WESTERN TURBINE USERS

The nitty gritty of aero engine O&M

The first part of the CCJ’s report on the 22nd annual meeting of the Western Turbine Users Inc, held at the Pasadena (Calif) Convention Center last March 18 – 21, was published in the 1Q/2012 issue, available at www.ccj-online.com

It presented conference highlights and summarized current thinking on several engine-related topics, including:

  • The use of HEPA filters to maintain compressor cleanliness without washing, based on Alliance Pipeline’s experience.
  • Cycles tracking of engines to enable life management of critical parts.
  • Details on Black Hills Corp’s world-class Pueblo (Colo) Airport Generation Station, home to the latest LMS100 and LM6000 engines in commercial operation when the facility began operating on New Year’s Day 2012.
  • Rapid removal of water and particulates from turbine oil.

This part of the report digs into the details of top discussion topics aired during the breakout sessions for the LM2500, LM5000, LM6000, and LMS100 engines, as well as during the special technical presentations session conducted on Tuesday afternoon, after the exhibition closed. Sidebar 1 identifies the officers, directors, and breakout-session chairs responsible for the 2012 conference and exhibition.

1. Western Turbine officers, directors, breakout chairs

President: Jon Kimble, Wellhead Services Inc 

Vice Presidents:

Bill Lewis, PPL Generation LLC 

Jim Bloomquist, Chevron USA Inc 

Secretary: Chuck Casey, Riverside Public Utilities

Treasurer: Wayne Kawamoto, CAMS Juniper CA LLC, Corona Cogeneration Plant 

Directors:

Andrew Gundershaug, Wood Group Power Operations Inc, Calpine Greenleaf 

Alvin Boyd, Kings River Conservation District, Malaga Peaking Plant 

David Merritt, Kings River Conservation District 

Don Haines, Wood Group Power Operations Inc, Panoche Energy Center 

John Baker, Riverside Public Utilities, Clearwater Cogeneration Facility 

Bradley Hans, PE, Lincoln Electric System, Terry Bundy Generating Station

Don Stahl, Black Hills Corp, Pueblo Airport Generating Station 

Ed Jackson, Missouri River Energy Services 

Technical Consultant: Mike Raaker,  Raaker Services LLC 

Breakout Chairs:

LM2500. John Baker,  Riverside Public Utilities, Clearwater Cogeneration Facility 

LM5000. Andrew Gundershaug, Wood Group Power Operations Inc, Calpine Greenleaf 

LM6000. David Merritt, Kings River Conservation District 

LMS100. Don Haines, Wood Group Power Operations Inc, Panoche Energy Center 

Supporting Members: 

Wayne Feragen,  webmaster, E I Colton LLC, Agua Mansa Power Plant 

Charlene Raaker,  conference coordinator 

Joella Hopkins,  conference director, Simply Mumtaz Events Inc 

Jennifer Minzey, conference coordinator, Simply Mumtaz Events Inc 

 

If you’re involved in the operation and/or maintenance of aeroderivative gas turbines manufactured by GE Energy but not aware of the value proposition associated with attending WTUI’s annual meeting, a quick read of the material that follows should convince you to attend, without hesitation, the 2013 conference and exhibition in San Diego, March 10-13. Registration for the world’s largest and most technically comprehensive forum serving LM/LMS engine users opens November 1 at www.wtui.com.

Breakout sessions

A common thread running through the LM2500, LM5000, LM6000, and LMS100 breakout sessions during the two-and-a-half-day meeting was that current issues typically were carryovers from previous meetings; relatively few new problems were reported. That many of the issues discussed were not “new” did not detract from the level of interest, primarily because of the high percentage of first-timers in attendance.

LM2500

John Baker, plant manager of Riverside Public Utilities’ Clearwater Cogeneration Facility, a 1 x 1 LM2500-powered combined cycle in Corona, Calif, chaired the LM2500 breakout sessions. The all-important depot presentation was led by Kevin Singh of TCT, with support from Chris Martin of ANZ, Nico Brademann of MTU, and Antonio Errico of Avio. Contributions of the depots to the success of the Western Turbine meetings are acknowledged in Sidebar 2.

Session secretary was Chad Flowe of Charlotte-based Strategic Power Systems Inc (SPS), which compiles the minutes for each session. After approval by the WTUI leadership, these notes are published on the user group’s website where they remain available to all registered user members.

The depots’ agenda for Baker’s session, typical of that for all breakouts, included the following items:

  • Engine fleet statistics.
  • Recent service bulletins and service letters.
  • Review of the OEM’s Customer Web Center.
  • Depot findings in the last year.
  • Critical-parts life management.
  • Engine preservation, handling, and transportation.
  • Expected maintenance intervals.
  • The depot experience.

Singh breezed through a review of the LM2500 fleet operating status and recent service bulletins (SB) and service letters (SL) for the engine (acronyms are defined in Sidebar 3). He reminded user participants that access to SBs and technical documents was via GE Energy’s Customer Web Center (CWC). Important to remember is that not all SBs pertain to every engine. Owner/operators should carefully review each publication and determine its applicability for their engines.

Next, recent depot findings were reviewed in detail, starting with the compressor and moving aft.

