Sir,
It doesn't work that way. Successful WPS qualification with impact testing (and presuming that you meet all of the other WPS qualification requirements) will serve to demonstrate that the completed welds will meet the stated requirements if the completed welds are made in accordance with the WPS. There is no nondestructive testing method that will prove if the weld was performed in accordance with the WPS.

In order to do this, the welding operation itself must be monitored. That is why it is a requirement in many industries and in many project specifications to perform actual quality control activities related to welding process control. These included verification of all of the welding variables, including but not limited to: base and filler material selection, cleaning methods, joint preparation, welder qualification, welding parameters including amps, volts, travel speed, PWHT, etc.

Hope this helps.
Mankenberg

Dave:
As such, there is no NDT method available for verfying the impact requirement. In general, in non-critical applications it will be a part of welding procedure qualification. Once welding procedure is qualified, the weld shall be produced without changing the essential variables.

In critical applications such as nuclear applications and high thickness power boiler drums, test coupons are produced while a welding joint with the same machine with same setting. These coupons are prepared from the same heat number for the plate to be joined. When welding a long seam of the vessel, test plates are attached at one end fo the joint, so you make a continous weld and cut them off once welding is completed. Where as in circumferential welding, test plates are welded separately after completion of parent welding. Then, test coupons are tested by MT, RT/UT for any imperfections before sending to mechanical lab for impact testing. The NDT tests are for to detect any defective portion and discard them before mechanical testing.
If the application is critical and client makes requirement, they usually cover the extra cost associated with test coupon material, preparation, welding, NDT and mechanical testing etc.

I hope this helps.

Muthu