Holding steady under pressure — how 7Extend helps address casing and compressor degradation in 7E units

For 7E gas turbines, that strain shows up in more than one place. Casings and compressors alike are vulnerable to years of cycling and wear—and once tolerances slip, so does performance. The 7Extend upgrade* package offers a practical way to reset the clock, with component updates engineered to help address casing fatigue, compressor wear, and the risks they bring. 

Cracks, cycles, and casing creep

Turbine casings are the backbone of the machine. Especially in peaking units that start daily, repeated heating and cooling creates stress over time. The result can be cracks, ovalization, and expanded clearances that routine outages can’t fully correct. 

What operators are seeing:

• Cracks from long-term thermal cycling
• Out-of-round casings that affect blade clearances 
• Degradation that parts shortages can make harder to resolve 

With casings, unplanned failures can mean unplanned downtime—and in today’s operating environment, that’s a risk no operator wants—or needs—to take. 

Compressor wear and why it matters

Not all degradation is visible, but once stator vanes start to move, performance quickly follows. Over years of operation, compressors in 7E units are showing: 

• Slot wear at critical stages like S5 and S10 
• Corrosion in carbon steel vane rings, especially in humid or coastal environments 
• Lock-up and clash between stator and rotor blades 

Moisture from wet compression or inlet fogging often accelerates this damage—leading to issues that go beyond routine wear and tear. 

What 7Extend brings to the table

The 7Extend package helps address both casing fatigue and compressor degradation with updates built on decades of fleet data and real-world operating experience: 

• Refreshed turbine casings built to current 7E.03 standards 
• Updated sealing features such as the field-proven keyway configuration
• Material and fit-up improvements to support tighter tolerances 
• Upgraded stator vanes with stainless steel carrier rings 
• Corrosion-resistant coatings (GECC-1) to help limit degradation 
• Compressor discharge casing replacement to resolve slot wear and structural concerns 

These updates have already been applied in more than 130 units—with no reported R1/S1 clashing in those with stainless steel vane carriers. For many operators, simply addressing non-recoverable casing degradation has helped bring back 3–4 MW of output. 

In short

Casing fatigue and compressor wear are inevitable in aging 7E units—but performance loss doesn’t have to be. With 7Extend, operators can address both issues in a single package, helping to reduce risk, improve reliability, and support long-term operation.