Container Section [Weekly Question 2011.4.11~17] Discussion on the advantages and disadvantages of using GMAW for root welding in container fabrication

Those who work on pressure vessels probably rarely use GMAW. . . It should be used more for structural welding, as it has a fast welding speed. However, the penetration depth is low, and there are many slag and pores. . . I guess the X-ray won’t pass. . Anyway, our company has never used them on pressure vessels. . .

In terms of performance, using it just as a base layer isn’t a big problem. The key issue is that since a root pass is required, which means the weld must be inspected, it’s generally good to achieve double-sided formation with a single-pass root pass, without any defects such as incomplete penetration or lack of fusion. Here lies the problem: MIG welding does not yield good shape, and the aforementioned defects tend to occur easily. So use it as little as possible. Not recommended for use.

I’m just here to offer some input. I’m the one who designed it; I don’t know anything about welding. However, while observing the welding of the cylinder reinforcement rings in the workshop in real time, I saw that GMAW was used for that process (intermittent welding), but it’s rarely used in other areas. I asked about this. Answer 2: Welding: Fast welding speed, but defects are likely to occur~ Therefore, it is generally used for non-compressive welding. PS (when designing an LNG tank truck, use reinforcement rings with a thickness of 100 mm each~ No shielded metal arc welding is needed; otherwise, the workers will be upset~)

Reply to 4# SuperFree2316: Is the reinforcing ring of 100 mm used at the weld joint?

Reply to 5# mike1984: The spacing between the shell cylinders is about 100 mm (it might be 120; I can’t remember exactly). There is one reinforcement ring – it’s not a weld seam~

The advantages of MIG welding are its open-arc welding process, which facilitates full-automatic and semi-automatic welding in all directions. It generally uses bare welding wire; the arc heat is concentrated, resulting in a small heat-affected zone, as well as reduced tendencies for welding deformation and weld cracking. Its overall cost is only half that of manual arc welding and submerged arc welding. However, due to the difficulty in producing pure carbon dioxide, impurities such as water and nitrogen often cause significant amounts of dust and splatter, resulting in a rough appearance of the weld seam; therefore, a dryer must generally be installed in the gas supply line ； Another drawback is that carbon dioxide decomposes easily at high temperatures, producing carbon monoxide and oxygen, which leads to oxidation of the weld metal as well as the formation of pores and inclusions. (This is also one of the causes of pool spatter.) GMAW is mainly used for welding low-carbon steel and low-alloy steel structural components with a thickness of 25 mm or less. GMAW is rarely used on pressure vessels.