Tips of gas pipelines welding procedures

How to weld alloy 20 steel?

Alloy20(UNS N08020), mainly composed of 35Ni-35Fe-20Cr-Nb, is Austenitic Fe-Ni base corrosion resistant alloy, which has excellent resistance to stress corrosion cracking and local corrosion, and good resistance to oxidation and moderate reducing corrosion. The alloy has good corrosion resistance in many chemical media, including aggressive strong inorganic acid solution, chlorine and various mediums containing chloride, formic acid and acetic acid, acid anhydride, dry chlorine gas, seawater and brine, etc., is an ideal conveying material for this medium, has been widely used in flue gas scrubber, hydrometallurgy and device in the sulfuric acid industry. Alloy20 steel tube, steel plate and steel bar (N08020) are specified in these standards: ASME SB462, SB463, SB464, SB468, SB473, SB729.

Alloy 20 Chemical Composition


Alloy 20 Mechanical Property

Tensile strength, MpaYield strength, MpaElongation, %

Welding materials for alloy 20

Stick ElectrodeAWS A5.4 E320-16/ AWS A5.4 E320LR-16
MIG wiresAWS A5.9 ER320LR
Argon arc weldingAWS A5.9ER320LR

Alloy 20 Weldability

Similar to most Austenitic stainless steels, Alloy20 is prone to welding thermal cracks, intergranular corrosion and stress corrosion cracks during welding. At the same time, due to its high nickel content, liquid nickel fluidity is poor, welding is easy to produce unfusion, incomplete penetration and other defects, welding process should pay attention to the following tips:

1. Prevent heat cracking.

The welder should strictly control of sulfur, phosphorus, carbon and other harmful impurities in the welding, improve the weld crystal form; The multi-layer multi-pass welding with small current and short arc without a swing or small swing is adopted to strictly control the heat input, reduce the stiffness and constraint of the joint, and reduce the shrinkage stress in the crystallization process.

2. Prevent intergranular corrosion.

Using the welding material with low carbon content (<0.03%), containing stabilizing elements such as Nb or Ti. During welding, try to reduce overheating, minimize welding heat input, avoid cross weld and increase the cooling rate after welding, and strictly control the carburizing of weld area during welding.

3. Prevent stress corrosion.

Stress corrosion of weld metals can be alleviated or prevented by a reasonable welding sequence, minimizing joint constraint and stress-free pairs of pipes.

4. Other tips

  • Remove moisture, dust, grease, paint, etc. on the surface of the weldment before welding, especially the impurities containing sulfur and lead;
  • Direct contact between the base metal and welding material and carbon steel is strictly prohibited. Special stainless steel wire brush and grinding pieces are used.
  • Before welding, both sides of the groove shall be cleaned within the range of 50mm, and the groove and welding wire shall be cleaned with acetone;
  • The joints of each layer of weld pass shall be staggered, and the arc pit shall be filled at the end of the arc, and the arc pit defects shall be polished;
  • The next welding can be carried out only when the temperature between the control channels is not greater than 100℃.

What are solid cored welding wires?

Solid cored welding wire, also known as “bare welding wire”, is used for submerged arc welding, molten electrode gas arc welding and tungsten argon arc welding, plasma arc, electroslag welding and other filler welding wire. According to its materials, solid wire is divided into carbon steel , low alloy steel(steel wire) for gas welding, steel wire for fusion welding, copper and copper alloy wire, aluminum and aluminum alloy wire, nickel and nickel alloy wire, etc. Gas shielded welding wire mainly includes CO₂ gas shielded welding, tungsten gas shielded welding and plasma arc welding wire. Fusion welding steel wire mainly includes cold drawn steel wire used for submerged arc welding, electroslag welding, gas welding and other purposes. In order to prevent the rusting and keep cleanliness, the surface of the wire is generally coated with a copper layer, that’s why they show yellow-red. Today here we collect the type of solid welding wires for your reference.

Solid cored submerged arc welding wire

In submerged arc welding, the flux can protect the weld metal and play a metallurgical role. The welding wire, as a filler metal, adds alloying elements to the weld at the same time and participates in the metallurgical reaction. The commonly used types of submerged arc welding wires include:

  • Low carbon and low alloy steel welding wire

According to the content of manganese, it can be low manganese welding wire (AWS EL8), medium manganese welding wire (AWS EM12), high manganese welding wire (EH14).

  • High strength steel solid welding wire

This wire contains more than Mn1%, Mo0.3%~0.8%, such as ER55-C1, can be used for welding low alloy high strength steel with high strength. Also can add Ni, Cr, V and Re and other elements in the welding wire to improve the weld performance according to the performance requirements. Mn-Mo welding wire is mostly used for the weld metal with the tensile strength of 590MPa.

  • Stainless steel solid welding wire

The composition of the welding wire should be consistent with the base stainless steel to be welded. When welding Cr-stainless steel, ER410, ER430 and other welding wires should be used.

