The Weld Depth and Angle Acuity Effects on the Crack Growth Behaviour of P91 Feature Test Specimens

In this paper the creep crack initiation and growth path through the type IV region of large feature sized SEN(T) specimens of Mod. 9Cr-1Mo steel at 650 °C are investigated. The large SENT specimens contained 100mm long welds were tested with an initial EDM starter crack of 2mm placed at the surface. One specimen had a 10mm and the second had a 30mm weld at the centre depth tapering down to the surface shaped as an approximate semi oval. A third specimen with similar weld dimensions but of substantially smaller size was tested to identify the effect of size on crack path. The results suggest that despite the sharp angular direction of the welds, the crack path still went through the type IV region reaching an angle parallel to the load line direction and finally failing by net section rupture. The smaller specimen exhibited a faster deviation from the weld path compared to the thicker specimens. The approximated data for crack growth rates were correlated with the C* parameter and compared satisfactorily with standard compact tension weld test data. Metallographic observations were also performed to identify the region of the cracking and the damage associated with it. Specimen crack path showed clear indications that cracking follows the type IV region.