Welded Steel Pipe: Control of Welding Slag Inclusion and Stomata Defects

When steel pipe manufacturer (such as Prime Steel Pipe) producing welded steel pipe, it is unavoidable that some welding slag inclusion and stomata defects may appear if workers don't control very well during operation. So we will talk about the causing reason of welding slag inclusion and stomata defects here, and then we will give preventive measures for you. More details are as follows.

Causing reasons of welding slag inclusion:

1) Back chipping after backing welding is halfway, which results in the root slag did not completely overflow when heat welding rapidly.
2) The way to backing weld back chipping may be wrong, so that the groove on both sides of root pass is too deep, and shows "W". In the rapid heat welding, the slag flowing into the deep trough is too late to overflow and form slag.
3) At 6 o'clock position, arc too fast is also easy to produce slag.

Preventive measures:

1) Using grinding wheel to remove slag after the backing weld, back gouging must be thoroughly, each joint point must be flat.
2) When back chipping the root weld bead will be clear into the "U" shaped groove, and avoid to be the "W" shaped slot.
3) When retreating the arc at 6 o'clock we need to fill the molten pool, and then move arc to the forming of the weld to collect arc, and use flat swing method to extinguish the arc.

Causing reasons of stomata defect:

1) The molten pool is overheating when cosmetic welding, and adsorb a lot of ambient air.
2) The amplitude of swing of welding rod is too large when cosmetic welding, the molten pool is be protected badly.
3) The root gap is too small, which is easy to produce root needle bubble.
4) The electrode is not used for a specified period of time or prolonged exposure to air.

Preventive measures:

1) The current should not be too large when capping, we should use the small current, short arc, and welding with fast welding speed to avoid overheating and prevent surface pores.
2) We should use the appropriate transport technology to weld, otherwise it will make the molten pool ahead, and easy to cause long short circuit and the electrode stick on the weld, which is unfavorable to deoxidize and easy to produce pores. But the width of electrode swing should not exceed twice the diameter of the electrode, otherwise it is easy to produce pores.
3) We should prevent the group on the gap is too small, if the group on the gap is too small, it will cause overlarge base metal dilution effect in the welding, and impede the exhaust, which will results in the root of bubbles.
4) Electrode should be stored in the electrode insulation tube in the use of the process. It is strictly prohibited that welding rod is exposed outward, we need to prevent the welding rod damp.

Hot-rolled Seamless Steel Pipe

Hot-rolled seamless steel pipe is a large category of seamless steel pipe, which is divided according to the production method. Hot rolling is relative to cold rolling, cold rolling is carried out rolling at room temperature, and hot rolling is carried out rolling at the recrystallization temperature. Seamless steel pipe is named relative to the welded steel pipe, seamless steel pipe is usually made of round steel perforation and reprocessing, welded steel pipe is usually welded by steel plate in different ways. The diameter of hot-rolled seamless steel pipe is usually above 38mm. Seamless steel pipe with smaller diameter can be obtained by cold rolling or cold drawing.

The process of hot-rolled seamless steel pipe:

Hot-rolled seamless steel pipe is generally produced on automatic rolling mill units. The solid bar is inspected and cleared of surface defects. Then it is cut into the required length, and centered on face of the perforation end of the pipe billet. And then it will be sent to the heating furnace to heat, and bore a hole on the puncher. In the perforation, the solid bar will continue to rotate and forward at the same time, in the role of the roll and the head, the tube billet internal will be gradually formed cavity, that is said capillary. And then it will be sent to the automatic rolling mill to continue rolling. Finally, it will be reeled the wall thickness by reeling mill, sized by sizing mill, to achieve the specifications. It is a more advanced method that using continuous rolling mill to produce hot-rolled seamless steel pipe. Generally process of hot-rolled seamless steel pipe: round bars → heating → piercing → three-roll cross rolling, rolling or extrusion → detached → sizing (or reducing) → cooling → parison tube → straightening → hydrostatic test (or flaw detection) → mark → storage.

Welded Steel Pipe: Control of Welding Slag Inclusion and Stomata Defects

When steel pipe manufacturer (such as Prime Steel Pipe) producing welded steel pipe, it is unavoidable that some welding slag inclusion and stomata defects may appear if workers don't control very well during operation. So we will talk about the causing reason of welding slag inclusion and stomata defects here, and then we will give preventive measures for you. More details are as follows.

Causing reasons of welding slag inclusion:

1) Back chipping after backing welding is halfway, which results in the root slag did not completely overflow when heat welding rapidly.
2) The way to backing weld back chipping may be wrong, so that the groove on both sides of root pass is too deep, and shows "W". In the rapid heat welding, the slag flowing into the deep trough is too late to overflow and form slag.
3) At 6 o'clock position, arc too fast is also easy to produce slag.

