GMAW NC II flashcards

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

Hierarchy of control

Ranking of hazard controls from most to least effective: elimination, substitution, engineering controls, administrative controls, and PPE. PPE is the last barrier and never the primary control for welding fume.

Argon asphyxiation risk

Argon and CO2 shielding gases displace oxygen in poorly ventilated or low-lying areas. Oxygen must be tested before entry and monitored continuously in confined spaces, with a minimum safe level of about 19.5 percent.

Cylinder separation rule

Fuel gas and oxygen cylinders must be separated by at least 6 m (20 ft) or by a noncombustible barrier at least 1.5 m (5 ft) high with a 30-minute fire rating.

5S definition

Workplace organization method: Sort, Set in order, Shine, Standardize, Sustain. In a weld shop it keeps cables, gas hoses, and tools clear of hot work and reduces trip and fire hazards.

Hot work fire watch

A trained person watches for fire during hot work and for at least 30 minutes after welding ends. Combustibles within 11 m (35 ft) must be removed or protected, and extinguishers must be charged and accessible.

AWS arrow-side convention

Under AWS A2.4, a weld symbol placed below the reference line applies to the arrow side of the joint; a symbol above the line applies to the other side.

ISO 4063 process number 135

The ISO process number 135 designates gas metal arc welding (GMAW). It appears in the tail of a welding symbol to specify the process required for that joint.

All-around welding symbol

A circle placed at the junction of the reference line and arrow. It means the weld is applied around the entire perimeter of the joint, such as a pipe or box section.

Fillet weld leg size

The dimension placed to the left of a fillet weld symbol specifies the leg length by default under AWS. A dimension in parentheses indicates a concave fillet profile.

WPS essential variables

Parameters that must be specified and controlled: process, base metal and thickness range, filler classification, shielding gas and flow, current and polarity, voltage range, travel speed, and transfer mode.

WPS and PQR relationship

The procedure qualification record documents testing that proves a procedure works. The WPS must be written within the qualified ranges of the PQR; a WPS without a supporting PQR is not qualified.

Joint cleaning width

Base metal must be cleaned at least 25 mm (1 in) back from the joint on both faces, removing mill scale, rust, oil, paint, and moisture. GMAW is more contamination-sensitive than SMAW.

Shielding gas flow range

Typical GMAW shielding gas flow is 12-20 L/min (25-40 cfh). Too little flow causes porosity from air aspiration; too much causes turbulence that also draws in air.

Contact tip to work distance

The distance from the contact tip to the workpiece. Increasing CTWD raises electrical resistance heating, which lowers welding current and changes penetration, so the WPS value must be maintained.

Drive roll groove matching

Drive rolls must have a groove matched to the wire diameter, and tension must be set so the wire deforms slightly without crushing. A worn liner or wrong contact tip causes erratic feed and porosity.

Fixture and shrinkage restraint

Jigs and fixtures hold fit-up but restrain shrinkage, raising residual stress. Release sequence and clamping location must be planned, and copper or aluminum backing can control root profile.

Spray transfer conditions

Spray transfer requires current above the transition level and an argon-rich shielding gas. It produces fine droplets, deep penetration, and little spatter, but is limited to flat and horizontal positions.

Short-circuiting transfer

A low-current, low-voltage transfer in which the wire touches the puddle and pinches off. It works in all positions, produces more spatter, and uses inductance to control current rise.

Voltage versus current roles

Voltage sets arc length and bead width; current, controlled by wire feed speed, sets penetration and deposition rate. Raising wire feed speed without raising voltage shortens the arc and can stub the wire.

Inductance in short-circuiting

Inductance controls the rate of current rise during short-circuit transfer. More inductance softens the arc and reduces spatter; too little causes spatter and stubbing.

Push versus drag angle

Pushing (forehand) gives a flatter, wider bead with less penetration. Dragging (backhand) gives deeper penetration and a narrower bead. A 10-15 degree travel angle is typical.

DCEP versus DCEN

Direct current electrode positive puts more heat into the workpiece, giving deeper penetration, and is standard for solid wire. Electrode negative puts more heat into the wire and melts it faster.

Weave width limit

Weave width should not exceed about three times the electrode diameter. Wider weaving risks lack of fusion at the sidewalls and requires reduced travel speed or higher current.

Porosity causes and correction

Porosity comes from low gas flow, drafts, contaminated base metal, wet wire, or excessive CTWD. Correct by restoring gas coverage and cleaning the joint, then grind out the defect before repair.

Lack of fusion causes

Lack of fusion results from travel too fast, current too low, wrong torch angle, or a weave too wide for the parameters. Correct by raising current, slowing travel, or reducing weave width.

Undercut correction

Undercut results from excessive current or voltage or a steep travel angle. Reduce voltage and current and correct the angle; undercut beyond the acceptance limit must be repaired by welding.

Inspection sequence

Visual inspection of all welds comes first, then surface NDT such as PT or MT where specified, then volumetric NDT such as UT or RT. No paint or coating is applied before inspection is complete.

Fillet weld gauge use

A fillet weld gauge checks leg length and throat thickness against the drawing. Separate undercut and pit gauges quantify depth, and a hi-lo gauge measures internal pipe mismatch.

Stainless post-weld cleaning

Use dedicated stainless steel brushes to avoid iron contamination. Remove spatter and heat tint, then pickle or passivate if the specification requires it to restore corrosion resistance.

Post-weld heat treatment

A controlled heating cycle that relieves residual stress. It is specified by procedure and must be recorded with time-temperature charts, including ramp rate, hold time, and cooling rate.

Preventive maintenance intervals

Inspect contact tip and nozzle daily, liner and drive rolls weekly or per duty cycle. Replace any worn component that affects arc stability, wire feed, or gas coverage.

Weld traceability records

Record the base metal heat number and filler batch number so any failure can be traced to the material lot. These link to the WPS, PQR, qualification records, and inspection reports.