Welding Processes, Consumables and Parameter Control: Shielded Metal Arc Welding (SMAW)

Shielded Metal Arc Welding (SMAW) — The Original

Stick Welding: Still Essential

With SMAW, selecting the correct electrode for the application is the most important decision. For austenitic stainless or high-alloy steels, the electrode is first selected to match the mechanical and chemical requirements. Secondary requirements include welding position, penetration potential, deposition capabilities, and ease of slag removal.

Decoding the ANSI/AWS Standard

For SMAW electrodes, the classification code works as follows (example: E60XX):

• E = Low-carbon steel, metal arc welding electrode
• 60 or 70 = Approximate tensile strength of weld deposit in thousands of psi
• First of last two digits: Position usability (1 = all positions; 2 = flat/horizontal; 3 = flat only)
• Final digit (combined with above): Type of flux coating

Flux Coating Types and Characteristics:

AWS E60XX Electrodes

The E60XX electrodes provide welds with typical tensile strength of 58,000 to 65,000 lbf/in², depending on electrode type, base metal condition, chemistry, and weld dilution.

Characteristics of E60XX Electrodes (International Standards)

E6010/E6011 Electrode Sizes for Sheet Metal

Current Ranges for AWS E60XX Electrodes

Starting point rule: For sheet metal, start at the low end of the current range with electrodes 3/16 in. or smaller. For metals thicker than 10 gage, start in the center of the range. A high DC current may cause arc blow — switch to AC for improved results.

AWS E70XX Electrodes

Current Ranges for SMAW E70XX Electrodes

Characteristics of AWS E70XX Electrodes

Practical selection guide for E7018 vertical up welding:

• Plate 3/16 to 5/16 in. → 1/8 in. (3.2 mm) electrode
• Plate thicker than 5/16 in. → 5/32 in. (4 mm) electrode

For E7024 horizontal fillet welds:

• 10 gage material → 1/8 in. electrode
• Above 10 gage to 3/16 in. → 5/32 in. electrode
• 3/16 to 1/4 in. → 3/16 in. electrode
• Thicker than 1/4 in. → 1/4 in. electrode

Critical for low-hydrogen electrodes: Always follow manufacturers' instructions regarding storage to keep low-hydrogen electrodes free from moisture. Moisture in the electrode flux is one of the most common causes of hydrogen-induced cracking.

Gas Tungsten Arc Welding (GTAW) — Precision Incarnate

The Surgeon's Tool

GTAW (commonly called TIG welding) uses a nonconsumable tungsten electrode with a gas shield. Until the development of plasma arc welding, GTAW was the most versatile of all common manual welding processes.

The three primary considerations for any welding application:

1. Achieving a quality weld
2. Ease of welding
3. Cost

The logical approach: When several manual processes are available, first examine whether the job can be welded by GMAW or FCAW methods. Only when those options are inadequate does GTAW become the right choice.

GTAW Welding Current: Three Types, Three Purposes

A major benefit of GTAW compared with GMAW, FCAW, or SMAW is the highly concentrated, spatter-free, inert heat from the tungsten arc. GTAW can use three types of welding current:

DC Straight Polarity (DC−, Electrode Negative)

The most common GTAW current. The electrode connects to the negative terminal, the ground to positive. Electrons flow from the negative tungsten tip through the arc plasma to the positive workpiece.

What happens in the arc: When electrons collide with shielding gas molecules, they create plasma — a high-temperature, ionized, gaseous column. The electrons and plasma concentrate at the electrode tip (maximum pressure), then spread as they travel to the work. When electrons strike the work, they liberate significant heat.

Benefits:

• Maximum penetration potential
• Highest electrode current-carrying capacity
• Lowest electrode operating temperature
• Most of the arc heat is generated at the workpiece

DC Reverse Polarity (DC+, Electrode Positive)

The electrode connects to the positive terminal. Electrons flow from the negative work to the positive electrode.

The tradeoff: Approximately two-thirds of the heat is generated at the electrode tip, making it very hot even at low currents. DC+ requires large-diameter electrodes. At 100–150 amps, a ¼-in. (6.4 mm) electrode is needed — producing a weld puddle almost twice as wide as one from a 120-amp, 1/16-in. DC− electrode.

