MMAW NC I flashcards
MMAW NC I · Build recall with a focused review session.
34 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Acetylene working pressure limit
- Acetylene must never be used at gauge pressures above 15 psi (about 103 kPa). Above that pressure free acetylene can decompose explosively, so regulators are limited accordingly.
- Oxygen fitting thread direction
- Oxygen hose and regulator fittings use right-hand threads, while fuel-gas fittings use left-hand threads. This prevents accidental cross-connection of oxygen and fuel-gas hoses.
- Flashback arrester purpose
- A flashback arrester stops a flame from traveling backward through the hose into the regulator or cylinder. It is installed on both oxygen and fuel-gas lines.
- Fire watch duration
- A fire watch is maintained during hot work and for at least 30 minutes after the work ends. Longer periods are required where smoldering material or concealed combustibles create continuing risk.
- Heat input formula
- Heat input in J/mm equals arc voltage times current times 60, divided by travel speed in mm/min times 1000. It quantifies energy delivered per unit length of weld.
- Carbon equivalent definition
- Carbon equivalent combines carbon with other alloying elements to estimate hardenability. Higher CE means greater susceptibility to cold cracking and a greater need for preheat.
- Eutectoid composition
- In the iron-carbon system the eutectoid occurs at about 0.76 percent carbon and 727 degrees Celsius. Austenite then transforms to alternating layers of ferrite and cementite called pearlite.
- Martensite formation
- Martensite forms when austenite cools too fast for carbon diffusion. Carbon is trapped in a body-centered-tetragonal lattice, producing a hard, brittle structure that requires tempering.
- Sensitization of stainless steel
- Heating austenitic stainless steel to roughly 425 to 870 degrees Celsius precipitates chromium carbides at grain boundaries. Chromium depletion there promotes intergranular corrosion in service.
- E7018 electrode meaning
- E7018 indicates a low-hydrogen iron-powder electrode with 70,000 psi minimum tensile strength, usable in all positions, on AC or DCEP. Its coating requires dry storage.
- Cellulosic electrode polarity
- E6010 cellulosic electrodes run on DCEP only and produce deep penetration with a forceful arc. E6011 is the equivalent that also operates on alternating current.
- Low-hydrogen electrode storage
- E7018 and similar low-hydrogen electrodes are held in ovens at about 120 to 150 degrees Celsius. Electrodes exposed to moisture must be rebaked per manufacturer instructions before use.
- DCEP versus DCEN heat balance
- With direct current electrode positive, more heat goes into the workpiece, giving deeper penetration. With electrode negative, more heat goes into the electrode, giving shallower penetration and higher deposition.
- Duty cycle meaning
- Duty cycle is the percentage of a ten-minute period a machine can operate at a given current. A 60 percent rating at 200 amps allows six minutes of welding per ten.
- Short-circuit transfer requirements
- Short-circuit transfer uses low current and small wire, and requires carbon dioxide or a carbon-dioxide-rich shielding gas. The high surface tension lets the droplet bridge the arc gap stably.
- Spray transfer conditions
- Spray transfer needs argon-rich shielding gas and current above the spray transition point. It gives high deposition with low spatter but is unsuitable for vertical and overhead positions.
- Constant-voltage GMAW control
- In constant-voltage GMAW, wire feed speed sets welding current and arc voltage sets arc length. The two settings are adjusted together to balance heat and bead shape.
- Contact-tip-to-work distance effect
- Increasing contact-tip-to-work distance adds resistance in the wire extension, lowering current and penetration. Excess distance also risks poor gas coverage and porosity.
- Self-shielded FCAW polarity
- Self-shielded flux-cored wires such as E71T-11 use direct current electrode negative and need no external shielding gas. The flux provides both shielding and slag.
- FCAW wire classification suffix
- In a classification like E71T-1C or E71T-1M, the final letter shows shielding: C means carbon dioxide and M means a mixed argon-carbon dioxide blend.
- FCAW wind tolerance
- Flux-cored welding tolerates more wind and surface contamination than solid-wire GMAW because the flux supplements gas shielding. Self-shielded wires tolerate the most wind.
- GTAW electrode polarity
- Direct current electrode negative is standard for GTAW on steel, stainless, and titanium. It concentrates heat at the work while limiting heating of the tungsten electrode.
- AC GTAW for aluminum
- Alternating current is used for aluminum because the electrode-positive half-cycle breaks the tenacious surface oxide. The electrode-negative half-cycle limits heat buildup in the tungsten.
- Tungsten color code green
- A green-tipped tungsten electrode is pure tungsten, used mainly for alternating current on aluminum and magnesium. It balls readily and has lower current capacity than alloyed tungsten.
- Tungsten contamination response
- If the tungsten touches the puddle, filler, or base metal, stop welding. Remove the contaminated section and re-sharpen the electrode before continuing to avoid inclusions.
- Oxy-fuel cutting principle
- Oxy-fuel cutting preheats steel to its ignition temperature, then a pure oxygen jet oxidizes the iron. The molten oxide is blown out of the kerf by the jet.
- Neutral flame description
- A neutral flame has roughly equal oxygen and acetylene, producing a well-defined inner cone. It is used for most cutting and for welding steel without adding or removing carbon.
- Kerf drag lines
- Drag lines are the marks left in the kerf by the oxygen jet. Excessive drag indicates travel speed too fast or oxygen pressure too low for the plate thickness.
- Oxy-fuel limits on stainless
- Oxy-fuel cutting does not work well on stainless steel or aluminum because their oxides melt at temperatures above the base metal. Other processes such as plasma are used instead.
- Welding symbol arrow side rule
- A weld symbol placed below the reference line means the weld is made on the arrow side of the joint. A symbol above the line means the other side.
- Single-V groove geometry
- A typical single-V groove uses a 60 to 75 degree included angle, a root face of about 1.5 to 3 mm, and a root opening sized to the process and thickness.
- Discontinuity versus defect
- A discontinuity is any interruption in the weld, such as porosity or slag. It becomes a defect only when it exceeds the acceptance criteria of the governing code.
- Lack of fusion significance
- Lack of fusion is a planar discontinuity between weld metal and base metal or between passes. Being planar, it concentrates stress and is more harmful than rounded porosity.
- Magnetic particle limitation
- Magnetic particle inspection detects surface and near-surface discontinuities only in ferromagnetic materials. It cannot inspect austenitic stainless steel or aluminum.