LPG/LNG tanks are used to store liquefied petroleum gas or liquefied natural gas. Because of the immense gas pressure after being loaded, the improper operation would bring the danger of explosion. As a typical small-sized pressure container, LPG/LNG tanks face extremely strict criteria for manufacturing. The metal material is commonly Q235 or Q345 of 3mm in thickness. Maximum pressure reaches 2.1 Mpa (about 20.8 psi).
Min Sheng High-Pressure Vessel Manufacturing Co., Ltd. is a large-scale national enterprise with qualifications for the design and manufacture of Type I, II, and III pressure vessels. It is a certified metal manufacturing enterprise of chemical equipment, steel gas cylinders, and LPG tanks. The company has 80 certified welders for pressure vessels. It has gained the certification of GB/T19001: 2000, ISO9001, and ASME "U" authorization with a comprehensive quality assurance system.
The Technical Challenge
LPG/LNG tanks are welded up with the base, the upper head, the lower head, the valve fixture, the shield cap, and the outlet. The upper and lower heads are the most critical components, the welding result of which would determine the quality of the whole tank. High-pressure resistance and zero defects are quested to ensure a high safety level. A few common obstacles in welding on site:
1）Incomplete fusion at the ignition point;
2）High welding spatter brings an unclean surface, which is difficult to be cleaned up. It brings more challenges to painting after the welding.
3）Low welding speed. About 1 min would be needed to weld up a tank. Production efficiency is hard to be increased.
4）Special-purpose automatic welding system would be used. Power sources have to work with high amperage at long hours and often get over-used and damaged.
MEGMEET Equipment and Solutions
MEGMEET Artsen II PM500 F was recommended with pulse MIG/MAG process. Artsen II PM500 F adapts fully digital-control technology with the capability of full position welding of mild steel with DC MAG or Pulse MAG process.
1）Fully digital control to reach precise control of droplet transfer. Performance with galvanized steel is optimum with stabilized arc and low spatter.
2）The upgraded process ensures better arc centralization, deeper penetration, higher welding speed, and lower heat input. It's highly suitable for sheet metal.
3）Parameters of starting-arc and crater-arc are able to be adjusted independently to ensure better welding quality.
4）Wire-feeder is equipped with a high-performance motor, coded wheel, feedback mechanism, and four-roller structure. Precise and stable wire-feeding is ensured for high-quality welding.
5）Superb in reliability and consistency of welding parameters. Welding quality with massive quality and a long time span has been ensured.
Comparison of Welding Result
Together with the automatic welding system, Artsen II PM500 F has brought satisfactory results for the end-user. Welding speed was increased by about 33%. Only 40 seconds were needed for each tank. Welding results were bright and complete in fusion, and high in consistency. The online repair rate has decreased by 15%. Spatter was so strictly controlled that the surface was free of metal particles. Polishing and grinding were no longer needed. The total efficiency has therefore increased by 26%. The welding power source has been continuously used for over 2 years on the line with superb reliability and no defective record.
Welding Seam of LPG/LNG tanks
LPG/LNG tanks Welding Finished Products
The Automatic Welding Production Line