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PostPosted: August 16th, 2006, 3:17 pm 
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A lot of users of thermoplastic piping systems such as Polyethylene, Polypropylene, and PVDF piping systems aren’t aware of the ability to remove the internal weld bead, which is formed during the fusion welding process. Many will argue against the need to remove the internal bead because the friction factor on these materials is so low that the removal of the bead would virtually make no difference in the flow. I would like to review this standard of thinking. There are four reasons for why internal bead removal is an important factor:
1. Flow Restriction: Even though flow reduction is virtually nonexistent. There is still a restriction at the bead location. Among other reasons this can be a problem when pigging the pipe for blockage or when HDPE is used as a casing for telecommunication conduits.

2. Stimulated Blockage: It’s easy to understand how sediment can build against a bead during a slow flow rate. This is the beginning of blockage as large debris become embedded in the sediment. Think about push joint piping systems and how every 13’ or 20’ this problem occurs compared to thermoplastic fused pipe where welds at lengths of 40 feet or more in distance is the standard along with complete internal bead removal.

3. Bacteria Entrapment: Internal bead removal works in several systems in which thermoplastic butt fusion techniques are employed such as HDPE, Polypropylene and PVDF piping materials. In the silicon industry it is common to use these plastics in de-ionized water piping systems where bacteria or other particle entrapment is of great concern. In addition it isn’t unusual for bacteria to be a problem in other types of chemical industries such as anodizing metals. Most entrapment concerns are strongest where chemical purification can’t be used because of other reaction problems it brings.

4. Turbulence Wear: With increased flow the bead creates a turbulence that generates wear when slurries of abrasive materials flow through the system. Even though the bead will finally wear away and turbulence decreases, the final effect is a thinner wall cross-section in that location. In push joint pipe systems this turbulence can never be removed.

In thermoplastic piping systems engineers recognize the efficiency and advantages of having the internal weld bead removed from a system compared to a system that is not. Whether the issue is flow Restriction, or flow Reduction, or Stimulated Blockage, or Bacteria entrapment or Turbulence Wear. The concept of bead removal is an advancement in the thermoplastic piping industry that needs to be utilized, if for no other reason than higher efficiency.


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PostPosted: August 16th, 2006, 3:18 pm 
The previous writer makes some good points. However, don't let this line of thinking scare you away from polyethylene as your system of choice because you feel you have to remove the internal bead. The writer admits, "flow reduction is virtually nonexistent." Lets look at the applications where bead removal in NOT needed:
1. City and Rural Water Distribution Systems: The advantages of switching from a material such as cast iron or PVC to polyethylene far outweigh the "virtually nonexistent" flow restrictions of an internal bead. A complete list of the advantages would be a topic for another post.

2. Natural gas distribution systems: For decades polyethylene has been the material of choice for natural gas distribution. The internal bead has never been an issue.

3. Waste Water and Sewer: Polyethylene provides such a low friction factor, that even with the internal bead, flow is improved over concrete, cast iron and PVC.

4. Mining and Industrial: In these tough applications, polyethylene is the preferred material over steel in many cases. Internally beaded polyethylene, with its excellent resistance to wear and abrasion, can out last steel several times, even with high abrasive slurries. In these applications, polyethylene's erosion/corrosion performance is unaffected by the bead.

5. Conduit and Telecommunications: The issue of an internal bead in minimal in these applications. Most all commercially designed pigs can easily pass the internal bead. Once the cable is installed the bead has no effect. This industry simply prefers mechanical fittings in small sizes. This preference is largely due to the lack of knowledge about superior joining methods such as butt fusion, and not the lack of internal debeaders.

As an engineer, I disagree with the previous writer's comment that the internal bead should be removed if for no other reason than efficiency. If the time and cost of removing a bead far outweighs the increase in performance over the life of the system, the bead should be left in place. Keep in mind that polyethylene has the advantage of being coiled in sizes up to 6" IPS. These coils range in length from 500 to several thousand feet. Even the previous writer's products (which can be found at www.beadtrimmer.com ) cannot remove beads hundreds of feet down a small diameter pipe. In some special cases, it may be advantageous to remove the internal bead (and I’m sure he’d love to sell you a tool to remove them). But in most applications it simply is not necessary.


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PostPosted: August 16th, 2006, 3:18 pm 
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Mr. Perrault,
Thank you for responding to my topic. You are right on how the advantages of polyethylene piping so much out weighs any other material that even leaving the bead inside, the polyethylene systems would still out perform other piping systems. I do want everyone who reads this topic to understand that we are not discussing a problem with polyethylene, but rather an enhancement to an already superior product. My topic was to discuss and point out the additional advantages for removing this weld bead.

However, if I were to summarize our biggest disagreement it would be your statement that “the time and cost of removing a bead far outweighs the increase in performance over the life of the system”
You might not be aware of the capabilities of the bead removal tooling that is now available. These tools are a new generation from the bulky and technical tools of old. They require very little training (if any) and it takes less than 5 minutes to set up and less than a minute to remove the internal bead. All of which is done while the fusion weld is still in the fusion machine during its cooling stage.
The cost of these tools does have a price tag. But not compared to the cost of a single blockage repair over the entire life of the system. Keep in mind one of the great attributes of a polyethylene piping is its longevity. Additionally there are now rental houses through out the United States that can either sell or rent these tools, lowering the cost to a level that even a very small bead removal project is cost effective. With cost and time being excluded or minimized I can’t see where your argument can stand with any of the industries that you listed.
Additionally I have documented bead removal at a length of 250’ down a 12” DR 9 pipe system and farther in smaller diameters. I am not advocating the use of bead removal on coil piping because of other problems that occur but a distance can be achieved.

So I’ll finish with what I started “The concept of bead removal is an advancement in the thermoplastic piping industry that needs to be utilized, if for no other reason than higher efficiency.”


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PostPosted: August 16th, 2006, 3:18 pm 
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Is there any I.D. tools for the 62" machines?
And, what if there was another way to form the excess instead of having the I.D. bead?
Or, not having the I.D. bead at all?


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PostPosted: August 16th, 2006, 3:19 pm 
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The largest bead removal tool that I’m aware of is a 24” tool. I’m sure if there was an enough need a larger tool would be built. What has been the most common technique in large pipe diameter bead removal is to have someone crawl up inside the pipe while the bead is still warm and cut it out manually. The bead could also be ground out if removal was needed at a later time.
There have been other methods to reduce the bead size on the I.D. of pipes. One technique was to machine or router a 45 degree bevel on the inside wall of the pipe ends prior to fusing. Enough material would be removed so as to leave a recessed valley for the bead to fill into upon fusing the pipes together. This idea had some drawbacks because the section that was machined had less wall mass and weld strength was compromised. The fusion bead doesn’t add any strength to the recessed valley it fills.
Another technique used in other industries is to have a special balloon slid into the fusion area while the bead is just forming. The balloon would be expanded and force the bead to form flat against the inside pipe wall. This became limiting in larger sizes of pipe and not always did it make a smooth press.
Your idea of not having a fusion bead formed at all isn’t a bad wish. There are other methods in welding technology that can produce a fusion with very little excess material. However none of these methods have been proven to be as economical or as simple as the standard butt fusion machine.


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