First of all, Let me be the first to Weldcome you to this forum!!!

Now let's address your question... "is there anybody has twinarc experience on overlap joint?"

When you mention "twinarc" are you referring to the SAW process or "twin arc welding" which consist of two welders depositing welds from either side of the joint in order to deposit CJP (Complete Joint Penetration) without the need to backgouge if performed properly??? The latter I have experience with.

When you mention "overlap joint", what type of joint geometry, or configuration are you referring to???
I look foward to your response.

Merry Christmas to you and your family!!!

Respectfully,
Henry