Back-end burnout: How 7Extend and the upgraded radial diffuser can help relieve exhaust system stress

As 7E units age, the back end takes a hit—from cracking to seal failures and mounting backpressure. With 7Extend and the upcoming advanced radial diffuser, operators have new options to help bring life and output back into balance. 

The pain points

The exhaust section of the 7E turbine is no stranger to fatigue. Over time, common issues include: 

• Cracks in diffusers, turning vanes, and supports 
• Seal slippage and excessive leakage 
• Thermal stress that turns into weld-after-weld maintenance cycles 

These issues chip away at performance—and drive up both costs and outage hours. 

A two-part solution

The 7Extend package already includes upgraded exhaust components, including: 

• New diffusers and plenums with updated materials 
• Refreshed structures that help address fatigue and leakage 

Looking to go further? The advanced radial diffuser, coming in 2026, introduces a reimagined flow path: 

• No turning vanes, no vane-related fatigue 
• Improved geometry that helps ease backpressure 
• Strut redesigns to support airflow and pressure recovery 

Built on a proven 9E.04 concept, this update helps bring up to 1 MW of output recovery and up to ~0.5% heat rate improvement—all while helping to reduce future repair needs. 

In short

Exhaust fatigue doesn’t need to be a recurring issue. With 7Extend—and a look toward radial diffuser tech—7E operators can take real steps toward restoring performance and cutting unplanned O&M. Together, these updates help position your unit for what’s ahead—without the wait or cost of building new.