Dear all,

Please refer to ASME section IX “QW-402.24 Qualification with a cooling medium (water, flowing gas, etc.) on the root side of a test coupon weld that is welded from one side qualifies all thicknesses of base metal with cooling medium down to the thickness of the test coupon at the root or 1⁄2 in. (13 mm), whichever is less.”

Can you please tell me where or what is "the thickness of the test coupon at the root" in above sentence?

Thanks.