The benefit: Positive gas ions bombard and break up surface oxides on metals like aluminum and magnesium.

Alternating Current (AC)

Combines one half-cycle of straight polarity (penetration and heat) with one half-cycle of reverse polarity (oxide cleaning action). This is the method of choice for aluminum and magnesium welding.

The DC component problem: The surface oxides on aluminum and magnesium resist electron flow during the reverse-polarity half-cycle, creating a DC component that feeds back to the power source and may cause overheating. Power sources designed solely for SMAW must be derated for GTAW aluminum welding.

High frequency (HF) is essential with AC: To maintain arc stability when the reverse-polarity cycle is disrupted by aluminum oxide, high-frequency current assists arc ignition during each AC cycle.

• DC− welding of steels: Use HF arc start-only
• AC welding without oxide issues: HF arc start-only
• AC welding of aluminum, magnesium: HF continuous

Selecting the Tungsten Electrode Type

Use of the correct tungsten electrode composition is vital to good GTAW welds. Tungsten has the highest melting temperature of all metals.

Common Tungsten Electrode Compositions (AWS A5.12)

Electrode Selection in the supplied reference:

Electrode type characteristics:

• Pure Tungsten (EWP): Good AC arc stability. Low current capacity. Low contamination resistance. Good for low-amperage aluminum and magnesium. Risk of tungsten inclusions on medium-to-high current ferrous applications. Forms a desirable molten ball shape at tip during AC welding.
• Thoriated (EWTh): Higher melting temperature, ~50% more current capacity than pure tungsten. Superior arc starting and stability. First choice for critical DC applications. Tip should be ground to a tapered/fine point.
• Zirconiated (EWZr): Practical for critical applications. Less sensitivity to contamination. Superior current capacity vs. pure tungsten.

Current Ranges for GTAW Electrodes

Thoriated Electrodes (DC)

EWP and EWZr Electrodes (AC)

Recommendations for Welding Carbon, Low-Alloy, and Stainless Steels

Note: For stainless steel, reduce current by approximately 10%.

Recommendations for GTAW Welding of Aluminum (EWP, AC + HF)

Protecting and Prolonging Electrode Life

• Taper the tip per manufacturer's recommendations
• Provide preflow and postflow shielding gas coverage
• Use high frequency to avoid scratch starts (which contaminate the electrode)
• Employ the shortest possible electrode extension
• Never use a grinding wheel contaminated from other metals

Filler Metals for GTAW

AWS specifications for GTAW filler metals:

Non-negotiable: Filler metals must be kept dry and clean.

Shielding Gases for GTAW

Inert gases — primarily argon, and argon + helium mixtures — are used for GTAW. Helium provides greater thermal conductivity and additional arc voltage potential.

When to use argon + 30–75% helium:

• Manual welding of aluminum over 3/8 in. thick
• Mechanized welding of aluminum at high speeds
• Mechanized welding of carbon and stainless steels requiring good penetration
• Mechanized welding of stainless steel for penetration and speed
• Copper of 1/4 in. thickness and thicker

Gas purity requirements:

• Welding-grade argon: minimum 99.996% purity
• Helium: minimum 99.995% purity

Contamination test: With HF and power on, create an arc without welding and hold for ~30 seconds. Examine the electrode tip for unusual coloration, oxidation, or contamination — these indicate impure shielding gas.

Plasma Arc Welding (PAW) — GTAW Evolved

How Plasma Is Generated

When electric current passes between two electrodes through certain gases, molecular energy increases, collisions intensify, and binding forces between nuclei and electrons are exceeded. Electrons are released, creating an ionized gas capable of conducting electric current — this is plasma.

The PAW sequence:

1. Inert gas passes through the torch nozzle
2. High-frequency current creates a low-current pilot arc between the tungsten electrode (cathode) and the torch nozzle (anode)
3. The ionized path transfers from the electrode to the work
4. Preset plasma current is generated
5. Forcing ionized gas through the small nozzle orifice increases ionization and arc velocity
6. Arc temperatures between 30,000 and 50,000°F (16,650 and 27,770°C) are generated

PAW vs. GTAW: The Advantages

Compared with GTAW, plasma arc welding offers:

• Less sensitivity to arc length variations
• Superior low-current arc stability
• Greater potential tungsten electrode life
• Capability for single-pass, full-penetration welds on thick sections

Welding Gases for PAW

Plasma gas: Argon is preferred — easily ionized, sustains plasma at low voltage. The low thermal conductivity produces a concentrated hot core surrounded by a cooler outer zone.