2. WTUI’s depot partners

The success of Western Turbine conferences is underpinned by the technical and financial support provided by the five so-called depots licensed by GE Energy to inspect and repair the four engines addressed by the group.

Representatives of the depots work closely with the WTUI leadership to prepare “lessons” for each of the breakout sessions. Deliverables include notebooks, given to user participants, which review recent service bulletins and service letters issued by the OEM; summarize depot findings since the last meeting; explain causes of performance loss and how to correct them; and provide the fundamentals of critical-parts life management.

The knowledge contained in the notebooks, and that shared by subject-matter experts during the meeting, provide comprehensive, low-cost training for all those involved in the operation, inspection, and maintenance of LM/LMS aero engines. Electric power producers obviously agree with the value proposition offered by Western Turbine participation because each year first-timers comprise between about one-third and one-half of the user attendees.

The depots supporting the Western Turbine meetings are:

Compressor front frame (CFF). Delamination, complete in some cases, of Teflon stationary oil seals for the No. 3 bearing was reported. The seal body has been redesigned with stainless steel to better resist cracking and general damage, a depot rep told the group.

A user asked: If delamination occurs, will you see Teflon in the sump? “Yes,” was the depot response. At previous meetings, users had said they found bits of Teflon in the lube and scavenge-oil filter and that depots had suggested implementing the recommendations of SB 255 Rev 1. 

Another participant at the 2012 meeting told the group that his plant had experienced vibration issues because of delamination. Of note was the comment that Teflon breaks down into sand around the seal. The group was asked if any plant was experiencing cold-weather issues because of Teflon delamination. One user with a G4 engine responded affirmatively; he changed the seal.

Peeling of paint from the front frame was acknowledged and it was said that micro FOD/DOD can result from liberated flakes of paint and rust. The subject didn’t stimulate discussion at this meeting, but it did in 2009, when at least four users among the more than two score participating in the session reported seeing CFF corrosion. All those plants were at or near seacoast locations.   

At that time, the depot representatives suggested that every plant periodically inspect paint condition and check for corrosion. If corrosion was identified, they recommended full paint removal and repainting using a GE-approved process. Several coatings were mentioned, including white polyurethane.

HP compressor rotor (HPCR). There was considerable discussion on the HPCR. Topics included the following:

  • Spline adaptor wear. Red paste/sludge deposits have been found blocking the spline-adaptor oil galleries mounted on the Stage 2 disk, with heavy wear to both the adapter and the mating IGB gear shaft. Participants acknowledged that this was an old issue, but one that’s still occurring.

At the 2011 meeting, monitoring of oil pressure and A-sump scavenge-oil temperature was recommended, in addition to semiannual visual inspections, to provide early warning of impending issues. Suggested corrective action included (1) installation of the rugged oil nozzle with improved oil-jet impingement recommended in SB IND-160 and (2) the new spline adapter having four drain holes (SB IND-199), to improve the flow of oil through the spline interface.

The subject of oil came up this year as it has at previous meetings and attendees once again were urged to use “standard” oil, not the high-thermal-stability (HTS) product some operators believe should be better. The OEM warns against use of HTS oil in SB 10-03 R1. At last year’s meeting, a depot representative suggested that owner/operators reference the OEM’s qualified product list or ask their oil provider to differentiate between HTS and non-HTS oils.

This year, a user noted that he had switched to a synthetic oil and is seeing no sludge buildup.

  • IGB horizontal gear shaft wear. A user reported light wear on his unit’s horizontal gear shaft, attributed to friction associated with the seal oil ring for the inlet gearbox (P/N 9671M82P01/P02. There was no follow-on discussion. At the 2009 meeting, it was said that the light wear on the horizontal gear shaft sometimes experienced was caused by friction of the bronze ring seal and that this occurred most frequently on the early LM2500s. At that time, a Teflon-encased Viton O-ring was a suggested fix. It was said to provide better sealing.
  • Spool rub at Stages 14-16 reportedly caused light wear of the abradable coating. Coating was refurbished as a standard repair. There was no further discussion on this point.
  • Stage-16 blades. Several incidents of 16th-stage HPC platform cracking and/or tip liberation have been reported in the last few years. Last year, cracking of blade-tip corners was said to have been resolved for LM2500+ units by following the recommendations in SB IND-161 and IND-162, but that platform cracking also has been observed in some of these engines. Base-engine owner/operators were advised to consult SB 180. All users were advised to NDE Stage-16 blades when possible.

An announcement at this year’s meeting was that SB 236 addressing 16th-stage platform issues had been issued the day before the conference started.

One participant offered that his plant has had four issues with Stage 16-blades thus far, two causing major outages and two incidents involving minor damage. His plan was to fix the minor damage during hot-section maintenance.

Another user said he kept his engine running at about 7800 hours annually, even with blade trailing-edge damage, and had good luck. When asked he said that he hadn’t seen any change in unit performance or vibration level. The OEM advised that operating with damaged airfoils is at the operator’s risk. Yet another participant said his plant was not so lucky running with damaged blades; it had experienced significant consequential damage.

