Let’s take a look at five types of pipe welding used in oil & gas, power plants and construction that are typically used in the USA and Canada as well as in other countries.
With the exception of MIG Welding, we covered the basic principles and characteristics of Stick Welding (SMAW), TIG Welding, Flux cored (FACW), and SAW, which are used in most piping fabrication plants & field pipe welding jobs.
1. Stick Welding or SMAW (Sheild Metal Arc Welding) for Pipe Welding
1) Stick Welder Principle
Using a flux covered welding rod, an arc is generated between the base material and the welding rod.
The heat of the arc melts the welding rod and welding gases are produced by the burning of welding rod covering.
2) Applicable welding current/ polarity: AC, DCEP(DCRP), DCEN(DCSP)
Stick Welder Characteristics
- It is widely used as a form of most basic arc welding process.
- Portable welding process.
- Can be used for all welding positions.
- High welding skills are required for out of position welding.
- Can be used for welding of almost all metals. (Excludes highly oxidizing metals such as aluminum and titanium).
- Welding can be applied to all thicknesses (except for thin plate welding with a thickness of 2mm or less).
- The equipment setup is simple, and the price is low, making it easy to operate.
- No external welding shielding gas is required.
Basic equipment setup and principle diagram is shown in the below figure for stick welding.
Comparative review of AC-DC Stick Welder characteristics
| Features | DC Welder | AC Welder |
| Welding current | Direct current | Alternating current |
| Welding polarity | Yes (DCEP, DCEN) | AC |
| No-load voltage | Slightly lower (up to 60 volts) | High (80 ~ 100 volts) |
| Danger of electric shock | Low | Plenty (high no-load voltage) |
| Equipment setup | Complex | Simple |
| Power factor | Very good | Low |
| Welder Cost | Expensive | Low |
| Arc blow | No | Yes |
Stick Welding Amperage
- Current, speed, welding angle, and rod (bead width is 6 times the core wire for carbon steel, 4 times the core wire for stainless steel & Alloy steels)
- Current (when welding carbon steel) However, when welding stainless steel, it is about 10~20Amp lower compared to high-tensile welding rods.
| Welding position | Rods 3.2mm | Rods 4.0mm | Rods 5.0mm |
| Flat-F | 110 ~ 130 | 150 ~ 180 | 190 ~ 230 |
| vertical-V | 80 ~ 130 | 130 ~ 160 | 160 ~200 |
Learn about Stick Welding or SMAW in details.
2. TIG Welder for Pipe Welding
1) Principle
A non-consumable tungsten welding rod is used to generate an arc with the base metal, and the filler metal is melted with this arc heat to fuse base metals.
An external welding shielding gas is supplied to protect the molten weld pool from oxidation and contamination.
2). TIG Welder Applicable Current- Polarity: AC, DCEN (DCSP)
3) TIG Welder Characteristics
- Precise and beautiful welding quality. (No welding slags or spatters)
- Welding of all positions is possible.
- Root run welding quality is excellent. (Applied to Pipe, Tube welding)
- Manual welding operation allowing better control on welding heat input.
- It can be applied to most metal welding. High quality, good for thin plate welding, but low welding deposition efficiency.
- Low input heat welding is possible, which gives less heat to the base material. (When inverter pulse welding is applied).
- Best for welding exotic materials and alloys such as titanium, tantalum, magnesium alloys as well as aluminum.
Basic TIG Welder device and principle diagram is shown below.
TIG Welding Shielding gas
TIG Welding process mainly uses argon 99.99% (gas flow rate 8~15L/min or 20- 30 CFH), helium (gas flow rate: 15~30L/min).
– Helium gas has the characteristic of having a lot of heat input and forming wide beads as it supports high welding voltage during welding. But the gas flow rate is higher with helium compared to argon due to its low density.
6) Back Shielding Gas (Back purging)
Back Shielding or Back purging Gas refers to injecting inert welding gas inside the pipe ID to protect the weldment from inside (root side).
This is applicable for highly oxidizing materials such as stainless steel and aluminum as well as titanium, magnesium, etc.
