I85PREP
⌘ K
MMAW NC I study materials
MMAW NC I study resources

MMAW NC I practice questions

One question at a time. Build your MMAW NC I understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Welding Safety, Health, and Environment

Under the hierarchy of controls used in welding safety, which measure ranks highest for reducing fume exposure at the source?

  1. Administrative controls such as job rotation
  2. Personal protective equipment such as a respirator
  3. Training in safe work procedures
  4. Engineering controls such as local exhaust ventilation Correct answer.

Explanation

The hierarchy of controls places elimination and substitution first, followed by engineering controls. Local exhaust ventilation captures fume at the arc before it reaches the breathing zone, so it is preferred over administrative measures or PPE, which sit lower in the hierarchy.

Question 2Welding Safety, Health, and Environment

Which gas is the main asphyxiation hazard when welding inside a confined space with inadequate ventilation?

  1. Nitrogen dioxide from the arc
  2. Ozone produced by the arc
  3. Argon accumulating and displacing oxygen Correct answer.
  4. Carbon monoxide from the base metal

Explanation

Shielding gases such as argon and carbon dioxide are heavier than air and can collect in low areas of a confined space, displacing the oxygen needed for breathing. The atmosphere must be tested before entry and ventilated continuously because asphyxiation can occur without warning.

Question 3Welding Safety, Health, and Environment

What is the primary purpose of the flashback arrestor fitted to an oxy-acetylene torch set?

  1. To filter particles from the fuel gas
  2. To stop a flame from travelling back into the hose and cylinder Correct answer.
  3. To indicate when the cylinder is nearly empty
  4. To regulate the working pressure at the torch

Explanation

A flashback arrestor contains a flame-arresting element that quenches a flame front and a check valve that stops reverse gas flow. This prevents a flashback from reaching the hose, regulator, or cylinder, where it could cause an explosion.

Question 4Welding Safety, Health, and Environment

Which type of radiation from an electric arc is most effectively blocked by the filter lens in a welding helmet?

  1. Ultraviolet and infrared radiation Correct answer.
  2. Radio waves
  3. Microwaves
  4. X-rays

Explanation

The arc emits intense ultraviolet and infrared radiation that can burn the eyes and skin. The darkened filter lens is selected to attenuate these wavelengths, which is why the shade number must match the welding process and current.

Question 5Welding Safety, Health, and Environment

Before manually moving a gas cylinder, what must be done with the valve protection?

  1. Lay the cylinder on its side and roll it
  2. Fit the valve protection cap and move the cylinder on a trolley Correct answer.
  3. Remove the regulator and leave the valve open
  4. Attach a sling to the valve and lift it

Explanation

Cylinders must be moved with the valve protection cap fitted and secured on a purpose-built trolley. The valve is the weakest point; if it shears off, the cylinder can become a projectile, so it must never be used as a lifting or handling point.

Question 6Welding Safety, Health, and Environment

What is the main health effect of prolonged exposure to welding fume containing manganese?

  1. Skin cancer
  2. Loss of hearing
  3. Kidney stones
  4. Neurological effects resembling Parkinsonism Correct answer.

Explanation

Manganese in welding fume is associated with a neurological syndrome sometimes called manganism, with symptoms similar to Parkinson's disease. Exposure must be controlled by ventilation and respiratory protection because the effect can develop gradually.

Question 7Welding Safety, Health, and Environment

How should a welding return lead be connected to the workpiece to reduce the risk of electric shock and stray current?

  1. Lay it loosely so it can arc to the work
  2. Clamp it directly to clean metal as close to the arc as practical Correct answer.
  3. Connect it to a nearby water pipe
  4. Attach it to the metal bench through painted surfaces

Explanation

The return lead must be clamped to clean bare metal on the workpiece, close to the weld, so current returns by the intended path. Poor connections through paint or building services create stray currents, overheating, and shock risk.

Question 8Welding Safety, Health, and Environment

A welder is working in a tank and the oxygen reading is 19.0 percent before entry. What is the correct action?

