SJ301 is the preferred flux for LSAW steel pipe production.

1. Main characteristics of SJ301 flux

SJ301 is a silicon-calcium neutral sintered flux, conforming to F4A0-H08A in GB/T 12470 standard or F6A0-EL12 in AWS A5.17. It is mainly used in combination with low-carbon and low-alloy welding wires such as H08A, H08MnA, and H10Mn2. It is widely applied in the production of longitudinally submerged arc welded (LSAW) steel pipes. Especially, it is suitable for manufacturing large-diameter high-strength pipeline steel, such as X70 and X80 grade steel pipes complying with API 5L standard.

2.Specific applications in LSAW steel pipe welding

SJ301 belongs to the neutral flux, with an alkalinity of approximately 1.0 and a particle size between 10 and 60 meshes, that is, 0.3 mm to 2.0 mm. It has excellent slag detachment performance, beautiful bead formation, smooth transition, no undercut phenomenon, and strong anti-pore ability. It is particularly suitable for welding steel with a slightly higher silicon content. In the LSAW process, SJ301 is used for both internal and external welding. The same flux can be used for both internal and external welding, which is convenient for production management.

In specific applications, SJ301 is applicable to steel pipes with a diameter ranging from 219 mm to 2620 mm and a wall thickness from 6 mm to 40 mm, covering steel grades such as Q235B, Q345B, X52, X60, X70, and X80. Take a steel pipe with a diameter of 1219 mm, a wall thickness of 22 mm, and a steel grade of X70 as an example. For internal welding, usually 1 to 2 welding wires with a diameter of 4.0 mm are used, with a current of 800 to 1100 A, a voltage of 30 to 36 V, and a welding speed of 1.2 to 1.8 m/min. For external welding, 4 to 5 welding wires are arranged in series or parallel, with a current of 700 to 950 A, a voltage of 32 to 38 V, and a speed of 1.5 to 2.0 m/min. The covering thickness of the flux is generally maintained at 25 to 35 mm.

3.Advantages of SJ301 in LSAW

The advantages of SJ301 lie in its beautiful weld formation, stable mechanical properties, and good low-temperature impact toughness. The impact energy is usually greater than 47 J, even over 60 J at -20 °C. It has strong crack resistance. As a neutral flux, it can reduce the tendency of hot cracking. At the same time, it has a wide process adaptability and can be used for single-wire, multi-wire, series or parallel welding. It has a high cost-performance ratio. It is a mature domestic flux with a relatively low cost.

4.Typical mechanical properties of weld seams

When used in combination with H08MnA welding wire, the typical mechanical properties of the weld are: yield strength not less than 485 MPa, tensile strength of 570 to 650 MPa, elongation not less than 22%, and impact energy at -20 °C not less than 60 J, fully meeting the requirements of API 5L standard.

5.Precautions

Several points need to be noted during use: the flux must be dried at 350 °C for 2 hours to prevent pores; when recovering the flux, slag shells and fine powder should be screened out, and 20% to 30% of new flux should be added; avoid using high-manganese welding wires such as H08MnMoA to prevent carbon increase in the weld; the groove must be clean, removing oil, rust, and moisture to prevent pores or slag inclusions.

6.Comparison with imported welding fluxes (for reference)

Compared with imported fluxes, SJ301 has an alkalinity of 1.0, a diffusible hydrogen content not higher than 5 ml/100 g, and a price of approximately 3 to 4 yuan per kilogram, which is much lower than that of Lincoln 860 or OK Flux 10.71. It is suitable for the production of general pipeline steel. If ultra-low temperature high-toughness requirements, such as X80 at -40 °C, are needed, an upgrade to fluorine-alkali fluxes such as SJ101 can be considered.

In conclusion, SJ301 is one of the preferred fluxes for LSAW steel pipe production, especially suitable for large-diameter longitudinally submerged arc welded pipes with X70 and lower steel grades. It has good formation, easy slag removal, stable performance, and low cost. With reasonable parameters and flux management, it can stably meet the pipeline steel standards.