Discussion on the issue of electrode swing width
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DL/T 869-2004 5.3.7b) For weld seams of heat-resistant steels with a Cr content of ≥5% or a total alloy content of ≮10%, … the width of a single pass shall not exceed 4 times the diameter of the electrode. 5.3.7c) The width of a single pass for other materials shall not exceed 5 times the diameter of the electrode. Could any experts explain in detail why there are restrictions on the weld bead width? What is the role of the limitation on the width of the horizontal swing of the welding rod in 5G and 6G welding? Is it to control the heat input? As is well known, there is a relationship between welding heat input and welding speed; the welding speed determines the amount of welding heat input. While it is necessary to ensure proper melting, an appropriately high welding current should be used, rather than focusing solely on using a low current. Therefore, in 5G and 6G welding, the width of the molten pool generated by the horizontal movement of the welding electrode is discontinuous under appropriate process parameters; the width of the molten pool is not equal to the width of the electrode’s movement. Can the single pass weld width specified in DL/T 869-2004 be understood as meaning that the width of the molten pool formed during welding should not exceed 4 or 5 times the diameter of the electrode?
I believe that multiple passes of welding can reduce the welding stress in the weld; for welds of the same width, the welding stress resulting from multiple passes is lower than that resulting from a single pass.
Penetration and weld width are important parameters of welding specifications; larger penetration and weld width indicate higher welding current and voltage, which in turn means higher line energy. This can lead to undercutting and burn-through, as well as coarser grains in the heat-affected zone, resulting in reduced toughness.
Emphasize wire energy; do not focus too much on current and voltage, and the welding speed can be increased appropriately. An increase in melt width does not necessarily mean an increase in wire energy.
From the perspective of crystallization segregation in the weld metal, when welding steels with high contents of welding alloys, the molten pool is wide and deep, resulting in severe segregation. During the cooling and crystallization process of the molten pool, crystallization occurs from the edges toward the center; some elements do not have time to diffuse and are thus \"pushed\" toward the center of the molten pool, leading to localized compositional inconsistencies in the weld metal, which affects mechanical properties and corrosion resistance.
These days, container welding is generally carried out in multiple layers and passes. The advantage of this method is that the heat input is low; each subsequent pass acts as a kind of annealing effect on the previous pass, resulting in better joint quality. In contrast, single-pass swing welding involves high heat input, with the weld area remaining at high temperatures for an extended period, which can lead to coarse grains and a wider heat-affected zone. When we used to manufacture export equipment, we also employed swing welding, and when foreigners saw it, they said that our welding skills were not good enough
It doesn’t seem to be that strict in this case. The requirements for carbon steel and low-alloy steel aren’t high, but for high-alloy steel, especially austenitic steel, it is necessary to control the swing range strictly in order to prevent a large heat-affected zone. Austenitic stainless steels are sensitive to prolonged exposure to the heat-affected zone, as this can lead to coarse grains and embrittlement of the weld seam.
Low-alloy steel for pressure vessels also requires a width not exceeding 4-5 times the diameter of the welding electrode
My simple understanding is that if you use oscillatory welding, it’s difficult to determine your welding speed; as a result, the calculated welding heat input is not accurate, and this in turn leads to inaccurate welding process evaluations. As for actual product welding, with materials such as carbon steel and low-alloy steel that have good weldability, a slight amount of oscillation should not cause any problems – there’s no need to be too precise; understanding the principle is sufficient