Ever wondered how welders achieve perfect joints in challenging positions? 6GR welding is a specialized technique for welding pipelines with an obstacle ring at a 45° angle, crucial for ensuring structural integrity in various industries. This article unpacks the complexities and precise steps of 6GR welding, from pipe assembly to overcoming technical difficulties in backing welds. Dive in to discover how mastering these techniques can elevate the quality and reliability of your welding projects.
The 6GR welding technique for pipelines is a specialized and challenging welding position that simulates real-world conditions often encountered in field operations. This method involves positioning the pipe at a 45° incline angle, with an obstacle ring incorporated to replicate confined space welding scenarios.
The pipe’s longitudinal axis is set at a 45° angle relative to the horizontal plane, and this orientation remains fixed throughout the welding process. This angled position tests the welder’s ability to maintain consistent quality across various welding positions (flat, vertical, and overhead) within a single joint.
A key feature of the 6GR setup is the obstacle ring, which is positioned on the outer edge of the thick-walled pipe. The ring’s outer diameter typically exceeds that of the pipe by approximately 300mm, creating a restricted access situation that challenges the welder’s dexterity and spatial awareness.
The welding joint is precisely located, with the distance between the junction of the two pipes and the end face of the thick-walled pipe not exceeding 13mm. This tight tolerance emphasizes the importance of accurate fit-up and root pass execution.
The nomenclature “6GR” is derived from industry-standard welding position codes:
This welding configuration is particularly relevant for pipeline welders seeking to demonstrate proficiency in complex field conditions, often required for high-integrity applications in the oil and gas, petrochemical, and power generation industries.
Related reading: What Does 1G, 2G, 3G, 4G, 5G and 6G Mean in Welding?
The assembly and positioning of the welded pipes are crucial in ensuring the quality of the 6GR welding and the proper shape of the back side of the pipe joint.
If the groove type, assembly gap, and the size of the blunt edge are not suitable, it can easily lead to defects such as collapse, overlap, and incomplete penetration.
The shape of the pipe to be welded is depicted in Figure 1.
To ensure proper pipe alignment, the pipe butt joint should be performed on a specialized pipe aligner, and the positioning should be secured with rib plates (fixed at 2 points, 10 points, and 6 points).
The rib plate is made of 20 steel, and its shape is depicted in Figure 2.
The location of the rib plate positioning is shown in Figure 3.
The 6GR pipe incorporates a distinctive obstacle ring, with a 6mm thickness differential between the inner walls of the two connecting pipes. This design feature presents unique welding challenges.
According to the technical specifications, the back side of the pipe joint should be flush with the inner wall of the thick-walled pipe. However, to ensure optimal structural integrity and performance, the back side should be formed as a full penetration fillet weld.
Achieving proper backing welding in this configuration can be particularly challenging due to the obstacle ring and thickness variation. These factors can impede access to the weld root and complicate heat distribution during the welding process.
After extensive research, testing, and practical application, we have developed an effective method that successfully meets both the technical requirements and the need for a full penetration fillet weld. Our approach combines precise pre-weld preparation, specialized welding techniques, and rigorous quality control measures:
This method not only satisfies the flush inner wall requirement but also ensures a high-quality, full penetration fillet weld that enhances the overall structural integrity of the 6GR pipe assembly.
The primary challenge in backing welding for pipes is the oblique welding position, which leads to uneven heating and gravitational effects on molten droplets. To address these issues, it’s crucial to optimize the welding machine settings before starting. Set the arc starting current to position 5 and the arc force current to position 7. These adjustments facilitate easier arc initiation, enhance arc stiffness, and utilize the arc force to effectively transfer molten metal to the root of the thick-walled pipe, ensuring proper double-sided formation in single-sided welding.
Initiate the arc approximately 5mm past the 6 o’clock position. After ignition, employ a slight up-and-down motion of the welding rod within the groove. Once the root melts and forms a keyhole, quickly manipulate the arc height. Maintain the welding rod at an angle inclined towards the thick-walled pipe side. Utilize small, oblique, oscillating movements of the electrode, ensuring they are rapid, uniform, and stable.
