What is submerged arc welding process?
Submerged Arc Welding (SAW) is a joining process that involves the formation of an electric arc between a continuously fed electrode and the workpiece to be welded. A blanket of powdered flux surrounds and covers the arc and, when molten, provides electrical conduction between the metal to be joined and the electrode.
Why is the quality of welds produced by submerged arc welding very good?
Weld Quality
Because of the excellent protection of the weld metal by the blanket of molten slag, SAW can produce high-quality welds with fewer weld defects than other processes.
What is are the disadvantages of submerged arc welding SAW?
Disadvantages of Submerged Arc Welding
The use of a granular flux and the fluidity of the molten weld pool mean that welding is limited to positions 1F, 1G, and 2F. Another disadvantage of SAW is that welding is normally limited to long, straight seams or rotated vessels or pipes.
What is the limitation for submerged arc welding process?
Limitations of Submerged Arc Welding
SAW can only be used for welding of ferrous materials like steel or stainless steel and some nickel based alloys. Submerged arc welding process requires relatively troublesome flux handling systems. Submerged arc welding process requires inter-pass and post weld slag removal.
Why it is called submerged arc welding?
The arc is submerged beneath the flux blanket and is not normally visible during welding. This is a well established and extremely versatile method of welding. The electrode may be a solid or cored wire or a strip made from sheet or sintered material.
What type of welding is used in submerged welding?
Submerged arc welding (SAW) is a welding process where the tubular electrode is fed continuously to join two metals by generating heat between electrode and metal. The area of the arc and molten zone gets its protection from the atmospheric contamination by submerging under a blanket of granular flux.
What causes porosity in submerged arc welding?
Common causes of porosity are: Contamination of joint surfaces with oil, paint, grease, hydrated oxides, etc. These decompose in the arc to give gaseous products which can cause elongated ‘wormhole’ porosity often located along the centreline of the weld.
What type of electrode is used in submerged arc welding?
The submerged arc welding process uses either direct or alternating current, but the direct current is used for most of the applications. Both direct current electrode positive (DCEP) and direct current electrode negative (DCEN) are used.
Which type of electrode is used in submerged arc welding?
Which type of flux is used in submerged arc welding?
The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds.
What are 3 main causes of porosity?
Cause. Porosity is caused by the absorption of nitrogen, oxygen and hydrogen in the molten weld pool which is then released on solidification to become trapped in the weld metal.
How can you prevent porosity?
7 Ways to Eliminate Porosity in Your Welds
- Check your gas flow rate.
- Make sure you gas flow rate is not see too high.
- Check for gas leaks.
- Keep an adequate contact-tip-to-work distance (CTTWD).
- Avoid drafty conditions.
- Clean the surface to be welded.
- Watch your travel angle.
What is the main purpose of submerged arc flux?
The functions of the flux are: to assist arc striking and stability. to form a slag that will protect and shape the weld bead. to form a gas shield to protect the molten filler metal being projected across the arc gap.
Is code for submerged arc welding?
IS 4353: Submerged Arc Welding of Mild Steel and Low Alloy Steels – Recommendations.
What is the purpose of submerged arc by the flux?
The primary purpose of the welding flux in submerged arc welding is to protect the weld puddle from contamination. In addition, some fluxes are formulated to provide additional benefits such as high impact toughness, high travel speeds etc.
What are the 4 types of porosity in welding?
There are four types of weld porosity that can manifest in different forms.
- Surface Porosity. What is this?
- Subsurface Porosity. Subsurface or distributed porosity can also be hidden beneath the surface of the bead.
- Wormholing. What is this?
- Cratering.
- Contamination.
- Shielding Gas Problems.
- Mechanical Problems.
- Technique.
How much porosity is acceptable in a weld?
When it comes to porosity, the American Welding Society dictates that the sum of the diameters of visible porosity should not exceed 3/8 inches, or 9.5 mm, in any linear inch of the weld, or exceed 3.4 inches or 19 mm, in any 12-inch length of a weld.
How do you correct porosity in welding?
What are the 3 functions of flux?
In soldering of metals, flux serves a threefold purpose: it removes any oxidized metal from the surfaces to be soldered, seals out air thus preventing further oxidation, and by facilitating amalgamation improves wetting characteristics of the liquid solder.
Where is submerged arc welding used?
Submerged arc welding is ideally suited to the longitudinal and circumferential butt welds required for the manufacture of line pipe and pressure vessels.
How much porosity is acceptable?
How Much Porosity Is Acceptable In A Weld. When it comes to porosity, the American Welding Society dictates that the sum of the diameters of visible porosity should not exceed 3/8 inches, or 9.5 mm, in any linear inch of the weld, or exceed 3.4 inches or 19 mm, in any 12-inch length of a weld.
Can you weld over porosity?
The only way to properly repair a weld porosity is to remove the porous section of the weld down to the base material. Attempting to weld over the affected bead will only end in the same result.
How do you reduce porosity in welding?
What causes bubbles in welds?
Watch your voltage / arc length. The further away the gun is from the weld site, the more likely air and gas will seep into the weld puddle causing bubbles to form which will in turn make a weak weld. Preventing porosity in your weld will overall increase the durability and purity of your weld.
What is the symbol for flux?
Φ
Magnetic Flux Symbol
Magnetic flux is commonly denoted using the Greek letter Phi or Phi suffix B. Magnetic flux symbol: Φ or ΦB.