1. Small diameter pipe butt joint horizontal fixed base layer welding technology

(1) Test piece material: 20 seamless steel pipe.

(2) Specimen specification: 60mm x 4mm, L = 200mm, see picture

(3) Groove size: 60° V-shaped groove, blunt edge 0.5-1mm.

(4) Welding materials: E4303 or E5015 electrode, diameter 2. 5mm or 3. 2mm.

(5) Welding requirements: Single-sided welding and double-sided forming.

(6) Test piece assembly

1) Grind the blunt edge to 1-1. 5mm, without burrs, and the misaligned edge is <0. 5mm.

2) Clean the specimen. Use an angle grinder, file, emery cloth and wire brush to clean away oil, moisture, oxides, burrs and rust within 20mm on both sides of the groove until the metallic luster is revealed.

3) Assembly and positioning welding of test pieces. Align the cleaned test piece, leaving a gap of 3-4mm. Use formal welding technology and welding materials to tack weld one spot at the inclined flat position (uphill climb) in the groove of the test piece. Place the tack welding spot Processed into a slope shape with appropriate anti-deformation.

After assembly and inspection, the pipes are fixed on the operating frame according to the welding position and appropriate height to be welded.

2. Small diameter pipe butt joint horizontal fixed base layer welding technology

(1) Arc ignition---arc ignition for continuous arc welding

When welding with alkaline electrodes, during the arc starting process, due to reasons such as less slag and less protective gas in the arc, the molten pool protection effect is not good, and the weld is very prone to dense pores, mostly N2 pores.

In order to prevent this kind of phenomenon from occurring, the scratching method is often used for arc ignition of alkaline welding rods. After striking the arc 10mm in front of the 6 o'clock position of the starting welding point, pull the arc to the starting welding point, that is, the 6 o'clock position of the clock for arc preheating. When "sweating" is found at the root of the groove, move the welding rod towards Push into the groove gap. After hearing the "pop" sound, stop for a moment to melt 1-2mm on each side of the blunt edge and form the first melting hole. At this time, the arc starting work is completed.

Alkaline welding rods require about 10% less current than acidic welding rods of the same diameter. For this reason, the welder is required to have steady hands and high skills during the arc striking process, and the arc striking and return movements must be fast and accurate.

(2) Arc ignition for arc breaking welding

Start the arc at 6-5 o'clock on the clock, that is, the overhead welding position, and use a long arc to preheat. When the end of the welding rod appears molten, use your wrist to shake off the first and second droplets at the end of the welding rod.

At the same time, when observing the "sweating" phenomenon in the preheating area, quickly and accurately send the molten droplet of the welding rod into the gap at the starting end of the welding. While swinging left and right, push the welding rod back and upward slightly, and then tilt it diagonally. The lower part is arced and extinguished, and the first molten pool is formed, and the arc ignition work is completed.

(3)Welding rod angle

1) At the starting point of the welding, that is, at 5-6 o'clock on the clock, the angle between the tangent line of the welding rod and the welding direction tube is 80-85°.

2) At the 7-8 o'clock position of the clock, it is upward welding and slope welding. The angle between the welding rod and the tangent line of the welding direction tube is 100°-105°.

3) In the vertical welding position, that is, the 9 o'clock position of the clock, the angle between the tangent line of the welding rod and the welding direction tube is 90°.

4) In the vertical climbing welding position, that is, during the welding process at the 10-11 o'clock position of the clock, the angle between the welding rod and the tangent line of the welding direction tube is 85-90°.

5) When welding in the flat welding position, that is, the 12 o'clock position of the clock, the angle between the tangent line of the welding rod and the welding direction tube is 75-80°.

3. Small diameter pipe butt joint horizontal fixed cover surface layer welding technology

1. Clean up the slag

Carefully clean the slag at the angle between the base layer weld and the base metal on both sides of the groove, and the slag at the overlap between the welding spots and the welding spots.

2. Shipping method

At 5-6 o'clock on the clock, that is, after the arc is struck at the overhead welding position, the long arc preheats the overhead welding part and shakes off the first and second melted droplets, because the temperature of the droplets at this time is low and the fluidity is not good. good.

Then send the molten droplets upward in a short arc, and use the crescent-shaped strip transport or transverse zigzag strip transport method for welding.

Always maintain a short arc during the welding process, pause briefly when the welding rod is moved to both sides, and melt the edges on both sides of the groove by 1-2mm to make a smooth transition between the weld metal and the base metal to prevent undercut defects.

During the welding process, the molten pool always maintains an oval shape and consistent size, and the molten pool should be bright and clear. When closing the arc in the first half of the arc, the arc crater should be slightly filled with molten metal to make the arc crater slope-shaped, creating conditions for the closing of the weld in the second half of the arc.

Before the second half of welding, the welding slag at the beginning of the first half of the weld should be knocked off 10-15 mm, and the arc crater should be filled when the weld ends. When welding the cover layer with alkaline electrodes, always use short arc preheating and welding, and use the scratching method for arc ignition.

3.Welding rod angle

Since the root base layer weld has been welded, the cover layer weld has nothing to do with whether the root is welded through. The main technical issue is that the cover layer weld should be well formed, the reinforcement should comply with the technical regulations, and the weld and the base metal should have a smooth transition. No undercut. For this reason, the angle between the tangent line of the welding direction of the welding rod and the pipe should be slightly larger than that of the base layer welding by about 5°.

(1) In the overhead welding position, that is, at the 6-7 o'clock position of the clock, the angle between the tangent line of the welding rod and the welding direction tube is 85°-90°.

(2) In the upward slope welding position, that is, at the 7-8 o'clock position of the clock, the angle between the tangent line of the welding rod and the welding direction tube is 105°-110°.

(3) In the vertical welding position, which is the 9 o'clock position of the clock, the angle between the tangent line of the welding rod and the welding direction tube is 95°.

(4) In the vertical climbing welding position, that is, at the 10-11 o'clock position of the clock, the angle between the tangent line of the welding rod and the welding direction tube is 90°-95°.

(5) In the flat welding position, that is, the 12 o'clock position, the angle between the welding rod and the tangent line of the welding direction tube is 75°-80°.

4. Steps and precautions

1) Be familiar with the pattern, clean the bevel surface and file the blunt edges.

2) Assemble the test piece according to the assembly requirements, perform positioning welding, and fix the test piece horizontally on the welding bracket at a height of 800-900mm from the ground to be welded.

3) Start welding from the upward welding position of the pipe, weld the right half circle first in a counterclockwise direction, and use the arc breaking method to weld to the flat welding position.

4) Clean the welding slag and grind the upward and flat welding joints into a gentle slope.

5) Change the welding position, weld the left half circle, start at the gentle slope of the upward welding position or cut it into a gentle slope with arc and then start again, use the same operation method as the right half circle to complete the welding of the base layer.

6) Clean up the welding slag and spatter, weld the cover layer, still use the two-half circle welding method, and use the crescent or transverse zigzag strip welding method during welding. Pay attention to filling the arc crater when closing the arc.

7) After welding, clean the welding slag and spatter from the inner and outer welds of the pipe fittings, and check the welds on both sides.

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