According to AWS A3.0 document the porosity is determined as “continuity transgression in the form of hollow space, formed by captured gas in consolidation process”. Thus we have a right to examine pores as certain hollow spaces or gas pockets inside consolidated metal of welded joint. Thanks to characteristic spherical form the pores are considered to be the least dangerous continuity transgression. At the same time in case, when we are talking about welded joint of the vessel, where gas or liquid are kept, the pores are able to cause big damage.
As in the case of fracturing, different types of pores have different names. Usually, they signify certain location of porosity zone of form of separate pockets of porous area. That is why for more precise determination of porosity phenomenon we use such names,as uniformly distributed porosity, pores agglomeration, chained pore, and also tunnel pores. Single cavity is called pore ore cavity.
“Uniformly distributed porosity” term is related to numerous pores, distributed by all welded joint without certain clear order. “Pores agglomeration” and “chained pores” terms are used for indication certain order of pores arrangement. Pores agglomeration is several pores, located as a group, and “chained pores” term is related to several cavities, grouped as straight line.
There are some types of pores, when some pore pockets have elongated form instead of spherical. This pore type is often called worm-hole. Similar surface state can be a result of gas capturing between melted metal and indurated slag. This phenomenon can occur under conditions of surplus depth of granule flux, used in the process of submerged arc welding. At that the flux mass is so significant, that it prevents appropriate gas outlet.