LM6000 breakout at Western Turbine invaluable to owner/operators

The LM6000 is the most popular of Western Turbine’s four breakout sessions, attracting more participants (300 plus at the 2017 meeting in Las Vegas) than the LM2500, LM5000, and LMS100 breakouts combined. Andrew Gundershaug, plant manager of Calpine Corp’s Northern California Peakers, chairs this group.

Gundershaug’s day job is to manage seven LM6000 peakers at different sites, so there isn’t much in the way of “issues” with these engines that he hasn’t experienced firsthand. That, plus two decades of work on LM engines, exposure to problems faced by others as a WTUI conference attendee since 2001, and excellent speaking and audience-engagement skills, place Gundershaug among the most capable of user-group floor leaders.

The primary responsibility of breakout chairs at WTUI is program development. While that’s true for steering committee members of other user groups as well, at Western Turbine this is pretty much a second full-time job; the work is year-round, with no financial remuneration of course.

Gundershaug works collaboratively with subject matter experts at the Authorized Service Providers and the OEM, as well as Western Turbine colleagues, to develop the annual “LM6000 O&M Bible” presented to each participant in the breakout session to facilitate learning and note-taking. This year’s 200-page full-color book had three major sections:

      • ASP findings in the shop, and in the field, the previous year.

      • Details on the OEM’s efforts to resolve fleet issues, plus mods and upgrades available to owner/operators to improve performance, safety, etc.

      • Notes on topics for the package discussion integrated into the busy agenda.

The first three hours of the breakout was devoted to presentations by ASP representatives who compiled the drawings, photos, and notes on significant issues identified in 2016—vital for users looking ahead to the next overhaul and all those responsible for engine operations. The presenters:

      • Ken Ueda of IHI Corp, 17 years of experience on LM6000 engines—including roles in R&D, maintenance engineering, customer support.

      • Ralph Reichert of MTU Maintenance, 21 years of GT experience—including aircraft mechanic, field service engineer, maintenance shop engineer.

      • Steve Willard of TCT, 15 years of LM engine experience, with involvement in component repairs, test-cell operations, project management, and engineering.

In all probability, nowhere except Western Turbine would you find such a capable “faculty” for sharing their knowledge on one of the world’s most popular gas turbines for electric generation.  Today, the fleet totals 1250 engines in round numbers—one-third of them equipped with DLE combustion systems.

As you read on, important to keep in mind that the editorial goal was to profile some of the session’s highlights, not to compile a comprehensive summary of the proceedings. You can get that via the Western Turbine website, where all the ASP and OEM presentations are posted along with a 35-page chronology of the LM6000 sessions, compiled by Steven Giaquinto of Strategic Power Systems Inc. SPS engineers help support the WTUI mission by taking notes for the membership during the breakout sessions. Note: Conference materials are available only to registered WTUI user members. Not a member of Western Turbine Users Inc? Sign up today at www.wtui.com.

After opening remarks by Chairman Gunderson, including the all-important safety message on how to evacuate in the unlikely event of an emergency, TCT’s Willard got the session rolling. He reminded attendees of the value proposition associated with the three Level 4 ASPs serving the LM6000 community:

      • Access to GE technical documentation.

      • Access to GE parts and service support as defined in the license agreement.

      • Approved vendor list for component repairs.

      • Departure records from GE to cover minor deviations to O&M and repair procedures.

Sidebar 1: Acronyms to remember

AGB—Accessory gearbox
   (also called the transfer gearbox)
AVR—Automatic voltage regulator
CCM—Condition maintenance manual
CCR—Customized customer repair
CDP—Compressor discharge port
CFF—Compressor front frame
COD—Commercial operating date
CPLM—Critical-parts life management
CRF—Compressor rear frame
CSM—Customer service manager
CWC—Customer web center (GE)
DEL—Deleted part
DLE—Dry, low emissions combustor
DOD—Domestic object damage
EM—Engine manual
FFA—Front frame assembly
FOD—Foreign object damage
FPI—Fluorescent penetrant inspection
FSNL—Full speed, no load
GG—Gas generator
   (consists of the compressor and hot sections only)
GT—Gas turbine
   (consists of the GG pieces with the PT attached)
GTA—Gas-turbine assembly
HCF—High-cycle fatigue
HGP—Hot gas path
HPC—High-pressure compressor
HPCR—High-pressure compressor rotor
HPCS—High-pressure compressor stator
HPT—High-pressure turbine
HPTN—High-pressure turbine nozzle
HPTR—High-pressure turbine rotor
IGB—Inlet gearbox
IGV—Inlet guide vane
IPT—Intermediate-pressure turbine (LMS100)
IRM—Industrial repair manual
LM—Land and marine
LCF—Low-cycle fatigue
LO—Lube oil
LPC—Low-pressure compressor
   (not on LM2500; just LM5000 and LM6000)
LPCR—Low-pressure compressor rotor
LPCS—Low-pressure compressor stator
LPT—Low-pressure turbine
LPTR—Low-pressure turbine rotor
LPTS—Low-pressure turbine stator
MCD—Magnetic chip detector
MOH—Major overhaul
NGV—Nozzle guide vane
OEM—Original equipment manufacturer
PB—Product bulletin
PN—Part number
PT—Power turbine
   (turns a generator, pump, compressor, propeller, etc)
PtAl—Platinum aluminide
RCA—Root cause analysis
RFQ—Request for quote
RPL—Replaced part
SAC—Single annular combustor
SB—Service bulletin
SL—Service letter
SUP—Superseded part
STIG—Steam-injected gas turbine
TA—Technical advisor
TAT—Turnaround time
TAN—Total acid number (lube oil)
TBC—Thermal barrier coating
TGB—Transfer gearbox
   (also called the accessory gearbox)
TMF—Turbine mid frame and thermal mechanical fatigue
TSN—Time since new
VBV—Variable bleed valve
   (not on LM2500; just LM5000 and LM6000)
VBVD—Variable bypass-valve doors
VIGV—Variable inlet guide vanes
VSV—Variable stator vane
VSVA—Variable-stator-vane actuator

