Can Shrink Sleeves be Installed without Preheating Steel?
As I've discussed elsewhere in this blog, pre-heating the steel is an incredibly important step in the installation process. Other than surface preparation (cleanliness) I would say preheat is the single most important step. So, what happens when there is some kind of circumstance that is preventing you from properly preheating the substrate before shrink sleeve application?
Well first off I'd like to reiterate: wherever possible, pre-heating is needed and necessary. But I understand there are cases where preheat can be impossible. This would include an active pipeline where the mass amounts of product flowing through the line act as a tremendous heat sink; actually preventing any possibility of preheat. In those cases, we go back to one of Raychem's earlier technologies....and the associated logic of that product.
Once upon a time, Raychem was faced with a dilemma: How do we recreate a three layer coating system on the field joints so that we can have a homogeneous and consistent pipeline coating throughout an entire line? Well, those three layers are: epoxy, adhesive, PE backing. Naturally that is where they started. What was found as that family of products was developed was that introducing a layer of epoxy as the initial pipeline coating brought with it some benefits other than the technical advantages (improved cathodic disbondment results, etc).
What was learned was that the introduction of an epoxy layer meant there was a dramatically reduced preheat temperature. Thus the HTLP coating system was born -- HTLP stands for: High Temp, Low Preheat. How much lower were they able to move the preheat? Let's look at an early iteration of the WPC60 / HTLP60 product. When using the epoxy bonding agent (HTLP) - the preheat requirement was in the 140F range (for reasons I'll explain further below). The preheat temperature for the WPC60 product (no epoxy bonding agent) was a whopping 280 degrees F. The use of the epoxy cut the preheat temperature in half -- and improved the technical aspects of the coating. Win, win!
So, why still 140F for the preheat temperature on the HTLP60 sleeve system? Simple: economics. The epoxy material has a consistency similar to honey. As you probably know from your own Sunday morning breakfasts; honey is very thick when cool...but can get very thin when warm. For the HTLP60 system to properly function, only a very thin amount of epoxy is required (microns). When the pipe is preheated, the epoxy can be applied quite thinly. The system works great; meets all specifications and the cost of the epoxy is minimal since only a minimal amount is needed.
When applying this same S1301M epoxy to a pipe that is resting a temperature less than 140F; the coolness (so to speak) of the pipe prevents the epoxy from thinning out as much. As a result, there is a consistency quite close to a jar of honey that you've just pulled out of your refrigerator. The system still works great. The system still meets all expected technical parameters. The system still meets or exceeds all requirements from the manfacturer's specification. The difference is, the system used more epoxy (volume) than was really required. This means that the system cost a little bit more money than it really required. Some companies want to save every penny they can. Other companies aren't bothered by spending a few extra dollars. This sort of a sacrifice (less preheat time vs more cost) is worth it to some people, and not worth it to others.
So there you have it. As usual, I've tried to write more than any normal human would ever want to read about his topic! Any other questions about anything else? Shoot them to me: steve@Jsicoatings.com