The ferritic P22 and bainitic‐martenstic P91 steel welded joints operating at elevated temperatures are highly vulnerable to premature failure, because microstructure gradients can lead to cracking in the heat‐affected zone, commonly referred to as type IV cracking. Creep crack growth tests have been performed using compact tension specimens made of P91 and P22 weld joints at temperatures of 600 and 550 °C, respectively. The creep crack growth characterization through empirical equation of C* was the main fracture parameter for relating behaviour of component's regions. Results have shown that, for a specific value of C* parameter, the weld metal and heat‐affected zone had similar crack growth rates, which were about two times faster than base metal rates, because of lower creep strength that leads to a conclusion that the creep cracks will most likely initiate in the heat‐affected zone region.

The steels operating at elevated temperatures are well known to be exposed to premature failure due to cracking caused by constant thermal stress, i. e. secondary creep process. Therefore, creep crack growth tests were carried out on compact tension specimens machined from P91 weld joint at 600 °C to determine its behavior in realistic conditions. At the same time, numerical method for predicting the creep crack growth in compact tension specimens by a series of incremental steady-state finite element analysis were performed using Norton's law to represent creep behavior. Verification of the finite element predictions were obtained for weld metal and heat affected zone by comparison with experimental results, indicating at the same time that creep crack growth rates are significantly higher for weld metal than for base metal.