How to judge whether the welding effect of the electric fusion welding machine is qualified?

1. Appearance inspection
1. Fusion
Overall observation: After welding is completed, first observe the connection between the pipe and the fitting. The qualified welding effect should be that the fusion interface between the pipe and the fitting is uniform and continuous, without obvious gaps or stratification. If a clear dividing line can be seen at the weld, it may indicate incomplete fusion.
Microscopic inspection (if necessary): For some situations where the welding quality is extremely high, a magnifying glass (5-10 times) or a microscope can be used to observe the microstructure of the fusion interface. Under the ideal fusion state, the PE material should be mutually infiltrated and fused at the microscopic level, without unfused particles or gaps.
2. Surface flatness
The surface after welding should be flat, without obvious protrusions, depressions or irregular shapes. If a weld nodule (a protrusion formed by excessive accumulation of molten material during welding) appears, it may be caused by too long welding time, too high voltage or improper matching of the pipe and fitting; and depressions may be caused by insufficient fusion or insufficient insertion depth of the pipe.
3. Color change
The surface color of the PE material after normal welding should be uniform and consistent, usually slightly darker than the color of the unwelded part. If the welding part has a local color that is too dark (probably carbonization caused by overheating) or uneven color, such as spot-like depth, this may mean that the temperature distribution during welding is uneven, which is a manifestation of poor welding quality.
2. Dimension inspection
1. Pipe insertion depth
Check whether the depth of the pipe inserted into the pipe fitting meets the requirements. Generally, the recommended insertion depth will be indicated on the pipe fitting. If the insertion depth is insufficient, it may lead to insufficient welding strength; if the insertion is too deep, it may affect the internal structure of the pipeline system or cause material waste. Tools such as calipers can be used to measure the insertion depth, and the error should be controlled within the specified range (usually ±1 - 2mm).
2. Change in outer diameter (if necessary)
In some high-precision application scenarios, it is necessary to check whether the outer diameter of the pipe-fitting assembly after welding has changed significantly. Qualified welding should not cause the outer diameter to exceed the specified tolerance range, because the change in outer diameter may affect the subsequent installation and connection of the pipeline. You can use tools such as an outside diameter micrometer to measure and compare it with the size before welding.
III. Physical performance test
1. Strength test
Tensile test: Cut a sample from the welded pipe, fix it on a tensile testing machine, and apply tension in the axial direction until the sample breaks. Record the tensile force value at the time of fracture and compare it with the minimum tensile strength value specified by the relevant standards or pipe and fitting manufacturers. A qualified welded joint should be able to withstand the specified tensile force, and the fracture position should not always appear at the welding interface, which indicates that the strength of the welded joint is not lower than the strength of the pipe itself.
Bending test: For some pipeline systems that need to withstand bending stress, a bending test can be performed. Bend the welded pipe sample at the specified radius and angle to observe whether cracks or fractures appear at the welding part. The bending test can simulate the stress conditions of the pipeline during actual use. For example, the pipeline laid underground may be subjected to bending deformation caused by factors such as ground subsidence.
2. Sealing test
Air pressure test: Close one end of the welded pipeline system and connect the other end to the air pressure source. Fill the pipeline with a certain pressure of gas (usually 1.1-1.5 times the working pressure of the pipeline), then turn off the air pressure source and observe the changes in the pressure in the pipeline for a period of time (such as 30 minutes-1 hour). If the pressure drop does not exceed the specified value (such as less than 5%), it indicates that the sealing of the welded part is good. When conducting the air pressure test, pay attention to safety to avoid excessive pressure causing the pipeline to rupture.
Hydrostatic test: Similar to the air pressure test, water is injected into the welded pipeline system, and the water pressure is increased to the specified value through water pumps and other equipment. After a certain period of time, check for leaks. Hydrostatic test is a more intuitive sealing test method because it can directly observe whether there is water seepage in the welded part. For pipeline systems that transport liquids, hydrostatic test can better simulate the actual working environment.
IV. Nondestructive testing
1. Ultrasonic testing
Ultrasonic testing is a commonly used nondestructive testing method. The internal structure of the weld is analyzed by emitting ultrasonic waves to the welded part and then receiving the reflected waves. A qualified weld should have no obvious defects inside, such as pores, slag inclusions, and lack of fusion. In the ultrasonic test image, these defects will appear as abnormal changes in the reflected wave, and professionals can judge whether the welding quality is qualified based on the image.
2. Radiographic testing (if necessary)
Radiographic testing can provide intuitive images of the inside of the weld, similar to medical X-rays. It can detect internal defects, but due to the high cost of radiographic testing equipment, the operation requires professionals and involves radiation safety issues. It is generally used when the welding quality requirements are extremely high or serious internal defects are suspected. By observing the image on the radiographic film, it can be determined whether there are defects such as pores and cracks inside the weld.