Common Issues and Solutions for PE Pipe Hot Melt Welding

In modern pipeline projects, polyethylene (PE) pipes are widely used due to their excellent resistance to corrosion, flexibility, and long service life. However, the hot melt welding of PE pipes can sometimes face challenges that affect welding quality and the long-term stability of the pipeline. In this blog, we will address some common issues encountered during PE pipe hot melt welding and provide solutions to ensure high-quality welds.

1. Can PE Pipes with Different Wall Thicknesses Be Welded Together?

Problem：

When PE pipes with different wall thicknesses are welded directly, the heating plate is set to the same temperature for both pipes. Since the heat-affected area of each pipe differs due to varying wall thicknesses, the pressure applied during welding remains the same. This results in inconsistent weld bead formation, internal stress at the joint, and potentially poor adhesion between the pipes.

Solution：

For successful welding, it is recommended that PE pipes with the same wall thickness be welded together. If pipes with different wall thicknesses must be connected, further testing and adjustments should be made to ensure proper fusion. Additionally, welding should be performed under controlled conditions to achieve uniform heating and pressure application.

2. Can Pipes and Fittings Made from Different Grades of PE Resin Be Welded Together?

Problem：

Can PE pipes and fittings made from different grades of polyethylene resin be welded together successfully? This is a common concern because different PE grades may have different flow properties during welding.

Solution：

Generally, PE80 and PE100 resins with a melt flow rate (MFR) of ≤0.5g/10min (190°C/5kg) are considered compatible and can be welded together. If the resins are outside this MFR range, tensile and hydrostatic tests should be conducted to ensure that the welded joint meets the required strength and pressure resistance. For electrofusion connections, pipes and fittings made from different material grades can be connected, but for hot melt welding, it is recommended to use the same grade materials for optimal results.

3. What Causes Surface Pinholes or Bumps on the Welded Joint, and Do They Affect the Weld Quality?

Problem：

Sometimes, small pinholes or bumps may appear on the welded joint, commonly referred to as "surface pinpoints" or "bumps." This can be a concern for the overall quality of the weld.

Causes：

Moisture Absorption: If PE pipes are exposed to a humid environment for extended periods, they can absorb moisture, which leads to excessive water content at the welding point.

Improper Cleaning: In rainy seasons or high-humidity conditions, if the pipe ends are not thoroughly cleaned and dried before welding, moisture can cause pinholes or bumps at the weld bead.

Contaminants on Heating Plate: Dirt or foreign particles on the heating plate or the pipe surface can lead to surface defects like pinholes during the welding process.

Solution:

To prevent this issue, ensure that the pipes are kept in a dry environment before welding, and that the pipe ends and heating plates are properly cleaned. According to the "Technical Specification for Polyethylene Gas Pipeline Engineering" (CJJ63-2008), the presence of small bumps caused by moisture absorption does not significantly affect the weld quality. However, it is still recommended to minimize moisture exposure.

4. What Causes Irregular Bead Formation in the Weld Joint?

Problem：

Irregular or uneven weld beads can sometimes form during the welding process, leading to concerns about the strength and integrity of the welded joint.

Causes：

Rapid Plate Removal: In manual or semi-automatic hot melt welding, removing the heating plate too quickly can cause uneven fusion and result in a ragged appearance on the pipe ends.

Inconsistent Heating: If the heating time or temperature is inconsistent between the two pipe ends, it can cause uneven bead formation.

Material Mismatch: Differences in the melt flow index (MFI) of the materials being welded can cause heat absorption discrepancies, leading to inconsistent weld beads.

Contaminants: Dirt, oil, or other residues on the pipe ends or the heating plate can affect the fusion and cause uneven weld beads.

Solution:

To avoid irregular bead formation, ensure that both the heating temperature and time are consistent, and the pipe ends and heating plate are clean before welding. If using a manual or semi-automatic machine, handle the heating plate carefully to avoid disrupting the molten material.

5. Why Do Cracks Appear at the Welded Joint When Bending the Pipe?

Problem：

Cracking of the weld bead when the welded PE pipe is bent is another common issue that can compromise the strength of the joint.

Causes：

Inadequate Heating Temperature: If the heating temperature is insufficient during the welding process, the initial weld bead may lack the proper bonding strength, leading to cracking when the pipe is bent.

Short Heating Time: Insufficient heating time can prevent the polyethylene molecules from sufficiently merging, causing weak spots at the joint.

Contaminated Heating Plate: Oil or other contaminants on the heating plate can obstruct the complete diffusion and fusion of the material at the weld joint, leading to weak spots that crack under stress.

Solution：

Ensure the heating plate reaches the correct temperature and remains at that temperature for the recommended amount of time. Clean the heating plate thoroughly to remove any contaminants, and make sure that the pipe ends are properly prepared before welding.

6. What Can Be Done If the Pipe Ends Don’t Align Properly During Welding?

Problem：

Welding misalignment can occur if the pipe ends do not fit together properly, making it difficult to achieve a uniform and reliable joint.

Cause：

Pipe out-of-roundness is a major factor influencing the ease of alignment. The smaller the out-of-roundness, the easier it is to align the pipe ends.

Solution：

To minimize misalignment issues, pipes should be stored and handled carefully to prevent deformation, especially thin-walled pipes. It is recommended to implement a "first in, first out" (FIFO) inventory method to reduce the chance of deformation during storage and handling. Additionally, it is best to use pipes from the same batch and align the color stripes for better alignment during welding.

Conclusion

PE pipe hot melt welding is essential for ensuring a high-quality, reliable pipeline system. By understanding the common problems associated with hot melt welding and implementing the recommended solutions, you can avoid welding defects and ensure long-lasting, leak-free connections.

If you need further information or assistance with PE pipe fittings and welding technology, visit our website www.erapipefittings.com for more details.

Feel free to reach out if you have any further questions or require technical support regarding PE pipe fittings. We're here to help you achieve the best results in your pipeline projects!