Another Materials Problem with Jet Turbine?

[MolaKule]

From Flight Global


Quote:


GE identifies installation issue in GEnx, orders inspections
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By: Stephen Trimble Washington DC

49 minutes ago

Source:


General Electric has ordered inspections on all 120 GEnx engines operating on Boeing 747-8s and 787s to check for installation errors of a component now linked to an engine failure in China last month.

The service bulletin issued on 4 October calls for a one-time inspection of the first stage low-pressure turbine (LPT) nozzle, a non-rotating part that directs the air flow into the trailing LPT stages.

GE issued the bulletin four days after completing a tear-down inspection of a GEnx-2B turbofan that was damaged during a rejected take-off by an AirBridge Cargo 747-8 in Shanghai.

The National Transportation Safety Board and the US Federal Aviation Administration (FAA) initially linked the incident to two other LPT failures of GEnx engines in late July and early August caused by cracks on the forward end of the fan midshaft, which connects the LPT to the inlet fan.

But closer inspections of the AirBridge Cargo engine revealed that no cracks or fractures of the fan midshaft, which pointed to an installation problem within the LPT itself.

GE emphasises that the GEnx engine family has accumulated a reliable safety record despite the high-profile contained engine failures on the 747-8 and 787. The engine fleet has achieved a dispatch rating of 99.9% with 225,000 flight hours in less than two years of service.

The fan midshaft cracking and fracturing incidents were traced last month to a new, lead-free coating that allowed the component to corrode rapidly under certain conditions. GE switched to a leaded coating already used on the GE90 to correct the problem.

 

[stranger706]

Interesting. Thats like jet engine 101 stuff there. I wonder what kind of conditions caused the corrosion. Didn't they test the stuff before installing it on the fleet?

I've noticed that jet engines from the 70s and 80s have higher temperature limits than engines made today. People have told me that is because today's engines are made from lower quality materials.

 

[Astro14]

Originally Posted By: stranger706
Interesting. Thats like jet engine 101 stuff there. I wonder what kind of conditions caused the corrosion. Didn't they test the stuff before installing it on the fleet?

I've noticed that jet engines from the 70s and 80s have higher temperature limits than engines made today. People have told me that is because today's engines are made from lower quality materials.


I am sure they tested...but sometimes issues don't show up until the run time is longer.

But, lower quality materials? No way...the engines now are running at higher efficiency ratios, higher pressures, higher temps...that takes better materials...and better design. I doubt that 70's vintage engines are running higher temps than the new ones...where did you hear that?

 

[stranger706]

I agree that the design is better on newer engines but it seems the material used has peaked or gone down a grade in quality. Some of the older engines I maintain have a 1010 C max temp and a cruise temp of 970 C. Some of the newer engines seem to cruise in the 800s and max temp around 900.

 

[tom slick]

Do you work on t-56 engines?

 

[JetStar]

I have to wonder if the lower temps are not so much a material issue but perhaps a cost / longevity enhancement, or an effort to reduce Nox emmisions.

Additionally it sounds like another Pb (lead)free issue. We in the hi-rel electronics industry are dealing with that as well.

 

[Propflux01]

Originally Posted By: tom slick
Do you work on t-56 engines?


Sounds like it, IIRC, 1010 is max continous, 970 TIT max reduced in flight, with 1083 is absolute max for takeoff.