Welders must employ a multisensory approach, focusing on visual cues, auditory feedback, and tactile control:
Time each arc follow-up based on the molten pool’s solidification state. Excessive speed can cause liquid metal flow and beading, while insufficient speed may lead to inward compression and back weld depression. Generally, control liquid metal feeding to 1-1.5 seconds per cycle.
For arc extinguishment, create a keyhole above the molten pool, then gradually retract the molten metal 10-15mm. Terminate the arc at the groove side to decelerate solidification and prevent cold shrinkage voids. Form a sloped joint to facilitate subsequent passes. Avoid terminating the arc at the weld pool center or directly on the pool surface, as this can generate difficult-to-repair cold shrinkage cavities.
When restarting, initiate the arc on the slope 10-15mm below the still-hot weld pool and progress to the previous crater. As the crater temperature increases, guide the electrode along the prepared keyhole to the groove root. Upon hearing the “plop” sound, pause briefly, move the welding rod laterally, then resume normal welding. Key factors include precise electrode positioning, swift replacement, accurate keyhole observation, and maintaining stable movement. Prioritize hot connections between passes to ensure a smooth, aesthetically pleasing weld bead appearance.
After completing the backing weld, use an angle grinder to smooth out any uneven joints, ensuring a uniform surface for subsequent passes. Adjust the arc force (also known as dig or arc control) to setting 5 on your welding machine. This optimized arc force helps to effectively remove slag on both sides of the weld, significantly reducing the risk of slag inclusions in the final weld.
Employ a controlled weaving technique, moving the electrode in a deliberate zigzag pattern. Pause momentarily at each side of the groove to ensure proper fusion and penetration. Maintain a consistent travel speed and electrode angle to keep the molten pool horizontal throughout the welding process. This technique promotes uniform heat distribution and reduces the likelihood of defects such as lack of fusion or incomplete penetration.
To enhance weld integrity and minimize the risk of cracking, stagger the start and stop points of adjacent layers by 10 to 15mm. This practice helps to distribute stress more evenly across the weld and reduces the concentration of potential weak points.
Upon completion of the filler passes, ensure that the weld surface sits approximately 1 to 2mm below the level of the base metal. This slight underfill creates an ideal foundation for the final covering layer, allowing for proper fusion and a smooth transition between the weld and base material.
Throughout the filler welding process, maintain strict control over key welding parameters such as amperage, voltage, and travel speed to achieve optimal results. Regular visual inspection between passes can help identify and address any potential issues early in the welding sequence.
Prior to initiating the cover welding process, adjust the arc force (thrust) to position 2. This reduction in arc force enhances arc flexibility, mitigating the risk of undercut defects and promoting a smoother, more aesthetically pleasing weld bead.
For the overhead welding position, establish a triangular formation using the first half of the welding electrode. Transition to a horizontal welding direction, employing a crescent-shaped electrode manipulation technique to maintain optimal control and penetration.
Upon reaching the groove edge, momentarily pause while maintaining a level molten pool. This brief dwell allows for proper fusion and helps prevent edge defects.
For the second half of the welding rod, initiate the arc at an oblique overhead position. Gradually draw the triangular weld area horizontally towards the lower groove edge, ensuring overlap with the previous weld bead. Utilize a transverse weaving motion with the electrode to achieve uniform coverage and fusion.
As you approach the closing position, progressively reduce the weld pool size to facilitate proper tie-in. Fill the remaining triangular area completely before terminating the arc to ensure full coverage and minimize the risk of end crater defects.
The cover layer should exhibit a flat profile at both the arc initiation and termination points. Prior to extinguishing the arc, ensure complete crater filling to prevent shrinkage voids and improve overall weld integrity.
Throughout the process, maintain consistent travel speed, electrode angle, and arc length to achieve uniform weld bead appearance and properties. Regular visual inspection during welding is crucial to detect and address any potential issues promptly.
As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.
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