Preventive measures:

1) Using grinding wheel to remove slag after the backing weld, back gouging must be thoroughly, each joint point must be flat.
2) When back chipping the root weld bead will be clear into the "U" shaped groove, and avoid to be the "W" shaped slot.
3) When retreating the arc at 6 o'clock we need to fill the molten pool, and then move arc to the forming of the weld to collect arc, and use flat swing method to extinguish the arc.

Causing reasons of stomata defect:

1) The molten pool is overheating when cosmetic welding, and adsorb a lot of ambient air.
2) The amplitude of swing of welding rod is too large when cosmetic welding, the molten pool is be protected badly.
3) The root gap is too small, which is easy to produce root needle bubble.
4) The electrode is not used for a specified period of time or prolonged exposure to air.

Preventive measures:

1) The current should not be too large when capping, we should use the small current, short arc, and welding with fast welding speed to avoid overheating and prevent surface pores.
2) We should use the appropriate transport technology to weld, otherwise it will make the molten pool ahead, and easy to cause long short circuit and the electrode stick on the weld, which is unfavorable to deoxidize and easy to produce pores. But the width of electrode swing should not exceed twice the diameter of the electrode, otherwise it is easy to produce pores.
3) We should prevent the group on the gap is too small, if the group on the gap is too small, it will cause overlarge base metal dilution effect in the welding, and impede the exhaust, which will results in the root of bubbles.
4) Electrode should be stored in the electrode insulation tube in the use of the process. It is strictly prohibited that welding rod is exposed outward, we need to prevent the welding rod damp.

How to Increase the Stability of the SSAW Steel Pipe?

After the production of SSAW steel pipe, it should be stored.If we don’t do some measures to keep its stability, it will rust and be corroded. So we will talk about how to increase the stability of the spiral welded pipe today. Generally speaking, we have followed methods:

1. Small and medium-sized steel, wire rod, rebar, steel pipe with medium diameter, wire and wire rope, etc., can be stored in well-ventilated shed, but must put covering in the upper part of the goods and underlay at the bottom of the goods.

2. Some small steel shape, sheet steel, steel strip, silicon steel sheet, small diameter or thin-walled steel pipe, all kinds of cold-rolled or cold-drawn steel and the metal products with high prices and easy-to-corrode can be stored in warehouse.

3. The ground or warehouse to store spiral steel pipe should choose the place where is orderly and clean, and it is easy to fluently drain away water. It should stay away from the factories and mines that products harmful gases or dust. We also need to remove the weeds and all debris to keep the steel clean on the ground.

4. Large-scale structural steel, steel rail, large diameter steel pipe, forgings, etc. can be opened stack.

5. In the warehouse, SSAW steel pipe should not be stacked with the acid, alkali, salt, cement and other materials that have corrodibility on steel together. Different varieties of steel should be stacked separately, to prevent confusion and prevent contact corrosion.

Submerged Arc Welding Process of SSAW Steel Pipe

SSAW steel pipe refers to the metal pipe with spiral seam that using submerged arc welding process to weld. There are complete production line of SSAW steel pipe in Prime Steel Pipe, we are positioned as a steel pipe manufacturer and exporter for spiral welded pipe. If there is a need, please contact us without hesitation, we will do our best to meet your requirement.

Submerged arc welding (including submerged arc welding and electroslag welding, etc.), its full name is submerged automatic arc welding, it is a kind of method that arc burns under the flux layer to weld. Its inherent advantages (including stable welding quality, high welding productivity, no arc and few dust, etc.) makes it become the main welding methods used in pressure vessel, pipe section manufacturing, box beam and other important steel structure production.

Advantages of SSAW steel pipe:

1. High production efficiency. On the one hand, the wire length is shortened, the current and current density are improved, therefore, the penetration depth of the arc and the deposition efficiency of the welding wire are greatly improved. Generally, single-sided melting depth of can be up to 20mm if do not open the groove. On the other hand, due to thermal insulation of flux and slag, the arc basically has no loss of heat radiation, welding spatter is also few. Although the heat loss for melting the flux is increased, the overall thermal efficiency is still greatly increased.
2. High quality of weld seam. The protective effect of the slag from the air is good, the welding parameters can be stabilized by automatic adjustment, the requirement of the welder's technical level of is not high, the composition of weld seam is stable and the mechanical performance is better.
3. Good working conditions. In addition to reducing the labor intensity of manual welding operations, it does not have arc radiation, which is the unique advantage of submerged arc welding.

Disadvantages of SSAW steel pipe:

The flexibility of submerged arc welding is not as good as manual welding, it is generally only suitable for the weld seam that in horizontal position or small gradient. Workpiece edge preparation and assembly quality requirements are higher, which is cost more working time. Due to using submerged arc welding, we can not see the bath and weld formation process, so the welding specification must be strictly controlled.