At Rotation Group, we specialize in LM2500 twin shank to single shank conversions, helping operators unlock higher performance, improved reliability, and longer service life from their gas turbines. This article outlines the key differences between configurations, the engineering behind the upgrade, and why it matters for your operation.
Whether you’re running a power generation package, marine propulsion system, or industrial turbine, understanding the evolution from PB/PC to PE configurations is essential for making informed decisions.
From PB/PC to PE: What Changed?
The LM2500 has undergone significant design evolution over the years. The transition from PB/PC (twin shank) to PE (single shank) configuration was the catalyst to the big changes. PE (single shank) introduced a range of enhancements across the hot section, including nozzle and blade geometry, cooling strategies, materials, and rotor design. These HPT improvements became the foundation for the LM2500+ and LM2500+G4.
| PB (FFG Marine Engine) | PC | PE | |
|---|---|---|---|
| HPT Type | Twin Shank | Twin Shank | Single Shank |
| HP / MW Continuous | 25,000hp / 18.6 MW | 27,500hp / 20.5MW | 29,500hp / 21.9MW |
| T54 Continuous | 1378°F | 1408°F | 1461°F |
| HP / MW Maximum | – | 30,000hp / 22 MW | 32,500hp / 24MW |
| T54 Maximum | – | 1481°F | 1551°F |
| GG Speed Limit | 9850rpm | 9850rpm | 10100rpm |
Note: Power ratings are based on ideal conditions—59°F (15°C) ambient temperature at sea level, with no inlet duct or exhaust losses. These figures reflect performance from new engines with perfect clearances and no compressor contamination. In real-world operating environments, actual output is typically at least 5% lower than these published values.
HPT Stage 1 Nozzle: Cooling and Material Advancements
Cooling Geometry Improvements
The single shank Stage 1 nozzle features additional cooling holes, enabling more effective barrier air film cooling. This geometric design directs airflow more precisely onto the turbine blades, reducing metal temperatures and extending component life.
Structural Enhancements
Changes in both structural geometry and cooling geometry improve durability and were necessary for compatibility with the single shank turbine rotor. These enhancements reduce thermal stress and improve airflow distribution.
Material Options for Variety of Applications
Operators now have more flexibility in selecting nozzle materials:
- DS Cast or Single Crystal Technology
- Platinum Aluminide Bond Coats
- Ceramic Coatings: APS or EBPVD
These options allow customization based on fuel type, environmental conditions, and budget—making it easier to optimize performance and reliability.
HPT Stage 1 Blade: Efficiency and Reliability Redefined
Three Cooling Mechanisms
Single shank blades use a combination of:
- Internal Convection: Air flows through internal channels.
- Impingement Cooling: Air hits the inside of the leading edge.
- Film Cooling: A protective layer forms on the blade surface.
Design Enhancements
- More Cooling Holes: Improved air film coverage.
- Additional Leading-Edge Gill Holes: Better thermal protection.
- Reduced Blade Count: 88 blades (single shank) vs 108 (twin shank), improving efficiency and reducing defect risk.
Superior Manufacturing Technologies
- Directional Solidification (DS) and Single Crystal (SX) Casting
- OEM Options: Rene’ 80 (DS), Rene’ N-5 (SX)
- Aftermarket Options: CM186 (DS), CM186SX, SC4 (SX)
Elimination of Braze Joint
One of the most critical improvements is the removal of the braze joint found in twin shank blades. This joint is prone to separation, especially under overfiring conditions, leading to cooling losses and reduced blade life. The single shank design eliminates this failure point, improving reliability and reducing maintenance risk.
Stage 2 Nozzle and Blade: Cooling and Compatibility
Nozzle Assembly Enhancements
- More cooling holes and dimples for improved internal cooling.
- Structural upgrades for better compatibility with single shank rotors.
Blade Improvements
- Reduced blade count: 90 (single shank) vs 116 (twin shank).
- Improved coatings and elimination of the braze joint for longer life and better thermal performance.
HPT Rotor: Strength and Integrity
Bolt Count and Size
- Stage 1 Disk: 88 bolts (single shank) vs 54 (twin shank)
- Stage 2 Disk: 90 vs 58
- Aft Shaft Bolt Diameter: 7/16” (single shank) vs 3/8” (twin shank)
These changes enhance structural integrity, reduce vibration, and improve overall rotor reliability.
Performance Gains and Operational Benefits
Power Output
- PE base configuration: 21.9 MW continuous
- +Config: 32 MW
- +G4 Config: 36 MW
Efficiency
- Fewer rotating aerofoils within HPT: 178 (single shank) vs 224 (twin shank). 20% reduction.
- Less energy extracted from the hot gas path to drive the compressor, leaving more for the power turbine
Manufacturing Turnaround
- New aerofoils can be manufactured in 120 days
- New manufacture cost can be performed at similar prices to overhaul—making replacement a viable alternative to refurbishment
When Twin Shank Still Makes Sense
The twin shank HPT, is a reliable HPT. They powered the DC-10, the Lockheed C-5 Galaxy. They were fit to fly and established the CF6 engine line which became one of the most iconic and trusted engine lines for airliners.
Despite the advantages of single shank upgrades, twin shank configurations remain valuable in specific scenarios:
Existing Installations
If your package reliably produces ~18 MW, already uses a twin shank engine and has a generator output of 18 MW, there’s no need to upgrade. Overhaul costs may rise, but the engine remains dependable.
Peak Power Units
For standby applications running 50–100 hours/year, twin shank engines can deliver short bursts up to 20.5 MW. This allows operators to meet peak demand without capital expenditure associated with uprating.
Military Marine Applications
Marine frigates still use twin shank engines due to gearbox input limitations and change management complexity. Applying modern coatings to twin shank aerofoils can extend engine life without requiring a full conversion.
Every Gas Turbine Strategy Is Unique
From fuel type to operating environment, every LM2500 application has its own challenges. At Rotation, we help you navigate those complexities—whether you’re upgrading, maintaining, or optimizing your fleet.
Thinking about converting from twin shank to single shank?
There’s more to it than the parts we have mentioned above. Let’s talk about your specific configuration, goals, and budget. Then we can talk you through the process.
Contact us today to learn more about LM2500 twin shank to single shank conversions.