  1. Enter if a respirator is worn
  2. Enter with a second person standing by
  3. Enter quickly because the reading is close to normal
  4. Do not enter and ventilate until the reading is within the acceptable range Correct answer.

Explanation

Atmospheric oxygen must be confirmed within the acceptable range, commonly 19.5 to 23.5 percent, before entry. A reading of 19.0 percent is below that threshold, so the space must be ventilated and retested rather than entered.

Question 9Welding Safety, Health, and Environment

Why is it unsafe to use compressed oxygen from a cylinder to blow dust off clothing or a workpiece?

  1. Oxygen has a distinctive smell that causes headaches
  2. Oxygen saturates clothing and makes it burn violently if ignited Correct answer.
  3. Oxygen freezes the fabric on contact
  4. Oxygen cylinders are too heavy to move

Explanation

Oxygen is not a fuel but strongly supports combustion, so oxygen-enriched clothing or hair can ignite from a small spark and burn fiercely. Compressed air or a vacuum should be used for cleaning instead.

Question 10Welding Safety, Health, and Environment

Which factor most directly determines the shade number a welder should select for an arc welding helmet filter?

  1. The colour of the workpiece
  2. The ambient room temperature
  3. The welding current and process being used Correct answer.
  4. The length of the welding cable

Explanation

Filter shade selection is based on the welding process and the current level, with higher currents requiring a darker shade. The workpiece colour, room temperature, and cable length do not affect the arc's radiant intensity in the same way.

Question 11Welding Safety, Health, and Environment

When gas cylinders are stored, how should oxygen and fuel gas cylinders be separated?

  1. By a fire-resistant barrier or a minimum distance, with valves closed and caps fitted Correct answer.
  2. By leaving the regulators attached and valves open
  3. By stacking them together in a locked cage
  4. By storing them next to oily rags to absorb leaks

Explanation

Oxygen and fuel gas cylinders must be kept apart by a fire-resistant barrier or a specified distance so a leak and ignition in one cannot involve the other. Valves must be closed and protection caps fitted during storage.

Question 12Welding Safety, Health, and Environment

A welder develops a gritty, painful feeling in the eyes several hours after welding without eye protection nearby. What is the likely cause?

  1. Arc eye from ultraviolet radiation exposure Correct answer.
  2. Retinal detachment
  3. Foreign metal particles in the eye
  4. Conjunctivitis from fume

Explanation

Arc eye, or photokeratitis, is a burn of the cornea and conjunctiva caused by UV exposure, and symptoms often appear hours after exposure. The gritty, painful sensation and sensitivity to light are characteristic, and the affected person should seek medical attention.

Question 13Welding Safety, Health, and Environment

Why must a welding machine be switched off and isolated before changing electrodes or making adjustments?

  1. To keep the machine from overheating
  2. To remove the risk of electric shock from the open-circuit voltage Correct answer.
  3. To stop the gas from leaking
  4. To prevent the electrode from becoming magnetised

Explanation

Welding machines present open-circuit voltage at the electrode holder, and contact with it can cause a serious shock. Isolating the machine before changing electrodes or adjusting the set removes that voltage from the working area.

Question 14Welding Safety, Health, and Environment

Which precaution is essential when welding or cutting on a container that has held flammable liquid?

  1. Open the filler cap and begin welding
  2. Clean and purge the container and confirm it is gas free before applying heat Correct answer.
  3. Fill the container with water and weld immediately without testing
  4. Weld only at the top of the container

Explanation

Empty containers can retain flammable vapour or residue, so they must be cleaned, purged, and tested to confirm they are gas free before any hot work. Water filling may be part of the process but does not replace testing and purging.

Question 15Welding Safety, Health, and Environment

What is the purpose of a hot work permit before welding in a workshop area?

  1. To order consumables for the job
  2. To confirm fire precautions and authorise the work under controlled conditions Correct answer.
  3. To schedule machine maintenance
  4. To record the welder's qualification only

Explanation

A hot work permit verifies that fire hazards have been assessed, combustibles removed, firefighting equipment provided, and a fire watch arranged before welding begins. It authorises the work only for the stated location and time.

