6.1 State TWO causes of EACH of the following welding defects: 6.1.1 Undercutting 6.1.2 Lack of fusion 6.2 Explain how the ultrasonic test is conducted on a welding joint - NSC Mechanical Technology Welding and Metalwork - Question 6 - 2016 - Paper 1

1. A welding speed that is too fast can lead to lack of fusion as the weld may not penetrate adequately.
2. Using a welding current that is too low can also contribute to this defect, preventing proper melting of the base materials.

The ultrasonic test involves sending a high-frequency sound wave into the metal of the weld joint. This sound wave is carefully emitted using a transducer, which then receives any returning waves. The deflections in the received wave indicate possible defects present within the weld metal. Additionally, this method allows for the detection of subsurface flaws without damaging the component.

An advantage of conducting an ultrasonic test is that it is safer than using X-ray testing, as it does not involve exposure to harmful radiation.

The results of an X-ray test are typically recorded using photographic film or digitally on a computer monitor. The images produced show the internal structure of the weld, and any defects can be identified based on their appearance on the film.

The dye penetration test is used to detect surface or external flaws in a welded joint. The test involves applying a visible dye that seeps into any surface cracks or discontinuities, highlighting imperfections against the clean surface once the excess dye is removed.

1. Nick break test, which involves breaking the welded joint to examine the fracture surface for internal defects.
2. Tensile test, where samples are pulled apart to determine the strength and ductility of the weld.

1. Argon
2. Carbon Dioxide (CO2)

A - Weld Pool B - Arc/Weld Wire C - Contact Nozzle / Nozzle D - Gas Shielding Valve E - Electrode Holder F - Earth Clamp / Ground Wire