LSO SAW Tandem welding procedure for very thick plate apply for Tripod wind offshore structure

Double good jsc - tripod welding technology

Introduction

Tripod is one type of support structure for wind turbine offshore. The design is strictly guided by the functional requirements of a long lasting predominantly dynamic loaded structure in harsh environment. The tripod is generally more expensive than other types of foundation. However, for large turbines and higher water depth, the cost disadvantage might be compensated when durability is also taken into account.

The whole structure is made of steel and consists of a central cylindrical section, bracings, and three supporting pile sleeves. Once the tripod is transported to the site of installation, the structure is lowered to the seabed and a pile is driven through each sleeve. For securing the structure to the seabed, the connection between the pile and the sleeve is filled with grout or concrete. Tripod structures’ manufacture is relatively complex and time consuming, while the transportation and installation processes require large barges and heavy lifting cranes.

EXPERIMENTAL PROCEDURE

Recently, DGwelding successfully applied SAW Tandem Long stick out (LSO) welding technology to weld very thick plates (60, 80, 90 and 120mm). In this experiment, we use 02 Lincoln Power source AC/DC 1000 SD. Base metal was Q345B, and Groove angle 600 joints, double-V butt joint were prepared with weld face of 10mm.

We used Tandem Cruiser with laser tracker to determined the seam weld during welding. Lincoln Electric Premierweld EM12K (dia. 4.0mm) and flux F7A4 were used in this study. Below are some image of this experiment.

Groove weld joint of 120mm thickness plate
Welding sequence of 60mm thickness plate
Welding sequence of 80mm thickness plate
Welding sequence of 90mm thickness plate
Welding sequence of 120mm thickness plate
angle between two welding wires/ arc
setup tandem cruiser before welding
some recored welding data during experiements

RESULTS

Both samples shown better surface without any defect. The macro result proved weld beads was penetrated each others. Small HAZ zone presented LSO technologies is suitable for heavy structure like tripod foundation.

Finished weld surface
Marcro image of 60mm-plate weld joint
Marcro image of 80mm-plate weld joint
Marcro image of 90mm-plate weld joint
Marcro image of 120mm-plate weld joint

CONCLUSION

  • SAW Tandem LSO welding technology exhibited good results on heavy plate with very good weld surface and penetration between weld beads and base metal.
  • Although the plate have large thickness of 60-120mm, LSO can achieved limited number of weld bead, small HAZ and high deposition rate (up to 39 kg/h).
  • LSO can controlled the Heat input of each weld pass, then will be the best choice for heavy structure like Tripod foundation in wind offshore structure.

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