There is a hole in the second pic

 

Well, sometimes you trap a little unwanted gas or impurities and it burps up like that creating a little pin hole. This seems to happen more often on multiple passes and is the reason many do not leak. That one may or may not pass through to the inside of the header. If I had been welding this I would have hit that again for a just a second to close it over. That being said, it may not leak.

 

It's called a star crack. Sometimes referred to as a fish eye. The problem is the molten metal cooled off too fast resulting in a crack. Stainless is much more picky than carbon steel and there are certain steps that need to be taken in the process of welding.

All I'm getting at is fix it now before it goes on the truck. Save the headache. If the OP is like most other owners he wants his sh*t right. I don't know of many people that prefer a half @ss'd job.

 

I've welded up many star cracks, none of them looked like that LOL. Also, those pin holes can happen with about every weldable metal. That is certainly not specific to stainless. Sure, the guy could have put one more dot on the weld. Big deal.

 

yeah no leaks with the little bubble hole. the weld did not go through to the inside , the inside is smooth. all is good, its just a bung hole

 

Glad to hear it doesn't leak. In that application it may never fail, but it wouldn't pass inspection criteria.

My background involves nuclear power plants, natural gas power plants, coal fired power plants, pressure vessel construction and repair and anything related to the turbine generator at a power plant. My work is scrutinized at the highest level and so I always maintain a level of quality. I have to.