HP compressor stator (HPCS). Leadoff subject in this segment was VSV system wear, as it has been for the last few years. The depot representatives urged users to keep the system clean and to replace defective parts immediately. As for frequency of inspections, the depots recommended quarterly, although the OEM’s O&M manual specifies 4000 hours or 450 cycles as a guideline.

A user noted that system wear typically is found near leaking wash water, where most dirt accumulates. This always seems to be in the hard-to-see places, he continued. Adequate inspection in the field requires time for unit disassembly, to gain access to problem areas. A question from the floor: Can you borescope to see the 6 o’clock area? Response: It’s easier to climb under.

VSV lever-arm wear was brought to the floor by a user who observed a visual gap between the lever arms and half rings. He asked, “What methods are used to prevent this?” Answer: Hot water and scrubbing. Another participant mentioned the he pressure washes monthly, which helps mitigate wear. Meanwhile, depot reps said they were working with the OEM to determine the root cause of the gap.

Regarding VSV controllers, one owner said he was having issues with being “ahead of schedule” and that these problems surfaced after only 2000 hours of service. The OEM considered this unusual and recommended working with GE Energy’s Woodward Controls group to identify the root cause. Someone else mentioned he was experiencing the same thing, but after 10 years of service.

VSV pump improvements were mentioned. Several VG pumps were removed because of high lube-oil leakage. Pump misaligns because of spline looseness and installation anomalies. Correct installation is critical. Attendees were referred to SB 234, released in 1Q/2012.

Compressor rear frame (CRF). Expandable bolts were introduced as a topic of concern. Experience indicates that the relative motion among diffuser, CRF, and mounting pins contributes to reduced service life. Depot reps indicated that this issue has been around for a while and suggested that bolts be changed every 4000 hours.

DLE  users were asked about their experience regarding this issue. Response was that the whole fleet changed to new-style bolts and no problems were in evidence over the last five years. The OEM said a significant number of its customers haven’t followed the recommendations in SB 170 and ordered new bolts.

SAC combustor. Missing/burned material from splash plates was observed. Depot reps noted that the burning was not continuous, but occurred in various isolated areas. The OEM stressed the need for its involvement. Question: Was this a base-load unit? Yes, with a water injection rate of 1:1.

Another participant said he was having a similar problem after 3000 hours of operation on natural gas while running his unit with a water injection rate of 1:1.5. Thinking was that perhaps he was using too much water. Damage did not occur in a specific location at this site either; burning was totally random. Parts were replaced as necessary. The OEM urged verification that the fuel nozzles were correct as installed. Users asked if the OEM was considering a combustor redesign. Answer was “no,” current data did not support the need for a new design.

HPT Stage 1 nozzle assembly.  Increased NOx emissions suggested removal of the first-stage nozzle assembly. Outer seal plates were found broken; cause was high cycle fatigue/high-temperature stress. Resulting air inleakage caused hot spots. SB IND-221 was said to offer corrective action.

HPT rotor (HPTR). Hot-section upgrades and life-extension programs were a topic of discussion. The depots said three or four upgrades had been completed. Owner/operators were interested on experience to date. One user said he had two machines upgraded. One experienced cracking at 30,000 hours, the other at 45,000 hours. Both engines were at the depot during the meeting. Come to San Diego in the spring to get the rest of the story.

Turbine mid frame (TMF). Liner wear was one of the first topics addressed. The bottom line: The only way to deal with such wear is to replace the liner. The leaf-seal liberation issue was next. The fix, introduced with SB 229 is a new, shorter leaf seal, which had not been introduced before the meeting.

Depot reps said that seven TMFs had been converted to one-piece cast cases. It was said the cases are easy to replace during an overhaul. One depot said it has had good experience with cast cases, but that they are of a beefier design and available only for units with thick flanges. Recall that some units have thin flanges.

A user asked if a ring was added to the thick flange to make it thicker. The response was “yes.” However, it’s not available for units with thin-flange power turbines because the bolting is different.

Turbine rear frame (TRF). Chafing damage was mentioned but considered a very minor condition and easy to repair.

Miscellaneous. About a half dozen starter events were recorded over the last 18 months. Bad O&M practices were cited for blame. Corrective action was expensive. Bearing corrosion was another avoidable malady. Corrosion was attributed to water washing. Users were advised to conduct a fired start after washing to dry out the unit if layup was impending.

3. 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

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 gas generator pieces with the power turbine attached)

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

NGV—Nozzle guide vane

OEM—Original equipment manufacturer

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

VBV—Variable bleed valve (not on LM2500; just LM5000 and LM6000)

VIGV—Variable inlet guide vanes

VSV—Variable stator vane

 

LM5000

Session chair and discussion leader for the LM5000 breakout session was Andrew Gundershaug, plant manager, Solano Peakers, Calpine Corp; session secretary, Strategic Power Systems’ Daniel Murray. Depot representatives were ANZ’s John Leedom and MTU Maintenance’s Thomas Benisch.

Only 13 users attended the breakout sessions for this engine. The fleet continues to shrink, as expected. At the time of the meeting there were 50 operational LM5000s (six fewer than last year), plus 14 customer spares and nine GE lease engines. The current high-time engine has accumulated more than 180,000 operating hours.

