Welding Process Selection Guide — Which Process to Use and Why
Introduction
Choosing the correct welding process is one of the most important technical decisions in any metalworking project. There is no universal process — each one has its advantages, limitations and ideal applications. A qualified welder must understand which process to use for each material, thickness and type of application.
This guide presents the five most widely used fusion welding processes in industry, systematically comparing them in terms of compatible materials, thickness ranges, welding positions, deposition rate, typical industries and selection criteria.
---
Overview — Comparison of the 5 Main Processes
| Feature | SMAW/MMA 111 | MIG 131 | MAG 135 | FCAW 136 | TIG/GTAW 141 | SAW 121 |
|---|---|---|---|---|---|---|
| ISO 4063 Standard | 111 | 131 | 135 | 136 | 141 | 121 |
| Electrode type | Coated (consumable) | Continuous solid wire | Continuous solid wire | Continuous flux-cored wire | Tungsten (non-consumable) | Solid wire + granular flux |
| Shielding | Coating gases | Inert gas (Ar, He) | Active gas (CO₂, Ar+CO₂) | Internal flux ± gas | Inert gas (Ar, He, Ar+He) | Granular flux |
| Current | DC+, DC−, AC | DC+ | DC+ | DC+, DC− | DC−, AC (Al) | DC+, AC |
| Automation | Manual | Semi-auto / auto / robotic | Semi-auto / auto / robotic | Semi-auto / auto | Manual / auto / orbital | Automatic |
| Duty cycle | 25-30% | 60% | 60% | 50-60% | 15-25% | 90-100% |
---
Compatible Materials by Process
The compatibility between process and base material is determined by metallurgy, chemical reactivity and the type of shielding required.
| Material | SMAW 111 | MIG 131 | MAG 135 | FCAW 136 | TIG 141 | SAW 121 |
|---|---|---|---|---|---|---|
| Carbon steel (S235, S355) | ✅ Excellent | ❌ | ✅ Excellent | ✅ Excellent | ✅ Good (slow) | ✅ Excellent |
| Low alloy steel (Cr-Mo) | ✅ Good | ❌ | ✅ Good | ✅ Good | ✅ Excellent | ✅ Good |
| Stainless steel (304, 316) | ✅ Good | ✅ Good (Ar+He) | ✅ Good (Ar+CO₂ 2%) | ✅ Good | ✅ Excellent | ✅ Good |
| Duplex stainless steel | ⚠️ Limited | ✅ Good | ⚠️ Limited | ⚠️ Limited | ✅ Excellent | ⚠️ Limited |
| Aluminium and alloys (5xxx, 6xxx) | ❌ | ✅ Excellent | ❌ | ❌ | ✅ Excellent (AC) | ❌ |
| Copper and alloys | ❌ | ✅ Good (He) | ❌ | ❌ | ✅ Excellent | ❌ |
| Nickel and alloys (Inconel) | ✅ Good | ✅ Good | ❌ | ✅ Good | ✅ Excellent | ⚠️ Limited |
| Titanium and alloys | ❌ | ✅ (inert chamber) | ❌ | ❌ | ✅ Excellent (chamber) | ❌ |
Fundamental rule: Reactive materials (aluminium, titanium, magnesium, copper) require full inert shielding — only MIG 131 and TIG 141 are applicable. Active gases (CO₂) cause undesirable chemical reactions in these materials. MAG 135 and FCAW 136 are exclusive to ferrous materials.
---
Thickness Ranges by Process
Base material thickness is one of the most decisive criteria in process selection.
| Process | Minimum thickness | Optimum range | Maximum thickness | Notes |
|---|---|---|---|---|
| SMAW 111 | ~1.5 mm (ø1.6 mm) | 3-50 mm | No theoretical limit | Multi-pass for high thicknesses. Versatile but slow. |
| MIG 131 | 0.5 mm (short-circuit) | 1-12 mm | ~25 mm | Excellent for thin aluminium and stainless steel sheets. |
| MAG 135 | 0.8 mm (short-circuit) | 2-30 mm | ~50 mm | Above 50 mm, high risk of lack of fusion. |
| FCAW 136 | 1.5 mm | 4-40 mm | ~75 mm | Superior to MAG at medium-high thicknesses. Greater penetration. |
| TIG 141 | 0.3 mm | 0.5-6 mm | ~12 mm | Above 6 mm, becomes slow and uneconomical. Used as root pass. |
| SAW 121 | 5 mm | 10-100+ mm | No practical limit | High deposition. Flat and horizontal-vertical positions only. |
Practical note: In thick joints (>20 mm), it is common to combine processes. The root pass is frequently made with TIG 141 (quality and full penetration) and the fill passes with MAG 135 or SAW 121 (productivity). This combination is covered by ISO 15614-1 as a mixed welding procedure.
---
Welding Positions by Process
Not all processes work in every position. Positional capability directly influences process choice based on joint geometry and site conditions.
| Position (ISO 6947) | SMAW 111 | MIG 131 | MAG 135 | FCAW 136 | TIG 141 | SAW 121 |
|---|---|---|---|---|---|---|
| PA — Flat | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| PB — Horizontal (fillet) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| PC — Horizontal (butt) | ✅ | ✅ | ✅ | ✅ | ✅ | ⚠️ Limited |
| PD/PE — Overhead | ✅ | ✅ | ✅ | ✅ | ✅ | ❌ |
| PF — Vertical up | ✅ | ✅ | ✅ | ✅ | ✅ | ❌ |
| PG — Vertical down | ✅ (cellulosic) | ⚠️ | ⚠️ | ✅ (rutile) | ⚠️ | ❌ |
| H-L045 / J-L045 — Pipe 6G | ✅ | ✅ | ✅ | ✅ | ✅ | ❌ |
SAW 121 is the only process restricted to flat and horizontal positions, because the granular flux is deposited by gravity and does not adhere in vertical or overhead positions.