Shielding gas protects the narrow plasma arc column and weld pool. Options include argon, argon + hydrogen, argon + helium, or argon + O₂ + CO₂, depending on material compatibility. Flow rates: 5 to 35 cu ft/h (2.4 to 17 l/min).

PAW Equipment

• Uses electrode negative (DCEN) polarity, 25–400 amps
• Solid-state inverter units with nonmechanical contactors available
• Contains HF generator, small DC power supply, gas mixture controls, torch coolant control
• Weld sequencer recommended (especially for keyhole mode)
• Torches are liquid-cooled using deionized water
• Electrodes: typically tungsten with 2% thorium

PAW Applications

Fusion welding is the primary application — high-volume, repetitive, high-duty cycle operations on lap, flange, butt, and corner welds in all positions.

Low-current plasma fusion welding (below 1 amp): Ideal for metals down to 0.001 in. (0.025 mm) thickness. The pilot arc allows consistent arc starts with currents less than 1 amp, providing improved stability and reduced sensitivity to torch-to-workpiece distance.

Keyhole welding: Most metals that can be GTAW welded can be PAW keyhole welded (except aluminum, which requires variable polarity). Typical operation: square-butt welds in steel of 0.09 to 0.375 in. thickness with 100% penetration in a single pass.

Welding Aluminum with PAW

The Variable Polarity Plasma Arc (VPPA) process was developed for metals with oxide skins (primarily aluminum).

Typical VPPA cycle:

• 20 ms pulse of electrode negative (welding) polarity
• 3 ms pulse of electrode positive (cleaning) polarity
• Positive pulse set 30–80 amps higher than the negative pulse

This allows single-pass, square-groove, full-penetration welds in aluminum up to ½ in. (12.7 mm) thick with extremely low levels of porosity.

Plasma Arc Surface Coating

Beyond welding, plasma arcs can deposit coatings of metals, ceramics, and other materials onto workpiece surfaces for wear resistance, corrosion resistance, or thermal protection.

Plasma Arc Cutting

The plasma arc cutting process uses a high-velocity gas jet at temperatures of 20,000–50,000°F to sever metals. It is effective for cutting any electrically conductive material, including stainless steels, aluminum, and copper that resist oxy-fuel cutting.

Precision plasma arc cutting uses a magnetic field to stabilize the arc via Lorentz forces, causing it to spin faster and tighter. This produces a narrower kerf without reducing cutting speed, with results comparable to laser cutting.

Electron-Beam (EB) Welding — The Ultimate Precision

How It Works

Heat for melting is obtained by:

1. Generating electrons
2. Concentrating them into a beam
3. Accelerating them to 30–70% of the speed of light using voltages of 25–200 kV

Power specifications:

• ~6.3 × 10¹⁵ electrons/second in a 1 mA current stream
• Beam diameters: 0.01 to 0.03 in. (0.25 to 0.76 mm)
• Beam power: up to 100 kW
• Power density: up to 10⁷ W/in² (1.55 × 10⁴ W/mm²) — higher than most arc welding

At these power densities, an electron beam can penetrate steel up to 4 inches thick and form a vapor capillary or "keyhole."

Vacuum Requirements

The process is most efficient at high vacuum levels (10⁻⁶ to 10⁻³ torr):

• High vacuum: Narrowest width, deepest penetration, minimum contamination
• Partial vacuum: Compromise between quality and workpiece size constraints
• Atmospheric pressure: Requires beam-accelerating voltages above 150 kV, gun-to-work distance less than ~1.5 in.

What EB Welding Can Join

Carbon, low-alloy, and stainless steels; high-temperature and refractory alloys; copper and aluminum alloys. Single-pass, square butt welds in materials up to 1 in. thick at good speeds with 60 kW nonvacuum equipment. Dissimilar metals can usually be welded without problems.