The meeting opened with a general discussion on the level of support owner/operators could expect from ANZ and MTU as the engine navigated its twilight years. Users were told that support was not going away and maintenance manuals and service bulletins were being updated. Also learned was that the OEM’s LM5000 program manager position, rumored to have been eliminated, would continue to be supported. The group was assured that issues associated with availability of parts and the lead times for obtaining parts were being addressed. In fact, ANZ had purchased from the OEM parts totaling more than $22 million to improve customer service.

Technical manuals, documentation. Access to SBs and SLs are via the CWC, where owner/operators can register for electronic notifications. That way, when a new SB or a revision applicable to your unit becomes available, you will receive an email with a link to that documentation. Coming SB revisions announced March 19 were the following:

  • 215: LPCR Stage-0 Blade Aluminum Coating (platform installation).
  • 216: Stage-1 Compressor Stator Vane Shroud Improvement (depot repair).
  • 217: Air Collector and Front Frame Interface Improvement (depot repair).

A few items were discussed that the depots would like to see addressed by SBs. Perhaps the most important of these was the No. 1 Bearing Aft Housing Inspection and Repair. This would address holes found that should not be there. A depot visit would be required to make repairs.

LP compressor (LPC). Corrosion has been observed on LPCR Stage-0 blades of leased engines returning from the North Sea. Such corrosion often is found as well in land-based gas turbines of all types and models located on or near the coastline. Two mitigation strategies: (1) Increase the frequency of compressor water washes; (2) cover the inlet when the unit is not in operation.

Shaft-rim bolt-hole cracking seems to be experienced by at least one unit in the fleet annually. Cracks are the result of galvanic corrosion. Suggestion was to try an alternative grease or oil in this area of the engine. But be sure to discuss your choice with the OEM before making a switch. GE is testing torque values for different types of grease.

LPCS Stages 0 to 2/Stage-3 case flange-bolt/nut torque values should be maintained at 130-150 lb-in., and the Stage 3/Stage 4 case values between 100 and 120 lb-in., not the 55-70 lb-in. currently specified in the O&M manual—at least until the OEM can update its manuals.

Discussion migrated to front-frame/air-collector interface issues—specifically, improper seating of the air collector after final torqueing. Inspection revealed bolts were under-torqued. A depot took measurements from flange to skirt on multiple units and variations were noted among the engines inspected. One conclusion was that the feeler-gage check must be 360 deg around the cover. Technicians observed wavy metal in one or more areas of some machines. Depot is working with the OEM to achieve better fit-up.

Next issue put before the group was damage to the No. 3 stationary oil seal. It caused internal oil leakage which is conducive to vibration. Evidence of a leak often is found during a borescope inspection: An oil film is in evidence on blades. A depot rep said the Teflon seal had to be replaced on a depot visit. However, a user said he was told that the seal could be changed onsite. The depot rep took a half step backward: An onsite repair was not an easy job, he said, and success depended heavily on proper set-up of the job. There was an acknowledgement that such leaks happen “often” on the LM5000 but no running-time limits were offered for the Teflon seal.

HP compressor (HPC). Rotor vibration (compressor and turbine) often is caused by insufficient internal interference fit between rotor components caused by wear or shrinkage of parts. Suggested course of action: Tear down and take fit measurements; make sure they are in accordance with SL 5000-99-03. Use metal spray or other methods to bring fits back into spec. Plan ahead: Be sure to include fit measurements and corrections into your regular maintenance program.

Distorted, broken, and worn VSV hardware received significant attention. Failure to keep your eyes on such detail can contribute to engine stalls. Regular inspection was urged: More than 4 deg of movement demands replacement of defective parts. Recommendation is to remove all parts and inspect every 12,000 hours. But as the LM5000 fleet continues to migrate to peaking duty, inspections should be conducted more frequently. Users report significant wear at inspection intervals of 4000 and 8000 hours.

Worn pins, missing bushings, elongated pin holes, sheared lever arms, worn bearings, and worn trunnions can be expected. VSV components are relatively inexpensive, so “saving” by not replacing damaged parts is not a sound financial strategy: It increases the risk of costly damage to the HPC.

A comment from the floor was that while external bushings can be replaced in the field, that’s only a temporary fix. Both internal and external bushings must be replaced and that requires a depot visit.

HP turbine (HPT).  Most important discussion surrounded the failure of air tubes serving second-stage nozzles. Known as “spoolies,” these cooling-air tubes typically are found worn because of fretting, dislodged and rotated 90 deg thereby blocking air flow, or simply missing. Associated retaining rings and spring washers typically are dislodged and migrate elsewhere. Attendees were told that other LM engines have a similar issue.

Owner/operators were urged to replace all “spoolies” when exposed in the field and when an engine is sent to the depot. Total design airflow is required to minimize the danger of burning the disk.

LP turbine (LPT). An isolated issue identified with the LPT stator case was cracking on the circumference of the forward nozzle support hook. This was found on an engine in a depot for overhaul and was thought conducive to a catastrophic failure. Metallurgical evaluation was not complete at the time of the conference but the thinking was that replacement with “fresh” metal was necessary. Too much time—47,000 hours in this case—at high temperature was believed to be the underlying cause. One participant noted that engines are making it through the second major but not to the third.