- Purging gas prevents oxidation on the back of the weld.
- Gas supply pressure remains low and constant until root and hot pass is completed.
- In the case of stainless steel or high alloy steel, the back purging is maintained until 2-3 welding layers are stacked (minimum thickness 5mm). This means that if the weldment solidifies in the molten state and the protective gas inside the pipe is naturally blocked, back purging is not necessary.
Learn more about TIG Welding in detail.
3. MIG Welding (Gas Metal Arc Welding) for Pipe Welding
1) Principle
MIG Welding works by continuously supplying a solid filler wire through a wire feeder and an arc is generated between the base metal and the filler metal.
The filler metal is melted with this arc heat, and shielding gas is ejected around the weld to shield the atmosphere.
2) Applicable current/ polarity: DCEP(DCRP), DCN(DCSP)
3) MIG Welder Characteristics
- By continuously supplying filler metal and welding gas, the welding efficiency is higher than that of SMAW or TIG welding.
- Enables automation, improves equipment utilization.
- The equipment is complicated and the price is relatively high compared to stick welder.
- Various base material thicknesses can be welded (thick plate welding is possible).
- Easy to learn.
- Different transition modes depending on current, Wire diameter, shielding gas (Short-circuit, globular, spray).
- Pulse mode enables low-current, sheet welding, and minimal welding distortion.
Basic MIG Wedler device and principle diagram is shown below.
MIG Welding Gases
| Shielding Gas | Mild steel Solid wire | Mild steel Cored wire | Aluminum | Copper | Stainless Steel |
| CO2 100% | ✔️ | ✔️ | ✔️ | ||
| Ar (75%) + CO2 (25) | ✔️ | ||||
| Ar 100% | ✔️ | ✔️ | |||
| Ar (95~98%) + O2 (2~5%) | ✔️ | ✔️ | |||
| He (75%) + Ar (25) | ✔️ | ✔️ |
Learn more about MIG Welding in Detail.
4. FCAW (Flux Cored Arc Welding) for Pipe Welding
1) Principle
By continuously supplied cored filler metal containing the flux, an arc is generated between the base metal and the filler metal. The heat of welding arc melts the filler wire and deposit in the weld.
Welding Slag is generated by the flux burning and same time welding shielding gases are produced by it to protect weld pool from oxidation.
2) Applicable current- polarity: DCEP(DCRP), DCEN(DCSP)
3) Characteristics
- By continuously supplying filler metal and protective gas, the welding rate is higher than that of SMAW.
- Automation can improve equipment utilization.
- It can be applied to various welding thicknesses. (Thick plate welding is possible).
- The equipment is complex and relatively expensive.
- Lower welding power than SMAW is required.
- Globular, spray depending on current, wire, diameter, and shielding gas
- Beads are beautiful and can be welded evenly.
- Additional weld cleaning time required for slag removal compared to MIG welding.
Device and principle diagram of Flux cored welding is given below.
Shielding gas and wire type for Flux cored welding
FCAW welding is used with two variants:
- With welding shielding gas,
- Without welding shielding gas- called gasless MIG.
- Shielding gas: with CO2 gas
- Wire type: Dual type (external CO2 gas, combustion gas by internal flux)
Learn more about FCAW welding in detail.
5. SAW (Submerged Arc welding) for Pipe Welding
1) Principle
The filler metal is continuously supplied to the welded joint to which the flux is applied, and an arc is generated between the filler metal and the base metal to weld the filler metal with this arc heat.
The molten slag functions as a shield from the atmosphere as well as addition of alloying elements to the weld.
2) Applicable Current- Polarity: AC, DCEP(DCRP)
3) Characteristics
- Since filler metal and flux are continuously supplied, the welding efficiency is high.
- No manual feeding of wire & work movement.
- Automated transfer devices are used, and equipment operation efficiency is high.
- Less welding fatigue and no welding gas is required.
- High welding skills are not required.
- Although the heat input is high, it is possible to form a uniform and smooth bead without spatter due to automated welding process.
- Tandem welding is possible using tandem saw. (High efficiency)
Learn more about SAW welding in detail.
