China's natural gas pipeline construction has entered a period of rapid development, because the level of welding technology of natural gas pipeline directly affects the project quality, project safety and economic benefits during the pipeline operation, so it is necessary for us to discuss the welding technology in the construction of natural gas pipeline.
With the development of oil and gas, China's long distance pipeline to large diameter, high pressure, new material, advanced direction.
Similarly, with the development and application of X70, X80, X100 and other high grade steels, the welding process of long distance pipeline has also brought new topics.
But in order to ensure the safe development of petrochemical industry, we should pay attention to the quality of petrochemical pipeline.

1. Preparation before welding
Good preparation of welding process can guarantee the safety and quality of oil and gas pipelines.
Welding technicians should not only have a detailed understanding of the construction status of the pipeline engineering, but also develop scientific welding plans and instructions on the basis of the data learned about the welding work;When welding, it is necessary to choose the appropriate welding technology;
In addition to these, but also carefully analyze the process of welding is likely to appear some other problems, so as to carry out the corresponding early warning measures and solutions;
At the same time, but also strictly check the welding method, welding materials and welding wire, to see whether their quality problems are strictly in accordance with the provisions and standards;
In addition to these, we must evaluate the scientific nature of the welding process.Then according to the results of the evaluation to develop the welding process card;
In preparation for the start of work, welders need to be tested and trained, and they can only work formally after they are confirmed to be qualified.
These are to better guide the welding work, so as to strengthen the quality of welding, but also to ensure that the construction of the pipeline safety is higher.

2. The construction stage of welding
At the beginning of the welding construction, we should strictly live yo, so as to ensure the quality of welding. We should do every step of the work in strict accordance with the provisions. Only in this way can the welding work be carried out normally and the pipeline construction work be more smooth.
(1) root welding backing
Before the welding of the pipeline, the special beveling machine should be used to process the V-shaped groove according to the strict requirements and specifications, and then the two ends of the groove should be removed rust, and the outer alignment device should be used to pair the pipeline. After the completion of the welding, the heating belt should be used to preheat the groove, and the root welding can only be carried out after the completion of the preheating.
RMD should be used for root welding, and then the metal powder cored wire of Metalloy 80N1 should be selected for backing, so as to make the weld of root welding uniform and prevent welding penetration.
The following points should be paid attention to when welding root welding:
First, test the test welding of the test plate in advance to check whether there are doping impurities in the argon gas;
When welding to use the wind shed, in order to prevent because of the wind caused by the welding quality;
The preheating before welding must reach the specified temperature, prohibit welding crack;
Repeatedly check the welding quality, timely hot welding.
(2) hot welding and fill welding
Filling and hot welding shall be performed using a self-protecting cartridge semi-automatic welding method.
The use of E81T8-G welding wire: at any time to clean up because of the bottom welding after the remaining splash and slag, etc., especially pay attention to the interface;
Also pay attention to the bottom weld joint and the middle weld joint distance should not be less than 0.1cm;
The thickness of the weld shall be maintained between 0.3-0.5cm;
Timely discovery of problems, repeated inspection of the work, timely cleaning of residual impurities should be done in place.
(3) cover welding
The cover surface also uses the semi-automatic welding method of self-protection core-E81T8-G welding wire: the appearance of the welding seam should be smooth, the color should be as close as possible to the color of the pipeline, and the transition should be natural, so as to achieve seamless and give a person a visual feeling of one integrated whole;
The width of the weld is about 0.2cm larger than both sides of the groove, and the height is about 0.15-0.25cm.The residual objects on the surface of the cover surface should be treated in time, and the anti-corrosion work and heat preservation work on the cover surface should be done in an appropriate way. Only in this way can the phenomenon of erosion damage be prohibited, so as to improve the quality of welding;
(4) Record work
When welding pipes, welding technicians should not only strictly abide by the welding process instructions to implement the welding process, but also record the relevant data at any time.
For example, the voltage and current of electric welding, the material used for each layer of weld, pre-welding and post-welding heat treatment and so on.