Rim bolt-hole inspection for the first-stage disk was recommended using eddy current to identify any cracking that might have occurred. One disk with cracks was found by a depot in 2011. Refer to SB 5000 IND-0209 for guidance.

Critical-parts life management is a responsibility of owner/operators to protect against physical damage to property and to ensure the safety of plant personnel and the public at large.

Users should maintain cyclic life records of critical parts to enable their timely removal from service. Where such record-keeping has not been done consistently, owners can consult with the OEM regarding a “best estimate” of life expenditure and then collect and maintain follow-on data.

Participants pointed out during the session that they believed LM5000 parts were not made to accommodate the cycling required today. One user experienced vibration at startup following a normal shutdown. He found that running the generator fans for two hours after shutdown caused extended power turbine/generator spin down; thereafter startup was fine. Users were cautioned that the PT lube-oil pump (attached to the gearbox) is not running after shutdown.

The PT requires a sub-core idle warm-up and then a 10-min sub-core idle before bringing the unit to synch-idle. It is difficult to restart the LM5000 after a short shutdown. If you can wait eight hours, everything is good the users were told.

Humidity control is very important, the depot reps said, if a unit is scheduled to sit for long periods. Suggestion: Install large plastic sheet over the inlet to prevent moisture from entering the engine. If the unit will be idle for more than a month, owners should follow engine-oil preservation procedures.

Open user discussion. The subject of fire protection systems was raised but discussion was quickly extinguished. A user wanted to know how he could determine if the system was still in workable order and asked if anyone had the original test results for package testing. He was told there was not a product suitable for proper testing.

An owner reported a first-stage nozzle blade failure after 15,000 hours at 1410F to 1425F with full STIG. Unit started daily and ran for 13 hours. The user wanted to know what happened to cause this failure. The answer: End of life. Expect burn-through of first stage buckets and nozzles by 16,000 hours.

“How am I doing?” an owner asked, telling the group that he was able to bring the T44 spread down to 40 deg F. “Exceptional,” he was told; most are in the high 90s and above.

Regarding offline water wash, a user asked if sampling of wash water discharged was necessary to verify the cleanliness required. Answer: Not mandatory.

LM5000 STIG interface connection was considered a bad design by a user who was told to add stiffener legs similar to the LM6000 to support the manifolds and piping. This gets the weight off the engine.

OEM/depot, user discussion. Lifetime engine support was a topic of great interest to owner/operators, who had many questions for OEM and depot representatives. The OEM promised “continued” support, saying a budget had been approved for support, parts, and repairs, and that there currently was no plan to take the LM5000 out of service. An OEM rep said that if a strategy of the lifecycle were available, support could be continued five to 10 years.

At least some owners said they didn’t have the financial resources to convert to LM6000 and might want to run their engines another 15 years without extreme costs. You could see where this discussion was headed and words appeared carefully chosen.

In brief, the owners had these among other questions:

  • What are the inventory levels of critical parts, as well as of non-critical parts?
  • Could they be assured no long turnaround times when parts were needed?
  • If parts were unavailable, could they arrange for reverse-engineering of parts and give alternative suppliers OEM drawings?
  • Would the OEM support less stringent standards so owners could maintain their engines?

The OEM/depot reps responded predictably:

  • The depots need the following information from users to better determine the quantity of spares needed: run time, fired starts, hours per start.
  • The OEM has been discussing and investigating “conditional” repairs.
  • The OEM is not in the position to authorize support for non-standard parts.
  • The OEM is willing to work with a vendor having the quality standards to make needed parts.
  • New long-term service agreements are available to LM5000 owners. Plus there are nine engines in the lease pool to support the fleet.

Depot findings: Abnormal events. Several depot findings in the last year were classified as “abnormal events”—including the following:

  • LPC coupling nut, cracked/disengaged. The LPC rotor shifted back, stopped only by the PT. Why the nut failed was not completely understood at the time of the meeting. Experts believe the failure mechanism either is hydrogen embrittlement or pitting from moisture developed during operation. As a preventive measure, install a new nut in every unit sent to a depot for repairs. A similar issue was identified with the LM6000 about two years ago and that remains unresolved as well.
  • Airfoil separation on HPC eighth-stage vanes. This condition can be identified during a borescope inspection; however, a thorough inspection of the area could take days. It is best to inspect for this condition when the upper casing is removed. A root-cause analysis is forthcoming.
  • Cracking and degradation of the HPT outer seal, which apparently was caused by use of an oversize seal, a manufacturing issue. A final report is pending.
  • Debonding of the TMF cooling and vent seal.

Package discussion. 

  • Inlet-air filter house observations and recommendations: (1) Unit was operating normally with no issues until ambient conditions suddenly changed and turned to mud impurities that had been captured by the filters. The impact of ambient conditions on operations should not be underestimated. (2) Ensure proper calibration of pressure gages, especially differential-pressure gages. (3) Do not “puff” filters with the FOD sock installed. This will clean the debris from the filters, but it will remain in the filter house and re-clog filters. Install FOD socks for about two weeks following a major to help reduce corrosion from acidic environments.
  • Lube-oil system. Air/oil separator issues were reported by one user. Investigation found rags in lines at the tank. Suggestion was to cap open lines when removing an engine from service to prevent such problems. Subject of oil sampling was raised. One suggestion was to have a local company sample and analyze the oil monthly. Users were cautioned against bulk changeout of lube oil because detergents can cause engine deposits to break loose and cause problems.
  • Fuel system. Test and calibrate fuel nozzles annually. Heat rate is virtually sure to improve.

