MMAW NC I common mistakes
MMAW NC I · Understand the traps and how to avoid them.
Treating 'current' (amperage) as the variable that directly sets arc voltage, or assuming voltage and current can be adjusted independently without affecting arc length and bead shape.
Candidates memorize 'more amps = more penetration' but never build a mental model of the power source characteristic. On constant-current SMAW the arc length (voltage) is set by the welder's hand, so they conflate the two and pick the wrong answer when a question asks what changed when the arc got longer.
What to do instead
Learn the two power-source types cold: CC (SMAW/GTAW) holds amperage roughly constant and voltage floats with arc length; CV (GMAW/FCAW) holds voltage constant and the wire-feed speed sets current. Practice predicting bead effects: longer arc on CC raises voltage, widens and flattens the bead, and reduces penetration.
Answering heat-input questions by adjusting only one variable (e.g., 'lower the amperage') when the scenario requires changing travel speed, voltage, or preheat to control cooling rate.
Heat input is taught as a formula but candidates rarely apply it as a lever. They default to amperage because it feels most intuitive and ignore that travel speed and voltage sit in the same equation.
What to do instead
Memorize heat input = (voltage × amperage × 60) / (travel speed in mm/min × 1000), giving kJ/mm, and note the 60/1000 conversion so units are consistent. Work three numeric examples until you can state which variable raises heat input without changing the others, and link higher heat input to slower cooling, wider HAZ, and more distortion.
Selecting an electrode classification by the wrong digit, e.g., reading E7018 as '70,000 psi tensile and all-position' without knowing the third and fourth digits govern position and coating/current type.
The AWS classification string looks like a single number, so candidates memorize the tensile strength and stop. The suffix digits (position, coating, polarity) are the parts actually tested and the parts that determine whether the electrode suits the joint.
What to do instead
Drill the SMAW electrode system digit by digit: E = electrode, first two digits = minimum tensile strength in ksi, third digit = position (1 = all position, 2 = flat and horizontal), fourth digit = coating and current (e.g., 8 = low-hydrogen, iron powder, AC or DCEP). Do the same for FCAW (E71T-1 etc.) and GMAW (ER70S-6) so you can decode any string on sight.
Using the wrong polarity or current type for a given process - e.g., choosing DCEN for a rutile or cellulosic SMAW electrode, or DCEN for GTAW on aluminum.
Polarity is often memorized as a list of exceptions rather than derived from where the heat needs to go. Candidates forget that electron flow concentrates heat at the anode or cathode depending on setup, and that aluminum's oxide layer needs cathodic cleaning.
What to do instead
Anchor polarity to purpose: DCEP puts more heat at the workpiece (deeper penetration) and is standard for most SMAW covered electrodes and for GMAW/FCAW. DCEN concentrates heat at the electrode and is used for GTAW on steel and for some high-deposition electrodes. AC alternates and gives cathodic cleaning, which is why it is used for GTAW on aluminum. Build a one-page table of process, polarity, and reason.
Mixing up shielding gas selection and flow rates across GMAW, FCAW, and GTAW - e.g., using pure CO2 for GTAW, or setting flow by 'more is better' and running 30 CFH on a small GTAW cup.
Gases are taught as 'argon for TIG, CO2 for MIG' without the reasoning, so candidates cannot answer questions about gas mixes, reactivity, or what happens when flow is too high or too low. Excessive flow causes turbulence that aspirates air, which is counterintuitive.
What to do instead
Learn gas roles by property: argon is inert and gives stable arcs for GTAW and nonferrous GMAW; helium raises heat input and is used for thick aluminum and high-speed work; CO2 and O2 additions in GMAW mixes improve wetting and penetration on steel but are unacceptable for GTAW because the tungsten would oxidize. Set flow with a flowmeter, typically in the 15–25 CFH range for GTAW and 25–35 CFH for GMAW, and recognize turbulence at high flow as an air-entrainment cause of porosity.
Ignoring the difference between a discontinuity and a defect, and answering inspection questions as if any indication found by NDT automatically fails the weld.
