog of products.  

     TPS is availabe in 18" lengths.  WPCT is available in 11", 17", 24" and 34" widths (customs available as well).  Would love to chat with you about your upcoming project!  

     

Does a Heat Shrink Sleeve Overlap Onto Itself?

 How Much Overlap is Needed Onto Adjacent Factory Applied Coating?

    When installing shrink sleeves; there are two very important bits of information to never lose site of:  OVERLAP and OVERLAP.  Let me explain:

    So the first important overlap:  The sleeve must wrap around the pipe and then OVERLAP back onto itself.  The sleeve does not 'butt up' to itself --- it overlaps onto itself.  This is critically important.  In this manner we can be certain that the sleeve will have enough shrink in it to properly seal to the pipe.  In addition at the area where the sleeve overlaps onto itself, the sealant will flow and fill during proper installation and fill any possible leak path there (with a belt and suspenders solution we will also roll that overlap with a silicon roller as one of the final steps of the installation process.

     The second important overlap discussion:  a sleeve needs to be wide enough to coat all bare steel and overlap onto the adjacent factory applied coating by at least 3" per side.  This makes certain that our seal extends out onto already proven (and jeeped) coating.  Now we will have at least a few inches of seal separating our bare steel from the outside world - leading to an excellent field joint coating that will properly prevent corrosion on that field joint for the life of the line.  

Heat Shrink Sleeve Coating Thickness

Coating Thickness of Heat Shrink Sleeves

      When determining coating thickness of different heat shrinkable sleeve options, there are several things you will want to consider.  I will look at each individually below and then sum up at the end.  Those three components are:  Backing Thickness; Adhesive Thickness and (where applicable) Epoxy Thickness.  First up:  Backing Thickness.

     It is important to note that much literature for heat shrinkable sleeves will contain two different thickness for backing.  These two things are 'as supplied' and 'fully recovered.'  Some folks find these confusing so let me explain.  First of all - let's change gears and look at a really big rubber band like you might use for rehabilitation of a shoulder injury.  At rest (fully recovered) that rubber band is going to be at its thickest point.  Now stretch that rubber band out as far as it will go (or as far as it can go) and you will notice that it is thinner when stretched out (this can illustrate supplied thickness).  Relax the rubber band again and you will see the thickness grow back to its resting state.

     The supplied thickness of any particular shrink sleeve is that 'stretched' out version of the rubber band.  The fully recovered thickness would be that rubber band at rest.  Because of the nature of heat shrink sleeves:  acting as a vehicle for applying adhesive to a substrate and pressuring that adhesive into all cracks, voids, imperfections and step down areas, that heat shrink sleeve really needs to be able to shrink to something smaller than the substrate diameter.  So a shrink sleeve on a 6" pipe really needs to be manufactured in such a way that it will fully conform to that 6" pipe.  How is that done?  By making a shrink sleeve that would actually shrink down to something like 5.5"....IF IT WERE ABLE TO.  Because it is unable to on a 6" pipeline, the shrink sleeve applies its pressure to the adhesive; forcing a good bond to the substrate and the PE jacket; and holding that pressure throughout the life of the pipeline.  Based on all of that -- the 'fully recovered thickness of the backing' that you will see on a data sheet is very often going to be slightly thicker than what you would actually see during an install.  In the field; heat shrink sleeves simply do not 'fully recover' because the substrate does not allow it.  Hopefully that makes sense.

     When considering the adhesive thickness; generally only one data point is recorded: adhesive thickness as supplied.  This is an excellent and accurate number when purchasing a proven, high quality product like Covalence (Seal for Life / formerly Raychem) manufactures.  What is there to discuss beyond that?  Plenty.  The adhesive actually gets quite a bit thicker during installation.  How does that happen?  Let me give a slightly oversimplified example:  say you have a 10 foot section of WPCT material.  Now say you shrink that down fully.  When you are finished; that WPCT section is going to be something closer to 7.5 feet long.  This is because WPCT is designed to shrink 25% to 31% (so in reality, that 10 foot section could shrink to just under 7 feet long).  So the surface area of the PE crosslinked backing has diminished by 25+%; and now the adhesive thickness that was covering 10 feet of material will not be covering only 7.5 feet of material.  In theory; an increase in thickness of 25%.  But it doesn't end there.  When the shrink sleeve is installed, one of the purposes of the shrink sleeve is to force adhesive out at the edges of the sleeve; creating an impenetrable barrier that water and oxygen will be unable to permeate.  So some of that 25% added thickness will be lost; but certainly not all of it.  How much is left?  That is a complicated question as it will be hinged on how snugly the sleeve was wrapped around the pipe; how properly the pipe was preheated; how much the shrink sleeve was heated and shrunk; how much adhesive might have been pushed around when rolling the overlap area of the sleeve; etc; etc.

     Finally, we can look at epoxy thickness where applicable.  Products that utilize an epoxy are generally:  HTLP60; HTLP80 and DIRAX.  With some products; epoxy thickness is critical and difficult to manage.  With stand alone epoxies it is not unusual that you need to work up multiple layers of epoxy in order to achieve 30 mils; 45 mils or even 60 mils of thickness in order to meet whatever end user specification you are working from.  That isn't the case with our product.  With our products we are generally looking for a thickness of epoxy that would be measured in microns.  Certainly visible to the eye.  Certainly covering every single square millimeter that the heat shrink sleeve will touch (and beyond in order to act as an inspection tool for construction foremen).  But there is no difficult thickness requirement and really not even a thickness gauge required. 

     So there you have it.  More than you ever wanted to know about heat shrink sleeve coating thicknesses.  Tomorrow I will follow up with a post outlining data from some of our actual products. 

