Final answer:
In the radiographic assessment of a standard SMAW welder's test plate, the centre 50 mm (2 in) of the weld is usually radiographed to check for weld defects. This ensures an evaluation of the critical central zone of the weld where starts and stops are more likely to have occurred.
Step-by-step explanation:
When using radiography to assess a welder's test in SMAW (Shielded Metal Arc Welding), a specific portion of the weld is examined to evaluate the quality of the weld. According to standard procedures, the centre 50 mm (2 in) of the weld is typically radiographed. This is done to ensure that the most critical part of the weld, which is generally at the center of the test plate where the welding starts and stops, is examined for defects such as porosity, inclusions, and cracks.
An answer to the options listed in the question: 'centre 75 mm (3 in) of weld' is usually not standard practice for such tests, nor is 'all 150 mm (6 in)' or 'outside 50 mm (2 in)' on both sides usually required. It is critical that specific standards and procedures are followed when conducting and evaluating radiographic testing to ensure the safety and integrity of the weld.