How to Repair Cross-Linked Polyethylene

Although cross-linked polyethylene is not very common, it is sometimes used for fuel tanks, kayaks, canoes, and older ATV parts. It is an extremely durable plastic, and unfortunately, it is not easily repaired. Cross-linked polyethylene is a thermoset plastic, which means it is not meltable. The plastic identification symbols for cross-linked polyethylene are XPE, XLPE, PE-Xb, and PEX. If there is no identification symbol, the best way to determine if the polyethylene is cross-linked or thermoplastic is to try to melt it. Thermoplastic polyethylene will melt easily, but cross-linked polyethylene will not melt; it may turn brown or become soft and flexible, but it will not melt.

Because cross-linked polyethylene is not meltable, we cannot use the nitrogen plastic welder or airless plastic welder to create a fusion weld. Instead, we will use Polyvance's KCWPRO airless plastic welder and flat low density polyethylene (LDPE) welding rod to make a bonded repair to a puncture, a crack, and a hole in this cross-linked polyethylene fuel tank. High density polyethylene (HDPE) welding rod can be used for this repair, but we recommend using low density polyethylene welding rod because it is easier to work with.

The thermoplastic polyethylene welding rod will be used as a hot melt adhesive. This process is similar to how we apply FiberFlex welding rod.

Video Timestamps:

• Repairing a puncture - 2:01
• Repairing a crack - 4:00
• Repairing a hole - 5:00
• Testing the welds - 6:18 (air pressure test 6:27, water test 7:04)

Note:
Any Polyvance airless plastic welder with the 6031 flat tip can be used for this repair. High density polyethylene welding rod can be used for this repair, but we recommend using low density polyethylene welding rod because it is easier to work with. Use the flat polyethylene welding rods with the 6031 welding tip.
The best DIY kit for this repair is the KCWPRO.
If you already have a Polyvance airless plastic welder, you can use this list to determine what you need for this repair:

• KCWPRO (includes the 6031 flat tip, and also includes 10 feet of flat LDPE OR HDPE welding rod in the color that you choose)
• The integrated airless welder on our nitrogen welding systems (all welders include the 6031 flat tip, and some welders include a small amount (10 feet each) of natural colored flat LDPE and HDPE welding rod.)
• 5700HT Mini-Weld Model 7 (includes the 6031 flat tip, but does not include flat polyethylene welding rod)
• 5210 FiberFlex Repair Kit (includes the 6031 flat tip, but does not include flat polyethylene welding rod)
• ATVPRO (does not include the 6031 flat tip, and does not include flat polyethylene welding rod)
• 5211 PolyPro Welder (does not include the 6031 flat tip, and does not include flat polyethylene welding rod)
• 5212 Plastic Radiator Tank Repair Kit (does not include the 6031 flat tip, and does not include flat polyethylene welding rod)

Always wear proper safety gear while working!

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Products Used:

Note: This is a list of the Polyvance products that can be used to make this repair. This list does not include sanders, grinders, or other common tools you will need. If you have any questions, please don't hesitate to call technical support at 800-633-3047.

• 1000 Super Prep Plastic Cleaner (three options available) OR 1001-4 EcoPrep Plastic Cleaner
• KCWPRO Airless Plastic Welder (See above list for more information about the other airless plastic welders that can be used)
• 6121-T Tear Drop Cutter Bit
• 6125 Tapered Burr

Video Notes:

• We used blue and natural colored welding rod in this video to show contrast on the tank. You can use welding rod that matches your cross-linked polyethylene part so the repair will not be as visible.
• English Closed Captions have been provided for this video. Click on the CC button to turn them on or off.
• The length of this video is in no way representative of the actual time required to perform a complete repair and therefore should not be used for estimating purposes.

Music Credits:

• "Super Friendly" Kevin MacLeod (incompetech.com)
  Licensed under Creative Commons: By Attribution 3.0 License
  http://creativecommons.org/licenses/by/3.0/
• "Wallpaper" Kevin MacLeod (incompetech.com)
  Licensed under Creative Commons: By Attribution 3.0 License
  http://creativecommons.org/licenses/by/3.0/

English Transcript:

This fuel tank is made of cross-linked polyethylene, an extremely durable plastic. Unfortunately, cross-linked polyethylene is also not easily repaired. Cross-linked polyethylene is a thermoset plastic, which means it is not meltable. Because it is not meltable, we cannot use a nitrogen plastic welder or airless plastic welder to create a fusion weld. Instead, we will use Polyvance’s KCWPRO airless plastic welder and low density polyethylene welding rod to make a bonded repair to a puncture, a crack, and a hole in a cross-linked polyethylene fuel tank.

