Hi, Vadivel Mahadevan,
You may refer to AWS QC-1 for the qualification/experience requirements of CWI.
You can check your your person who is doing your inspection task of welding performed, that matches to AWS QC-1.
If that satisfies you may create a procedure describing the training requirement.
This is in detail about the topic covered for training [may be the welding process that you are using and the inspection governing code/ standard that you are using] and the examination requirement. This procedure for qualification to be reviewed and approved by a competent person of your organization.
According to the above manufacturers documented procedure for qualification you may provide training and assess your welding supervisor and qualify them as welding inspector.
Certification thus provided may in compliant with API 6D requirement.
Thanks,
MANIVANNAN.P