Is there porosity on stainless welding?

Porosity is caused by molten puddle problems: oil, dirt, etc near weld, lack of shielding gas (tank is empty, or wind is blowing away gas. local vaccums for ventilation also can cause gas problems.) If mig welding, if you don't balance wire speed to amps, you may see porosity. Lastly, long arc'ing (too much distance from end of mig wire, to material) can cause bubbling.