(i) Radiographic Testing

A non-destructive testing method that uses penetrating radiation (X-rays or gamma rays) to detect internal flaws in materials. The radiation passes through the material, and variations in its intensity are recorded on a X-ray film. Darker areas on the image correspond to denser regions (defects) within the material. X-ray radiography is better suited for smaller defects, while gamma radiography can penetrate thicker materials and detect larger flaws.

Advantages:

• Highly sensitive to internal discontinuities
• Relatively less time-consuming
• Produces permanent records.

Disadvantages:

• Involves radiation hazards, requiring specialized training and safety precautions
• Necessitates skilled operators
• High initial equipment cost.

(ii) Ultrasonic Testing

Employs high-frequency sound waves (ultrasonic) to detect internal and sometimes surface flaws. The ultrasonic waves are transmitted into the material, and any reflections caused by discontinuities are detected and measured. Methods include pulse-echo (single transducer sends and receives waves) and through-transmission (separate transducers transmit and receive).

Pulse-echo method:

Transmission method:

Advantages:

• Effective at detecting deep-seated flaws
• Determines flaw depth, size, and location
• Portable and relatively easy-to-use equipment
• Good accuracy and reliability.

Disadvantages:

• Sub-surface discontinuities near the surface may be difficult to detect
• Challenging to examine irregularly shaped or rough components
• Requires skilled interpretation of the results.

(i) Metal locking is a cold-working repair method for fractured castings. The process involves precisely aligning and clamping the fractured pieces. A series of holes are drilled perpendicular to the crack and then shaped to accept interlocking metal keys. These keys are inserted, followed by studs driven into the holes, each stud biting into the preceding one to create a tight, secure join. Finally, the studs and keys are ground smooth for a polished finish. This method avoids the use of heat.

(ii) TIG (Tungsten Inert Gas Welding): TIG welding uses a non-consumable tungsten electrode and an inert shielding gas (Argon or Helium) to protect the weld from atmospheric contamination. A filler metal is often, but not always, used. A constant-current power supply creates an arc, ionising the gas and metal vapour to fuse the materials. TIG welding is ideal for thin sections of stainless steel and non-ferrous metals like aluminium, magnesium, and copper alloys. It produces high-quality welds but is slower and more complex than other methods.

MIG (Metal Inert Gas Welding): MIG welding uses a consumable wire electrode that melts and fuses with the workpiece material. A shielding gas is also used to protect the weld. Both AC and DC currents can be employed. MIG welding is suitable for steel, aluminium, and other non-ferrous materials. Its advantages include faster welding speed and easier automation.