T53-L-703 GP Blade Tip Section Erosion
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. Original Post May 5, 2018
