knslash, I believe you will get numerous opinions on this issue.  Just do a search on this forum for question..try "grinding", "qualification", "testing", or any other keyword that may bring up the post.  There was a rather lengthy one a while back.

Now, for my answer - I allow the use of grinders for weld tests - that's all I will say.

There are a wide variety of opinions on this subject, so what I would suggest is to also learn how to weld the test without a grinder.  Inspectors, just as welders, are all different and do things differently.  Some will allow grinders, some will not....also depends on what code or in-house standards are in place.  I would also suggest finding out BEFORE the test what the requirements are, so you are fully prepared.

It's a test, can the welder make a sound weld or not. Once again, I'll say that insofar as possible, I will only go to the letter of the code. Given your reference to pipe and oil field, I'll Use ASME Section IX and API 1104 as examples
However; Section IX has a little sentence that states:
"The performance test may be terminated at any stage of the testing procedure, whenever it becomes apparent to the supervisor conducting the tests that the welder or welding operator does not have the required skill to produce results."

When testing to API 1104 the only latitude afforded the supervisor/inspector is in the following paragraph:
"For a qualification test weld to meet the requirements for
visual examination, the weld shall be free from cracks, inadequate
penetration, and burn-through, and must present a neat
workman-like appearance."

Assuming there are no company specific work instructions, nor any other instruction in writing ASME Section IX allows far more latitude for inspector opinion than does 1104.
In effect, the inspector is given the latitude to determine what constitutes "apparent" and "required skills".

In 1104 the latitude comes in the cap. The final weld must have a "neat workman-like appearance". That to is opening the door for inspector interpretation but only insofar as the final weld is concerned. That is in contrast to Section IX in which it could be at any point in the process.

To my specific answer now:

For Section IX test, if I get the impression the grinder is being used as a crutch, I'll bust him out under the apparent clause. If they are using it in a manner that is consistent with good work practices in the field, I'll let it ride. (good work practices being grind stop starts, or small areas where the bead isn't just so etc. this in contrast to bad work practices where the bead looks like hell the entire length and they use it to take off half the bead just to get a smooth surface to start with again.)

1104 does not give that option directly. The emphasis for it is on the appearance of the cap / root.
My experience tells me, if they can't make the root or cap "neat-workman-like appearance" the likelihood of making the fill is near to zero.
I will have made it clear before hand that the root is to be inspected before continuation of test if accessible. If it looks good, I stand back and watch.
The welder can grind till hell freezes over as there is nothing specific I can say code wise. However; when it comes to the cap, and they are still grinding heavy,
that's the end of the road for them. neat-workman like appearance does not mean ground smooth to me, it means laid in properly with only start stops and slag cleaning allowed.

For all of them the intent is to make a sound weld with 1104 throwing in the only clause for busting ugly that I am aware of.

Either way you cut it, if i see the welder knows what they are doing, I say nothing about grinding if they use it properly. In neither case would I allow using the grinder to make the final pretty.

My opinion for what it's worth,
Gerald