Engine handling, transport. The group was told that whenever an engine is installed in a shipping container, ensure that the straps over the container are not too tight, to prevent crushing. Fasten the container securely to the transportation trailer from the base of the container.

Storage, preservation. If you plant to keep an engine out of service for a month or more, put it in a properly pressurized container to prevent corrosion damage. Hook up the storage container to nitrogen and blow out all of the air, leaving the container pressurized with a maximum of 3 psig of nitrogen. Follow the OEM’s manual for storage and preservation.

LM6000

Session chair and discussion leader for the LM6000 breakout sessions was Bryan Atkisson, plant manager, Riverside Public Utilities; session secretaries, Senior VP Tom Christiansen and Weston Trimble of Strategic Power Systems. More than 150 owner/operators participated in this engine forum, about two-thirds of them first-timers. They were joined by representatives of the OEM and its authorized LM6000 Level-4 service providers—TransCanada Turbines, MTU Maintenance, and IHI Corp.

The breakout sessions at Western Turbine meetings are rigorous. For the experienced, they provide the opportunity to catch up on new issues identified by the depots which should be incorporated into inspection/maintenance routines. For those still getting familiar with the engine, the eight-hour program for each LM/LMS engine, spread over the three days of the annual conference, is an invaluable training exercise.

Two questions Atkisson asked the group before digging into the technical aspects of LM6000 O&M: “Who had an unscheduled outage this year?” By show of hands, 15%. “Who had to remove an engine because of an unscheduled outage?” About two-thirds of those experiencing a forced outage.

Erosion caused by issues associated with the Sprint™ system, on engines so equipped, monopolized the early discussion. Recall that Sprint is an acronym for “spray intercooling,” which is used to increase compressor mass flow by cooling the air during compression.

Demineralized water atomized by high-pressure air extracted from the eighth stage is injected via spray nozzles into the compressor. The water flow rate is metered, using the appropriate engine control schedules. Sprint’s effectiveness is most pronounced in hot weather. Example: While power output is 9% greater at ISO conditions than for the same LM6000 model without Sprint capability, at 90F ambient it is 20% greater.

On high-pressure-ratio gas turbines like the LM6000, compressor discharge temperature often is the criterion limiting power output because compressed air is used to cool hot-section components. By reducing the compressor outlet temperature using Sprint, the engine can operate on its natural firing-temperature control, thereby boosting output and improving efficiency.

Many users with Sprint-equipped engines have reported erosion of variable inlet guide vanes and of the LPC. Regarding the latter, erosion grooves in the LPC cases of two engines—one with 8000 hours of service, the other with only 3000—were reported at the meeting. The erosion groove formed at the drop-down edge of the zero- and first-stage LPC blades in both cases.

A user asked if the holes in the Sprint nozzles were too large. Not; the spray angle was completely different from that recommended. The group was told that if you change nozzle position, you change the droplet size. A best practice gleaned from the user discussion: Annually, change out Sprint nozzles, or test them to assure that the spray patterns are acceptable.

LPC disk corrosion and pitting have been found in a couple of instances—more often than expected. Current thinking is the wear and tear could be related to moisture in the engines. This issue is important to correct given the cost of replacement wheels.

A photo was flashed up on the screen showing HPT first-stage blades that apparently had taken a beating from FOD or DOD. Suggestion was that in such cases you might want to just run them until replacement is necessary because rejuvenation was unlikely. By contrast, if only flaking was in evidence, rejuvenation might be possible. Advice was to discuss with a depot rep before finalizing a decision.

Next subject was LPT first-stage-blade shroud gap. Only a couple of years ago, if any gap existed, you were supposed to remove the engine from service and repair. But 15,000 to 20,000 hours later the gap typically would reappear. Users pushed for a change in limits because units were being taken out of service based on gap alone and owners thought it unnecessary. Investigation revealed that having a gap was not the problem believed, as long as the wear was uniform. New rule that has significantly improved availability and reduced O&M cost: Repair now is necessary only if wear is not uniform.

Regarding LPT fifth-stage-blade shroud wear, this condition has not been reported since the two events that occurred three years ago. Borescope inspections confirm regularly that shroud wear and overlap are not occurring. This is important because loose engagement will allow the blade to vibrate back and forth, a condition conducive to fracture at the base.

Critical parts life management received plenty of air time. A show of hands revealed that only 20% to 30% of the attendees were tracking cycles. Users were urged to track the operating times of parts as accurately as possible. Pushback: A user noted that the OEM’s O&M manual still had the life limits of some parts as TBD (to be determined) and asked when the information would be available. Sometime this year was the reply.

