Abstract
Narrow gap welding is a prevalent technique used to decrease the volume of molten metal and heat required to fill a joint. Consequently, deleterious effects such as distortion and residual stresses may be reduced. One of the fields where narrow groove welding is most employed is pipeline welding where misalignment, productivity and mechanical properties are critical to a successful final assemblage of pipes. This work reports the feasibility of joining pipe sections with 4 mm-wide narrow gaps machined from API X80 linepipe using cold wire gas metal arc welding. Joints were manufactured using the standard gas metal arc welding and the cold wire gas metal arc welding processes, where high speed imaging, and voltage and current monitoring were used to study the arc dynamic features. Standard metallographic procedures were used to study sidewall penetration, and the evolution of the heat affected zone during welding. It was found that cold wire injection stabilizes the arc wandering, decreasing sidewall penetration while almost doubling deposition. However, this also decreases penetration, and incomplete penetration was found in the cold wire specimens as a drawback. However, adjusting the groove geometry or changing the welding parameters would resolve this penetration issue.
Highlights
Narrow gap welding (NGW) is a technique used to weld thick joints with the aim of reducing the molten metal deposited volume, decreasing distortion and residual stresses caused by thermal stresses developed during welding
It is noted that the periodic pattern observed in the oscillograms of gas metal arc welding (GMAW) for root pass was not observed for the entire sampling period in cold wire gas metal arc welding (CW-GMAW) of 2000 ms
This suggests the sidewall erosion was mitigated during CW-GMAW, since sidewall penetration causes the periodicity in the observed signal
Summary
Narrow gap welding (NGW) is a technique used to weld thick joints with the aim of reducing the molten metal deposited volume, decreasing distortion and residual stresses caused by thermal stresses developed during welding. A review of the applications of CMT emphasizing the low dilution and the effect of post weld heat treatments (PWHT) in various materials can be found in [4] One alternative to these sophisticated welding processes is the cold wire gas metal arc welding (CW-GMAW), which consists of the standard gas metal arc welding (GMAW) with an extra cold wire (non-energized) fed into the arc-welding pool system. Previous research [8] demonstrates the possibility of welding U-grooves using CW-GMAW with pure carbon dioxide as shielding gas, and this method was primarily developed to be applied in shipbuilding The feasibility of this process to weld a 5 mm wide groove was recently studied on ASTM A131 grade A steel, revealing that, due to the pinning of the arc to the cold wire, the sidewall erosion was considerably reduced in comparison to welds manufactured with standard. The arc attachment to sidewalls can be ascribed to the arc shortest electron path according to Zhang et al [12]
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