Cautions:

• Edges require precision machining for good alignment and minimum gap
• Rapid solidification causes cracking in certain materials (e.g., low-ferrite stainless steel)
• Radiation shields are essential for worker safety (X-rays are generated)
• Adequate ventilation is required to remove ozone and other gases

Weld and Welding Symbols — The Universal Language

Why Symbols Matter

Graphical symbols for welding provide a complete means of conveying welding information from designer to welder by means of drawings. Governed by ANSI/AWS A2.4, these symbols are the international language of welding communication.

Critical distinction: A weld symbol is an ideograph indicating the type of weld desired. A welding symbol is a complete symbol made of up to eight elements conveying explicit welding instructions.

The Eight Elements of a Welding Symbol

1. Reference line — The basis of the entire symbol. All other elements are oriented to this line.
2. Arrow — Connects the reference line to one side of the joint (the "arrow side"). The opposite side is the "other side."
3. Basic weld symbols — Placed on the reference line to indicate weld type.
4. Dimensions and other data — Size, length, spacing of welds.
5. Supplementary symbols — Weld-all-around, field weld, contour symbols.
6. Finish symbols — Contour requirements (flush, convex, concave).
7. Tail — Contains specification, process, or other reference information.
8. Specification/process reference — Detailed instructions in the tail.

Basic Weld Symbols

Groove Weld Symbols:

Other Weld Symbols:

Supplementary Symbols:

Reading Welding Symbols: Placement Rules

• Welds on the arrow side of the joint → Symbol placed on the lower side of the reference line (toward the reader)
• Welds on the other side of the joint → Symbol placed on the upper side of the reference line (away from the reader)
• Welds on both sides → Symbols on both sides of the reference line

Welding Codes, Rules, Regulations, and Specifications

Codes recommending procedures for welding various structures are established by societies, institutes, bureaus, and associations worldwide. Key organizations include:

Letter Designations for Welding Processes (ANSI/AWS A2.4)

A comprehensive selection of the most common designations:

Pipe Welding — Where Precision Meets Pressure

The Challenge of Pipe Welding

Pipe welding is commonly performed manually, either with the pipe joint stationary (requiring the welder to work in all positions) or held in a rotation fixture to keep the weld in the flat position. Field welding of stationary pipe demands proficiency in all four basic positions:

Critical Setup Parameters

For satisfactory pipe welding, you must consider:

• Chemical composition and thickness of the metal
• Electrode material composition and size
• Current, voltage, and wire feed rate
• Joint preparation and edge beveling
• Fixturing and tack welds

Tack welds: High-quality tacks, each about 1.5 inches (38 mm) long and projecting about 1/16 in. (1.6 mm) beyond the inner wall, hold the assembly in position during welding.

The Transition from SMAW to MIG in Pipe Welding

SMAW was used almost exclusively for pipe welding until MIG welding arrived with its far greater deposition rates. Practices suitable for SMAW cannot be transferred to MIG welding — greater expertise is required.

Wire feeder sensitivity: An increase of one increment on the dial (e.g., from 9 to 10 o'clock position) can increase wire feed by 70 in./min. That single adjustment can raise current from 110 to 145 amps and voltage by 1 volt — a 40% increase in energy to the weld.

Wire stick-out sensitivity: In low-parameter, short-circuit welding, a small change in wire stick-out can alter weld energy by 20 to 30%.

The Root Pass: The Most Critical Weld

The root pass determines the degree of weld penetration and affects the amount of lack-of-fusion in the finished weld. During the root pass, the arc should reshape the gap between joint sides into a pear-shaped "keyhole" that is continuously filled on the trailing side.

MIG short-circuit root weld specifications for carbon steel pipe:

Use of Flux-Cored Electrodes in Pipe Welding

Flux-cored E71T-1, 0.035-in. diameter wire provides a continuous, medium-energy, open arc with a practical current range of 135 to 165 amps — similar to optimum MIG short-circuit range but 25–30% less current than minimum open-arc spray transfer.

