MTTC Welding Trade Test cheat sheet

Oxygen and acetylene cylinders must be stored at least 20 ft apart or separated by a noncombustible barrier at least 5 ft high with a fire rating of at least 1/2 hour.

Acetylene cylinder pressure must not exceed 15 psig; free acetylene is unstable above 15 psig and can decompose explosively.

The threshold limit value (TLV) for manganese fume is 0.02 mg/m3 as an 8-hour time-weighted average; welding fume containing manganese can cause manganism.

Hexavalent chromium fume, produced when welding stainless steel, has a TLV of 0.005 mg/m3; use local exhaust ventilation and respiratory protection.

Arc welding radiation includes ultraviolet (UV), visible, and infrared (IR); UV exposure can cause arc eye (photokeratitis) and skin burns.

A welding helmet must have a filter lens with a shade number appropriate to the process and current; for example, SMAW at 100 A requires shade 10 minimum.

Confined space entry requires atmospheric testing for oxygen (19.5-23.5%), flammables (below 10% LEL), and toxics before entry and continuous monitoring during welding.

Hot work permits are required before welding, cutting, or brazing in areas where flammable materials may be present; the permit must specify fire watch and precautions.

Fume extraction efficiency is improved by keeping the extraction hood within 12 inches of the arc; capture velocity at the arc should be at least 100 ft/min.

SMAW uses a constant-current (drooping) power source; amperage is set on the machine and voltage varies with arc length.

GMAW uses a constant-voltage (constant-potential) power source; wire feed speed controls amperage and voltage is set on the machine.

GTAW uses a constant-current power source and a nonconsumable tungsten electrode; direct current electrode negative (DCEN) concentrates heat on the workpiece for deep penetration.

In GMAW, the short-circuit transfer mode uses low voltage (14-20 V) and low current, producing small, rapidly freezing welds suitable for thin sheet.

Spray transfer in GMAW requires a current above the transition current (approximately 200-250 A for 0.035 in. wire) and an argon-rich shielding gas.

FCAW uses a tubular wire filled with flux; self-shielded FCAW does not require external shielding gas, while gas-shielded FCAW uses CO2 or argon-CO2 blends.

SAW uses a granular flux blanket that shields the arc and produces high deposition rates; it is limited to flat or horizontal positions.

The duty cycle of a welding machine is the percentage of time in a 10-minute period that the machine can operate at rated output without overheating.

Shielding gas flow rates for GMAW typically range from 30 to 50 cubic feet per hour (cfh); excessive flow can cause turbulence and porosity.

On a welding symbol, the reference line is horizontal; the arrow line points to the joint, and the tail contains process or specification references.

The weld symbol is placed below the reference line for the arrow side and above the reference line for the other side.

A fillet weld symbol is a right triangle; the leg size is placed to the left of the symbol, and the length and pitch are placed to the right.

A groove weld symbol includes the groove type (V, bevel, U, J) and the groove angle or root opening; the size is placed to the left of the symbol.

A circle at the junction of the reference line and arrow line indicates a weld all around the joint.

A flag at the junction of the reference line and arrow line indicates a field weld to be made at the job site.

In a welding symbol, the number to the left of the weld symbol is the size (e.g., leg size for fillet, groove depth for groove weld), and the number to the right is the length.

A broken arrow line indicates that the arrow side is the side toward which the arrow points; the other side is the other side of the joint.

First-angle projection places the top view below the front view; third-angle projection places the top view above the front view (common in U.S. drawings).

The iron-carbon phase diagram shows the eutectoid composition at 0.76% carbon and 1333°F (723°C), where austenite transforms to pearlite.

Carbon equivalent (CE) = %C + %Mn/6 + (%Cr + %Mo + %V)/5 + (%Ni + %Cu)/15; a CE above 0.40 increases hardenability and cracking risk.

Preheat temperature for carbon steel is often calculated using CE; for CE = 0.40, a typical minimum preheat is 200°F (93°C).

Austenitic stainless steel (300 series) is not magnetic and cannot be hardened by heat treatment; it is susceptible to sensitization (chromium carbide precipitation) between 800°F and 1500°F.

Aluminum alloys are classified by heat treatment: 6061-T6 is precipitation hardened and loses strength if welded without post-weld heat treatment.

The heat-affected zone (HAZ) is the base metal that has been metallurgically altered by welding heat but not melted; it is often the weakest region in high-strength steels.

Hydrogen-induced cracking (cold cracking) occurs when diffusible hydrogen, residual stress, and a susceptible microstructure (martensite) are present; low-hydrogen electrodes and preheat reduce risk.

Solidification cracking (hot cracking) occurs in the weld metal during cooling and is influenced by sulfur and phosphorus content and weld shape (depth-to-width ratio).

The five basic joint types are butt, lap, tee, corner, and edge.

A single-V groove weld requires a root opening (gap) typically 1/16 to 1/8 in. and a groove angle of 60° to 75° included for complete penetration.

A root face (land) of 1/16 to 1/8 in. is used on a V-groove to prevent burn-through during root pass.

Fit-up tolerances: misalignment (high-low) should not exceed 10% of plate thickness or 1/8 in., whichever is less, for many codes.

