PE pipeline welding quality control

PE pipes, also known as polyethylene pipes, are widely used due to their advantages of corrosion resistance, good seismic performance, high toughness, flexibility, easy installation, and economical transportation costs. The research and application of PE pipeline in China started relatively late, and began to be promoted and applied around 1990. With the recent development and progress of polyethylene materials technology and process level in various aspects, the country began to increase In order to pay attention to pipe production process standards, gradually establish and improve production standards and specifications, so PE pipes have been widely used in many industries. The current annual production and application of PE pipes is about 300,000 tons, and this data is positive Showing explosive growth.

The quality control method of hot melt welding machine welding

The so-called hot-melt welding refers to the use of mechanical equipment such as a hot-melt welding machine to heat the surfaces of the two welded parts until a certain melting temperature is reached, so that the two are mixed into one. Hot-melt welding is divided into hot-melt butt welding, hot-melt socket welding and hot-melt saddle welding according to its welding method. Among them, hot-melt butt welding is a more common connection method and the most widely used connection method for PE pipes. The welding equipment is relatively simple, the connection cost is relatively economical, the welding joint is strong and reliable, the welding joint that exceeds the strength of the base material, and the sealing of the welding are good. Therefore, the hot-melt butt welding method is selected for this project.

Butt welding procedure of hot melt welding machine

Hot-melt butt welding must use a hot-melt butt welding machine to heat the end face of the PE pipe, so that the surface is quickly melted and bonded, under a certain pressure, and after cooling, the two are welded. Polyethylene pipes of different sizes can be welded by this method, preferably a polyethylene pipe with a nominal diameter of not less than 90 mm. Hot-melt butt welding is economical, even when the joint is pulled or compressed, it can produce higher strength than the pipe itself.

Specifically:

1) Pipe components can be clamped, the pipeline can be flattened by the bracket, and the concentricity can be adjusted and controlled, and the out-of-roundness of the pipeline can be checked and corrected by the fixture, and a certain welding distance can be reserved in advance;

2) Milling the welding surface, milling a certain thickness, ensuring that the welding end surface is smooth and parallel, ensuring that the gap of the butting end surface is not more than 0.3mm, and the amount of wrong side is not more than 10% of the wall thickness of the welding place. If re-clamping, re-milling is required;

3) Measure and check the drag pressure, as long as the welding is performed, the measurement and recording work must be carried out;

4) Heating is a relatively important link. First, the heating plate must be placed, and the welding pressure (P1) is adjusted = dragging pressure (P dragging) + welding specified pressure (P2). If the height of the circumferential curling protrusion at the welding place around the heating plate exceeds a certain value, reduce the pressure to P drag;

5) Switch the docking, pull out the heating plate within a certain time, quickly fit the welding surface, and steadily increase the pressure to P1 to avoid high-pressure collisions;

6) Disassemble the pipeline components, cool for a period of time, and wait for the pressure to drop to zero to disassemble the pipeline components.

Hot melt butt welding process control

The control of the hot melt welding process is carried out for the hot melt welding step, rather than the quality judgment of the final weld joint quality. Among them, several influencing factors are very important, including temperature, time and pressure. Because polyethylene pipe hot-melt welding is easily affected by external factors, and there is no uniform set value for hot-melt welding parameters. The use of hot-melt welding abroad is equipped with a relatively complete set of operating procedures and parameter setting calculation methods. The parameter setting of hot-melt welding of polyethylene pipes in China is provided by the manufacturer, so the relevant parameters provided by each manufacturer There is a big difference. In addition, in actual construction, even ignoring any factors such as temperature, time and pressure will cause serious quality problems. The following hot melt butt welding process must be strictly controlled.

(1) Selection of hot melt welding machine. Choose a hot melt welding machine that can perform standard and standardized welding according to preset data parameter curves, and ensure that the cross section of the PE pipe welding interface is smooth and clean, the preheating temperature meets the relevant requirements, and the cross section of the pipe mouth faces the equalization of the joint pressure .

(2) Welding site control. The welding construction site should be determined according to the actual situation. In case of wind and rain, a mobile working tent should be set up in time to prevent the welding port from being affected by dust and rain, and to ensure the preheating temperature. If welding is performed in the field, a template should be laid under the welding machine to ensure that the welding machine is placed horizontally, and the protrusions under the welding machine must also be placed to affect the welding process; during the welding process of PE pipes, the pipeline around the welding machine It should be erected on the rolling guide bracket to prevent a certain friction between the pipe and the ground debris, and ensure that the pipe surface will not be damaged.

(3) Equipped with UPS regulated power supply. Because PE pipe welding work is mostly carried out in the field, the power and output voltage of the generator may be unstable, resulting in a situation where the welding quality does not meet the requirements. Therefore, a UPS regulated power supply is required.

(4) Ensure that the planer of the pipe mouth is clean and free of debris, and the working surface of the heating plate of the welding machine is clean and tidy; the heating plate should be placed in a clean insulation tube during non-working; the welding personnel should master the manual centering and hydraulic propulsion methods of the PE pipe , To be familiar with the use of concentric fixtures, smooth thrust, this will help to avoid the wrong side of the weld.

Main control of welding process inspection

1) Check the status of the on-site welding construction operator's certificate, whether it has obtained the relevant employment certificate, and the welding is performed within the permitted operation range.

2) Check the welding construction environment to ensure that it meets the requirements of the operation, and also take certain preventive measures to avoid the adverse weather affecting the welding quality.

3) Check the welding surface cleaning work, whether it is clean and tidy without debris, whether the milling end face and oxide layer scraping meet the requirements.

4) Check the whole welding process according to the construction sequence.

5) Check the data parameters of the input welding to ensure that the data is correct. The key to the hot-melt butt welding is the drag pressure, welding pressure, heat absorption time, and cooling time. Check these parameters.

Welding quality inspection

The construction of polyethylene pipelines is relatively complicated, and there are many influencing factors. At this stage, the non-destructive testing technology for the quality of PE pipeline welding joints is not yet mature, so it is very necessary to strengthen the inspection of welding quality.

Check the welding data of the welding machine and record the data. The inspector shall extract the number of welded seams, and check the quality of the interface according to the above inspection points. The data of the spot check shall be greater than 10%, and the number of spot checks of each welder shall be greater than 5. Interface destructive testing is required for each project. Since automatic hot-melt butt jointing is adopted, 5% of the welds are to be extracted. Each welder must be greater than 3. The destructive test can cut the weld into more than four. Check the fusion inside the pipe. If there is no complete fusion, it can be regarded as a failure. Of course, it can also be checked by tensile test, and it can be carried out according to relevant standards and specifications [8]. If the quality of the interface does not meet the technical requirements, the welder's interface will be double-checked and inspected. If the failure is found again, all the interfaces welded by the welder will be reworked until the inspection is qualified.