GTAW NC II cheat sheet

OHS duties follow the hierarchy of controls: eliminate the hazard, substitute, engineer controls (fume extraction, screens), then administrative controls and PPE last.

GTAW arc produces ozone and nitrogen oxides; welding fume is a Group 1 carcinogen per IARC, so local exhaust ventilation or supplied-air respiratory protection is required in confined or poorly ventilated spaces.

Hot work permit is required before any arc strike outside a designated welding area; the permit verifies fire watch, 11 m (35 ft) combustible clearance, and extinguisher availability.

Arc-eye (photokeratitis) is caused by UV exposure; shade number for GTAW at 50-200 A is typically shade 10-11, and higher current or larger electrodes require a higher shade.

Confined-space entry requires atmospheric testing (oxygen 19.5-23.5%, LEL below 10%, H2S/CO within limits), an attendant, and a rescue plan before entry.

Cylinder handling: acetylene cylinders are stored upright, argon cylinders are secured upright with valve caps fitted during transport; oil or grease must never contact oxygen fittings.

Electric shock risk is highest with high-frequency start and wet conditions; dry insulation, intact torch body, and a work-return clamp bonded directly to the workpiece reduce the hazard.

PPE for GTAW: flame-resistant clothing, leather gauntlets, welding helmet with correct filter, safety glasses under the helmet, and hearing protection where noise exceeds 85 dB(A).

Environmental controls: collect grinding dust and tungsten dust separately, dispose of thoriated tungsten as low-level radioactive waste per local rules, and segregate metal scrap for recycling.

The reference line is the horizontal line in a welding symbol; the arrow line points to the joint, and the tail holds the process reference (e.g., GTAW) or specification number.

Symbols below the reference line mean weld on the arrow side; symbols above the line mean weld on the other side; symbols on both sides mean weld on both sides.

A fillet weld size is written to the left of the fillet symbol and a length-pitch value to the right (e.g., 6-50/100 means 6 mm leg, 50 mm weld length, 100 mm pitch).

A groove symbol with no size shown is a full-penetration groove weld; the size is only given for partial penetration.

Supplementary symbols: a circle at the junction means weld all around, a flag means field weld, and a filled-in tail or note governs the applicable specification.

A number in the tail or a note may cite a WPS/PQR; the drawing governs geometry and the WPS governs current, gas, and technique.

The standard drawing units and tolerance block must be read before dimensioning; a weld length tolerance of +/- 5 mm is common but always per the drawing's own title block.

A double-sided V-groove symbol with an arrow side and other side indicates two separate bevels; a single-bevel symbol with a break in the line denotes a partial joint penetration detail.

For pipe drawings, the isometric shows spool numbers, joint numbers, and weld symbols; joint numbers must match the weld map used for traceability.

Carbon steel: grind or wire-brush the joint and 25 mm each side to bare metal to remove mill scale, rust, oil, and moisture before welding.

Stainless steel: use dedicated stainless brushes and grinding discs never used on carbon steel; iron contamination causes rust bloom and localized corrosion.

Aluminum: remove the oxide layer with a dedicated stainless brush or carbide burr immediately before welding (oxide melts near 2072 degC versus 660 degC for aluminum), and degrease with acetone.

Tungsten preparation: grind electrode longitudinally on a dedicated diamond wheel; a 2.4 mm electrode is typically pointed to about 30-60 degrees included angle for DCEN work, and balled for AC aluminum work.

Backing and purging: stainless and reactive metals need argon purge on the root side; a soluble or ceramic backing may be used where purge is impractical.

Fit-up: check root gap, land, and bevel angle with a gap gauge and bevel protractor; typical V-groove bevel is 30 degrees per side (60 degrees included) with a 1.5-2.5 mm root gap.

Equipment check before use: verify gas flow with a flowmeter (typically 8-15 L/min), check torch cable and collet body condition, and confirm work-return clamp connection to bare metal.

Work area: clear combustibles within 11 m (35 ft), set up screens to protect others from arc and UV, and verify the welding machine is grounded and the polarity switch is set for the process.

DCEN (electrode negative) puts about 70% of heat into the work and is used for carbon steel, stainless steel, and titanium; it gives deep penetration and a stable arc.

DCEP puts most heat into the electrode and is rarely used alone; AC alternates and is the standard for aluminum because the positive half-cycle breaks the oxide while the negative half cools the tungsten.

Constant-current (drooping) power source is required for GTAW; the drooping volt-ampere curve limits current changes when arc length varies.

High-frequency (HF) start ionizes the gas gap without touching the work, avoiding tungsten contamination and weld-mark defects; touch-start is only acceptable when the WPS permits it.

Pulse GTAW alternates peak and background current; it reduces heat input and distortion on thin sheet and improves out-of-position control on pipe.

Typical DCEN parameters for carbon steel: 1.6 mm tungsten at 60-100 A, 2.4 mm at 100-160 A; argon flow 8-12 L/min; electrode extension about 3-6 mm.