Although cross-linked polyethylene is not very common, it is sometimes used for fuel tanks, kayaks, canoes, and older ATV parts. The plastic identification symbols for cross-linked polyethylene are XPE, XLPE, PE-Xb, and PEX. If there is no identification symbol, the best way to determine if the polyethylene is cross-linked or thermoplastic, is to try to melt it. Thermoplastic polyethylene will melt easily, but cross-linked polyethylene will not melt; t may turn brown or become soft and flexible, but it will not melt, as can be seen here. Now that we have determined we have cross-linked polyethylene, we can begin the repair process. Any Polyvance airless plastic welder with the 6031 flat tip can be used for this repair. However, you must use polyethylene welding rod. High density polyethylene welding rod can be used for this repair, but we recommend using low density polyethylene welding rod because it is easier to work with.

First, clean the plastic with EcoPrep plastic cleaner. Next, grind away the plastic around the punctured area to create a gradual bevel. The depth of the slope needs to be around 80% of the thickness of the base material, and the gap of the hole should be around 1/16 of an inch to allow melted plastic into the void. The beveled area and the gap will be the surface the filler rod will bond to. Hand sand the area with coarse sandpaper to roughen the surface or use a 50 grit Roloc disc on low speed. This will allow the filler rod to stick to the plastic by giving the plastic some tooth. Now that the surface is prepped, it is time to apply the filler rod.

Melt the surface of the rod with the airless plastic welder, flip it over and stick it to the plastic. Force it down into the puncture mark. Do this a few times to cause the melted plastic on the inside to mushroom out. This will allow the filler rod to form a plug on the inside of the hole. After creating the plug, continue applying plastic to the beveled area by melting the filler rod, sticking it to the plastic, and smoothing it into the sanding scratches. Remember, do not try to melt the base material. Let the welder do the work, and make sure the rod is completely melted through. Apply just enough pressure to force the melted rod into the sanding scratches. When the entire beveled area is filled, gently smooth the area with your welder, and your repair is complete. Wait until the repair is completely cool before pressure testing it. If desired, you can sand the repair smooth, but this is not necessary.

First, clean the plastic with EcoPrep plastic cleaner. Next, v-groove the crack with a die grinder, and then bevel the plastic around the crack. Use coarse sand paper or a 50 grit Roloc disc to roughen up the plastic. Next, melt the surface of the welding rod with the airless plastic welder, flip it over, and stick it to the plastic, forcing it down into the crack. Fill the crack with the melted welding rod to create a seal. Remember, do not try to melt the base material. After the crack is filled, continue laying the filler rod down, making sure to smooth the rod into the sanding scratches, letting the heat do the work. When the entire beveled area is filled, your repair is complete.

First, clean the plastic with EcoPrep plastic cleaner. Although not shown in previous segments, sometimes it’s helpful to draw a circle around the hole as a guide for making the bevel. Use a die grinder to make a gradual bevel around the hole, using the circle you drew as a guide. Use 50 grit sandpaper on a Roloc disc to roughen up the plastic you just beveled.

Melt the surface of the rod with the airless plastic welder, flip it over, stick it to the plastic, and force it down into the hole. Do this a few times to build up the plastic and force the melted plastic into the hole, causing it to mushroom out, forming a plug inside the hole. After creating the plug, continue applying plastic to the beveled area by melting the filler rod, sticking it to the plastic, and smoothing it into the sanding scratches. Remember, do not try to melt the base material. When the entire beveled area is filled, your repair is complete. If you want, you can sand the repair area, as we did here, but this step isn’t necessary.

To demonstrate the strength of this repair, we put the welds through two different tests. The first test was a pressure test. We connected an air supply to the tank fitting and taped the vent hole on the cap of the tank to reduce the leakage. 6 pounds of air pressure was applied to the tank, and then the tank was checked for leaks at each of the repair areas using soapy water. As you can see, none of the repairs produced any bubbles, so the tank was leak free at 6 psi. We then turned the pressure up to 10 psi. Again, no bubbles formed at the repair areas, so even at 10 pounds of pressure, the repairs are leak free.

For the second test, we completely filled the tank with water, and all three repairs held without a problem. If you have a cross-linked polyethylene part, remember that a high quality, reliable repair is possible using low density polyethylene filler rod and Polyvance’s airless plastic welder. With the proper tools and technique, you can achieve impressive results.

Thanks for watching! Make sure you subscribe to our channel and hit the bell to be notified when we post a new video. Let us know in the comments what you thought of this repair, and check out our other videos for more plastic repair tutorials.

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