Certificate III in Engineering – Fabrication Trade (MEM31925) has no formal entry requirements at the national level — you don't need to be an apprentice or hold a training contract to complete it.
Through RPL, what matters is whether your hands-on experience covers the skills the qualification requires. You're likely to be eligible if you've built genuine experience in fabrication work — welding, sheetmetal work, structural steel erection, blacksmithing or surface finishing — whether that came from paid work, an apprenticeship (complete or incomplete), informal on-the-job training, or work overseas.
Get in touch and your consultant will talk through your background to confirm whether your experience is likely to meet the units of competency, before you commit to anything.