From the discussion one quickly concluded that cycles tracking was not something users relished doing. Fingers seemed to be pointing in all directions. Customers are asking the depots for cycles, but the depots said that information is virtually impossible to provide unless owners give them the relevant operating information.

The depots believe cycles tracking starts with the users because they have all the information. Owners are looking for the OEM to track cycles automatically by way of software. The users were told that the new software for the PG and PH models of the LM6000 has the capability to produce counter readings which then must be applied by the user for the applicable part. An OEM rep also said cycles tracking will be offered as an upgrade for older software, except for that on PA and PB engines.  

A user asked: “Where do we start with cycles tracking when we don’t know the past?” One thought is that it’s better to be conservative and replace parts sooner than you might have to; then you can begin accurate cycles counting with new parts. For parts that are original to the engine, you can collect data for a year or two and average it backwards to the installation date if you believe the GT’s operating profile has not changed much over the years.

“Are you supposed to pull a part once it has exceeded its cycle limit?” Yes, the owner was told.

Engine preservation. Depot reps suggested to users that they keep logs of engine preservation maintenance, saying they were important both for insurance reasons and for refreshing your recollection of what was done.

Outage preparations. Before every outage, be sure all lifting equipment has been load-tested and is operational. One user remarked, “I think we all load-test the crane before using it. How do we load-test the fixture?” Response: The manufacturer should provide a certificate and unless you overload it, there’s no real reason to test the hook. If you think you’ve overloaded the fixture, the depot rep continued, find a local company capable of testing it. Another voice: Some fixtures come with manual and/or local guidelines for testing. IND 278, covering weight limits on lift fixtures, is now available via the CWC.

A user was looking for an outage checklist to be sure everything is covered six months ahead of time. His last outage was extended because everything needed was not in place. He was told that checklists do exist—in fact, some have been published in the CCJ (search at www.ccj-online.com).

OEM exchange. Here are several bullet points extracted from the exchange between the OEM and the owner/operators:

   1. A couple of users said they did not have access to LM technical documents. This means they’re not finding out about improvements. Suggestion was to register immediately on the CWC.

   2. Owners now can update SB compliance online if desired.

   3. Quarterly bulletins now are issued on what information resources you are missing for your unit.

   4. Water washing. There was a question regarding IND 11-103, “Water Wash Guidelines.” This was misinterpreted by some users to be a standard for everyone, but water washes cannot be generalized for everyone, the group was told. Water washing is determined by site conditions. Everyone: Be sure to protect electronics underneath the engine against water leaks.

   5. Controls demanded considerable discussion time with several specific issues brought to the floor. Most users want to keep up on obsolescence. The OEM said there are three different status designations for its series of Mark controls: enterprise, legacy, obsolete. Discontinued parts still are covered for enterprise but not obsolete parts. Mark V controls will become obsolete in 2014, Mark VI in 2019 (entering the legacy phase now), Mark VIe in 2026.

OEM  reps talked about the benefits of a controls upgrade. Examples: Reliability improves because the probability of having forced outages is reduced; plus, engines are easier to troubleshoot, maintain, and upgrade.

   6. PC to PG upgrade kit enables a 10% increase in both air and exhaust flows with no changes to existing mounts. However, a gearbox is required as well as 8 ft of additional space. Time from order to installation is 12 months or less, plus a 45-day outage.

   7. Remote monitoring and diagnostics service is now offered. It provides 24/7 support for the operations team, access to technicians, etc, and promises measurable impact on reliability, availability, and operability.

   8. HPC blade release. One incident involving an third-stage blade release and two involving releases of fifth-stage blades were discussed. Cracks originated in the dovetail areas; no other hardware or operational anomalies were identified. Examination of remaining blades in the affected rows revealed wear-coating depletion.

   9. Splitting of the rubber boot for the radial drive shaft occurred on five units, allowing oil to spill into the packages. Investigation revealed that the supplier changed its manufacturing process. Addition of a solvent to provide reinforcement resulted in poor bonding between layers of Viton. Situation improved by returning to the original manufacturing process and revising the design of boot and clamp for better retention.

   10. G39/G40/G42 PC combustor experience continues to demonstrate improved results compared to the G35. Splash-plate burning has been reduced, swirler thermal barrier coating has improved erosion resistance, and the bore wear rate has been reduced. However, swirler cracking still is in evidence.

   11. SAC swirler cracking was attributed to environmental attack and thermal stress from NOx water. Long-term improvement plan focuses on leveraging the PG and LMS swirl cup design to improve durability.

   12. SAC TBC loss has been observed after only 600 hours of service, with coating material liberation “beyond normal erosion.” Coating release has been attributed to high shear stress at the TBC to swirler interface. Plus, some swirlers examined did not meet specifications. Improvement: The hybrid G42/G32 combustor. Erosion process proceeds faster but it is less damaging as wear occurs. The thinking is that a user would rather replace a combustor with a less effective coating more often and protect the HPT blades against impact damage from liberated large particles of advanced coatings. 

   13. Accelerated SAC primary-swirler bore wear has forced at least one engine out of service in less than 2000 hours. A new coating, T800, has shown promise in trials. No evidence of wear after 4000 hours. Release to the fleet was promised.