 ER316, ER316L, ER316LSI welding wire for Cr-Ni stainless steel; When welding ultra-low carbon stainless steel, the corresponding low carbon welding wire such as ER316L, should be used. The flux can be either melted or sintered, requiring very little oxidation to reduce the loss of alloying elements, of which sintered flux is the most commonly used.

Gas shielded solid welding wire

Gas shielded welding can be divided into inert gas shielded welding (TIG and MIG welding), active gas shielded welding (MAG welding) and self-shielded welding. The shielding gas of TIG welding is pure Ar, Ar+2%O2 or Ar+5%CO₂ for MIG welding, MAG welding mainly usesCO₂ gas, as well as CO₂+Ar or CO₂+Ar+O2 mixed gas or use the flux cored wire directly.

  • TIG welding wire

TIG welding can sometimes need not filling the welding wire, the base metal is directly jointed to the base metal after heating and melting. Because the protective gas is pure Ar and has no oxidation, the composition of the filler welding wire does not change basically after melting. The welding wire composition is the weld composition,which should be consistent with the base metal. TIG welding welding energy is small, weld strength and plastic, good toughness, can easily meet the performance requirements.

  • MIG and MAG solid welding wires

MIG is mainly used for the welding of stainless steel and other high alloy steel. A proper amount of O₂ or CO₂ gas is added into the Ar gas to improve the arc characteristics, that is, MAG welding. When welding alloy steel, Ar+5%CO₂ can improve the porosity resistance of welding seam. The welding of ultra-low carbon stainless steel can only use Ar+2%O₂ mixture gas to prevent the welding seam from carburizing. At present, the MIG welding of low alloy steel is gradually replaced by the MAG welding of Ar+20%CO₂.

Due to the oxidation of the protective gas, the content of Si, Mn and other deoxidizing elements in the welding wire should be properly increased during MAG welding. When welding high strength steel, the content of C in the weld is usually lower than the base metal, and the Mn content is the opposite. This is not right to deoxidize, but also the requirement of weld alloy composition. In order to improve the low temperature toughness, the content of Si in the weld should not be too high.

  • CO2 welding wire

CO₂ is an active gas with strong oxidation, so the welding wire used for CO₂ welding must contain high Mn, Si and other deoxidizing elements. CO₂ welding usually uses C-Mn-Si wire, such as ER70S-2, ER70S-3, ER70S-6, etc. The diameter of CO₂ welding wire is generally 0.89 1.0 1.2 1.6 2.0mm. ER70S-6 welding wire is a widely used CO2 welding wire, which has better process performance and is suitable for welding low alloy steels below 500MPa grade.

Nonferrous metals and Cast iron welding wire

  • Surfacing welding wire

At present, the hard alloy welding wire used for surfacing mainly includes high chromium alloy cast iron (Solmait) and cobalt based (Stelli) alloy. High chromium alloy cast iron offers good oxidation resistance and cavitation corrosion resistance, high hardness and good wear resistance. Cobalt-based alloys, on the other hand, maintain high hardness and good corrosion resistance at 650°C. The low carbon, low tungsten wire has good toughness while high carbon, high tungsten welding wire has high hardness but poor impact resistance. Carbide surfacing wire can be surfaced by oxygen-acetylene, gas welding and other methods. Oxygen-acetylene surfacing is more widely used, which need simple welding equipment, the melting depth is shallow, the melting of the base metal is less, but a low production efficiency.

  • Copper and copper alloy welding wire

Used for welding copper and copper alloys. Brass welding wire is also widely used in brazing carbon steel, cast iron and carbide tools. The filling metal of copper and copper alloy is suitable for different welding methods. Oxygen-acetylene gas welding should be used together with gas welding flux.

  • Aluminum and aluminum alloy welding wire

Filling material for argon arc welding and oxygen – acetylene welding of aluminum alloy. Different aluminum alloy welding wire should be considered according to the type of base material, joint crack resistance, mechanical properties and corrosion resistance and other requirements. In general, the welding wire with the same or similar grade as the base metal composition is used to obtain better corrosion resistance; However, the composition of the welding wire is different from that of the base metal when the heat treatment of the aluminum alloy with a large tendency of hot crack is strengthened due to the crack resistance.

  • Cast iron welding wire

Mainly used for welding cast iron by gas welding. Because the temperature of oxy-acetylene flame (less than 3400℃) is lower than that of arc temperature (6000℃), and the hot spots are not concentrated, it is more suitable for the welding of gray cast iron thin-wall castings. In addition, a slightly lower gas welding flame temperature can reduce the evaporation of the spheroidizer, which is beneficial to ensure the weld to obtain ductile iron structure. At present, there are mainly two kinds of ductile iron welding wire used for gas welding: rare earth magnesium alloy and yttrium based heavy rare earth. Due to the high boiling point of yttrium, its ability of resisting spheroidization decline is stronger than that of magnesium, which is more conducive to ensuring the spheroidization of the welding seam, and is widely used.