The fast and practical method and qualification determination of hot melt connection and welding joint of polyethylene hdpe carat pipe are also a bottleneck in the construction of PE pipe.
HDPE pipe fitting suppliers take hot melt connection as an example. The current method is to visually check the appearance of the welding ring to check its quality. Although some problems can be found by the appearance of the welding ring, some internal problems cannot be reflected by the surface, such as "fake welding", whose appearance is almost the same as the qualified appearance. However, the long-term strength cannot be guaranteed. A company once formed "false welding" due to PE pipe melting, and the pipeline foundation was damaged during the construction of other pipelines. Under the action of unbalanced external force, the pipelines were squeezed and cracked, resulting in water leakage.
In terms of electric fusion connection, it is not accurate to judge the quality of welding only by whether the observation hole on the final electric fusion pipe fitting is protruding or not. The observation hole is only used as a basis for judging welding. The final quality of electric fusion welding joint mainly depends on strict control in the process. Therefore, the rapid and practical method of HDPE (polyethylene) carat pipe joint quality is of great significance to ensure the engineering quality.
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In terms of hdpe high-density carat pipe connection construction, although it is simple and easy to master, both hot melt connection and electric melt connection must be strictly controlled for the process of the steps, that is, the process control, rather than a single final welding to the joint quality of qualified judgment. Take hot melt welding as an example. temperature, time and pressure are the three important factors in the welding process. Because hot melt welding of PE pipe is easily affected by environmental changes and man-made factors, there is no uniform value within the range, but a relatively perfect and mature calculation method for making procedures and parameter setting has been formed in some early use of pipe. In the construction of many PE pipeline projects in our country, the setting of three important factors are generally provided by PE manufacturing enterprises, so there are great differences.
In addition, in many places, the quality accidents caused by the construction personnel are also frequent. Hot melt welding, although in the temperature, time and pressure three important factors more attention, but the whole process of other details are often overlooked. For example, milling of the end face to be welded, how to keep the end face clean and the cooling process and time of the final welding port and other details, these problems are ignored may not be shown from the end of the welding port, so that the internal performance of the welding port can not be guaranteed. Therefore, the correct and effective implementation of welding process and procedures is important, and closely related to the stability of welding equipment performance and the responsibility of the personnel.
In the aspect of electricity connection, it is not enough to ensure the stability of the input voltage and the accuracy of welding time of the electron pipe fitting, and the preparation work before welding, such as: whether the end face of the pipe fitting to be welded is clean, if there are impurities, the final fusion must be affected; the failure of welding may be caused by the scraping, non-scraping or insufficient scraping of the oxide layer. The quality of final welding will also be affected by the correct assembly of fused pipe fitting and pipe fitting to be welded. In addition, whether the storage condition of the welding tube meets the standard and whether the cooling process after welding is proper are the factors that affect the final welding quality. However, the specification and necessary construction technology in these aspects are behind the development and application speed of HDPE pipe, which restricts the popularization and application of winding reinforced structural wall pipe to a certain extent. Therefore, the training of engineering and technical personnel and construction personnel, gradually realize the certificate on the job is an effective way to make PE pipeline construction towards regular and good development. Acceptance can take the following methods:
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(1) Check the welder welding data records of all welding ports.
(2) Self-inspection of appearance quality shall be carried out. The supervision and acceptance unit shall select a certain proportion of welding joints for appearance inspection according to the construction quality. The quantity shall not be less than 30% of the number of welding joints, and the number of welding joints for each welder shall not be less than 9. The appearance quality inspection can be carried out according to the following inspection points.
● Hot melt docking:
(1) Check whether the rolling edge is normal and uniform, and use the rolling edge measuring device to measure its width within the specified size range;
(2) After cutting the winding edge, check the bottom of the winding edge and the welding interface of the pipeline should not have pollutants;
③ Check the welding interface at the bottom of the roll should not appear cracks caused by melting and insufficient;
(4) Bend the rolled edge to the back, there should be no cracks caused by melting and insufficient;
⑤ Check that both ends of the pipe should be aligned in a straight line on the interface.
● Electric fusion connection:
(1) Check the whole circumference of the pipe at both ends of the pipe fitting should have scraping marks;
(2) Check that there is no leakage of the fuse in the fusion process;
(3) Check pipe fittings should be in the middle of both sides of the pipeline positioning line;
(4) Check that the fusion indicator needle (if there is such a device) has been raised;
⑤ Check that pipes and fittings are aligned in a straight line.
(3) For the welding joints of automatic hot melt butt, the acceptance personnel should extract a certain number of welding joints to cut the edge, according to the above inspection points to check the quality of the interface. The number of spot checks shall not be less than 10%, and the number of spot checks shall not be less than 5 per welder.
(4) The internal quality of polyethylene pipe interface can only be checked by destructive test. Polyethylene pipe is prone to damage and leakage of the part is the pipe interface. The key to project success and failure is the quality of pipeline connection. So strict interface quality acceptance is important for underground pipeline engineering. If it is electric fusion connection, 3% welding joint should be extracted, it is recommended that no less than 1; if it is automatic hot melt docking, 5% of the welding joint should be extracted, and each welder is not less than 3. Destructive test can cut the welding joint into 4 or more, check the internal fusion, not fusion as unqualified, can also do tensile test, to see whether the tensile strength meets the requirements.
(5) If the interface quality is unqualified, double spot check shall be carried out on the welder's interface. If it is found unqualified again, all the interfaces constructed by the welder shall be reworked. Through the above acceptance methods, if qualified, the quality credibility of polyethylene pipe interface can be considered to be similar to that of steel pipe welding.
When the ambient temperature is too low. When the construction environment is lower than minus 5 degrees Celsius, the welding of PE pipe will be affected, because the PE welding temperature is set at about 210 degrees, too low temperature will lead to rapid cooling of PE pipe, resulting in adhesion, and too low temperature will lead to crystallization of the fusion surface, resulting in adhesion. When the temperature is low, the construction should set up wind and cold prevention measures at the joint, and adjust the welding process parameters through welding test to ensure the welding quality. The above method is for reference only, because the climatic conditions of each region are different and every, this recommendation is not used as the hot melt welding standard!