CSWIP 3.1: Leading Multiple Choice Questions with Full Explanations

Q1. Which is the best destructive test for showing lack of sidewall fusion in a 25mm thickness butt weld?

Nick break
Side bend
Charpy impact
Face bend test

Q1a. With reference to the previous question and the correct answer, what type of test is this?

Qualitative
Tentative
Quantitative
Sensitive

Answer – Q1: b. Side bend & Q1a: a Qualitative

Explanation: The Side bend test reveals the sidewall fusion issues upon bending, making it the best option. Why other other options are not correct or less correct?

Nick break: This test is carried out for butt weld and the sample is notched so that the fracture path will be in the central region of the weld. We can detect internal defects like lack of fusion, solid inclusions and porosity that are visible on the fracture surfaces but for lack of sidewall fusion this would not be an appropriate test because the fracture is done on the centre of the weld.

Charpy impact: This test measures the toughness of the weld by striking a notched specimen, but it does not directly show fusion defects.

Face bend: This test bends the weld from the face of the weld, but it is less effective in detecting sidewall fusion issues compared to the side bend test.

Explanation for Question 1a:

Destructive tests can be divided into two groups, those used to:

Quantitative tests: Measure a mechanical property (Numerical data)
Qualitative tests: Assess the joint quality

Let us analyse each options:

Qualitative: The side bend test is qualitative because it visually assesses the weld’s integrity by bending the specimen and observing any defects like cracks or separations. Hence, this is the most appropriate option.
Tentative: This term does not apply to the nature of the test.
Quantitative: This term refers to tests that measure numerical data, which is not the case for the side bend test.
Sensitive: This term does not describe the type of test.

Q2. Which of the following is a planar imperfection?

Lack of sidewall fusion
Slag inclusion
Linear porosity
Root concavity

Q2a. With reference to the previous question and the correct answer, how could this defect be caused?

Amperage to high
Voltage too high
Amperage too low
Gas flow rate too low

Answer – Q2: 1. Lack of sidewall fusion, Q2a: 3. Amperage too low

Explanations: Welding discontinuities are categorized into two main types based on their dimensional characteristics:

Volumetric Discontinuities: These are three-dimensional defects that have length, width, and thickness. Examples include slag inclusions and porosity.
Planar Discontinuities: These are two-dimensional defects that lie on a single plane. Examples include lack of fusion and cracks. Hence, option 1 i.e Lack of sidewall fusion is the correct answer.

Explanation for Q2a:

Amperage too high: High amperage can cause excessive penetration or burn-through, but it is not typically associated with lack of fusion
Voltage too high: High voltage can lead to a wider, flatter bead, but it does not directly cause lack of fusion
Amperage too low: Low amperage can result in insufficient heat input, leading to poor fusion between the weld metal and the base material, causing lack of sidewall fusion. Hence, this is the correct answer.
Gas flow rate too low: Low gas flow rate can cause porosity due to inadequate shielding, but it does not directly cause lack of fusion

Q3. A fillet weld has an actual throat thickness of 8mm and a leg length of 7mm, what is the excess weld metal?

2.1 mm
3.1 mm
1.8 mm
1.4 mm

Q3a. With reference to the previous question and the correct answer, if this excess weld metal was removed the fillet would be a?

Concave fillet weld
Convex fillet weld
Undersized fillet weld
Mitre

Answer – Q3: 2. 3.1 mm & Q3a: 4. Mitre

Explanations:

The theoretical throat thickness for a fillet weld is calculated as (a X .7) = 7×0.7=4.9 mm
The excess weld metal is the difference between the actual throat thickness and the theoretical throat thickness: 8−4.9=3.1 mm.

Explanation for Question 3a

A convex fillet weld has a curved outward face.
A concave fillet weld has a curved inward face.
A mitre fillet weld has a flat face. Hence when the excess weld metal will be remover the weld profile will become similar to mitre fillet weld.

Q4. BS EN 17637 allows the use of a magnifying glass for visual inspection, but recommends that the magnification is:

X 2
X 2 to x5
X 5 to x10
Not greater than X20

Q4a. With reference to the previous question, what likely defect will this help to find?

Excess weld metal height
Root concavity
Internal lack of fusion
Undercut

Answer – Q4: 2. X 2 to x5 & Q4a: 4 Undercut

Explanations: X 2 to x5: This range is recommended by BS EN 17637 for visual inspection as it provides sufficient magnification to detect finer surface defects

Explanation of Question 4a: Undercut: This defect, which appears as a groove along the weld toe, can be more easily detected with magnification in the range of X 2 to x5. Hence, it is the most appropriate answer. Let us analyse other options:

Excess weld metal height: This defect is usually visible to the naked eye and does not require magnification.
Internal lack of fusion: This defect is internal and cannot be detected by visual inspection with a magnifying glass.
Root concavity: This defect is typically visible without magnification.

Q5. Pipe bores of some materials must be purged with argon before and during TIG welding to:

Prevent linear porosity
Prevent burn-through
Prevent oxidation of the root bead
Eliminate moisture pick-up in the root bead

Q5a. With reference to the previous question and the correct answer, what material would this pipe be?

All materials
Aluminium and stainless steel
Stainless steel
Carbon steel and stainless steel

Answer – Q5: 3. Prevent oxidation of the root bead & Q5a: 2. Aluminium and stainless steel

Explanations: Let us understand, why purging is required on rood bead from the back side?

Root bead is first pass, vulnerable to air inside pipe. Oxidation weakens weld, reduces corrosion resistance. Since, Argon is inert gas. It displaces oxygen and prevents reaction with hot metal i.e oxidation. Hence, correct option is Prevent oxidation of the root bead (option no.3)

Why Other Options are Less Correct:

(1) Prevent Linear Porosity: Argon helps, but oxidation prevention is primary.

(2) Prevent Burn-Through: Shielding indirectly affects heat, but purging isn’t burn-through control.

(4) Eliminate Moisture: Argon reduces moisture, but oxidation prevention is main goal. “Eliminate” is too strong.

Explanation for question Q5a:

Correct: (2) Aluminium and stainless steel

Reason: These metals are highly reactive with oxygen at welding temperatures.

Essential: Purging is critical to prevent oxide formation, ensuring weld quality & corrosion resistance.