Carefully inspect the appearance of PPH and PVDF pipes and pipe fittings to ensure that there are no cracks, depressions, deformations, impurities, and other defects. At the same time, check whether the specifications and models of the products are consistent with the design requirements.

Confirm the material certificates of pipes and pipe fittings to ensure that they meet the corresponding standards and specifications, which is crucial for ensuring welding quality.

Select appropriate welding equipment, such as hot - melt welding machines, butt - welding machines, etc., and ensure that the equipment is in good performance and the parameters are accurate. For example, the temperature of the heating plate of a hot - melt welding machine should be accurately controlled within the temperature range required for PPH and PVDF welding.

Prepare cleaning tools such as scrapers and sandpapers to clean the welding parts of pipes and pipe fittings, removing surface oil stains, dust, and oxide layers to ensure the cleanliness and smoothness of the welding surface.

The welding environment temperature should be controlled between 5℃ and 40℃. If the temperature is too low, the welding joint will cool too quickly, increasing internal stress and affecting the welding strength; if the temperature is too high, the material may decompose and carbonize, reducing the welding quality.

The relative humidity should not exceed 80%. A humid environment may cause moisture to enter the welding area, resulting in defects such as pores.

Temperature Setting: The welding temperature of PPH is generally between 260℃ and 270℃, and that of PVDF is between 230℃ and 250℃. According to factors such as the wall thickness and material of pipes and pipe fittings, accurately adjust the temperature of the heating plate.

Heating Time: Determine the appropriate heating time according to the specifications of pipes and pipe fittings. Generally, the thicker the wall thickness, the longer the heating time. For example, for a PPH pipe with a wall thickness of 10mm, the heating time is about 60 seconds.

Welding Pressure: During the welding process, apply appropriate pressure to make the pipes and pipe fittings fully integrate. The initial pressure should not be too high to avoid excessive deformation of the material; during the pressure - maintaining stage, maintain a certain pressure to ensure the tightness of the welding joint.

Centering and Positioning: Accurately center the pipes and pipe fittings to ensure the concentricity of the welding parts and prevent the occurrence of offset. Special positioning fixtures can be used to improve the centering accuracy.

End - Face Treatment: Use a special milling cutter to mill the welding end - faces of pipes and pipe fittings flat, ensuring that the end - faces are perpendicular to the axis and the surface roughness meets the requirements.

Welding Current and Voltage: Reasonably adjust the welding current and voltage according to the material and specifications of the pipes and the performance of the welding equipment. For PVDF pipes, the welding current is generally between 50A and 100A, and the voltage is between 10V and 20V.

Welding Time: Control the welding time well. If the time is too short, the welding is not firm; if the time is too long, the material will overheat and deform. Usually, for a PPH pipe with a diameter of 100mm, the butt - welding time is about 30 - 60 seconds.

Upsetting Pressure: After the welding is completed, quickly apply upsetting pressure to make the welding joint closely combined and extrude the oxides and impurities generated during the welding process.

Observe the appearance of the welding joint. The surface should be smooth and flat, without pores, cracks, depressions, protrusions, and other defects. The flash of the welding joint should be uniform and full, and the height and width meet the relevant standard requirements.

Check the offset of the welding joint. Generally, it should not exceed 10% of the wall thickness of the pipe. If the offset is too large, it will affect the strength and sealing performance of the welding joint.

After the welding is completed, conduct a pressure test on the pipeline system. The test pressure is generally 1.5 times the working pressure, and the pressure - maintaining time is not less than 30 minutes.

Observe whether there is any leakage in the pipeline system during the test. If leakage is found, promptly find the cause and repair it, and then re - conduct the pressure test until it is qualified.

For important pipeline systems or occasions with high welding quality requirements, a destructive test can be carried out. Cut samples from the welding joints and conduct mechanical property tests such as tensile and bending tests to check whether the strength and toughness of the welding joints meet the requirements.

According to the test results, analyze the rationality of the welding process and existing problems, and promptly adjust the welding parameters and process to improve the welding quality.