Welding of carbon steel elbow is common in production

TIME：2019-05-25

In the production of carbon steel elbow in the common welding methods are: automatic welding of large diameter and thick wall (more than 21 mm) pipeline often use u-shaped groove or complex groove, because the u-shaped groove, composite groove machining time, draining pipe welding efficiency. The v-shaped groove is simple to process, save time and effort, but the welding defects can be caused by the improper selection of welding process parameters when the large diameter and thick wall pipeline V groove are fully automatic welding.

The welding method adopts STT root welding + crc-p260 automatic welding, filling and covering. Welding equipment: Lincoln STT welder, Lincoln dc-400, crc-p260 automatic welder. Protective gas: STT root welding is 100% CO2, fully automatic welding is 80%Ar+20% CO2. Carbon steel elbow automatic welding commonly used compound groove or u-shaped groove, or v-groove can be used in small wall thick pipeline, and their common feature is that the gap between upper and lower groove is smaller. The wall thickness of the secondary pipeline is 21.0 mm, and the upper width of V groove is about 22mm. This width is close to the limit of the crc-p260 welding gun. Such groove type is a great challenge for automatic welding. The welding parameters of automatic welding test are determined according to previous experience. The above parameters are used for automatic welding test. In test welding, it is found that the defects of automatic welding seam are not fused, the side wall is not fused, the dense stoma, and the excess of the overhead weld are high.

In order to guarantee good cover surface forming effect, the cover surface of weld in choosing the smaller welding speed at the same time try to reduce the welding torch swing frequency, make the cover of weld thin and wide, so as to reduce the presence of molten pool time, achieved the purpose of reducing overhead welding position more than high. According to the test results and analysis, the STT root welding +CRC automatic welding filling and covering process parameters are determined. According to the welding parameters of table 3 welding, the weld of carbon steel elbow has been tested for defects such as porosity, crack, and incomplete fusion. The weld mechanical properties are tested by the welding technology center of China petroleum and natural gas pipeline science research institute, and the various indexes meet the construction requirements of the second-line contact line of the west gas east line. The successful application of STT root welding + crc-p260 automatic welding in large-caliber, thick wall (v-type groove) pipeline is fully reflected in the characteristics of high quality, high efficiency and low labor intensity of automatic welding technology.