Page 3 of 4
Laboratory oxidation testing of plain and coated specimens at 650°C (1,202°F), 750°C (1,382°F) and 800°C (1,472°F) at 0.1 and 1.7 MPa (14.5 and 246.6 psi) with some at exposure times of 10,000 hours, have produced some interesting results [10]. Steam-side oxidation rates and weight loss were lower for materials with chromium content of more than 12 percent with ferritic steels and 19 percent Cr for iron-based austenitic materials. Shot peening or blasting was effective for USC (620°C/1,148°F) steam generators. Surface cold work treatment of non-nickel-based materials used above 700°C (1,292°F) does not produce effective results [11, 12].
Fireside corrosion from attack by molten coal ash, containing elements such as sodium, sulfur and chlorine forming alkali sulfates, etc., thin the outside tube surfaces. Low NOX burners and unburned carbon may also contribute to corrosion of the waterwalls, superheater and reheater [13]. With a dependence on the fuel type, the corrosion rates typically increase up to a maximum, at about 690°C to
| Advertisement |
|---|
|
|
Laboratory tests with Eastern, Midwestern and Western coal ash and in situ testing programs exposed various materials and coatings/claddings [8, 9, 15]. Western coal is a less aggressive fuel for A-USC. Higher chromium content in the base material, or with coatings at a level of about 27 percent, will help reduce the corrosion rates. Testing with conditions for oxy-combustion CCS are in progress [15].
Fabrication processes were tested to acquire knowledge on handling the new alloys in processes such as bending, machining, swaging and welding. Shop welding practices, particularly with dissimilar metal welds (DMW), were tested in many combinations of product forms and materials.
Field welding procedures were evaluated when installing and repairing test sections to determine procedural limitations [9, 16].
The extension to higher steam temperatures requires careful evaluation and selection of materials for the furnace enclosure at these conditions. The temperature pickup along the enclosure is steep.
Ferritic alloys SA213T23 and SA213T92 with coatings are some of the materials being considered for higher sulfur fuel and low NOX combustion. B&W PGG-funded R&D trial panels that were fabricated using T23 and T92 to develop the shop and field practices for welding and repairs (Figure 5).
Design by ASME Section I
The design methods for ASME Section I have used formula that underwent improvements in the history of the Code to meet high standards of safety and better calculation techniques for the product form. Analysis to support new formula, provide rules and knowledge on these new materials, and develop work processes was supported by the DOE/OCDO Materials Development Program for A-USC technology.
