The challenges associated with the welding of high-strength pipeline steels, such as X-80 and X100, are well established. While there are many filler metals that provide either adequate strength or good impact toughness, it is difficult to find products that provide both. Add to that the need for all-position welding and high deposition rates, and the options become almost non-existent.
Several years ago, Hobart® Filler Metals began working on a line of flux-cored arc welding (FCAW) consumables that are unique in the welding industry. The products have a basic slag system, but do not operate like traditional EXXXT-5 electrodes. Traditional T-5 electrodes have a low-melting, fluid slag, which makes welding out-of-position especially difficult. They also have a high level of calcium fluoride, which affects the stability of the arc and causes weld spatter. While the weld metal mechanical properties and crack-resistance are excellent, the welder appeal and ease-of-use tend to be sorely lacking in most EXXXT-5 electrodes.
The new approach utilizes aluminum for deoxidation, which has the added benefit of very clean weld deposits. The composition has been carefully optimized with appropriate levels of carbon, silicon, nickel and manganese. Alternative fluorine sources are used in place of calcium fluoride, which results in very good welder appeal and all-positional capabilities, including vertical down. The novel use of aluminum in a gas shielded process results in very low oxygen, nitrogen and sulfur content, providing exceptionally clean, tough weld deposits.
Although the new products have been produced over a range of strength levels, the primary emphasis of this paper is on E691T5-GC (E101T5-GC) and E831T5-GC (E121T5-GC) electrodes. Testing shows that tensile strength levels ranging from 700–880 MPa (100–128 ksi) can be achieved, with toughness levels of 120 J at −60°C (90 ft-lbs at −76°F) or better. The highly basic slag, combined with low weld metal hydrogen (less than 4 ml/100 gm), provides excellent resistance to cracking. The product can be used in all positions, including vertically down, making it an especially appealing choice for welding high-strength pipe.