We do not have inspection test plans for fabrication and welding. Laboratories that test materials are accredited to ISO 17025 while inspection bodies are to the ISO 17020 standard. ISO 17025 assessment checks are applicable for testing activities, not inspection. It is ISO 17020 that covers the activities of inspection bodies. The test plans of course would cover requirements and standards specific to the welding and fabrication industry. The inspectors in most cases, would also require personal certification, to provide competence assurance. I suggest you contact your professional association / regulatory body for further information.