Question 16Welding Safety, Health, and Environment

Which control best protects nearby workers who are not welding from arc radiation?

  1. Welding only in the afternoon
  2. Using a longer welding cable
  3. Increasing the welding current
  4. Screening the welding area with opaque welding screens Correct answer.

Explanation

Opaque screens or booths block UV radiation and protect passers-by from arc eye and skin burns. Increasing current or cable length does not reduce the radiation reaching others.

Question 17Welding Safety, Health, and Environment

A carbon dioxide fire extinguisher is most appropriate for which type of fire likely in a welding area?

  1. A fire in electrical equipment Correct answer.
  2. A fire involving magnesium
  3. A fire in a pile of oily rags
  4. A fire in a solvent storage drum

Explanation

Carbon dioxide extinguishers are suitable for electrical fires because the agent is non-conductive and leaves no residue. They are less effective on deep-seated Class A fires or reactive metals, which need different agents.

Question 18Welding Safety, Health, and Environment

A welder notices the regulator on an acetylene cylinder shows a rising pressure and a hissing sound after being opened. What should be done first?

  1. Adjust the regulator to a higher setting
  2. Close the cylinder valve and evacuate the area and call for help Correct answer.
  3. Spray soap solution on the regulator while it leaks
  4. Continue welding and monitor the gauge

Explanation

A hissing, rising-pressure leak indicates a serious gas release that could ignite or explode. The first action is to close the valve if safe, evacuate, and summon emergency help rather than continue working or adjusting equipment.

Question 19Welding Safety, Health, and Environment

Why is local exhaust ventilation positioned close to the arc more effective than general ventilation alone?

  1. It reduces the welding current needed
  2. It eliminates the need for a welding helmet
  3. It cools the weld faster
  4. It captures fume before it enters the welder's breathing zone Correct answer.

Explanation

Local exhaust ventilation removes fume at the source before it disperses into the breathing zone, whereas general ventilation only dilutes fume after it has spread. Correct hood position and airflow are essential for it to work.

Question 20Welding Safety, Health, and Environment

A welder must enter a confined space to weld. Which combination of controls is required?

  1. An open access hatch alone
  2. A respirator alone
  3. A welding helmet and gloves
  4. Atmospheric testing, continuous ventilation, a permit, and a trained standby person Correct answer.

Explanation

Confined space welding requires pre-entry and continuous atmospheric testing, ventilation, a permit, and a trained standby person with rescue arrangements. PPE alone does not address oxygen deficiency, toxic gas, or entrapment hazards.

Question 21Welding Safety, Health, and Environment

Which situation most clearly indicates that a welding fume extraction system is not performing as intended?

  1. The hood is mounted above head height
  2. The filter was changed last month
  3. Visible fume drifts into the welder's breathing zone during welding Correct answer.
  4. The extraction fan runs quietly

Explanation

The purpose of extraction is to keep fume out of the breathing zone, so visible fume drifting toward the welder shows the capture velocity or hood position is inadequate. Quiet operation or a recent filter change does not confirm effective capture.

Question 22Welding Safety, Health, and Environment

When assessing the risk of an electric shock from a welding set, which combination of factors is most relevant?

  1. Electrode diameter and travel speed
  2. Base metal thickness and joint type
  3. Shielding gas flow rate and nozzle size
  4. Open-circuit voltage, damp conditions, and the condition of cables and insulation Correct answer.

Explanation

Shock risk depends on the voltage present, the conductivity of the environment, and the integrity of insulation and connections. Damp conditions and damaged cables lower body resistance and increase the chance of a fatal current path.

Question 23Welding Safety, Health, and Environment

A worker reports dizziness and headache while welding with a gas-shielded process in a poorly ventilated corner. Which is the most appropriate first response?

  1. Stop work, move to fresh air, and have the atmosphere assessed before resuming Correct answer.
  2. Increase the shielding gas flow rate
  3. Open a window and keep welding
  4. Continue welding and take a short break

Explanation

Symptoms suggest exposure to fume or an oxygen-deficient atmosphere from shielding gas accumulation. Work must stop, the person moved to fresh air, and the atmosphere assessed and ventilation corrected before welding resumes.

