Perhaps you need to understand how a qualification test works. The test coupons should already be prepared with a bevel. They should provide you with a backer bar. You set it up and tack it together. You then weld up the root pass, you are not typically not allowed to use a grinder. You then weld up the rest of the test. Once you have completed the test coupon you give the completed test to the testing authority and they perform a visual examination. They are looking for defects, porosity, undercut, underfill, overfill, anything that falls outside the acceptance criteria listed in the weding code they are using.
Assuming it passes visual inspection the test person will then section the test and perform whatever tests are required by said code. This can include, bends, tensiles, macroetch, etc. The testing authority will remove the backer bar, at least this is the common practice. I would never recomend arc gouging as a suitable removal method as it adds heat to the part and heat is your enemy. Do not quench the test piece to cool it down, let it slow cool. Why? Better chance that it wont break when they bend it. Backer bar can usually be removed easily after sectioning by simply placeing it in a vice and twisteing it off using a large wrench. If this fails I like to machine the backer off.
I remove the backing bars after cutting the straps. It is only 3/8, 3/4, or 1 1/2 wide straps usually and therefore not as big of a task as it would be as removing the whole bar. I put it in a vise and use a grinder.
What ever is easiest for you if given that option. Not all test booths are created equal. I've had to drag the material (pipe and plate) out of the racks, cut with torch or saw, prep... do everything including run the "ol one-armed johnny" to bend. This has happened on more than once. The reason I was given, was to see if you could work in a safe methodical manor and familiarity with the basic tools of the trade, and if the visual was in that gray area, a klutz could be "looked out". Looking back on it (of course it sux to have all that x-tra sweat involved. We don't always have the luxury of when a job is NECESSARY!) I think it is a fair test that allows an employer to weed out future slackers. Years later, I've done it myself. We were paying xlnt wages, busy and did not have the time for coupon prep or extensive interviews.
As far as method of removal goes, I've used all methods possible and can't ever recall seeing one fail mysteriously. There was always an identifiable defect. Never say never though...Good luck on your test.
I leave the backing bar on the coupon and go ahead and cut the 3/8" strips out of it, then take and turn those 3/8" strips upside down and turn the grinder wheel on edge and grind into the backing bar just at the edges of where the root is fused...this way you are only grinding about a 3/8 x 3/8 area...no big deal and it is pretty quick...just be careful of the grinder and make sure the guards are used.
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