Abstract: This article delves into the casting process of a steel casting for the exhaust end of an ultra-high pressure outer cylinder for a 1000MW ultra-supercritical thermal power turbine. Based on the structural characteristics, performance, and application requirements of the exhaust end casting, the MAGMA software is employed to simulate the filling and solidification processes. Leveraging extensive experience in manufacturing large steel castings, a reasonable casting and heat treatment process plan is adopted to ensure proper feeding, dross removal during pouring, and high-performance requirements of the casting. After production verification, the casting meets the ultrasonic inspection standards, and no exposed defects are found in the threaded holes after finishing.
Introduction
The National Electricity Council’s analysis and forecast report on the national power supply and demand situation for 2023-2024 indicates that in 2023, the total electricity consumption nationwide reached 9.22 trillion kWh, with a year-on-year increase of 6.7%. Among this, coal-fired power generation accounted for nearly 60% of the total. It is projected that in 2024, the total electricity consumption nationwide will reach 9.8 trillion kWh, representing a 6% increase compared to 2023. Given China’s energy endowment characterized by “relatively abundant coal, lack of oil, and scarcity of gas,” coal-fired power remains the primary power source for China’s electricity supply in the future, playing a crucial role in ensuring a stable power supply. Driven by positive factors such as advancements in environmental protection technology, reduced generation costs, and increased electricity demand, the future development prospects for the thermal power industry are optimistic. The 1000MW large-capacity ultra-supercritical turbine unit, with steam temperatures of 625°C and steam pressures of 32 MPa, can improve unit efficiency by about 5% and reduce CO2 emissions by about 10%, aligning with the development goals of high efficiency, high quality, high recyclability, low consumption, low pollution, and low carbon emissions for thermal power equipment. The high operating parameters place stricter quality requirements on the supporting steel castings.
This paper focuses on the casting process of the exhaust end of an ultra-high pressure outer cylinder for a 1000MW ultra-supercritical steam turbine, analyzing the casting process, pouring system design, heat treatment process, and production verification to ensure the quality of the steel casting.
1. Basic Parameters, Technical Requirements, and Structural Characteristics of the Casting
1.1 Basic Parameters and Technical Requirements
The exhaust end of the ultra-high pressure outer cylinder is one of the critical components for the 1000MW ultra-supercritical condensing steam turbine produced by Shanghai Turbine Plant. The 1000MW ultra-supercritical condensing steam turbine represents the largest single-unit power fire-generation set in China. This product operates under high temperatures and bears high pressure within the turbine. the cylinder adopts an integrated structure for the upper and lower halves, eliminating the horizontal split plane between them. The exhaust end and the inlet end are connected via bolts, improving the stress conditions of the cylinder but increasing the overall manufacturing difficulty.
The contour dimensions of the ultra-high pressure outer cylinder exhaust end are 3550mm x 2760mm x 1660mm, with a net weight of 25.6 tons. The maximum wall thickness at the flange end is 345mm, the maximum wall thickness at the bearing seat end is 300mm, and the wall thickness of the cylinder is 125mm. The material used is ZG17Cr1Mo1V, with specific chemical composition and mechanical property requirements detailed in Tables 1, 2, 3, and 4.
Table 1: Chemical Composition Requirements (Mass Fraction, %)
| Element | ZG17Cr1Mo1V |
|---|---|
| C | ≤ 0.18 |
| Si | 0.15-0.50 |
| Mn | 0.40-0.80 |
| P | ≤ 0.030 |
| S | ≤ 0.030 |
| Cr | 1.00-1.50 |
| Mo | 0.45-0.65 |
| V | 0.20-0.35 |
| Ni | ≤ 0.30 |
| Cu | ≤ 0.30 |
| N | ≤ 0.020 |
Table 2: Mechanical Properties at Room Temperature
| Property | Requirement |
|---|---|
| Tensile Strength (MPa) | ≥ 585 |
| Yield Strength (MPa) | ≥ 380 |
| Elongation at Break (%) | ≥ 18 |
| Reduction of Area (%) | ≥ 40 |
| Impact Absorption Energy (J) | ≥ 39 (at -20°C) |
Table 3: Hardness Requirements
| Hardness Test | Requirement |
|---|---|
| HBW | ≤ 241 |
Table 4: Additional Mechanical Properties (if specified)
| Property | Requirement |
|---|---|
| Creep Strength (MPa) | (As per agreement) |
| Fatigue Strength (MPa) | (As per agreement) |
| Stress Relaxation Rate (%) | (As per agreement) |
The above tables outline the essential chemical composition and mechanical properties for the ZG17Cr1Mo1V material used in the ultra-high pressure outer cylinder. The values provided ensure the material’s suitability for high-pressure and high-temperature applications, offering excellent strength, ductility, and resistance to creep and fatigue where specified. All tests and inspections shall adhere to the relevant industry standards and specifications to guarantee the quality and reliability of the component.