Question 24Welding Safety, Health, and Environment

Why is it important to check that a fire watch remains in place for a period after hot work is completed?

  1. Hidden smouldering material can ignite after the welder has left Correct answer.
  2. The welder needs time to pack up tools
  3. The gas cylinders need to cool down
  4. The permit requires a signature only

Explanation

Sparks and slag can lodge in crevices and smoulder for a considerable time before bursting into flame. A fire watch after hot work is finished ensures any smouldering material is detected and extinguished.

Question 25Welding Theory, Metallurgy, and Heat Input

In MMAW, what is the primary function of the electrode coating that burns to form a shielding gas?

  1. It increases the electrical conductivity of the core wire during arc initiation
  2. It cools the weld pool rapidly to refine the grain structure
  3. It acts as a flux to lubricate the wire feed rollers
  4. It prevents atmospheric nitrogen and oxygen from contaminating the molten weld pool Correct answer.

Explanation

The decomposing coating releases gases such as carbon dioxide and hydrogen that blanket the arc and weld pool, excluding atmospheric nitrogen and oxygen. This protection is essential because nitrogen and oxygen cause porosity and embrittlement in the solidified weld.

Question 26Welding Theory, Metallurgy, and Heat Input

Which constituent of a rutile electrode coating is mainly responsible for arc stability and easy slag removal?

  1. Calcium fluoride
  2. Titanium dioxide Correct answer.
  3. Iron powder
  4. Cellulose

Explanation

Rutile is titanium dioxide, and it ionises readily to stabilise the arc while producing a dense, glassy slag that detaches easily. This is why rutile electrodes are favoured for positional work and smooth bead appearance.

Question 27Welding Theory, Metallurgy, and Heat Input

In MMAW terminology, what does the 'arc length' refer to?

  1. The length of the weld bead produced from one electrode
  2. The distance between the earth clamp and the workpiece
  3. The distance between the tip of the electrode and the surface of the molten weld pool Correct answer.
  4. The total length of the coated electrode before striking the arc

Explanation

Arc length is the gap the arc must bridge, measured from the electrode tip to the molten pool surface. It controls arc voltage and therefore heat input and bead profile.

Question 28Welding Theory, Metallurgy, and Heat Input

Which type of current gives the deepest penetration in MMAW when the electrode is connected to the positive terminal?

  1. Alternating current with a low open-circuit voltage
  2. Direct current electrode positive (DCEP) Correct answer.
  3. Direct current electrode negative (DCEN)
  4. Alternating current at high frequency

Explanation

With DCEP the workpiece is the cathode, so electrons bombard it and concentrate heat there, producing deeper penetration and a wider bead. DCEN reverses this, putting more heat into the electrode.

Question 29Welding Theory, Metallurgy, and Heat Input

A welder needs to reduce heat input without changing the electrode size. Which combination of changes achieves this?

  1. Decrease travel speed and increase arc length
  2. Increase travel speed and reduce welding current Correct answer.
  3. Decrease travel speed and increase welding current
  4. Increase welding current and increase arc length

Explanation

Heat input per unit length rises with current and arc voltage and falls as travel speed increases. Raising travel speed and lowering current therefore both reduce the heat put into the joint.

Question 30Welding Theory, Metallurgy, and Heat Input

Why is hydrogen deliberately excluded from the coating of electrodes intended for welding high-strength steels?

  1. Hydrogen lowers the open-circuit voltage of the welding set
  2. Hydrogen reduces the deposition efficiency of the electrode
  3. Hydrogen dissolved in the weld can cause cold cracking after the weld cools Correct answer.
  4. Hydrogen increases the slag volume and makes cleaning difficult

Explanation

Hydrogen absorbed into the weld metal diffuses to regions of high stress and can initiate delayed cold cracks, particularly in high-carbon-equivalent steels. Low-hydrogen basic electrodes are therefore specified for such work.

