Selection Criteria for Welding Consumables for ERW Welded Pipes

Selection criteria for welding consumables for ERW welded pipe:

Standard of welding rod
(1) Classified by slag properties
Welding rods can be divided into two categories: acid welding rods and alkaline welding rods. The electrode whose slag is mainly acid oxide is called acid electrode. The electrode whose slag is mainly alkaline oxide and calcium fluoride is called alkaline electrode. Among carbon steel electrodes and low-alloy steel electrodes, low-hydrogen electrodes (including low-hydrogen sodium type, low-hydrogen potassium type and iron powder low-hydrogen type) are alkaline electrodes; other coating types are acid electrodes.

Compared with the acid electrode of the same strength level, the alkaline electrode has higher ductility and toughness, lower diffusible hydrogen content, and strong crack resistance. Therefore, when the product design or welding process regulations stipulate that alkaline electrodes are used, acid electrodes cannot be used instead. However, the welding process performance of the alkaline electrode (including arc stability, slag removal, splashing, etc.) is poor, and it is highly sensitive to rust, water, and oil, and it is easy to vent holes. There are many toxic gases and smoke and the toxicity is also high.

Comparison of characteristics of acid electrode and alkaline electrode:

(2) Acid electrode
1. Not very sensitive to water and rust, baking at 100~150℃ for 1h before use
2. Stable arc, AC or DC welding can be used
3. Large welding current
4. Long arc operation possible
5. Poor transition effect of alloying elements
6. The penetration depth is shallow, the weld formation is better
7. The slag is glassy and it is easy to remove the slag
8. Normal and low temperature impact toughness of weld
9. The weld has poor crack resistance
10. The high hydrogen content of welds affects plasticity
11. Less smoke and dust during welding

(3) Alkaline electrode
1. High sensitivity to water and rust, baking at 300~350℃ for 1~2h before use
2. DC reverse welding is required; after the coating is added with arc stabilizer, AC and DC welding can be used
3. The acid welding agreement of the same specification is about 10% smaller
4. Short arc operation is required, otherwise it is easy to cause air holes
5. Good transition effect of alloying elements
6. Slightly deeper penetration, general weld formation
7. The slag is crystalline, and the slag removal is not as good as the acid electrode
8. The normal and low temperature impact toughness of the weld is higher
9. Good crack resistance of the weld
10. Low hydrogen content in the weld
11. Slightly more smoke and dust during welding

(4) Classified by electrode use
It can be divided into: structural steel electrode, molybdenum and chromium-molybdenum heat-resistant steel electrode, stainless steel electrode, surfacing electrode, low temperature steel electrode, cast iron electrode, nickel and nickel alloy electrode, copper and copper alloy electrode, aluminum and aluminum alloy electrode and special 10 categories such as welding rods.

Tips: ASTM A53 covers seamless and welded steel pipe with nominal wall thickness. The surface condition is usually black and hot-dipped galvanized. ASTM A 53 is produced mainly for pressure and mechanical applications, and is also used for transport of steam, water, gas line pipes.

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