SNT-TC1a allows Level II's to inspect to, and Accept/Reject items to specific criteria, in accordance to a written procedure. The written procedure requires approval by a Level III, prior to allowing a Level I or II to implement it. ASME Code makes these same requirements.
It sounds like your SOP/Work Instruction may fall under these requirements. However, if there is a specific NDE Procedure that can be utilized for your SOP/Work Instruction, and that Procedure is approved by a Level III, your individual Work Instructions probably do not require individual approval from a Level III. You would just reference, and work to, the approved NDE Procedure.
Roger, I have the latest edition of SNT-TC-1A and on the front cover it clearly says that this is for guidance only and should NOT be used as a strict procedure.
I just got screwed by the local government body who will not give me a permit to work as they cannot read English and also say as per SNT-TC-1A stipul;ates all proceedures need to be approved by a level III. I have about 230 written proceedures and this would just not be possible.
Where SNT-TC-1A is a set of guidelines for an employer to develop its own personnel certification procedure, CP 189 is a standard, ie once agreed all its clauses are mandatory.
CP 189 defines a procedure as "A detailed written instruction for conducting a nondestructive test or certifying personnel. Method procedures shall be approved by the NDT Level III certified in the applicable method." This is subjective though as procedures are necessarily very detailed as to how the test is done in general, but it cannot be written in advance to cover all essential parameters for an unknown component. If the procedure has been verified and approved by an appropriate Level III then individual component test parameters can be raised by the level II.
For obvious reasons many large end users specify CP 189 rather than SNT-TC-1A as it sets out a minimum standard.
You could have a few procedures according to the number of NDT methods you wish to utilise and then addend the different instructions to the relevant procedure. Provided the instructions are written by an appropriately qualified Level II and conform with the procedure they should not require Level III approval.
Hope this helps prevent your premature return home!