SMALL PUNCH TESTING OF THICK WALLED PIPE MADE OF THE STEEL P92 WITH HETEROGENEOUS MICROSTRUCTURE

The paper deals with the small punch testing of material properties including short-term creep resistance and microstructure analysis a thick-walled pipe made of P92 steel, where metallographic analysis revealed numerous internal defects, especially close to the inner surface of the pipe. These defects had their origin in the shrinkage porosity of the continuously cast slab and remained in the microstructure probably due to insufficient deformation during pipe rolling. The local material properties at the both inner and outer surfaces were compared by metallography, tensile tests, hardness tests, Charpy-V notch tests as well as small punch and small punch creep tests. The obtained results are compared with the material requirements for P92 steel and an attempt is made to evaluate the possible influence of the inhomogeneity of the microstructure and properties on the long-term service life of the pipe under creep conditions.