AWS Welding Inspection & Testing 2 — Questions and Answers
Question 1: According to AWS D1.1, what is the minimum preheat temperature required for ASTM A36 steel with a thickness greater than 38 mm (1.5 in.) when using a low-hydrogen process?
- 107°C (225°F) (Correct answer)
- 149°C (300°F)
- 66°C (150°F)
- No preheat required
Correct answer: 107°C (225°F)
AWS D1.1 Table 4.2 requires a minimum preheat and interpass temperature of 107°C (225°F) for A36 steel greater than 38 mm thick when using a low-hydrogen process.
AWS D1.1 Structural Welding Code — Steel provides preheat and interpass temperature requirements in Table 4.2 based on base metal category, thickness, and process. For Category I steels such as ASTM A36, the minimum preheat for thickness over 38 mm using low-hydrogen electrodes is 107°C (225°F). Preheat is required to slow the cooling rate, reduce hydrogen cracking susceptibility, and minimize hardening of the heat-affected zone. Using non-low-hydrogen processes on thicker material requires higher preheat temperatures.
Question 2: Which destructive test is specifically used to evaluate the toughness (notch toughness) of weld metal and HAZ?
- Charpy V-notch impact test (Correct answer)
- Guided bend test
- Tensile test
- Hardness test
Correct answer: Charpy V-notch impact test
The Charpy V-notch (CVN) impact test measures the energy absorbed when a notched specimen is fractured by a swinging pendulum, providing a direct measure of material toughness at a specified temperature.
The Charpy V-notch impact test (AWS B4.0, ASTM E23) is the standard method for measuring notch toughness of weld metal and heat-affected zone material. A square cross-section specimen with a standardized V-notch is struck by a pendulum; the energy absorbed to fracture the specimen (in joules or ft-lbs) is recorded. Testing is performed at specified temperatures to evaluate ductile-to-brittle transition behavior. CVN testing is required in many structural and pressure vessel codes (ASME Section VIII, API 1104) for service in low-temperature environments.
Question 3: During visual inspection of a completed weld, what measurement tool is used to verify weld size (leg size) of a fillet weld?
- Fillet weld gauge (weld gauge) (Correct answer)
- Micrometer
- Caliper only
- Tape measure
Correct answer: Fillet weld gauge (weld gauge)
A fillet weld gauge (such as an AWS fillet weld gauge or bridge cam gauge) is specifically designed to measure the actual leg size of fillet welds quickly and accurately during visual inspection.
Fillet weld gauges are purpose-designed tools that allow the CWI to verify the actual leg size of a fillet weld against the specified size on the drawing or WPS. Common types include the AWS fillet weld gauge set (individual gauges in various sizes), the bridge cam gauge (measures fillet size, undercut, reinforcement, and misalignment), and the fillet weld gage with a sliding scale. Per AWS D1.1, the convexity and concavity of the weld face must also be measured and checked against allowable limits, for which adjustable gauges are used.
Question 4: Which nondestructive testing (NDT) method is most effective for detecting subsurface discontinuities in austenitic stainless steel welds that cannot be detected by UT due to coarse grain structure?
- Radiographic testing (RT) (Correct answer)
- Magnetic particle testing (MT)
- Liquid penetrant testing (PT)
- Visual testing (VT)
Correct answer: Radiographic testing (RT)
Radiographic testing (RT) uses X-rays or gamma rays that penetrate the weld regardless of grain structure, making it effective for detecting internal voids, porosity, and inclusions in austenitic stainless steel where UT may be unreliable.
Austenitic stainless steels have a coarse, anisotropic grain structure that causes significant scattering and attenuation of ultrasonic beams, creating 'grain noise' that can mask real defect signals and limit UT effectiveness. Radiographic testing (RT) is not subject to this limitation because X-rays and gamma rays penetrate based on material density and thickness rather than acoustic properties. RT is the preferred method for inspecting austenitic stainless steel and nickel alloy welds for internal discontinuities. MT cannot be used on austenitic stainless steels because they are non-magnetic.
Question 5: What does the term 'interpass temperature' mean in welding inspection?
- The maximum temperature of the weld deposit and surrounding base metal between passes in a multi-pass weld (Correct answer)
- The temperature of the filler metal before welding
- The temperature at which a weld is post-weld heat treated
- The ambient temperature in the welding area
Correct answer: The maximum temperature of the weld deposit and surrounding base metal between passes in a multi-pass weld
Interpass temperature is the temperature of the weld joint area (weld deposit and adjacent base metal) at the time of welding just before each subsequent pass is started in a multi-pass weld.
Interpass temperature controls are critical in multi-pass welding. The maximum interpass temperature limits the heat buildup in the joint to prevent excessive grain growth, HAZ softening (in hardened steels), sensitization (in stainless steels), and loss of toughness properties. AWS D1.1, ASME Section IX, and other codes specify maximum interpass temperatures for specific material groups. The CWI measures the actual temperature with contact pyrometers or temperature-indicating crayons (Tempilstiks) before starting each pass. Minimum interpass temperature is also controlled and is the same as the minimum preheat temperature.
Question 6: In liquid penetrant testing (PT), what is the purpose of the developer?
- Draw the penetrant out of discontinuities and provide a contrasting background to enhance defect visibility (Correct answer)
- Remove excess penetrant from the surface
- Activate the penetrant's fluorescent properties
- Prevent the penetrant from drying in open discontinuities
Correct answer: Draw the penetrant out of discontinuities and provide a contrasting background to enhance defect visibility
The developer draws (blots) the penetrant that has been trapped in surface-open discontinuities back to the surface by capillary action and absorption, spreading it to create a visible indication against the white developer background.
In liquid penetrant testing, after the excess penetrant is removed from the surface, the developer is applied. Developer (dry powder, water-soluble, or nonaqueous wet) works by: (1) capillary absorption — drawing the trapped penetrant out of discontinuities back to the surface, creating a spread, bleed-out indication; and (2) providing a white contrasting background (in color contrast PT) or UV-absorbing background (in fluorescent PT) to maximize the visibility of indications. Development time (dwell time) must be observed per the PT procedure to allow sufficient bleed-out before interpretation.
AWS Welding Inspection & Testing 2
According to AWS D1.1, what is the minimum preheat temperature required for ASTM A36 steel with a thickness greater than 38 mm (1.5 in.) when using a low-hydrogen process?