when bad things happen to good turbines - frame 6...

When Bad Things Happen to Good Turbines

PAL Turbine Services, LLC

ALFRED SHUMAN - Senior Staff Engineer Engineering Specialties

Gas Turbine Maintenance CMU Modifications Product Service Engineering Technical Training

Experience 41-years gas turbine experience

Senior Consulting Engineer for PAL Turbine Services since 2000

GE Field Engineer Lead Technical Training Specialist, FEP GE Service Supervisor, Baltimore, MD GE Senior Installation Engineer, Futsu Japan site for

14 MS9001E STAG plants (5-year project) Performed numerous major overhauls on GE model

series including MS5001, 6001, 7001

Education

E6, Machinist Mate, Class A, US Navy Submarine Nautilus

AAS Mechanical Design Engineering, Wentworth Institute of Boston, MA

GE Training Programs: Field Engineering Program (FEP) Gas Turbine Maintenance Schools Six Sigma Training

PAL Turbine Services, LLC Office: 518-371-1971 Fax: 518-371-1756

Note That Some of the Examples Shown are from Not Only MS-6001B Units, but also MS-5001N and MS-7001EA Units

Bolting Issues

1. Plated Bolting 2. Rusted Bolting


World War II Liberty & Victory Ships

• These ships were the first to be built completely welded with no use of rivets – Components for ships built modularized in many different

locales and then welded together at the assembly shipyard • This process drastically reduced the time to build these

ships at a time when the Allies were desperate for war materials

• Some of the issues of Embrittlement, due to temperature along with contaminants and also with an excess of Hydrogen in the welds, led to significant failures of hulls during launching


Launch of Liberty Ship from Dry Dock


Catastrophic Failure of Launched Hull Due to Embrittlement


Successfully Built Liberty Ship Helping the Allies War Effort


Case #1 Cadmium & Zinc Plated Bolting

• Do not use Cadmium plated bolts in the combustion, hot section or exhaust.

• Above 4500 F the cadmium melts & attacks the grain structure of the bolts and the bolt fails.

• The failure mode is called Liquid Metal Embrittlement and it is similar in nature to Hydrogen Embrittlement.


Failed Cadmium Plated Bolts


Failed Cadmium Plated Bolts & Nuts



Combustion Can Cover, with Fuel Nozzle & Pigtails, Blew Off

Collapsed Liner & Flow Sleeve


Discussion of the Root Cause of

this Failure


Case #2 Rusted Bolting in Inlet Ducting


Rusted Bolting in Inlet Ducting


Inlet Bellmouth Bernoulli Effect: Pressure Drop Produces Increase in Flow Velocity All GE Heavy Duty GTs produce a Velocity increase of Mach 0.5 Typical 295 lb/sec (1,062,00 lb/hr)

Velocity = Mach 0.5

Why Does Foreign Object Damage Occur So Rapidly Within the “Flange-to-Flange”

Pond And Lucier, LLC

Pressure & Temperature Across Gas Turbine Typically, the Delta-P Across the Inlet Throat Results in a Delta-T of 230F

T4 = 1000 ºF P4 = 14.7 psia

T1 = 59 ºF P1 = 14.7 psia

T2 = 450 °F P2 = 196 psia

Flame Temp = >3000 ºF

T3 = 2035 ºF P3 = 196 psia

1 2

3 4

Collateral Damage From Failed Bolting



this Failure



• During reassembly, ensure that crew understands to report when something gets dropped into an open turbine. – No one will be fired or censured for

dropping something into the machine as long as it is promptly reported.

• Two case histories of when bad things happened because of dropped/missing parts

Cautions with Open Casings

Case #3: MS-7001EA after a HGP & subsequent restart

• Unit’s MW output was significantly less then before the outage.

• Pcd read higher than expected, but output was still lower than expected.

• Significant testing indicated a problem in the Turbine section.

• Decision made to open Combustion system in order to inspect Stage 1 Nozzle



View of Stage 1 Nozzle from inside Wrapper


Damage which Choked Nozzle (Note how TE is pushed upstream)

Note how TE is pushed upstream


Damage as Viewed from Turbine


Bucket Denting & Splatter


1st Stage Bucket F.O.D.


2nd Stage Bucket Splatter & F.O.D.


Setting Pressure Ratio (PR)

Nozzle Throat Dimension The Tightest Orifice in the Hot Gas Flow Path

Typical Nozzle Throat Dimension Check Points



Damage which Choked Nozzle & caused High Pcd

1st Stage Nozzle F.O.D. & Buckling


1st Stage Nozzle Impact Zone



this Failure


Case #4: MS-6001B After Major Inspection

• Complete Major Overhaul, with replacement of all HGP parts along with a refurbished CDC Inner Barrel.

