Fluoride flux for pipeline steel

Welding flux

Welding flux is also called welding agent, which is something similar to SMAW electrode coating. It is granular, non-metallic mixture made through mineral powders mixing, sintering. SAW flux and wire are necessities in submerged arc welding. SAW flux is to form slag and produce protection gas in metal welding. Thus, weld metal is shielded from atmospheric oxygen and nitrogen.

Fluoride flux for gas/oil pipeline steel

Now China is at the peak of pipeline construction. Welded pipes are developing towards high grade, thick wall, large diameter. For example, steel pipe in West-to-East Gas Transmission Project is X70 grade, 1016mm*14.6mm in size. Steel pipe in Shanxi-to-Beijing line is X70 grade, 1016mm*17.5mm in size. To produce SSAW pipes by double-sided welding process, welding flux SJ101 and SAW wire H08C is used. However, when welding speed is higher than 1.4m/min, welding defects (pinholes and slag inclusion) increase significantly. Impact toughness is unstable, sometimes even not up to the standard. Weld pass formation ratio is low by only one operation. For thin sheet welding (thickness 6.4-9.5mm), when welding speed is higher than 1.6m/min, undercuts, slag inclusion, pinholes increase. To solve this problem, Gongyi Yulin Welding Material developed fluoride flux SJ101G for pipeline.

High welding speed, high toughness fluoride flux is one of the SJ101 series developed by Yulin Welding Material. Fluoride flux mainly consists of MgO, Al2O3, CaF2, MnO. It improves weld metal height, width, smoothness, slag removal by adjusting slag viscosity, surface tension, melting point, particle size, loose specific weight, etc. Fluoride flux increases welding speed from 1.3m/min to 1.7m/min, production efficiency is improved by 30%. Addition of small ferrous alloy, MnO, CaO could guarantee mechanical properties and low temperature toughness of weld metal. Fluoride flux, together with SAW wire H08C, could weld steel pipes and meet APL 5L, GB/T9711.1, GB/T9711.2 standards for pipeline.

Slag system

Slag systems are categorized into fluoride type, silicon-calcium type, alumina-rutile type, alumina type, silicon-manganese type. The last four types are featured with excellent welding performance, but low impact toughness at low temperature. They can’t meet the mechanical properties requirement for long pipeline. However, fluoride flux could get high toughness together with suitable wires. Fluoride flux is optimal for pipeline steel. Its slag is mainly MgO, CaF2, Al2O3, MnO.

Production and service

Fluoride flux SJ101G is applied in long pipeline construction after we got success. As to now, Yulin Welding Material company designed capacity has reached 25,000 tons annually, and sales volume has reached 10,000 tons annually. Fluoride flux is used in Ukrainian line, Lianyungang line, Indian line, etc. Pipeline steel ranges from L290MB to X70 grade. Wall thickness ranges from 6.4mm to 17.2mm. Welding speed could be as high as 2.0m/min.