GP Blade Tip Section Erosion  T53-L-703 model Gas Turbine

Reference cooled 1st GP Turbine Blade 1-100-362-06/08

Problem Statement

Air Technology Engines Inc. (ATE) has been communicating with Honeywell Engineering

since mid-2016 in reference to an observed deterioration/erosion of the cooled 1st GP

Blade Leading edge, outer, blade tip section. See attachment labeled GP Blade Tip

Erosion. This deterioration has been ATE observed in approximately 50% of the engines

received for a 2500-3000 hour inspection. The outer, leading edge, blade tip sections of

many/most blades are eroded through the parent metal exposing the internal blade

cooling core. The designed blade cooling is lost when the internal cooling core is

exposed to the gas path. All blades require replacement. The effect of this blade

internal cooling loss on other GP cooled turbine components is unknown at this time.

Background Information

The L13B model engines exhibited similar GP blade erosion in approximately 25% of the

engines returned for 2500 hour inspection and overhaul. ATE determined that by

controlling all combustor liner air cooling gaps, repairing/replacing the GP nozzle curl

and combustor liner inner wall detail, and practicing a 600 hour time between fuel

manifold flow testing, the noted GP blade erosion was reduced to under 10% of the

engine population serviced.

The L13B model engines use the 1-130-780-01 combustor liner design. The L-703 model

engines use the 1-130-780-03 combustor liner design.

The -03 combustor liner design incorporated a change in the juncture of the GP nozzle

curl and the inner wall of the combustor liner. This change altered the boundary cooling

air being supplied to the GP blade tip and cylinder sections. The liner inner wall was

extended 0.5 inches and shrouded the boundary cooling holes introduced in the GP

Nozzle curl detail (1-100-262-06). The change was implemented to reduce/eliminate

wear occurring between the GP nozzle curl and the combustor liner inner wall dimples

(detail 1-130-253-03).

Observations

The boundary air introduced in the inner wall of the 1-130-780-01 combustor liner

design supplies cooling air to the gas path metal surfaces and the GP Blade tip section

region. Since the GP blades are rotating components, they experience an average

temperature and profile based upon the net effects of the cooling air introduced

upstream of the turbine operating plane. The effectiveness of the boundary cooling air

can be seen by observing the air flow “wake” or “foot print” from the air delivered

through the 44 liner dimples and exiting over the GP Nozzle curl. See attachment

labeled L13B curl. The boundary air introduction appears excellent. The wear patterns

from the liner dimples are also evident.

T53-L-703 Background Information

The Certification of the T53-L703 model engine was performed with the 1-130-780-01

combustor liner design. More than 3000 hours of engine endurance were demonstrated

at turbine inlet temperatures above the L-703 specification with no evidence of turbine

blade erosion or deterioration. The GP Blade material at that time was INCO 713, not

the improved material (C101) currently approved.

Observations

The L-703 engine uses the 1-130-780-03 Combustor liner design. This design change was

introduced to reduce the fretting damage incurred on the GP Nozzle curl from the

contact surfaces of the dimples on the combustor liner inner wall (detail 1-130-253-03).

The change also lengthened the inner wall 0.5 inches for unknown reasons. It is the

opinion of John Moore, Ed Pease, and Jack Sweet (Combustor Design Expert), that this

inner wall extension adversely affected the introduction of the boundary cooling air

being introduced to cool the GP Turbine blade tip section. The effectiveness of the -03

boundary cooling air introduced by the modified combustor liner (1-130-780-03) can be

observed from attachment titled L-703 curl.

The boundary cooling air effectiveness is witnessed by the “wake” or “foot print” as

seen from the brownish stains on the GP Nozzle curl. There is a significant reduction in

“wake” or boundary air “foot print”. The fretting wear still exists between the liner

dimples (now 88 Vs 44) and the nozzle curl. As previously stated, it is the opinion of AT

et al, that the shrouding of the GP nozzle curl boundary cooling holes has dramatically

reduced the effectiveness of their air introduction and function.

Side Discussion Comment(s)

ATE has determined that the axial gap between the combustor curl/deflector (1-100-

500-0x) and the air diffuser and combustor housing outer flange interfaces, can

significantly influence the occurrence of “combustor rumble”. This “rumble”

phenomenon was experienced during the certification testing of the T53-L13, and

occurred in the idle speed range. Raising the engine idle speed resolved the rumble

mode concern. ATE has introduced a build requirement defining the axial gap

requirements to eliminate the occurrence of combustor rumble within the operating

envelop of the T53 engines. It is the opinion of ATE that combustor rumble contributes

to the degree of fretting occurring on the GP nozzle curl, and may in fact be the root

cause for the curl wear.

Summary and Recommendations

The background information and current observations presented herein support the

need to restore the design intent of the T53-L-703 certification combustor assembly bill

of material. The introduction of the post certification combustor liner design (1-130-

780-03) did not retain the design intent with respect to the boundary cooling air

introduced to cool the 1st GP Blade tip region. Furthermore, the -03 design change

introduced has demonstrated a significant reduction in durable service life of the 1st GP

Blade (1-100-362-06/08).

The design changes recommended by ATE, are supported by our extensive knowledge of

the T53’s operation and many years of design and field experience. See attachment

labeled “design changes recommended”.

Closing statements

The intent of this Summary is to communicate the most recent findings and

observations relevant to the subject being discussed. Air Technology Engines Inc. is

recognized as a leader in the T53 overhaul and repair business. We desire to continually

improve and expand our T53 technical knowledge and maintenance expertise through

shared communication and mutual understanding.

ATE is hereby requesting Honeywell approval to proceed with the design modifications

defined in the attached layout drawing provided above. Reference to the .38 inch

cutback of combustor liner inner forward wall and introduction of 44 holes/slots equally

spaced between existing dimples.

I look forward to your positive and timely reply.

John E. Moore

Air Technology Engines Inc.

Naples Florida

July 10th, 2017

Cc: Mike Turner, Ed Pease, Jack Sweet, Mike Jose, Paul Benz, Brenda Wise, Greg Carloni,

Doug Kult, Bob Dorsey, file. Honeywell service centers (NA), Robert Baito, Paul Elliott.

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