---
Industries and Typical Applications
| Industry / Application | Dominant processes | Reason for choice |
|---|---|---|
| Structural steelwork (buildings, bridges) | MAG 135, FCAW 136 | High productivity, medium thicknesses, controlled costs |
| General fabrication (gates, railings, handrails) | MAG 135, SMAW 111 | Versatility, thin to medium sheets, mobility |
| Industrial piping (oil & gas, petrochemical) | TIG 141 (root) + SMAW 111 or MAG 135 (fill) | Full root penetration, radiographic quality required |
| Shipbuilding (hulls, decks, superstructure) | FCAW 136, SAW 121, MAG 135 | Thick sections, productivity, diverse positions |
| Automotive (body panels, chassis) | MIG 131, MAG 135 (robotic) | High speed, thin sheets, full automation |
| Food and pharmaceutical | TIG 141 (orbital) | Stainless 304L/316L, sanitary welds, zero porosity |
| Pressure vessels and boilers (ASME, PED) | SMAW 111, TIG 141, SAW 121 | Certified quality, 100% radiography, multi-pass |
| Maintenance and repair (site, field) | SMAW 111 | Total mobility, no shielding gas, works outdoors |
| Aerospace | TIG 141 (inert chamber) | Titanium alloys, Inconel, extreme quality |
| Wind energy (towers, flanges) | SAW 121, MAG 135 | Thick sections (up to 150 mm), high deposition |
| Aluminium fabrication (tanks, cisterns, facades) | MIG 131, TIG 141 | Only options for aluminium — 100% inert shielding |
---
Deposition Rate and Productivity
| Process | Typical deposition rate | Consumable efficiency | Relative cost per metre |
|---|---|---|---|
| SMAW 111 | 1-3 kg/h | 55-70% (stub + coating losses) | High (slow, low efficiency) |
| MIG 131 | 1.5-5 kg/h | 95-98% | Medium |
| MAG 135 | 1.2-5 kg/h | 93-98% | Medium-low |
| FCAW 136 | 2-7 kg/h | 80-88% | Medium |
| TIG 141 | 0.2-1.5 kg/h | 95-100% | Very high (slow) |
| SAW 121 | 5-20+ kg/h | 98-99% | Low (high volume) |
---
Selection Criteria — Decision Tree
1. Base material — The material automatically eliminates incompatible processes. Aluminium or titanium rule out MAG, FCAW and SAW.
2. Thickness — Thin sheets (<3 mm) favour TIG or MIG in short-circuit mode. Medium thicknesses (3-30 mm) are MAG and FCAW territory. High thicknesses (>30 mm) point to SAW, FCAW or combinations.
3. Welding position — If the joint is overhead or vertical, exclude SAW. For 6G pipe, TIG+SMAW or TIG+MAG are the standard combinations.
4. Quality requirements — 100% radiography or nuclear/aerospace applications favour TIG. Standard structural applications accept MAG or FCAW with visual and NDT inspection.
5. Required productivity — High-volume welding in flat position points to SAW. Robotic series production points to MAG or MIG.
6. Working conditions — Outdoor site work without wind protection favours SMAW 111 (no external gas) or self-shielded FCAW (FCAW-S 114). Gas-shielded processes are sensitive to draughts.
7. Cost — SMAW 111 has the cheapest equipment but lowest productivity. MAG 135 typically offers the best cost/benefit in workshop environments. SAW 121 requires high investment but pays off in large production runs.
---
Process Combinations
| Combination | Application | Advantage |
|---|---|---|
| TIG 141 (root) + MAG 135 (fill) | Piping, pressure vessels | Perfect root + fast filling |
| TIG 141 (root) + SMAW 111 (fill) | Offshore piping, boilers | Perfect root + site versatility |
| TIG 141 (root) + FCAW 136 (fill) | Shipbuilding, heavy structures | Perfect root + high positional deposition |
| MAG 135 (root + fill) + SAW 121 (cap) | Beams, wind towers, bridges | MAG flexibility + SAW speed in flat position |
| SMAW 111 cellulosic (root) + SMAW 111 basic (fill) | Pipelines (downhill) | Cellulosic for penetration, basic for toughness |
---
Quick Summary — When to Use Each Process
| If you need to... | Use... |
|---|---|
| Weld outdoors, on site, without three-phase power | SMAW 111 |
| Robotic series production of steel | MAG 135 |
| Weld aluminium, copper or titanium | MIG 131 or TIG 141 |
| Sanitary welds on food-grade stainless steel | TIG 141 orbital |
| Maximum deposition in flat position | SAW 121 |
| Positional welding of thick sections | FCAW 136 |
| Perfect root pass with full penetration | TIG 141 |
| Fast fill after TIG root | MAG 135 or FCAW 136 |
| Emergency maintenance in the factory | SMAW 111 |
| Thin stainless steel sheets without distortion | TIG 141 (pulsed) |
---
Reference Manufacturers
Leading welding equipment and consumable manufacturers worldwide: Lincoln Electric, ESAB, Fronius, Kemppi, Miller, voestalpine Böhler Welding. Shielding gases: Air Liquide, Linde.
---
*Article based on EWE/IWE modules 1.7-1.12 (AWS Welding Handbook), ISO 4063 (process classification), ISO 15614-1 (procedure qualification), AWS Welding Handbook Volumes 1-3. Published at WeldFC Academy — the technical reference in metalworking.*