Due to global higher needs trend for energy consuption, demands for durability and reliability of steamboiler componennts are much more emphasized. That leads to modern steamboiler materials application in extraordinary heavy service conditions (creep, fatigue, thermo mechanical load in service, corrosion in aggresive medium, ...). Nowadays, in modern steamboiler components and plants production which operate in heavy service conditions, new modern materials P91, P92 and Ni based alloys are used. Due to fact that those materials are relatively new and ther is not enough experience from service and also from special laboratory investigations, this paper gives some practical data from several years practical application in workshop and special laboratory investigations.