Root gap or butted tight is down to wall thickness. Typically with exhaust stuff you'd butt it up to make the pipe fitting/fabrication easier and (thin wall stuff aside) use a v prep instead.-When you say proper fit up ?
-Because at the tutorial section, says, if you want to have full penetration in a butt weld, you have to have a small gap at the begining. Proper fit up you mean full contact prior to butt welding ?
- This weld is surely with filler. (the other weld at the corner pic shows filler)
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As the manifold is heat cycled there'll be expansion/contraction forces compounded by the uneven temp spread...-Another thing i noticed is that usually tube manifold cracks develop in the inside radius of the pipe.