Candidates conflate 'indication' with 'rejection' and never learn that acceptance is governed by a code's acceptance criteria. They also confuse surface and subsurface methods, so they pick magnetic particle testing for internal porosity.
What to do instead
Separate the three terms: a discontinuity is any interruption in uniformity; a defect is a discontinuity that exceeds acceptance criteria; an indication is a signal from an inspection method that must be evaluated. Then map methods to what they detect: visual and PT for surface-breaking, MT for surface and near-surface in ferromagnetic material, UT and RT for internal. State the acceptance criterion before judging a result.
Misreading welding symbols - putting the weld on the wrong side of the reference line, confusing the arrow side and other side, or ignoring the tail and supplementary information.
Symbols are visual and candidates skim them. The convention that the weld symbol below the line means arrow-side welding is easy to invert under time pressure, and candidates rarely practice reading a full symbol including groove preparation, size, length, pitch, and finish.
What to do instead
Practice reading complete symbols aloud: reference line, arrow, weld symbol position (below = arrow side, above = other side, both = both sides), size to the left of the symbol, length and pitch to the right, tail for process or spec, and supplementary contour and finish symbols. Redraw ten symbols from written descriptions and check them against a symbol chart until the mapping is automatic.
Treating joint preparation and fit-up as cosmetic - accepting excessive root gap, poor bevel angle, or contamination on the faying surfaces because 'the weld will fill it'.
Candidates focus on arc time and underestimate how prep and fit-up control penetration, distortion, and defect formation. They also skip cleaning and preweld inspection because it does not look like welding.
What to do instead
Learn the prep variables as defect causes: root gap too large causes burn-through and excess penetration; too small causes lack of penetration; wrong bevel angle changes groove volume and sidewall fusion; mill scale, oil, paint, and moisture cause porosity and hydrogen cracking. Always clean to bright metal within the joint and adjacent surfaces, check gap and alignment before striking an arc, and use tack welds that will be consumed into the final weld.
Underestimating oxy-fuel safety specifics - using the wrong tip size, setting acetylene pressure above the safe limit, or lighting the torch with the oxygen valve fully open.
Candidates learn 'red is acetylene, green is oxygen' and stop. They miss that acetylene is unstable above roughly 15 psi working pressure in a hose and that tip size must match material thickness, both of which are common exam targets.
What to do instead
Memorize the safety envelope: acetylene working pressure must not exceed 15 psi (about 1 bar), never use acetylene on copper, and always purge lines and check for leaks with soap solution, never a flame. Select the tip by plate thickness, set neutral flame for steel cutting, and follow the lighting sequence - open acetylene, light, then add oxygen. Know the difference between a carburizing and oxidizing flame and what each does to the cut.
Answering metallurgy questions from a single keyword - e.g., 'carbon = hardenability' or 'preheat = less cracking' - without connecting composition, cooling rate, and microstructure.
Metallurgy is the least hands-on domain, so candidates memorize isolated facts and cannot reason through a scenario about cracking, hardness, or weldability of a specific steel.
What to do instead
Build one causal chain and reuse it: carbon and alloy content raise hardenability, fast cooling forms martensite, martensite is hard and crack-sensitive, so higher-carbon or thicker sections need preheat and controlled heat input to slow cooling. Link this to hydrogen: low-hydrogen electrodes, clean dry surfaces, and preheat together prevent hydrogen-assisted cracking. Practice applying that chain to a scenario rather than recalling a single fact.
Skipping PPE and fume-control specifics and answering safety questions with generic 'wear protection' language instead of the correct item or control measure.
Safety feels obvious, so candidates read it quickly and miss the precise item the question asks for - shade number, ventilation type, or the specific hazard of a process such as GMAW's ozone and metal-fume exposure or FCAW's fume volume.
What to do instead
Memorize the concrete numbers and controls: lens shade by process and amperage (e.g., shade 10–13 for SMAW at typical currents, lighter for low-current GTAW), leathers and gauntlets, respiratory protection where ventilation is inadequate, and local exhaust ventilation at the arc. Know that GMAW and GTAW on aluminum and stainless produce ozone and that FCAW produces high fume volumes, and match the control to the hazard rather than reciting 'wear PPE'.