Backing may be permanent (steel backing bar) or removable (ceramic or copper); it supports the root pass and prevents melt-through.

For fillet welds, the leg size should be at least the thickness of the thinner part, but not exceed the thickness of the thinner part by more than 1/16 in. for plates over 1/4 in.

A backing gas (e.g., argon) is used on the root side of GTAW welds in stainless steel or titanium to prevent oxidation.

Tack welds should be of sufficient size to hold the joint in alignment and should be removed or fused into the final weld if they are cracked or defective.

A Welding Procedure Specification (WPS) is a written document that provides the welding parameters for a specific application; it must be supported by a Procedure Qualification Record (PQR).

A PQR records the actual welding parameters and test results used to qualify a WPS; it is a record of the qualification test.

Essential variables in a WPS include process, base metal thickness, filler metal classification, preheat, and post-weld heat treatment; changes require requalification.

AWS D1.1 Structural Welding Code-Steel governs welding of carbon and low-alloy steel structures; it defines prequalified joints and qualification requirements.

ASME Section IX covers welding and brazing qualifications for pressure vessels and piping; it uses essential, supplementary essential, and nonessential variables.

API 1104 is the standard for welding pipelines and related facilities; it includes procedures for girth welds and qualification of welders.

A welder performance qualification (WPQ) tests the welder's ability to produce sound welds; it is separate from the WPS/PQR procedure qualification.

The American Welding Society (AWS) filler metal classification system uses a prefix (ER for electrode/rod, E for electrode) followed by tensile strength in ksi (e.g., ER70S-6).

Visual inspection (VT) is the most common and least expensive inspection method; it detects surface defects such as undercut, overlap, and crater cracks.

Liquid penetrant testing (PT) detects surface-breaking discontinuities in nonporous materials; it is not suitable for porous materials like cast iron.

Magnetic particle testing (MT) detects surface and near-surface discontinuities in ferromagnetic materials; it cannot be used on austenitic stainless steel or aluminum.

Ultrasonic testing (UT) uses high-frequency sound waves to detect internal discontinuities; it requires a coupling medium and a skilled operator.

Radiographic testing (RT) uses X-rays or gamma rays to detect internal discontinuities; it is sensitive to density differences and requires safety precautions.

A tensile test measures the strength and ductility of a weld; the specimen is pulled until failure, and the yield strength and ultimate tensile strength are recorded.

A bend test evaluates the ductility and soundness of a weld; the specimen is bent around a specified radius, and the convex surface is examined for cracks.

A Charpy V-notch impact test measures the toughness of a weld or HAZ at a specified temperature; it is required for applications where brittle fracture is a concern.

Weld discontinuity acceptance criteria are specified in the applicable code; for example, AWS D1.1 limits undercut to 1/32 in. for certain thicknesses.

Oxyfuel cutting uses a preheat flame to bring steel to its ignition temperature (approximately 1600°F or 870°C) and an oxygen jet to oxidize the metal.

The neutral flame in oxyacetylene cutting has equal parts oxygen and acetylene; an oxidizing flame has excess oxygen and a carburizing flame has excess acetylene.

Plasma arc cutting uses a constricted arc and high-velocity gas to cut electrically conductive materials; it can cut stainless steel and aluminum.

Air carbon arc cutting (CAC-A) uses a carbon electrode and compressed air to gouge or cut metal; it is often used for back gouging.

Brazing occurs at temperatures above 840°F (450°C) but below the melting point of the base metals; the filler metal melts and flows into the joint by capillary action.

Soldering occurs at temperatures below 840°F (450°C); common solders are tin-lead or lead-free alloys, and fluxes remove oxides.

Brazing filler metals include copper-phosphorus (for copper), aluminum-silicon (for aluminum), and silver-based alloys; flux selection depends on the base metal and filler.

Laser cutting uses a focused laser beam to melt or vaporize material; it produces a narrow kerf and is suitable for thin sheets.

A job hazard analysis (JHA) identifies hazards for each task and specifies controls; it is a key tool for shop safety management.

The hierarchy of controls is elimination, substitution, engineering controls, administrative controls, and personal protective equipment (PPE), in order of effectiveness.

Preventive maintenance schedules for welding equipment include checking cables, connections, gas hoses, and cooling systems; a maintenance log documents these activities.

Inventory management uses a first-in, first-out (FIFO) system to ensure that consumables such as electrodes and filler metals are used before they expire or absorb moisture.

Career readiness includes the ability to read and interpret a WPS, perform basic math (e.g., travel speed, heat input), and communicate effectively with inspectors and engineers.

Heat input (J/in.) = (voltage × amperage × 60) / travel speed (in./min); it is used to control cooling rates and mechanical properties.

Instructional practice in welding education includes demonstrating proper technique, providing immediate feedback, and using performance-based assessments aligned with AWS or state standards.

Shop layout should separate hot work areas from flammable storage, provide adequate ventilation, and maintain clear egress routes.

Recordkeeping for welder qualification includes the WPQ test results, date, and expiration; qualifications may require renewal every 6 months under some codes.