What service? What specific kind of copper-nickel alloy?
What physical characteristics? Dia, schedule, pressure, temperature, above-below ground, what length, what is the failure that needs to be fixed/repaired/repalced?
What is your schedule and budget limits?
What resources do you have available? Doesn't matter how good a repair could be, if you can't do that kind of repair?
What country? What are your liabilities if the repair fails? Are people or products or environment death/injuries/leaks possible if the repair fails?