About the welding process of LNG cryogenic storage tank

The single refrigerant liquefaction process of LNG cryogenic storage tanks is also called cascade refrigeration liquefaction process or cascade liquefaction process. Through the title of the process, we can understand that a certain refrigerant is mainly used for the use of this process, and the manufacturing and installation of the bottom of the LNG cryogenic storage tank.

1. Before laying the bottom plate, draw the cross center line on the foundation, lay the center strip first according to the plan plan, and then lay the middle and side panels on both sides, lay the side and align it, and fix it temporarily with a fixture or spot welding . The allowable deviation of the overlapping width of the bottom plate is ±5mm.
2. The type and size of the butt joints between the tank bottom middle plate and between the middle width plate and the marginal plate should conform to the requirements of the planning drawings. The transition from the lap section to the butt joint is used for heating and bending with acetylene flame, which is wrong. The margin is not more than 1mm.

3. The welding sequence of the bottom plate of the LNG storage tank is very important, and the welder is strictly required to perform the following process.
4. For the welding of medium plates, the short seams should be welded, and then the long seams; before the short seam welding of the slats, the temporary welding points between the slats and the two side slats or side plates should be shoveled; When welding long seams, the welders should be spread evenly and symmetrically, from the center to the outside, using the stepwise retreat method for welding. 5. The lap joints at the margins of the bottom plate should be transformed into butt joints. When welding, the gaps should be symmetrically scattered and jump welds should be evenly reserved. The gaps should be filled and welded and the surface of the weld should be smooth and flat.
6. In order to reduce welding distortion, the annular fillet welds between the bottom plate and the bottom ring plate should be symmetrically dispersed on the surface of the LNG tank by several pairs of welders, and then stepped back and welded in the same direction. It is also possible to weld the inner ring first and then the outer ring. The welding sequence of the ring is performed.

7. The lap weld of the marginal plate shall be back welded in sections from the outside to the inside.
8. Then weld the connecting seam between the middle plate and the marginal plate. Before welding, the position of the welding seam between the two plates should be cleaned up, and the welders should be evenly distributed along the circumference and jump welded in sections.