Process control is the correct answer.

My first recommendation would be to study the contents of the following book.
Certified Welding Supervisor Manual for Qualify and Productivity Improvement

This book has the body of knowledge for the Certified Welding Supervisor designation

Without more specific details about your problems a general answer is all that can be provided.

Do you mean in process repairs to bad work?  Items that need attention prior to approval for shipping? 

Thus, you are the manufacturer/fabricator and items being welded need repairs and there are way too many of them and the time is wasting away the profits on the job?

If so, sounds like some serious training followed by write ups with teeth in them.  Unpaid time off, fired after X number of write ups, etc. 

Are we talking UT repairs, discontinuities like arc strikes, undercut, undersized welds, etc or a combination of the two?

Brent

You must evaluate the reasons for rejects. Identify the possible causes, and review what can be done to control the possible causes.

Is the acceptance criteria being exceeded. Are defects related to a specific welder, material, WPS, crew, etc...

Have great day and some more information could be useful.
Gerald Austin