FCAW advantages for pipe:

• Open arc with no short circuits — continuous arc energy
• Broader weld metal coverage from tubular wire periphery and center
• Higher current density (less cross-sectional area due to flux core) = improved penetration
• Slag serves as a mold to hold fluid metal in vertical-up and overhead positions
• Less operator skill required
• Fill passes completed in 30–50% less time than MIG short circuit or SMAW

Best practice: When FCAW is used for fill passes, use MIG short-circuit welding for the root to reduce the possibility of slag entrapment.

Pipe Welding Procedure: Thick-Walled Carbon Steel

Root welding (MIG short circuit):

• Wire feed: 200–230 in./min
• Current: 125–135 amps
• Voltage: 19–22 volts
• Optimum starting point: 210 in./min (~130 amps, 21–22 volts)
• Electrode stick-out: ½ to 5/8 in.
• Contact tip: Flush with nozzle end
• Fine-tune voltage by listening for a consistent rapid crackle sound

Thin-Walled Carbon Steel Pipes

The fill and cover pass sequence:

1. Remove MIG surface slag islands between passes
2. No fill pass thicker than 1/8 in. (3 mm)
3. Use straight weave across the root face
4. At the bevel, use a slight upward motion (no greater than wire diameter)
5. Use a slight back step for added bevel fusion and to avoid undercut
6. For the cover pass, leave 1/32 to 1/16 in. of groove depth for optimum profile

Multi-pass circumference sequence (for larger pipe diameters):

1. First pass: 7 to 4 o'clock position (start with slight forehand angle)
2. Second pass: 10 to 1 o'clock position (grind stops/starts for at least 1 in.)
3. Third pass: 4 to 1 o'clock position
4. Fourth pass: 7 to 10 o'clock position

Nondestructive Testing (NDT) — Trust, But Verify

What NDT Does

Nondestructive testing examines a component or assembly — usually for surface or internal cracks or other nonhomogeneities — to determine structure or measure thickness by means that will not impair its intended use.

The NDT Methods

NDT Symbol Application (ANSI/AWS 2.4-79)

NDT symbols follow a structure parallel to welding symbols:

Testing symbol elements:

• Reference line
• Arrow (connects to part being tested)
• Basic testing symbol
• Test-all-around symbol
• (N) Number of tests
• Test in field indicator
• Tail (specification or other reference)

Placement rules:

• Tests on the arrow side → Symbol on the lower side of the reference line
• Tests on the other side → Symbol on the upper side of the reference line
• Tests on both sides → Symbols on both sides

When specifying a certain length to test, the actual length or percentage is shown to the right of the basic test symbol. The number of tests on a joint is shown in parentheses.

NDT and welding symbols can be combined on the same reference line, providing a complete fabrication and inspection callout in a single drawing notation.

Engineering takeaway

You now have in your hands the most comprehensive single-source reference for production arc welding that exists in this format. But knowledge without application is just trivia.

Here is your action plan:

If you are a beginner: Start with GMAW. Master the 0.035-in. electrode on sheet steel. Learn to set parameters by sound. Then progress to the 0.045-in. electrode for thicker materials. Only after GMAW feels natural should you move to FCAW and SMAW.

If you are experienced: Audit your current electrode selections against the deposition rate tables above. Are you using the optimal diameter? Are you running at 60–80% of the electrode's current capability? If not, you are leaving money on the table every hour of every shift.

If you are a shop owner or manager: Print the deposition rate tables. Post them at every welding station. The difference between a 0.035-in. and a 0.045-in. electrode on ¼-in. steel is a 30% reduction in labor cost per unit of weld deposited. Multiply that across every welder, every shift, every year.

If you are specifying welds: Learn the symbol system. A properly specified welding symbol eliminates ambiguity, prevents rework, and protects structural integrity. One misread symbol can mean the difference between a weld that lasts a century and one that fails under first load.

The question that separates professionals from amateurs is not "Can you weld?" — it is "Can you weld the right process, with the right electrode, at the right parameters, in the right position, on the right material, every single time?"

Now you can.

Bookmark this guide. Reference it before every new project. Share it with every welder who has ever struggled with porosity, spatter, rework, or wasted consumables. The information above does not expire — it is as valid today as it will be a hundred years from now, because the physics of the arc does not change.