• Performance was ~9% lower than before the outage.

• Significant testing & a borescope inspection

• Unit reopened



Borescopic View of Stage 1 Bucket Airfoil


Borescope View of Stage 2 Bucket Shroud


Note Gouges on Inside of Inner Barrel


Close up of Gouges in Inner Barrel


Distance Piece Interface with Stage 1 Wheel


Stage 1 Bucket Pressure Side Deposits


Stage 1 Nozzle Inner Sidewall Deposits


Stage 1 Nozzle LE & PS Deposits


Stage 2 Bucket Shroud Tip deposits


this Failure


Case # 5: Effects of Turbine Clearances

Being Too Tight

• Rubs & Consequential damage are most often a low speed event.

• Damage usually occurs during very first start-up after outage.

• Make sure that you fully understand the true costs of trade offs made during reassembly.


Effects of Turbine Clearances Being Too Tight

• Power Plant Users often believe that, since they are going to change out Turbine Nozzles and Buckets during an outage, it is not important to take all of the Internal Clearances when opening the unit and again, when closing the unit.

• They believe that they can save outage time by not expending the effort to take accurate readings and compare them to what they were at the last outage; such a belief quickly becomes a False Economy.



• Turbine, Compressor, and Bearing Clearances are indeed where the “rubber meets the road”.

• The OEM’s Design Engineers view the Clearance Diagrams with their specific tolerances as the “Bible” for setting the performance and reliability parameters for any Heavy Duty Gas Turbine.



• It is crucial that the person taking the clearances not only has a good understanding of how and where to take the clearances accurately, but also understands that this task is one of the most important of the outage.

• Adherence to the designed tolerance range affects optimum performance. You must review all of the before/after clearances; the Turbine is speaking to you. If you understand the inseparable dimensional relationship between the Rotor and the Stator during various phases of operation, then you can determine where to make judgments as to where to go outside of the optimum clearance envelope. PAL Turbine Services, LLC

MS6001 Turbine Clearance Composite


Bucket to Honeycomb Shroud Clearance


Correcting Clearances Below Minimum Values on Stage 2 and 3 Buckets


MS-6001B Stg 2 Shroud Rub


Stg 2 Bucket Shroud Rail Rubbed Off


Comparison of Buckets



this Failure


Effects of Ignoring Recommendations Case #6

• MS-6001B Stage 2 Bucket Shroud lift phenomenon • Unit was open for a HGP • Customer chose not to follow OEM’s TIL

recommendation to change to new buckets due to potential cracking on airfoils.

• Customer installed a set of buckets from another unit on site which had shown marginal shroud lift readings.


What it Looked Like at First Outage


What It Looked Like at 2nd Outage


Stg 2 Bucket Stubs


Stg 1 Buckets are only lightly damaged


Collateral Damage to Exhaust Frame Outer Barrel


2nd & 3rd Stage Stator Damage



this Failure


Corrosion Case #6

• Contaminating reagents can enter the gas path via: • Ambient air • Fuel (oil/gas) • Diluents/Misting/Evaporative Cooling

• Contaminants from all sources are additive in concentration & impact


Stage 1 Nozzle Exposed to Boiler Carryover in Steam Injection Attemperation


Stage 1 Nozzle Partitions



this Failure


Case #7: Rush to make-up lost time in MS6001B Major Inspection Schedule leads to the “Law of Unintended Consequences” Results in an Order of Magnitude more lost time along with replacement and/or rework of Critical Components


View of S1 Vane Through VIGV’s & R1 Blades


Damage to Stator Dovetail Slot Along with Rubs & Dings to Blades & Vanes


Arrows Show Where Retaining Keys “Should Be” Locked in Place


Note Rubbing Damage to Dovetail Slot Caused by Rotation of Blade Rings in Service


Note Damage to Stator Vanes & Blade Ring



this Failure


Conclusions & Recommendations

• Hug your Gas Turbines! • Treat them well, especially during outages! • Confirm that “Proper Form, Fit, & Function”

parts are being used as replacements! • If schedule is causing an inordinate rush …

stop to think, review situation, and act accordingly! • Work Safely & Work Smart!

Conclusions & Recommendations

• Account for every single tool removed & every part installed properly before closing up Gas Turbine!

• Following Good Engineering Practices will always trump False Economy!


Centuries of experience In maintaining gas turbine generators

when bad things happen to good turbines - frame 6...

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