thanks for answer, 

I would like to analyze situation when air is closed in box for example 300x300x100mm (thicknes = 10mm), this box is made by welding on full penetration six pieces of plate, next it will stay for a month in temperature 20C so we can assume that temperatur steel box and air will be the same, during welding we will have a smal hole (radius = 5mm) in one plate, closed by welding when temperature of steel box and air reaches the value 20C. I'm aware of welding stresses, but I would like to omit them and consider only influance pressure from expansion air after heating, considerated in the same time expansion of steel box (non-linear material).

I would like to analized sucha a situation in ansys, I builded model of box in this program in analysis system "Static structural" but I think that in this system I can't analyzed situation with air closed in box