Abstract: This article addresses the challenge of limited space welding during the maintenance of the bottom inlet/outlet water pipes of Residual Heat Removal Heat Exchanger. A maintenance equipment suitable for replacing the bottom inlet/outlet water pipes of the Residual Heat Removal Heat Exchanger has been designed. Three-dimensional modeling has verified that it meets the construction space requirements. To address the issue of concave weld seams in full-position self-fusion welding of pipes, a Φ33.4×3.4mm pipe butt welding molten ring has been designed. A full-position welding process for pipes using the molten ring has been developed, resulting in uniform weld formation without concavity, meeting the process requirements. Subsequent to the completion of equipment fabrication, adaptability tests will be conducted using the equipment and process to verify their effectiveness, providing a new solution for the maintenance of nuclear power equipment.