Small Punch Testing of Exposed High-Pressure Steam Pipelines

Non-disruptive material sample scooping is frequently applied to a range of operating components since it is supposed that removal of small amount of material from the surface has no effect on components integrity. As-removed material is then subjected to mechanical testing by small punch test to estimate tensile, creep and fracture properties necessary for assessment of residual life of the component. The question arises whether the assumption that measurements on surface specimens are representative for the characterization of whole component is justified. For the verification of this assumption, four steam pipes after either plant- or simulated-exposure up to 104 000 hours were used. Small punch specimens were prepared from different positions within pipes. The dimensions of specimens enable to estimate mechanical properties for several dozens of specimens along available power-plant pipes’ walls. The paper summarizes the results of small punch tests at both constant deflection rate and constant force and at room and elevated temperature, respectively. In the walls of the investigated pipes, the results obtained on surface specimens do not differ substantially from the results on specimens prepared from central parts.