Question 31Welding Theory, Metallurgy, and Heat Input

What does the carbon equivalent (CE) of a steel indicate for a welder?

  1. Its susceptibility to hydrogen-assisted cold cracking and the preheat likely to be needed Correct answer.
  2. The amount of carbon that will burn out during welding
  3. The maximum current the electrode can carry
  4. The depth of penetration achievable at a given arc voltage

Explanation

Carbon equivalent combines carbon and other alloying elements into a single index of hardenability. Higher CE means a greater risk of hard, crack-sensitive heat-affected zones and usually calls for preheat and controlled heat input.

Question 32Welding Theory, Metallurgy, and Heat Input

Which microstructural change occurs in the heat-affected zone immediately adjacent to the fusion line of a low-alloy steel weld?

  1. The steel is heated into the austenite region and may transform to hard martensite on rapid cooling Correct answer.
  2. The steel recrystallises into coarse pearlite regardless of cooling rate
  3. The steel becomes fully austenitic and stays that way at room temperature
  4. The steel remains fully ferritic because it never reaches the transformation temperature

Explanation

The region next to the fusion line experiences peak temperatures above the upper critical temperature, so it becomes austenite. Fast cooling then transforms this to hard phases such as martensite, which raises cracking risk.

Question 33Welding Theory, Metallurgy, and Heat Input

Which slag system is characteristic of a basic (low-hydrogen) electrode coating?

  1. High silica with sodium silicate binder only
  2. Calcium fluoride and calcium carbonate with little titania Correct answer.
  3. Predominantly rutile with iron powder additions
  4. High cellulose with a thin coating

Explanation

Basic coatings rely on calcium carbonate and fluorspar to give a low-hydrogen, high-basicity slag. They offer good toughness and crack resistance but a less stable arc and harder slag removal.

Question 34Welding Theory, Metallurgy, and Heat Input

A weld shows fine porosity distributed along the bead. Which MMAW practice most directly causes this defect?

  1. Using a travel speed that is too slow for the current
  2. Using a damp electrode or excessively long arc that allows atmospheric gas pickup Correct answer.
  3. Welding with the electrode connected to the negative terminal
  4. Using too short an arc with a tight weave

Explanation

Moisture in the coating and an over-long arc both allow hydrogen and nitrogen to enter the pool, producing scattered porosity. Correct storage and a short arc are the standard preventive measures.

Question 35Welding Theory, Metallurgy, and Heat Input

What is the main metallurgical reason for preheating a thick section of medium-carbon steel before MMAW?

  1. To burn off surface rust ahead of the arc
  2. To increase the electrical conductivity of the workpiece
  3. To slow the cooling rate and reduce the formation of hard, crack-sensitive martensite Correct answer.
  4. To reduce the electrode melting rate for better control

Explanation

Preheat lowers the temperature gradient between the weld and the parent metal, slowing cooling through the transformation range. This reduces martensite formation and allows hydrogen to diffuse away, lowering cold-cracking risk.

Question 36Welding Theory, Metallurgy, and Heat Input

Which statement correctly describes the effect of increasing arc voltage while current and travel speed are held constant?

  1. Heat input per unit length increases and the bead tends to become wider and flatter Correct answer.
  2. The arc becomes more stable because voltage is independent of arc length
  3. Heat input per unit length decreases and penetration deepens
  4. Heat input per unit length is unchanged because only current matters

Explanation

Arc voltage is roughly proportional to arc length, and heat input depends on both current and voltage. Raising voltage at fixed current and travel speed therefore raises heat input and spreads the arc, widening and flattening the bead.

Question 37Welding Theory, Metallurgy, and Heat Input

In MMAW, why does a very short arc reduce the risk of nitrogen porosity?

  1. The short gap limits the time and space available for atmospheric gas to reach the molten pool Correct answer.
  2. It reverses the current polarity automatically
  3. It increases the electrode melting rate so the pool freezes faster
  4. It lowers the arc voltage below the ionisation potential of nitrogen

Explanation

The coating gases form a protective envelope around the arc, and a shorter gap keeps that envelope compact. This limits the opportunity for air to be drawn into the arc stream and the pool.