Mention of the service bulletins (total of 17) and service letters (five) released since just before the 2016 meeting was made next. Willard noted that it was a busier year than usual concerning document release.

He then passed the mic to IHI’s Ueda, who presented on CRF vent duct improvement, engine monitoring, IGB housing deformation, and a No 4B bearing event. See Sidebar 1, “Acronyms to remember” if you’re unfamiliar with the shorthand.

The CRF vent duct has experienced cracking (attributed to high levels of stress) at the fillet weld that joins the wear sleeve to the duct body. Oil leakage is a possibility. A smoky condition in the package would suggest that. Service bulletin (SB) LM6000-IND-320, “Improved CRF vent duct,” eliminates the fillet-weld wear sleeve and identifies a material change from Type 321 stainless steel to Inconel 625 (to increase the strength margin).

An increasing T3 (HPC discharge temperature) difference among the four sensors provided (A/B/C/D) was detected; the T3-D signal was abnormal. Inspection of cable, connectors, and T3 sensors were recommended by Ueda. A user mentioned that one of his engines exhibited discrepancies in T3 signals but they couldn’t identify the cause.

Another attendee reported seeing black marks in connectors that were removed by cleaning but reappeared a few months later. That led to the question, “Is there another cable design to improve this? We are getting oxidation in there.” An OEM representative said he was not fully aware of repeated issues on connectors and asked that users provide more information on these occurrences.

Cabling can be problematic. Yet another user said engine oscillations can cause connectors to wiggle loose, sometimes resulting in an engine trip. A colleague said a robust maintenance program was required to mitigate cable issues. At his plant cleaning and tightening is done twice annually.

No. 4B bearing failure. A B-sump alarm alerted to high scavenge oil temperature and high deltaP across the scavenge oil filter. Metal particles were found in the sump. Engine sleuths went to work, identifying deep flaking on the outer race of the No. 4B bearing at the 6 and 12 o’clock positions. They said such deep flaking at these positions indicated damage was done while the engine was not running. The root cause: An air-ride truck was not used for ground transportation and the damage occurred from excessive and repeated vertical shocking.

MTU’s Reichert was next to the podium. He addressed the following:

      • CRF oil leak, SB 307/308.

      • TRF D/E sump, SB 323.

      • SB 322 HPT second-stage nozzle retainer update.

      • High C-sump oil temperature/pressure.

      • DLE combustor improvement.

      • LPT second-stage blade shroud deformation.

      • Peak versus baseload component degradation considerations.

Again, if any of these speaking points of interest to you are not summarized below, consult the presentation materials available on www.wtui.com. Access is denied to all but user members of the organization.

CRF oil leaks got considerable attention from the group. Here’s the background: Service Bulletins 233 and 236, issued September 2008, superseded SB 154 with the objective of mitigating the risk of oil leakage in the sump area. Shortly thereafter, some engines were found to have deformed J-tabs; three had oil leaks in the C sump area. J-tab distortion was attributed to an interaction between thermal expansion in the sump area and oil-tube (manifold) vibration.

In January 2015, SB 307 (SAC)/308 (DLE) replaced 233 and 236, specifying the following: removal of the heat shield, a wider wear sleeve, and a wider P-clamp for the affected oil manifold. SBs 154, 233, and 236 were canceled.

However, while the recommended fixes in SB 307/308 stopped the leaks, they were not without issues. Bent J-clamps were found after about 300 to 500 hours of operating time on a couple of engines. The good news is that the OEM does not view distorted clamps alone are a reason to pull the engine. Periodic monitoring of the J-clamps is recommended.

