What Does 6GR Mean and How to Weld?

Definition of 6GR welding of pipeline

The 6GR welding of the pipe is a fixed welding of the pipe with an obstacle ring at an inclined angle of 45 °.

The axis of the pipe forms a 45 ° angle with the horizontal plane, and the position is fixed without change.

The outer diameter of the obstacle ring is about 300mm larger than the outer diameter of the thick wall pipe, and it is installed on the outer edge of the thick wall pipe.

The distance from the joint of the two pipes and the end face of the thick wall pipe is ≤ 13mm.

“6” stands for oblique welding position, “G” stands for groove, the first letter of groove, and R stands for obstacle ring.

Related reading: What Does 1G, 2G, 3G, 4G, 5G and 6G Mean in Welding?

What Does 6GR Mean and How to Weld? 1

Pipe assembly and positioning

The assembly and positioning of welded pipes is the key to ensure the 6GR welding quality and the good shape of the back side of the pipe joint.

If the groove type, assembly gap and the size of the blunt edge are not appropriate, it is easy to cause collapse, overlap, incomplete penetration and other defects.

The form of the pipe to be welded is shown in Fig. 1.

What Does 6GR Mean and How to Weld? 2
Figure 1 Pipe fitting form

In order to ensure the pipe misalignment, the pipe butt joint shall be carried out on a special pipe aligner, and the positioning shall be fixed with rib plates (2 points, 10 points and 6 points are fixed with rib plates).

The rib plate material is 20 steel, and the rib plate form is shown in Fig. 2,

What Does 6GR Mean and How to Weld? 3

The positioning position of rib plate is shown in Fig. 3.

What Does 6GR Mean and How to Weld? 4

6GR Operation Features and Difficulties

The 6GR pipe has an obstacle ring, and the thickness difference between the inner walls of the two pipes is 6mm.

The technical requirement is that the reverse side of the pipe should be formed flush with the inner wall of the thick wall pipe.

In fact, the reverse side of the pipe should be formed as a full penetration fillet weld.

Backing welding is very difficult.

Through a lot of exploration and practice, we found a set of practical methods to make it meet the requirements.

Backing weld

The main difficulty of backing welding operation is the oblique and oblique welding position of the pipe.

Because the pipe bears uneven heat, it is difficult for the molten droplet to transfer to the back weld, and the gravity makes the molten droplet flow down.

In order to make the molten droplet overcome the adverse effects of gravity and uneven heating on the upper and lower ends of the groove, the molten droplet can smoothly transfer to the molten pool, and form a full weld on both sides.

To ensure that the arc is in the proper position when welding at the root is the key to realize the double side forming of single-sided welding.

Therefore, before welding, adjust the arc starting current of the welder to the position of 5, and the arc blowing force (thrust) current to the position of 7, which is easy to start the arc, improve the arc stiffness, and make full use of the arc blowing force to send molten iron to the root of the thick wall pipe, so that the reverse side can be formed well.

The welding rod strikes the arc at about 5mm after 6 o’clock.

After the arc is ignited, the welding rod swings slightly up and down in the groove.

After the root melts to form a molten hole, the welding rod should quickly top and lower the arc.

The angle of the welding rod should be inclined to the side of the thick wall pipe.

The small oblique serrations are used to move the electrode back and forth.

The action should be fast, uniform, and stable.

The welder is required to pay close attention to the welding rod, so as to “look”, “listen”, and “feed”.

The so-called “look” should pay attention to the fact that the temperature of the molten pool and the shape of the molten hole keep basically the same, and pay special attention to whether the arc length melts the root of the thick wall pipe.

The size of the molten pool should be 1/2 on the inside and 1/2 on the outside of the groove.

The time for each arc follow up should be based on the fact that the molten pool is close to solidification.

If the follow up is too fast, the liquid molten pool will increase, and the liquid metal is easy to flow down to form weld beading.

If the follow up is too slow, the liquid molten pool will be compressed inward, and the liquid metal.

 It is easy to form a depression in the back weld.

Generally, the feeding time of liquid metal shall be controlled within 1~1.5s each time.

“Listen” – Pay attention to whether there is a “plop” sound from the edge of the pipe groove caused by the arc breakdown.

 “Feed” – according to the gap contraction during welding, adjust the arc length and molten pool size through appropriate arc length, electrode angle, welding speed and electrode handling method to accurately send molten iron to the root of the groove.

If the three cooperate properly, good reverse forming can be achieved.

During arc extinguishing, first make a molten hole above the molten pool, then slowly bring the molten iron of the molten pool back 10~15mm, stop the arc at the groove side to slow down the solidification speed of the molten pool, prevent the molten pool from producing cold shrinkage holes, and make the joint form a slope to facilitate the next joint,

At this time, it is not allowed to back weld and stop the arc at the center of the weld pool to prevent cold shrinkage cavity, nor to directly stop the arc on the weld pool, otherwise, cold shrinkage cavity may be generated on the surface of the weld pool at the back, which will become a defect difficult to repair.

When the arc crater is still in the red hot state, start the arc on the slope 10~15mm below the weld pool and weld to the arc crater.

At this time, the temperature of the arc crater gradually rises, and the electrode should be pushed along the prepared hole to the root of the groove.

After hearing the “plop” sound, pause slightly, swing laterally, and then resume normal welding.

At this stage, the key points are to transport the welding rod in place, replace the welding rod quickly, observe the melting hole accurately, and make sure the gesture is stable.

The joint shall be hot connected as far as possible to ensure the smooth and beautiful appearance of the reverse side of the weld.

Filler welding

After the completion of backing welding, use an angle grinder to polish the uneven joint, adjust the arc blowing force (thrust) to position 5, and use the arc blowing force to excavate both sides of the weld to effectively prevent slag inclusion.

The electrode moves in a zigzag manner, and the electrode pauses at both sides of the groove. The molten pool is always kept in a horizontal position.

Note that the starting and extinguishing points of adjacent layers should be staggered by 10~15mm.

After the completion of filling welding, the weld should be 1~2mm lower than the base metal, To facilitate the welding of the covering layer.

Cover welding

Before welding, adjust the arc blowing force (thrust) to the position 2, which is used to reduce the arc blowing force, weaken the arc rigidity, and the arc is soft, which can control the generation of undercut defects of the weld, make the weld appearance smooth and smooth, and improve the appearance quality of the overlay.

The triangular area to be welded shall be formed at the overhead welding position of the first half of the welding rod, and the welding shall be carried out in the horizontal direction by the crescent shaped electrode moving method.

When the welding rod swings to the edge of the groove, it shall pause for a while, and the molten pool is basically horizontal.

After the arc striking at the oblique overhead welding position of the second half of the welding rod, the tip of the triangular area to be welded left from the front half of the welding rod shall be pulled horizontally to the lower edge of the groove, so that the molten pool overlaps the weld to be welded at the beginning of the first half of the welding rod, and the electrode shall be carried by the transverse serrated electrode moving method.

In the second half of the closing method, when the electrode is transported to the tip of the area to be welded at the closing position, the weld pool shall be reduced one by one until the triangle area is filled before the arc is stopped.

The arc stopping and arc extinguishing parts of the cover layer welding shall be flat, and the crater shall be filled before the arc is extinguished.

Leave a Comment

Your email address will not be published. Required fields are marked *