Question 38Welding Theory, Metallurgy, and Heat Input

What does the 'deposition rate' of an MMAW electrode measure?

  1. The mass of weld metal deposited per unit of time Correct answer.
  2. The depth of penetration per unit of current
  3. The volume of slag produced per unit of time
  4. The number of electrodes consumed per metre of weld

Explanation

Deposition rate is expressed as mass of deposited weld metal per unit time, usually kilograms per hour. It depends on current, electrode efficiency and coating type, especially iron powder content.

Question 39Welding Theory, Metallurgy, and Heat Input

A welder switches from a rutile electrode to a basic low-hydrogen electrode and finds the arc harder to strike and maintain. What is the best explanation?

  1. The basic coating melts at a much higher temperature than the core wire can sustain
  2. The basic electrode requires alternating current to function at all
  3. The basic coating contains fewer easily ionised elements, so the arc is less stable at the same current Correct answer.
  4. The basic coating has a thinner flux layer that cannot shield the arc

Explanation

Rutile coatings contain readily ionised titanium compounds that stabilise the arc, whereas basic coatings lack these. Welders often need a slightly higher current or a different current type to run basic electrodes smoothly.

Question 40Welding Theory, Metallurgy, and Heat Input

Which grain structure is typically found in the weld metal of a single-pass MMAW bead on a ferritic steel?

  1. Columnar grains grown from the fusion boundary toward the weld centreline Correct answer.
  2. A single large austenite grain spanning the whole bead
  3. Amorphous glassy structure with no grain boundaries
  4. Fully equiaxed fine grains throughout the bead

Explanation

Weld metal solidifies by epitaxial growth from the partially melted base metal, so grains grow as columns toward the centreline along the heat-flow direction. Subsequent passes can refine this structure in the reheated zones.

Question 41Welding Theory, Metallurgy, and Heat Input

Why does excessive heat input in a single MMAW pass on a quenched-and-tempered steel reduce joint toughness?

  1. The arc voltage falls so low that the weld does not fuse
  2. The heat-affected zone is tempered back beyond its design condition and grain growth occurs Correct answer.
  3. The weld metal absorbs excess carbon from the coating and becomes pearlitic
  4. The slag becomes chemically basic and attacks the grain boundaries

Explanation

Overheating a quenched-and-tempered steel softens the tempered structure and allows prior-austenite grain growth in the heat-affected zone. Both effects lower toughness and strength compared with the intended properties.

Question 42Welding Theory, Metallurgy, and Heat Input

Which statement about alternating current in MMAW is correct?

  1. The current is constant in magnitude and direction but pulsed in frequency
  2. The current reverses direction each half-cycle, giving a compromise between penetration and electrode melting Correct answer.
  3. The current flows only from electrode to workpiece throughout the weld
  4. The current is used only for non-ferrous metals because it cannot strike an arc on steel

Explanation

AC alternates polarity, so heat is shared between the electrode and the workpiece over the cycle. This gives moderate penetration and good arc stability on many rutile electrodes, and it helps break up arc blow.

Question 43Welding Theory, Metallurgy, and Heat Input

What is 'arc blow' in MMAW, and what commonly causes it?

  1. Deflection of the arc by magnetic fields, often near the ends of a joint or with DC welding Correct answer.
  2. Loss of shielding gas caused by a damaged coating
  3. Extinction of the arc caused by a damp electrode coating
  4. Spatter thrown from the pool by excessive arc voltage

Explanation

Arc blow is magnetic deflection of the arc, typically when welding near the earth connection or at the ends of a joint with DC. Changing the earth position, using AC or reducing current helps control it.

Question 44Welding Theory, Metallurgy, and Heat Input

Which combination best describes the effect of electrode diameter on MMAW welding parameters?

