On-Plant Test of TUV HCMl2 and ASME T23 Alloys for Use as Water Wall Materials

摘要

The development of Ultra Super Critical power plants has emphasised the need for stronger alloys for use as water walls. For this purpose Try HCM12 and T23 have been tested at 2 Danish power plants. TUV RCM12 and T23 have been tested for their weldability, for thermal fatigue properties and for their oxidation properties under steam conditions 435-520 C, 26-27 MPa. The test included application of different weld methods and testing of the mechanical properties of the weld seams. The weld parameters giving the optimal properties were chosen to manufacture two pieces of water wall (l times l.5 meter). The two test pieces each had two separate steam loops, which could be feed by steam having different steam parameters. Each test piece was installed in a coal fired power plant (steam parameters 540` C, 25 MPa) and exposed to alternating steam conditions. In each test piece one loop was subject to constant steam parameters (434`deg C, 27 MPa) and another loop was subject to alternating steam parameters (switching between 485`deg. C, 25.9 MPa and 434 C, 27 MPa). Steam parameters were switched app. 2000 times. By this exposure each test piece was subject to alternating thermal stress, corresponding to the stress, which appear in the water walls of an USC plant. The exposure was performed in the stress region close to the yield strength limit and cracks appeared in one of the materials. The tests have revealed that Try HCM12 is difficult to weld but develops no thermal fatigue crack whereas T23 is easy to weld but develops thermal fatigue cracks.