Typical AC parameters for aluminum: 2.4 mm tungsten at 120-180 A on 3-6 mm plate; balance control shifted toward cleaning (about 30-40% DCEP) for heavily oxidized surfaces.

Heat input (kJ/mm) = (voltage x current x 60) / (travel speed in mm/min x 1000); record it where the WPS specifies a maximum.

Argon is standard shielding gas; helium or argon-helium mixes increase heat input for thick aluminum and copper, and 1-2% hydrogen additions are used only on austenitic stainless steel per WPS.

Carbon steel root pass: use a small-diameter electrode, tight arc, and controlled keyhole; back-purge is not needed but a slight root gap with a consumable insert can improve consistency.

Stainless steel: keep interpass temperature below 150 degC (or per WPS) and use low heat input to avoid sensitization and chromium carbide precipitation in the 425-870 degC range.

Austenitic stainless steel needs argon or argon-hydrogen purge on the root side; oxygen content in the purge should be below 0.1% to prevent sugaring (oxidation) on the root.

For 6G pipe, the welder rotates around a fixed pipe; position progression from 6 o'clock upward controls gravity effects, and the arc is kept short to prevent sagging.

Filler metal selection: ER70S-2 or ER70S-6 for carbon steel; ER308L for 304/304L and ER316L for 316/316L stainless steel, matched to the base metal and WPS.

Weave width should be limited to about three times the electrode diameter; a wide weave overheats the base metal and increases distortion.

Crater treatment: taper current with the slope-out control and add a small amount of filler to avoid crater cracks, especially in stainless steel.

Distortion control: use balanced welding sequence, back-step technique, and tack welds that are later consumed by the root pass.

Aluminum conducts heat about five times faster than steel and has no color change on heating; use a heat-input ramp and watch the puddle, not the metal color.

AC is standard for aluminum; the cleaning (DCEP) portion of the cycle removes the aluminum oxide, and the balance control sets the proportion of cleaning versus penetration.

Tungsten for AC aluminum is usually balled or a zirconiated (EWZr) or lanthanated (EWLa) electrode is used; pure tungsten (EWP) is traditional for AC but has lower current capacity.

Filler for aluminum: ER4043 (5% Si) for 6061 general work, ER5356 (5% Mg) for higher strength and anodized parts; never use ER5356 where service temperature exceeds about 65 degC.

Preheat is often required for thick aluminum sections (above about 6 mm); preheat temperature is typically 90-150 degC and must be controlled to avoid loss of temper.

Copper and copper alloys need high heat input and often helium-rich shielding gas; preheat is common and the puddle must be watched for zinc or lead fume if brazing alloys are present.

Titanium and reactive metals require a trailing shield and full inert gas coverage until the weld cools below about 425 degC; any color other than silver or light straw indicates contamination.

Magnesium requires high-frequency AC and careful fire control; magnesium chips and dust are flammable and must not be extinguished with water.

Visual inspection (VT) is the first test; it detects undercut, overlap, spatter, incomplete fusion at the surface, and crater cracks before any NDT.

Porosity appears as rounded dark spots on a radiograph or as gas holes on a fracture surface; causes include moisture, oil, drafts, and insufficient gas flow.

Tungsten inclusion shows as a high-density white spot on a radiograph; it is caused by dipping the electrode into the puddle or by touch-start.

Incomplete fusion (lack of fusion) appears as a linear indication on RT or UT and is caused by insufficient heat input, wrong travel angle, or inadequate cleaning.

Undercut is measured against the acceptance criteria; for many structural codes, undercut deeper than 0.8 mm or longer than 25 mm in a 300 mm length is rejectable.

Liquid penetrant testing (PT) detects surface-breaking defects in non-porous materials; it cannot detect subsurface defects and requires cleaning before and after.

Radiographic testing (RT) detects volumetric and planar internal defects; ultrasonic testing (UT) is better for planar defects such as lack of fusion in thick sections.

Correction: grind out a defect to sound metal, verify with PT, and reweld per the repair WPS; the number of repairs may be limited by the applicable code.

A WPS (welding procedure specification) lists the variables: process, base metal, filler, current type and range, gas, and technique; the welder must work within its qualified ranges.

A PQR (procedure qualification record) documents the test that qualified the WPS, including test results and essential variables.

A welder performance qualification (WPQ) records the welder's name, test joint type, position, thickness range, and date; requalification is required after a lapse (commonly 6 months) or a change in essential variables.

The weld map or joint log ties each joint number to the welder, WPS number, date, and NDT result for traceability.

Travel speed, current, voltage, and heat input should be recorded per pass or per joint where the WPS specifies limits; heat input is often a required record.

Consumable records: filler lot numbers, gas cylinder lot, and tungsten type are recorded when the specification requires material traceability.

Nonconformance reports (NCR) record the defect, disposition (repair, rework, or accept by concession), and the corrective action taken.

Final documentation package typically includes the WPS, PQR, WPQ, weld map, NDT reports, and the inspection and test plan (ITP) sign-offs.