Why are FCAW and GMAW welding methods not recommended? Some standards explicitly prohibit the use of FCAW – why is that?
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Why are FCAW and GMAW welding methods not recommended for pressure vessels? Some standards explicitly prohibit the use of FCAW. Why?
During welding, pores and slag inclusions are likely to occur, and a proper molten pool cannot be formed, which prevents stable welding quality.
Given current smelting technologies, there should be no relation to carbon
Today, high-quality GMAW and FCAW welds can be inspected using radiographic and ultrasonic non-destructive testing methods. An appropriate gas mixture ratio and proper welding techniques can help prevent defects such as welding pores.
There are good GMAW and FCAW welds, as well as poor ones; once there are more good ones, the standards will need to be revised
The main issue is that the instability in welding cannot be resolved by improving the skill level of the operator. Additionally, the presence of CO2 leads to a reduction in the amounts of Mn, Si, and other deoxidizing elements in the deposited metal, which increases the likelihood of porosity. The gas concentration during welding has a direct impact on the mechanical properties of the material. In terms of usage, MIG welding requires preheating to room temperature (25°), and after stopping welding, the weld seam needs to be preheated to 135°+; this makes the process more complicated compared to using electrodes.
I think it’s still a problem with the alloy composition and pores; preheating on-site is now an easy solution
This post was last edited by Forgetting = Forgetting on 2021-12-8 at 13:25. The composition of the alloy elements remains roughly the same before and after cladding; it is the welding environment that ultimately has an impact. In practical applications, it is difficult to control the mechanical properties. Preheating is often used in field conditions by treating MIG welding equipment as electrodes. Even in such environments, it is not possible to fully control the influence of MIG welding on H and S. No one dares to determine the exact extent of the impact of these harmful elements; otherwise, the standards would have been adjusted
It’s probably a problem with the penetration depth; after all, the welding wire is much thinner than the welding rod. It was agreed that welders would be able to pass the non-destructive testing, but more of them failed it; therefore, it was simply banned. If one day most of it can be passed without any issues, it will definitely be made available.
GMAW is not recommended for use on pressure vessels, possibly due to the relatively low impact toughness of the joints, especially with FCAW wire. The welding quality is unstable.