LH-D electrodes are designed for any vertical down welding application where low-hydrogen weld metal is demanded, such as high-strength pipe welding.
Although these are designed specifically for vertical down welding of pipe joints, the LH-Ds are useful in any vertical down application where a low hydrogen deposit is required.
The low-temperature impact properties are superior to cellulosic electrodes that possess the same level of strength. As downhill electrodes, they have significantly greater deposition rates than both vertical-up electrodes and downhill cellulosic electrodes of equal diameter; this increases the potential for greater productivity, while meeting high-strength requirements.
Semi-automatic Processes
Semi-automatic processes can be categorised into, gas shielded and shelf shield.
Gas shield GMAW would typically be fully mechanised, because the welding area needs to be protected from the elements. If the contractor is prepared to protect the welding area, it is more feasible to use a fully automatic set-up. This leaves self-shielded flux-cored arc welding as the only serious semi-automatic welding option for consideration, the obvious advantage is that you gain from the reduction in stop starts, without the need for ancillary shielding.
Mechanised Processes
GMAW and flux-cored arc welding using a gas are the most common means of mechanised welding for fill and cap passes on pipe. The current techniques are based on either short arc or pulsed spray transfer with high wire feed speeds. The advancement and development of welding power source technology could conceivably yield significant productivity improvement Along with the improvements and welding characteristics of solid or cored electrodes, it will be possible to improve the welding performance and deposition. Mechanised GMAW holds tremendous potential for the future, because it requires less training, and results in lower hydrogen levels, higher productivity and better quality.
Conclusions
The direction of the welding community must follow two clearly defined channels:
Enhancement of Current Welding Processes
By advancing the designs of current basic low hydrogen manual and semi-automatic consumables, to better control hydrogen, strength and toughness. Although this methodology may prove successful for the X-80 applications, the increasing demand for greater hydrogen control and higher toughness will likely drive the industry to new technological advances in consumables and processes.
Innovation in Welding Consumables and Welding Power Source Design
Pipe contractors and fabricators have much to benefit by adopting these new technologies.
- The development of the Controlled Short Circuit Transfer utilises the latest technology to enable previously unattainable control over several arc variables.
- Advances in pipe spacing, clamping, ‘bug and band’ systems and multiple arc equipment can save time, increase quality and reduce costs for pipeline projects.
- Advancements in solid and cored electrodes will limit hydrogen and will enable manufacturing flexibility.
With quality and productivity in mind, Lincoln Electric is in the forefront of pipe-welding processes and is constantly seeking solutions for these highstrength steel challenges.
Category:
Transportation
| 
Download PDF
References