Heat Shrinkable Materials

Heat Shrinkable Materials Technology

     High energy ionizing radiation provides an economic process to crosslink specific polymeric compounds which can then be converted to heat shrinkable tubing, molded shapes or wrap around products.  The phenomena of heat shrink ability is best explained by understanding that a typical thermoplastic consists of crystalline and non-crystalline phases.  When a thermoplastic is heated above the crystalline melting point, the polymer softens and flows readily.  However, if this same polymer is subjected ti ionizing radiation, crosslinks form between the individual polymeric molecules.

     When the crosslinked polymer is heated above the crystalline melting point, the crystalline areas "melt" but the polymer itself does not flow since it possesses form stability due to the presence of the crosslinks.   At this stage the polymer is similar to an elastomer.   If the shape of this heated material is changed, it will return to its original shape.  That is, it will remember the form it possessed at the time it was crosslinked.  However, if this polymer is held in a new shape while above its melting point, and then is allowed to cool in this condition, crystalline areas will reform.  crystalline forces will then keep the crosslinked polymer from returning (shrinking) to its original crosslinked shape. 

     Once the polymer is reheated above its melting point, thereby eliminating the crystalline forces, the elastomeric forces will cause it to recover back to its original crosslinked shape.  The term "elastic memory" is used to describe this phenomenon. 

     When the object to be covered is placed inside the heat shrinkable tubing and the tubing is heated, it will shrink around and conform to the shape of the object as it attempts to return to its original crosslinked shape.  Therefore, heat shrinkable products are useful in covering objects whose size is between the expanded diameter (the supplied size) and the original crosslinked diameter which is the freely recovered diameter of the tubing. 

     Since heat shrinkable polymers are crosslinked, they do not melt and flow.  They, therefore, have useful properties above their melting point. Because these heat shrinkable polymers often operate at elevated temperatures, only selected nonvolatile antioxidant systems can be utilized.  Also, since ionizing radiation can render most antioxidants ineffective, antioxidant technology had to be advanced in order to establish superior long-term thermal stability properties. 

Heat Shrink Sleeve Release Paper

Release Paper on Heat Shrink

      Once upon a time we received a telephone call from a frantic contractor out on a job site.  He had a major problem:  the shrink sleeves he was installing were not sticking to the pipe!  Wow - that is a serious problem.  How many have you installed?  (About six.)  Are you preheating the pipe to the temperature recommended by the installation sheet? (Yes.)  Have you cleaned the pipe using either a wire brush or a grit blaster? (Yes.)  What are the materials you're trying to bond to?  (Bare steel and FBE.)  Dang, I'm really baffled here.  I'm wracking my brain thinking of any other thing that could possibly be going wrong.  A shrink sleeve has two layers:  a heat shrinkable PE and a sticky mastic adhesive....are you installing the sleeve with the sticky mastic adhesive down on the pipe?  (Our sleeves don't have a sticky side.  We have a black side with 'COVALENCE WPCT' written on it and we have a white side with 'COVALENCE' written on it.  A white side??  Well that is the release paper.  You have to peel that off before you wrap the shrink sleeve around the pipe!  It sounds like your guys forgot to remove the release paper, so I'm not surprised that the release paper isn't sticking to the pipe surface.

     I know that if you're 'shrink sleeve educated' you might have a hard time understanding how someone could forget to remove the release paper prior to installing the shrink sleeve, but you can't possibly know what you don't know.  Without the proper training, without the proper explanations, without the proper installation sheets, without the proper customer service post-order -- these are the sorts of problems that become HUGE problems down the road.  

     I learned a valuable lesson that day.  Always respect your customers - but never, ever assume they know nothing about our product...and never, ever assume they know everything about our product.  We all started somewhere.  At one point, none of us knew anything about pipeline coating.  At one point, I couldn't tell the different between a WPCT and a DIRAX.  At one point, I couldn't tell the difference between a wrap and a tube.  At one time, I couldn't tell where the release paper started and the shrink sleeve ended.  And I still wouldn't know any of those things if I hadn't had someone who was willing to patiently teach me and answer my questions - no matter how obvious or silly they might appear to be.  That's what we're willing to do for you as well if you're curious, if you're interested, if you have questions. 

Heat Shrink Pipe Coating

Heat Shrink Pipe Coatings

     Heat shrink pipe coatings have been in use for more than four decades (along with heat shrink used for wire splicing, cable repair and many other applications).  For most of those decades, Raychem Corporation was THE industry leader in heat shrinkable technologies; led by their visionary leader: Paul Cook (who essentially commercialized and popularized radiation crosslinking and radiation chemistry).  The rest, as they say, is history. 

Here we see a field joint, just prior to heat shrink sleeve installation.

     Though the most obvious use for a heat shrink sleeve is on polyethylene coated pipe (as seen in the photo above), by far the most common pipeline coating combination is fusion bond epoxy (FBE) as the mainline pipeline coating and heat shrink sleeves as the field joint coating.  We sell (literally) hundreds of thousands of heat shrink sleeves per year - and I can honestly say that ~90% of those will be used on FBE coated pipelines. 

     When determining what specific heat shrink sleeve material to use on your pipeline girth welds (which is hopefully happening very early in the specification process...rather than happening while construction crew is standing on a pipeline spread staring down at some welded pipe joints....) it is important that you are making an informed decision.  There are number of factors that are very important...such as:

1. Pipeline operating temperature (once the line is in service - sometimes called Design Temp)
2. Outside Diameter of the pipeline (hopefully this is an easy one!)
3. Factory applied mainline pipeline coating and cutback sizes
4. Soil conditions (rocky? sandy? clay? subsea? above ground?)

     If we have access to that information, we have a good head start on making sure you are going to be using an appropriate material.  The fastest way to a coating / corrosion problem is to select and use an inappropriate product for your pipeline.