NCCER Welding cheat sheet

Acetylene in hoses, torches, and piping must never exceed 15 psig working pressure; above that, free acetylene can decompose violently even without oxygen present.

Open an acetylene cylinder valve no more than 1.5 turns; open oxygen cylinder valves fully so the valve seats and the stem packing seals.

Oxygen and fuel-gas cylinders stored in the same area must be separated by at least 20 ft, or by a noncombustible barrier at least 5 ft high with a 1/2-hour fire rating.

Install flashback arrestors at the regulator outlet and at the torch inlet. A backfire is a momentary burn-back at the tip with a pop; a flashback travels back through the hose toward the regulator.

Arc welding open-circuit voltage limits (OSHA 1910.254): 80 V maximum for AC machines, 100 V maximum for DC machines.

OSHA filter-lens table: SMAW with electrodes 1/32-5/32 in = minimum shade 7, typical shade 10; 3/16-1/4 in = minimum 8, typical 12; GMAW/FCAW on ferrous metal up to 5/32 in = minimum 7, typical 10.

Combustibles within 35 ft (10.7 m) of the arc must be moved or protected, and a fire watch is posted wherever floor or wall openings or combustible material can be ignited by sparks.

Clamp the work lead directly to the workpiece or its table; never ground through building steel, chains, slings, or a gas cylinder.

Stainless steel welding fume contains hexavalent chromium and carbon steel electrodes contribute manganese; control both by capturing fume at the arc, not by general room dilution.

A neutral flame is one part oxygen to one part acetylene with a single sharply defined inner cone; it is the standard flame for cutting and for heating carbon steel.

Neutral oxyacetylene flame temperature is about 5,580 °F (3,080 °C); oxypropane and oxyhydrogen flames are cooler and preheat more slowly.

A carburizing (reducing) flame has excess acetylene and three zones: inner cone, feathery intermediate zone, and outer envelope; a long feather means a strongly reducing flame, used for brazing and surfacing.

Preheat steel to about 1,400-1,600 °F (dull cherry red) before opening the cutting oxygen; the oxygen jet then oxidizes the iron and blows the slag out of the kerf.

Hold the inner cone about 1/16-1/8 in above the plate while cutting; touching the work overheats the tip and causes backfires.

For thicker plate, go to a larger cutting tip instead of raising acetylene pressure; acetylene delivery stays roughly 3-7 psig while oxygen pressure increases with thickness.

Never draw more than about 1/7 of an acetylene cylinder's contents per hour; faster withdrawal carries acetone vapor into the hose and distorts the flame.

Oxyfuel cutting will not work on aluminum or stainless steel because their refractory oxides melt above the base metal (aluminum oxide about 3,700 °F); use plasma or powder cutting instead.

Too fast a cutting speed leaves drag lines angled sharply backward and may leave uncut metal; too slow a speed rounds the top edge and welds slag to the kerf.

AWS D1.1 requires the joint surfaces and at least 1 in (25 mm) on each side to be free of scale, rust, slag, oil, paint, and moisture before welding.

Standard V-groove for SMAW: 30-37.5 degrees bevel per plate, giving 60-75 degrees included angle, with a root face near 1/16 in and root opening of 1/16-1/8 in.

Joint types are butt, corner, T, lap, and edge; groove types are square, single or double V, bevel, U, and J.

Undercut is caused by excessive current, too long an arc, an incorrect electrode angle, or excessive travel speed.

Porosity comes from moisture, oil, paint, rust, a long arc, damp low-hydrogen electrodes, or loss of gas shielding.

Incomplete fusion and incomplete penetration result from low current, fast travel, wrong electrode angle, poor fit-up, or failure to remove slag between passes.

Distortion is controlled by backstep welding, balanced or alternating passes, skip welding, presetting the joint, and keeping heat input low.

AWS A2.4 symbol placement: the arrow side is shown below the reference line, the other side above; weld size is written left of the symbol and length right of it.

Fillet weld size is measured as leg length; theoretical throat equals 0.707 times the leg for an equal-leg 45-degree fillet.

E7018: E = arc welding electrode, 70 = 70,000 psi minimum tensile strength, 1 = all positions, 8 = low-hydrogen iron-powder coating for AC or DCEP.

E6010 and E6011 are cellulosic electrodes with a deep digging arc; E6010 runs DCEP only, E6011 runs AC or DCEP, and both are standard root-pass electrodes for pipe.

Low-hydrogen electrodes are held at 250-300 °F in a holding oven and are limited to about 4 hours of exposure to air before redrying is required.

DCEP (reverse polarity) concentrates heat at the work for deeper penetration; DCEN (straight polarity) gives shallower penetration with higher deposition.

Arc blow - arc deflection from magnetic forces - is reduced by relocating the work clamp, shortening the arc, lowering current, backstepping, or using AC.

Amperage scales with electrode diameter: roughly 3/32 in = 60-100 A, 1/8 in = 90-140 A, 5/32 in = 130-190 A, 3/16 in = 200-270 A.

Arc length should approximate the electrode diameter; a long arc raises voltage and produces spatter, porosity, and undercut.

Weave beads should not exceed about 2.5-3 times the electrode diameter; wider weaving loses penetration at the edges and traps slag.

A 60% duty cycle at 200 A means 6 minutes of welding in any 10-minute period at 200 A; the remaining 4 minutes are cooling.

GMAW uses a constant-voltage power supply: wire-feed speed sets amperage and voltage sets arc length, with DCEP as the standard polarity.

Short-circuit transfer uses low current and small wire for thin sheet and all positions; spray transfer requires at least 80% argon and current above the transition value, restricting it to flat and horizontal.

GMAW contact-tip-to-work distance is about 3/8-1/2 in; increasing it lowers welding current and raises the risk of lack of fusion.

FCAW uses a tubular flux-cored wire: gas-shielded E71T-1 runs DCEP with CO2 or Ar/CO2, while self-shielded E71T-11 needs no gas and tolerates wind, often on DCEN.

GTAW uses a constant-current (drooping) supply and a non-consumable tungsten electrode; DCEN puts about two-thirds of the arc heat into the workpiece.

Aluminum is GTAW welded on AC so the electrode-positive half cycle breaks up the refractory aluminum oxide; zirconiated tungsten is standard for this.

Grind tungsten longitudinally to a taper 2-2.5 times the electrode diameter; radial grinding grooves cause arc wander and a split arc.

Typical shielding gas flows: GTAW 15-25 cfh argon, GMAW 20-35 cfh; a gas lens improves coverage on GTAW.

GTAW torch angle is about 70-80 degrees to the work, with filler wire added at the leading edge of the puddle at a low angle.