  1. Larger diameter electrodes require higher current and give higher deposition but less precise control on thin sections Correct answer.
  2. Larger diameter electrodes run best on DCEN at very low current
  3. Larger diameter electrodes require lower current and give deeper penetration
  4. Electrode diameter has no effect on current setting; only coating type matters

Explanation

Current setting scales with electrode diameter because a larger core wire needs more heat to melt at the correct rate. Larger electrodes deposit more metal but are unsuitable for thin plate where burn-through is a risk.

Question 45Welding Theory, Metallurgy, and Heat Input

What is the purpose of the 'weave' technique in MMAW?

  1. To distribute heat and fill wider joints by oscillating the electrode across the weld line Correct answer.
  2. To cool the weld pool rapidly between passes
  3. To remove slag from the previous pass while welding
  4. To increase arc voltage so that penetration becomes shallower

Explanation

A controlled weave spreads the arc over a wider area, helping fill wider joints and control bead shape and heat distribution. Excessive weave width, however, can reduce penetration and trap slag.

Question 46Welding Theory, Metallurgy, and Heat Input

A weld on a restrained joint in a medium-carbon steel shows a crack that appears hours after welding. Which type of cracking is this most likely to be?

  1. Solidification cracking in the weld centreline
  2. Hydrogen-assisted cold cracking in the heat-affected zone Correct answer.
  3. Hot tearing caused by high sulphur in the weld metal
  4. Lamellar tearing caused by through-thickness shrinkage

Explanation

Delayed cracking appearing hours after welding is the classic signature of hydrogen-assisted cold cracking, driven by hydrogen, hard microstructure and restraint. Preheat, low-hydrogen electrodes and controlled cooling are the countermeasures.

Question 47Welding Theory, Metallurgy, and Heat Input

Which factor most strongly increases the risk of solidification cracking in an MMAW weld?

  1. A rutile coating with fine iron powder
  2. A low welding current with a wide weave
  3. A high depth-to-width ratio in the weld bead with high restraint Correct answer.
  4. Welding with the workpiece connected to the negative terminal

Explanation

Deep, narrow beads concentrate solidification strains at the centreline, where low-melting constituents can tear under restraint. A wider bead shape and appropriate current reduce this susceptibility.

Question 48Welding Theory, Metallurgy, and Heat Input

What is the main effect of adding iron powder to an MMAW coating?

  1. It converts the electrode into a non-consumable type
  2. It lowers the melting point of the core wire so less current is needed
  3. It eliminates the need for a slag covering on the bead
  4. It increases the deposition rate and improves productivity for the same arc time Correct answer.

Explanation

Iron powder in the coating melts into the pool and adds to the deposited metal, raising deposition efficiency and productivity. It can also improve arc stability and bead appearance.

Question 49SMAW (Shielded Metal Arc Welding) Fundamentals

In shielded metal arc welding, what is the primary function of the electrode coating (flux covering) as it burns in the arc?

  1. It conducts the welding current more efficiently than the bare core wire
  2. It generates shielding gas and slag to protect the molten weld metal from the atmosphere Correct answer.
  3. It cools the weld pool rapidly to refine the grain structure
  4. It magnetically stabilizes the arc by increasing arc blow

Explanation

The covering decomposes in the arc heat to release shielding gases and form a slag layer that blankets the cooling bead. Together these exclude oxygen and nitrogen from the molten metal, which would otherwise cause porosity and embrittlement. The covering also contributes arc stabilizers and alloying elements, but atmospheric protection is its defining job.

Question 50SMAW (Shielded Metal Arc Welding) Fundamentals

Which electrode identification system uses a four- or five-digit number in which the first two or three digits indicate minimum tensile strength in ksi?

  1. The AWS A5.1/A5.20 classification system for covered electrodes Correct answer.
  2. The AWS D1.1 joint designation system
  3. The ISO 9606 welder qualification coding
  4. The ASME Section IX procedure qualification number

Explanation

Under the AWS classification, an electrode such as E7018 begins with E for electrode, and the 70 denotes 70,000 psi minimum tensile strength of the deposited weld metal. The remaining digits encode welding position and coating/current type. The other systems classify welders, joints, or procedures, not consumable strength.