CWI Destructive Testing and Properties Questions and Answers — Questions and Answers
Question 1: Which of the following destructive tests is specifically designed to evaluate the notch toughness of a material, particularly its susceptibility to brittle fracture at various temperatures?
- Tensile Test
- Hardness Test
- Charpy V-Notch Test (Correct answer)
- Macroetch Test
Correct answer: Charpy V-Notch Test
The Charpy V-Notch (CVN) test measures the amount of energy a standardized notched specimen absorbs during fracture from a pendulum strike. This absorbed energy is a direct measure of the material's notch toughness, which is critical for assessing its resistance to brittle fracture, often across a range of temperatures.
Question 2: A Procedure Qualification Record (PQR) for a groove weld on a 1-inch thick plate specifies side bend tests instead of root and face bend tests. What is the primary reason for this requirement?
- The welding process used has a very high deposition rate.
- Side bends are less expensive and faster to prepare.
- The material thickness is too great for a meaningful root or face bend test. (Correct answer)
- The test is for a fillet weld qualification instead of a groove weld.
Correct answer: The material thickness is too great for a meaningful root or face bend test.
Welding codes such as AWS D1.1 and ASME Section IX require side bend tests for thicker materials (typically 3/8" or 10mm and greater). On thick sections, a root or face bend would place extreme strain on the outer fibers, making a valid test of weld soundness difficult. A side bend tests the entire weld cross-section for ductility and discontinuities.
Question 3: A CWI performs a macroetch test on a cross-section of a fillet weld as part of a procedure qualification. Which of the following observations would be a primary focus of this examination?
- The precise ultimate tensile strength of the weld metal.
- The weld's profile, including depth of fusion and leg size. (Correct answer)
- The presence of microscopic cracking not visible to the naked eye.
- The electrical resistivity of the heat-affected zone.
Correct answer: The weld's profile, including depth of fusion and leg size.
A macroetch test involves polishing and etching a weld cross-section to reveal its metallurgical structure at a macroscopic level. It is used to evaluate the overall weld profile, depth of penetration, fusion to the root, leg sizes, and the presence of large discontinuities like porosity, lack of fusion, or cracks.
Question 4: During a transverse tensile test of a welded specimen, which of the following properties is NOT directly determined from the test data?
- Impact Strength (Correct answer)
- Ultimate Tensile Strength (UTS)
- Location of fracture
- Ductility (via elongation)
Correct answer: Impact Strength
A transverse tensile test measures a material's response to a slow, static pulling force, which is used to determine its ultimate tensile strength, yield strength, ductility (elongation and reduction of area), and the fracture location (weld metal, HAZ, or base metal). Impact strength, which is a measure of toughness under a high strain rate, is determined by a dynamic test like the Charpy V-Notch test, not a tensile test.
Question 5: A welder's performance qualification test requires a nick-break test on a groove weld. What is the primary objective of this specific destructive test?
- To measure the weld's ultimate tensile strength.
- To determine the hardness of the heat-affected zone (HAZ).
- To reveal the internal soundness and fusion of the weld metal. (Correct answer)
- To calculate the percentage of elongation for ductility.
Correct answer: To reveal the internal soundness and fusion of the weld metal.
The nick-break test involves cutting notches into the weld and then fracturing the specimen along the weld line. This exposes the internal fracture surface, allowing for a visual examination of the weld's internal quality. It is specifically used to check for discontinuities such as slag inclusions, porosity, and lack of fusion.
Question 6: In the context of material properties, which statement best describes the typical relationship between hardness and toughness in the heat-affected zone (HAZ) of a carbon steel weld?
- As hardness increases, toughness always increases proportionally.
- An increase in hardness, often due to rapid cooling, generally leads to a decrease in toughness. (Correct answer)
- Hardness and toughness are independent properties and have no correlation.
- Hardness measures resistance to impact, while toughness measures resistance to indentation.
Correct answer: An increase in hardness, often due to rapid cooling, generally leads to a decrease in toughness.
For many carbon and low-alloy steels, there is an inverse relationship between hardness and toughness. Rapid cooling rates in the HAZ can create hard, brittle microstructures (like martensite), which increases the material's hardness but significantly reduces its ability to absorb energy before fracturing, thus lowering its toughness.
CWI Destructive Testing and Properties Questions and Answers
Which of the following destructive tests is specifically designed to evaluate the notch toughness of a material, particularly its susceptibility to brittle fracture at various temperatures?