Significant discussion ensued. A user asked, “Can you fix clamps in the field?” An ASP representative replied, “This is a Level 4 service bulletin and not recommended for the field.” A follow-on comment made by someone else at the front of the room, “The clamps move and then fretting occurs and tubes leak; then the engine smokes. Important to recognize, an ASP rep said, is that you can monitor the clamps with a borescope. If a clamp bends, he continued, don’t worry; sometimes clamps stop bending. The important thing is look for oil, which will tell you when to think about repairs.

Yet another question: “Which is worse, a twisted clamp or a broken one?” ASP response: “With a twisted clamp, the support is still there. However, there have been some cases where the clamp was removed and the engine came back to the shop with no adverse effect.”

Peak versus baseload operation. An important presentation; it was made last year as well. Photos of damage attributed to “hard” operation are available online and offer valuable lessons for the O&M staff. The takeaway for owners of peakers is that they will cost you more to operate because hardware takes more of a toll than it does on baseload units. The LM6000 can handle the service, it was said, but the frequency of shop visits might increase.

Reichert passed the mic to TCT’s Willard, who began by discussing experience with HPC airfoils, covering SB 310 in the process. TCT would make nine additional presentations that afternoon. Those listed below of interest to users registered with WTUI can be accessed on the organization’s website:

      • HPC fifth-stage lever-arm event.

      • HPC glass-bead findings.

      • SB 301 and G33 combustors.

      • DLE-combustor ferrule events.

      • HPTN1 leaf seals, SB 306.

      • LPT mid-shaft crack update.

      • VBV door bushing wear.

      • PB/PC PCC manifold.

      • SB 313 RDS housing and clamp update.

Case history: Third-stage HPC blades. S3 blades on the unit under discussion were removed in the field and heavy wear was noted on the faces of the dovetail coating. The engine was removed from service and sent to a repair facility for evaluation.

Most blades in Stages 3-5 were scrapped because of heavy wear that penetrated the coating and continued into the parent material. The 3-9 spool was declared non-repairable at this time. Blades for Stages 3-5 can be replaced in the field or shop following the guidelines in SB 310. Many attendees indicated by show of hands that SB 310 had been implemented at their plants.

Several airfoil options are available to owner/operators implementing SB 310—standard single-intensity peened (SIP), the OEM’s new dual-intensity peened (DIP), and overhauled SIP-to-DIP blades—but all have 1500-hr start limits. This not a guarantee of no event occurring below 1500 starts, but the risk of failure increases beyond 1500.

Note that blades older than “K” (T, A, and C) cannot be upgraded through the SIP-to-DIP process. Also, converted SIP blades become “M” type with a part number change. The new part numbers are noted in the presentation.

Background: Multiple HPC S3-5 dovetail events have been reported over the last several years. According to the OEM, there are two primary causes of this: VSV off-schedule and so-called edge of contact (EOC). The latter is described this way:

      • Dovetail coating wears.

      • An indication develops in the blade-to-spool EOC area.

      • Dovetail liberates driven by LCF and HCF.

      • A stall event and secondary damage typically are experienced next.

The OEM solution to resolve the S3-5 issues was presented during its podium time the following day. The “enhancement plan” reflects a change in the blade material from titanium to Inconel 718 and a more generous dovetail geometry (airfoil geometry remains unchanged). These changes are said to improve the resistance to dovetail pressure-face fretting and reduce peak EOC stresses.

LPT mid-shaft crack. This was a follow-up to the presentation made last year on the subject, which was not covered in CCJ. Background: At least 10 LP mid-shafts have been found with cracks/indications within the threads; they can be located with white light. Pitting corrosion also was found following removal of the nickel plating on the threads.

Separate investigations by TCT and GE and by MTU reported similar findings, including the following:

      • Multiple crack origins.

      • No inherent material defect.

      • No over-torqueing of the coupling nut.

The probable cause is corrosion attack on the base material where the nickel plating was depleted. Cause of the depleted nickel plating has not yet been identified.

Corrective action: ASPs are inspecting exposed threads in the shop during overhauls regardless of repair scope. Threads can be inspected in the field as well.

Important: Repair procedures have been changed. Removal of nickel planting as part of the inspection process is now mandated, with re-application after repairs are complete. There is no repair plan for cracked or highly pitted/corroded threads at this time.

GE presentations the following day covered the following engine topics:

      • HPC S3-5 blades.

      • LPT S1 blades.

      • VSV bushing durability.

      • CRF CDP customer bleed gasket.

      • Bleed-valve durability.

      • VSV/VBV actuator control module upgrade.

Once again, registered user members can access this material on the Western Turbine website

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