GTAW NC II flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hierarchy of controls

A ranked order of hazard controls: elimination, substitution, engineering controls, administrative controls, and PPE last. Used to select the most effective protection against welding fume, arc radiation, and noise.

Hot work permit

A written authorization required before arc welding outside a designated area. It verifies combustible clearance, fire watch, extinguisher availability, and ventilation before any arc is struck.

Shade number for GTAW

The helmet filter darkness rating. For GTAW at 50-200 A, shade 10-11 is typical; higher current or larger electrodes require a higher shade to prevent arc-eye.

Confined space atmospheric limits

Entry requires oxygen between 19.5% and 23.5%, flammable gas below 10% of the lower explosive limit, and toxic gases within exposure limits, tested before entry and monitored during work.

Thoriated tungsten disposal

Thoriated tungsten contains a low-level radioactive additive and must be collected and disposed of under local radioactive waste rules, not mixed with general metal scrap.

Arrow side and other side

On a welding symbol, a weld symbol below the reference line means the arrow side of the joint; a symbol above the line means the other side.

Weld all around symbol

A small circle placed at the junction of the arrow line and reference line. It directs the welder to apply the weld continuously around the entire joint perimeter.

Fillet weld size notation

The leg size is written to the left of the fillet symbol and the length and pitch to the right. For example, 6-50/100 means a 6 mm leg, 50 mm long welds on a 100 mm pitch.

Groove weld without size

When a groove weld symbol shows no size, the weld is full penetration. A size is shown only when the drawing calls for partial joint penetration.

Tail of welding symbol

The fork-shaped end of the reference line that carries the process reference, specification number, or WPS number governing the weld, such as GTAW or a procedure code.

Aluminum oxide removal

Aluminum oxide melts near 2072 degC while aluminum melts near 660 degC, so the oxide must be removed by a dedicated stainless brush or carbide burr immediately before welding.

Stainless steel contamination control

Stainless steel must be cleaned and ground only with brushes and discs reserved for stainless. Carbon steel contamination causes rust bloom and localized corrosion in service.

Electrode grinding direction

Tungsten electrodes are ground longitudinally along the axis on a dedicated diamond wheel. Grinding across the axis creates arc wander and an unstable arc.

Root purge for stainless

The root side of stainless steel is purged with argon to displace oxygen before welding. Oxygen below 0.1% prevents sugaring, an oxidized and brittle root surface.

Typical V-groove bevel

A common plate preparation is 30 degrees bevel per side, giving 60 degrees included, with a root gap of about 1.5-2.5 mm and a small land.

DCEN heat distribution

With the electrode negative, about 70% of the arc heat enters the workpiece. DCEN gives deep penetration and is used for carbon steel, stainless steel, and titanium.

AC for aluminum

Alternating current alternates polarity. The positive half-cycle breaks the aluminum oxide while the negative half-cycle limits tungsten heating and provides penetration.

Drooping characteristic

A power source volt-ampere curve in which voltage falls steeply as current rises. Constant-current GTAW machines use it so arc-length changes do not cause large current swings.

High-frequency arc start

A high-voltage, high-frequency pulse ionizes the gas gap so the arc starts without touching the tungsten to the work, preventing tungsten inclusions and start marks.

Heat input formula

Heat input in kJ/mm equals voltage times current times 60, divided by travel speed in mm per minute times 1000. Recorded when the WPS sets a maximum.

Pulse GTAW

The current alternates between a peak and a background level. Pulsing lowers average heat input, reduces distortion on thin sheet, and improves out-of-position control.

Stainless sensitization range

Austenitic stainless steel held in the 425-870 degC range can precipitate chromium carbides, depleting chromium at grain boundaries and reducing corrosion resistance. Interpass temperature is limited to avoid it.

Stainless sugaring defect

A rough, oxidized, dark root surface caused by oxygen reaching the molten root. Prevented by an argon purge on the root side before and during welding.

Filler for 304 stainless

ER308L is the usual filler for 304 and 304L stainless steel. The L designation indicates low carbon, which improves resistance to sensitization in the weld.

6G pipe position

A pipe fixed at a 45-degree angle, welded all around. The welder progresses upward from the 6 o'clock position, controlling gravity with a short arc and controlled keyhole.

Weave width limit

Oscillation of the torch across the joint should stay within about three times the electrode diameter. Wider weaving overheats the base metal and increases distortion and hot cracking.

ER5356 service limit

ER5356 aluminum filler contains 5% magnesium and should not be used where service temperature exceeds about 65 degC because of reduced corrosion resistance at elevated temperature.

Aluminum heat indicator

Aluminum shows no color change as it heats. The welder judges heat by puddle formation and by a heat-input ramp rather than by metal color.

Titanium shielding requirement

Titanium welds must be shielded by inert gas until they cool below about 425 degC. Any color other than silver or light straw indicates contamination and possible rejection.

Tungsten inclusion indication

On a radiograph, a tungsten inclusion appears as a small, very bright high-density spot. It is caused by dipping the electrode into the puddle or by touch-starting.

Liquid penetrant testing

A surface NDT method that draws penetrant from surface-breaking defects. It cannot detect subsurface defects and requires cleaning before application and after inspection.

Weld map traceability

A joint-by-joint record linking each weld number to its welder, WPS, date, and inspection result. It supports traceability and repair history for the final documentation package.