Turbine casings contain the steam pressure and direct the flow path through the blade stages. The horizontal joint (where upper and lower casing halves meet) must maintain a steam-tight seal under extreme temperature and pressure, the bolts, gaskets, and joint surfaces are critical maintenance items.
AQ Process Systems sources and exports casing bolts, horizontal joint sealing materials, exhaust expansion joints, casing drain valves, extraction connections, and thermal insulation components for steam turbine casings across all frame sizes and manufacturers.
Casing joint integrity directly affects turbine availability and safety. Steam leakage at the horizontal joint reduces efficiency, creates erosion damage, and can pose a burn hazard. We supply the parts that ensure reliable casing sealing.
| Component | Specification | Description |
|---|---|---|
| Horizontal Joint | ||
| Casing Bolts & Nuts | Cr-Mo-V alloy steel | High-temperature rated | Various sizes | Turbine casing horizontal joint bolts and nuts, high-tensile alloy steel rated for the casing operating temperature. |
| Joint Sealant / Gasket Compound | Metallic paste or RTV silicone | High-temperature | Horizontal joint sealing compound applied between the casing halves, metallic paste type for high-temperature HP/IP joints. |
| Dowel Pins | Alloy steel | Casing alignment | Alignment dowel pins maintaining casing half registration during assembly and thermal expansion. |
| Exhaust System | ||
| Exhaust Expansion Joints | SS bellows | Fabric or metallic | Large diameter | Expansion joints between the LP turbine exhaust and the condenser, absorbing thermal movement and condenser vacuum loads. |
| Exhaust Hood Spray Nozzles | SS | Desuperheating spray | LP exhaust cooling | Water spray nozzles in the LP exhaust hood, preventing exhaust temperature from exceeding casing design limits during low-load operation. |
| Rupture Diaphragms | Bursting disc | LP casing overpressure protection | Atmospheric relief devices protecting the LP casing from overpressure, bursting discs calibrated to the casing design pressure. |
| Casing Accessories | ||
| Casing Drain Valves | Gate or globe | HP/IP/LP casing drains | Drain valves for removing condensate from the turbine casing during startup, preventing water induction damage. |
| Extraction Nozzle Connections | Flanged | Various stages | Replacement nozzle connections for steam extraction take-off points, for feedwater heaters and process steam supply. |
| Thermal Insulation | Mineral wool or calcium silicate | Removable blankets | Turbine casing insulation, mineral wool blankets with SS wire mesh outer covering, or removable insulation jackets for inspection access. |
| Insulation Fasteners | SS pins, clips, bands | Securing insulation | Stainless steel fastening hardware for turbine casing insulation, pins, clips, banding, and buckles. |
Parts are manufactured to OEM specifications with full material certification, dimensional inspection, and NDE documentation as required. Provide the turbine manufacturer, frame/model designation, and part number for precise identification.
The most common casing spares are horizontal joint bolts and nuts (checked for stretch and replaced if needed), joint sealant compound, dowel pins, casing drain valves (seat leakage), exhaust expansion joint bellows (fatigue cracking), and insulation blankets (damage during disassembly). LP exhaust spray nozzles may need cleaning or replacement.
Casing bolts are specified by diameter, length, thread form, material grade (typically Cr-Mo-V alloy steel such as 21CrMoV5-7 or ASTM A193 B16), and any surface treatment. Bolts must be rated for the casing joint temperature and pressure. Replacement bolts include material certificates and hardness test reports.
Exhaust expansion joints fail from fatigue (cyclic thermal expansion), corrosion (condensate and oxygen), and mechanical damage (excessive movement beyond design limits). Multi-ply stainless steel bellows last 15-25 years under normal conditions. Fabric expansion joints in lower-temperature zones may need more frequent replacement.
Water induction is the entry of liquid water into the hot turbine casing, from feedwater heater tube leaks, extraction line condensate, or HP drain valve failures. Water contact with the hot rotor and casing causes thermal shock, distortion, and cracking. Casing drain valves must function correctly during every startup to remove accumulated condensate.
Yes. We supply custom-fitted removable insulation blankets for turbine casings, valve chests, and piping, allowing rapid removal for inspection access and reinstallation afterward. Blankets use high-temperature mineral wool fill with stainless steel wire mesh outer and quick-release fasteners.
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