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Welding seam inspection of high-density polyethylene (PE) plastic pipes
Release time：2023-09-26
1. Background
High density polyethylene (PE) pipelines have the characteristics of light weight, hygiene and safety, low water flow resistance, energy saving, metal saving, improved living environment, long service life, safety and convenience, and are favored by the pipeline engineering industry. In recent years, driven by the rapid development of China's macro economy, plastic pipelines in China have experienced rapid development against the backdrop of the rapid development of chemical and building materials. In 2010, the national production of plastic pipelines exceeded 8 million tons. Plastic pipelines have many advantages over traditional metal pipes and concrete pipes in multiple fields, and therefore have been recommended for use in many regions.
Due to the characteristics of plastic pipes themselves, they have been widely used in industrial fields, and due to the shortcomings of adhesive connection methods, such as low strength, poor adhesion of PE materials, while fusion welding overcomes the shortcomings of adhesive and threaded connections, achieving higher strength and reliable tightness than the plastic pipes themselves.
Electric fusion connection process: Electric fusion connection is an advanced method of connecting the inner wall of the pipe fitting and the surface of the pipeline by using a specialized pipe fitting embedded with an electric heating wire. After connecting to the power supply, the electric heating wire is generated, which can melt the inner wall of the pipe fitting and the surface of the pipeline.
Electric fusion connection process: Electric fusion connection is an advanced method of connecting the inner wall of the pipe fitting and the surface of the pipeline by using a specialized pipe fitting embedded with an electric heating wire. After connecting to the power supply, the electric heating wire is generated, which can melt the inner wall of the pipe fitting and the surface of the pipeline.
Hot melt connection process: Hot melt connection is an advanced plastic welding process that uses specialized heating elements such as heating plates, heating rods, and heating sleeves to generate heat energy to complete the docking of plastic pipes and fittings, as well as socket and saddle connections (branch pipes). High welding quality and fast speed. It can perform manual, semi-automatic, and automatic welding.
2. Testing methods and equipment
The existing available ultrasonic testing methods include TOFD and PAUT, both of which require the use of proprietary water injection wedges for local water coupling.
The existing available ultrasonic testing methods include TOFD and PAUT, both of which require the use of proprietary water injection wedges for local water coupling.
3. Test results
3.1 Electric fusion welding seam
For plastic pipes welded by electric fusion, the phased array probe can be placed on the outer wall of the pipe fitting, so that the position and morphology of the resistance wires inside the pipe fitting can be seen. If there are other signals besides the resistance wire signal, it can be considered as fusion defects.
3.1 Electric fusion welding seam
For plastic pipes welded by electric fusion, the phased array probe can be placed on the outer wall of the pipe fitting, so that the position and morphology of the resistance wires inside the pipe fitting can be seen. If there are other signals besides the resistance wire signal, it can be considered as fusion defects.
The detection results are as follows, and the signal of the resistance wire can be clearly seen.
The impact of different focusing depths on the detection results is as follows. It can be seen that in PE tube detection, there are small differences in focusing depth and significant signal differences. Therefore, in process design, focusing depth becomes the key to setting.
The actual detection results of PE pipes are as follows:
![[CropImg]8.jpg](/d/file/p/2020-01-08/b470f9ed5e4ad69a28a0d552946fc9c3.jpg)
3.2 Hot melt welding inspection results
Using phased array technology to detect hot melt welds, a flat bottom hole is made horizontally at the end of the PE pipe to simulate unfused defects in the hot melt weld.
Using phased array technology to detect hot melt welds, a flat bottom hole is made horizontally at the end of the PE pipe to simulate unfused defects in the hot melt weld.
The detection results obtained by using phased array sector scanning are shown below, and all defects of different sizes and positions can be seen.
The following figure shows the detection results of phased array detection in hot melt welded pipes, showing obvious root unfused defects. Due to the PE pipe welding being a butt weld without a groove, the signal of unfused defects is displayed in a vertical direction.
The following figure shows the phased array detection results, with obvious defect signals visible. The signal is displayed in the depth B scan image as running through the depth direction and has a very short length.
The following figure shows the detection results of TOFD in hot melt welded pipes. Clear defect signals can be seen in the TOFD image, and the signal shows a clear upper endpoint signal (opposite to the phase of the straight wave), which causes significant disturbance to the bottom wave. It is determined that the ground opening type is not fused.
The following figure shows the detection results of TOFD in hot melt welded pipes. It can be seen from the figure that a clear defect signal at the root is a disturbance, while the straight wave on the upper surface is also disturbed. The scanning direction length is very short, indicating that the defect is a through-hole type defect.
Use TOFD detection technology to detect hot melt welded pipes. Below are TOFD images of grooves on the upper and lower surfaces and drilled holes in the middle. The defect signals in different parts of the weld seam are clearly visible in the image, and the material noise inside the plastic is relatively low, with a high signal-to-noise ratio.
Use TOFD detection technology to detect hot melt welded pipes. Below are TOFD images of grooves on the upper and lower surfaces and drilled holes in the middle. The defect signals in different parts of the weld seam are clearly visible in the image, and the material noise inside the plastic is relatively low, with a high signal-to-noise ratio.
The following are the test results of three different types of slag inclusions inside the weld seam.
4. Conclusion
The use of ultrasonic phased array technology can detect unmerged defects in electric fusion welding welds, and can clearly display the signal of the resistance wire and the bottom wave signal. The use of TOFD combined with phased array technology can detect unmerged defects in hot melt welded joints, especially the strong detection ability of TOFD for unmerged defects in the vertical direction;
In the current era, domestic and international technologies are constantly emerging, and technological innovation is constantly emerging. Mature technologies such as PE pipe testing, corrosion testing of steel pipes through insulation layers, testing of composite materials and fiberglass, bolt stress and internal defect testing, etc., have already been developed to achieve the expected results of testing; We, Ge Yu Technology (Shanghai) Co., Ltd., are committed to cutting-edge trends, delving into new foreign technologies and combining them with domestic technical characteristics and the needs of owners. We can provide targeted testing plans to users, meeting the different needs of different customers. Because of our professionalism, we are trustworthy. We will always serve the public with a devout heart and give back to society.
The use of ultrasonic phased array technology can detect unmerged defects in electric fusion welding welds, and can clearly display the signal of the resistance wire and the bottom wave signal. The use of TOFD combined with phased array technology can detect unmerged defects in hot melt welded joints, especially the strong detection ability of TOFD for unmerged defects in the vertical direction;
In the current era, domestic and international technologies are constantly emerging, and technological innovation is constantly emerging. Mature technologies such as PE pipe testing, corrosion testing of steel pipes through insulation layers, testing of composite materials and fiberglass, bolt stress and internal defect testing, etc., have already been developed to achieve the expected results of testing; We, Ge Yu Technology (Shanghai) Co., Ltd., are committed to cutting-edge trends, delving into new foreign technologies and combining them with domestic technical characteristics and the needs of owners. We can provide targeted testing plans to users, meeting the different needs of different customers. Because of our professionalism, we are trustworthy. We will always serve the public with a devout heart and give back to society.
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