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HP/IP/LP (High-Pressure, Intermediate-Pressure, and Low-Pressure) cylinders are the core pressure-bearing housing components within a steam turbine system. They are specifically designed to facilitate the steam expansion process across different pressure sections, converting thermal energy into mechanical work efficiently.
As critical structural elements, these heavy-duty forged turbine casings form a stable steam flow channel, withstand extreme high-temperature and high-pressure steam loads, and ensure precise alignment between the rotor system and stator components over long-term continuous operation. Their reliability is essential for maintaining the overall thermodynamic efficiency of the power plant.
Depending on specific pressure grades and power unit capacity requirements, the structural configuration, wall thickness design, and manufacturing techniques of our cylinder blocks are rigorously optimized. This targeted engineering ensures maximum strength, rigidity, and operational safety under varying load conditions, helping industrial users minimize downtime and reduce long-term maintenance risks.
Our heavy-duty HP, IP, and LP casings are engineered to safely contain and precisely direct extreme steam flows. By utilizing a graded material strategy based on specific service conditions, these turbine cylinders provide exceptional resistance to material creep, thermal fatigue, and sustained pressure loads. This robust containment performance is essential for continuous high-demand power generation, effectively protecting internal rotating components from steam leakage and mechanical degradation, thereby extending the lifecycle of the turbine equipment.
Modern power generation requires equipment capable of handling frequent load variations. Our casing designs incorporate double-shell or multi-cylinder configurations with strategically positioned steam inlets, extraction ports, and internal support structures. This advanced arrangement safely accommodates thermal expansion during turbine startup, load cycling, and shutdown phases, significantly reducing thermal stress and structural distortion. Guided by precise finite element analysis (FEA), the wall thickness transitions and flange geometries promote uniform temperature distribution, preventing localized overheating and preserving dimensional stability.
Maintaining tight tolerances is critical for turbine efficiency. Each casing is meticulously processed to ensure strict dimensional control on joint surfaces, diaphragm grooves, and gland seal fits. Horizontal joint flanges are expertly finished to achieve exact metal-to-metal contact, while split surfaces are designed for robust bolting and secure sealing. This rigorous approach minimizes inter-stage steam leakage, maximizes thermodynamic efficiency, and facilitates reliable, straightforward reassembly during scheduled maintenance outages.
The following specification table outlines the standard operational parameters, construction types, and inspection criteria for our HP, IP, and LP turbine casings. These parameters serve as a reliable baseline for project evaluation and can be adapted to meet specific power generation requirements.
| Parameter Item | HP Casing | IP Casing | LP Casing | Remarks |
| Steam Conditions | High pressure & temperature | Reheat intermediate | Low pressure / Vacuum | Designed per turbine class |
| Design Pressure | ≥ 12 MPa - 30 MPa+ | ≥ 4 MPa - 8 MPa | ≤ 1 MPa / Vacuum | Specification per drawing |
| Construction Type | Single/Double shell | Double shell | Double/Single flow welded | Based on capacity |
| Main Connections | Main steam / HP exhaust | Reheat steam / IP exhaust | Exhaust / Extraction | Custom per heat balance |
| Machining Equipment | Large CNC boring/milling | Large CNC boring/milling | Floor boring / Positioner | Ensures tolerances |
| Sealing Type | Flange bolting / Horizontal joint | Flange bolting / Horizontal joint | Flange / Welded seal | Leakage prevention |
| Quality Standard | JB/T 9632 / HEI / Customer spec | JB/T 9632 / HEI / Customer spec | JB/T 9632 / HEI / Customer spec | Includes NDT |
| Inspection Items | Dimension/Material/NDT/Hydrotest | Dimension/Material/NDT/Hydrotest | Dimension/Material/NDT/Vacuum test | NDT per code |
Manufacturing heavy-duty forged HP/IP/LP casing cylinders for steam turbines requires an uncompromising approach to material selection and precision machining. Because these critical components operate under extreme thermal and mechanical stresses, our manufacturing protocol is strictly designed to ensure long-term stability, structural integrity, and exceptional steam sealing performance for heavy industry applications.
The foundation of a reliable steam turbine lies in its metallurgical quality. HP/IP/LP casings are continuously subjected to intense high-temperature and high-pressure steam environments, requiring materials that can withstand rigorous operational demands without failure. We utilize premium-grade high-quality alloy steel and high-strength carbon steel materials, specifically chosen based on project requirements:
Low-alloy high-strength steel: Selected for optimal structural rigidity and load-bearing capacity.
High-temperature resistant alloy steel: Engineered to endure extreme thermal environments without degrading.
Thick-plate welded structural steel: Ideal for robust, heavy-duty segmented assemblies.
These carefully selected materials provide essential characteristics that directly impact the operational lifespan and safety of the turbine casing:
Good high-temperature strength performance: They maintain stable mechanical properties and structural integrity even when continuously exposed to high-temperature steam environments, preventing operational failures.
Excellent creep resistance: The specific alloy compositions ensure that plastic deformation is highly unlikely to occur under long-term, high-temperature operational conditions, reducing the risk of casing distortion over decades of use.
Good welding performance: These materials are highly adaptable to multi-layer and multi-pass welding techniques, which is crucial for fabricating large, thick-walled structural components without compromising joint strength.
Higher fatigue resistance: They are engineered to withstand periodic thermal stress and mechanical stress fluctuations during turbine startup, continuous operation, and shutdown cycles.
Before entering the production line, all raw materials are subject to strict incoming inspection in accordance with relevant heavy industry standards. This guarantees that their chemical composition and mechanical properties strictly meet the design requirements of heavy-duty steam turbines.
The reheat casing of a steam turbine is a massive, thick-walled welded structural component. Its manufacturing process involves complex engineering and exceptionally high machining accuracy requirements to ensure perfect alignment and sealing. The main process flow utilizes advanced heavy-duty machining equipment and is executed as follows:
Material blanking and pretreatment: According to precise drawing requirements, heavy steel plates or forgings are accurately cut. Initial dimensional checks are carried out, and preheating treatment is performed when necessary to prepare the metal for heavy-duty welding and minimize thermal shock.
Advanced Welding: The HP/IP/LP turbine shell adopts a highly engineered segmented assembly and welding structure. Multi-layer and multi-pass welding technology is used during this critical phase to control the interlayer temperature and significantly reduce welding deformation. After welding, necessary heat treatment will be carried out as required to eliminate residual stress, ensuring dimensional stability. This process is the core quality control stage, which directly affects the overall structural strength and pressure-retaining sealing performance of the outer casing.
Welding
Welding
Rough turning: The initial machining phase involves the rough turning of the outer circle, end face, and main mating surfaces. This step efficiently removes excess material while carefully managing the release of internal stresses within the heavy forging.
Semi-finish turning: We then process the internal flow channel profile, flange surface, and critical locating surfaces. This step brings the casing closer to its final dimensions, preparing the complex geometry for high-precision finishing.
Finish turning & Fine boring: The final machining stage requires extreme precision. We precisely machine the mating surfaces of the upper and lower cylinders to ensure absolute flatness, which is critical for preventing steam leaks during high-pressure operation. Furthermore, finish boring of the inner hole is carried out with strict tolerances to control coaxiality, ensuring perfect alignment with the turbine rotor.
Precision Milling: Complex features, joint faces, and structural mounting points are precisely milled to meet the exact assembly specifications of the heavy-duty casing, ensuring seamless integration into the final turbine unit.
Turning
Milling
