What does the abbreviation "B.C." mean on a weld joint diagram?

Question

A translator posted this diagram of a weld joint on a translator's forum (the figure below). What does the abbreviation "B.C." mean on the diagram?

Answer 1

I'm not aware of BC as standard English nomenclature for welding, but I have a guess for what they mean. The fact that there is a period after the B but not the C makes me wonder if something was cut off or whited out in the original.

I think they mean backgouge (BG) which would be a common process in a double sided vee groove weld it it needed to be a complete joint penetration (CJP) weld. This is sometimes indicated with a dotted line like that, although strictly of they backgouge as shown they should have drawn a u groove weld instead of a vee groove on the top side.

There welder will bevel the bottom side using a grinder or plate beveler. Then they will weld the bottom side, but the root of the bottom weld will be contaminated by air from the other side of the weld since there is no backer or backing gas and thus no shielding on the far side. On the top side, using a grinder or a carbon electrode they will remove all of the contaminated root metal and then begin the seconds side weld. This weld if protected on the back side by the metal of the first weld, yielding a sound weld through the whole depth of the joint.