I didn't see anything in the 2006 edition about interpass cleaning either.
The codes do not provide direction on "how" to conduct a welder qualification test. That's where the newbie CWI should be teamed with an experienced CWI to learn how to conduct a welder qualification test. Do you ask to see the "green" card or driver's license, is it alright to use a sledge hammer to break out fused slag and to straighten plates that have been distorted, Does the welder need to use strong-backs and how do they get attached, do you allow the welder to use the milling machine to remove the last weld bead down to sound metal to remove the slag inclusion and porosity before depositing the cover pass, etc.
Now is the time to consider formalizing the test rules for how you give the welder performance test. The welder needs to know what he can and can't do before the test starts, not half way through the test. Think hard and long about what the welder can do and what he can't do while taking the test. Are you going to allow grinding between each weld pass? Are you going to allow the welder to take the test plates down so that he can wire brush and chisel each weld bead? Remember the code provides very little detail in this matter, so you, the person that is signing the "Welder Cert" has to understand that your signature is what everyone sees when the welder gets into the field and screws up every weld he makes. They are going to ask themselves if they want to accept your paperwork on future projects. The welder you let slide because he was such a nice guy could put your job and future in question.
Best regards - Al