   14. Two instances of CRF oil leaks were identified with PC units—one after 455 starts and 10,000 hours of service, the other after 393 starts and 4900 hours. Repairs required depot visits. The reported issue was that the “P” clamp “walks” on the heat shield because of thermal cycling and the J-clamp bends. A diagram of the movement can be found among GE presentations on the CWC.

Work is ongoing to validate a new design featuring a wider clamp configured to stop it from catching and walking. If field tests are successful it will be released to the fleet. Discussion revealed that personnel some sites remove the clamp, which has a history of issues. Experts did not support this action, saying that it might be conducive to cycle fatigue of other parts or cause a natural-frequency issue.

CRF oil leaks have been discussed at LM6000 breakouts for several years. Such leaks can cause engine smoking and frame coking, as well as the loss of oil. At previous meetings, there was general agreement that one cause was elongation of loop clamps because of thermal growth and sump-area stresses that contribute to clamp distortion. Investigators found that clamps would slide off the oil-tube wear sleeves and wear through the tubes. A couple of years ago, users were referred to SBs 233 and 236 and told that if the recommended work was done during the next depot visit the leakage incidents would cease.

   15. DLE gas-manifold distress. Multiple incidences of C-ring distress were reported in the last year. The problem is separation of the brazed joint on the L manifold. The cause, in theory, is hydrocarbons igniting in the manifold when gas fuel is not flowing. Recommendation: Replace the brazed manifold with one of welded design. Under evaluation: Addition of a check valve at the C-ring outlet to prevent the back flow of combustion air.

   Plants were urged to maintain a leak-free gas fuel system and assure there is no oil carryover from the gas compressor, if installed. Plus, be sure the gas you’re receiving meets GE specs published in the O&M Manual, Appendix A1.

   16. Put the LPT fifth-stage blades on your watch list. There were two unscheduled engine removals in the last year attributed to fifth-stage blade issues. While both of these units had accumulated around 40,000 hours of operating time, don’t be complacent if you have a low-hours engine, the users were told: One LM6000PC had to be removed in about 5000 hours. PC owners were told there’s a one-in-10 chance their engines would be put “on watch” or removed from service because of fifth-stage blade issues.

   17. VBV expansion-joint material distress. Tears at the creases of the expansion joint typically are experienced. If tears exceed 3 in., recommendation is to replace the joint. Root cause of the problem is material deterioration; replace with silicone aramid to mitigate tearing.

User presentations. The first presentation in this group reflected a user’s first experience in removing an engine (an LM6000PD DLE in this case) for a depot visit. He began by asking two questions:

  • Who has not pulled an engine? Half the attendees raised their hands.
  • Who has and has had an unexpected surprise? About 10% acknowledged.

Next, the presenter revealed two issues faced at his plant the first time an engine was removed: (1) Restricted space between the package and adjacent building; (2) access platform blocking doors. Action taken: Platform was removed and modified; replaced crushed-stone access path to package with concrete.

The speaker urged his colleagues to review procedures with someone having experience in removing an engine to be sure all lifts, trollies, parts, tooling, etc, that might be needed would be available. His plant was not as well prepared as he and his colleagues thought and a lift had to be rented at the last minute, and a steel structure installed, to facilitate removal.

Surprises incurred during removal and at the depot: Coking on the TRF; oil-sump drain lines had been modified; work was required on the clutch; oil seals required refurbishment. A user asked how it was determined that the clutch was bad. It wasn’t, the speaker responded, the depot rep suggested that it be overhauled because no maintenance had been done on it previously. Another question related to the impact of coking. Drain-line diameter was increased by ½ in. to assure proper operation.

Timeline: Engine removal and reinstallation took three days each; the depot visit lasted 10 weeks.

The second case history involved an unplanned depot visit for an LM6000 (converted from an LM5000 about three years earlier) in base-load operation. Engine was borescoped at 21,000 hours and heavy rub damage was found on the leading edges of the LPT second- and fourth-stage seal lips, which was not serviceable in the field. Damage was said to have occurred about six months before the inspection was conducted. There were no prior issues—such as high vibration—that would have indicated a problem with the LPT—no vibration issues, etc.

A combustor/HGP inspection was done during the depot visit, and the B sump clamp inside the engine was modified. Latter action was taken because a sister unit’s oil line was leaking. There was no leakage associated with this unit; work was precautionary.

Next user presenter was from a plant where a dozen LM6000 were placed in commercial operation 10 months earlier. He shared issues faced with the new units, including these:

  • Evap cooling system. Fuel-valve solenoid control wire termination box was installed in the water path. Water entry shorted the electrical box. There was no fuse protection for the solenoid coils, causing the termination board to short out. Follow-up on a loss-of-suction incident with the evap-cooler circulating pumps three weeks after startup found impellers were set improperly. Couldn’t be fixed right away so 6 MW were lost to “no evap cooling available.”
  • NOx and fuel-valve driver failures attributed to sloppy installation practices required a team of technicians to check all wiring and connectors and then recalibrate NOx-water and fuel valves.
  • Grounding issues produced erroneous alarms, caused improper response from feedback circuits, etc. “Phantom problems” had to be rooted out and fixed, one at a time.

Questions from the field. The Western Turbine Users serves owner/operators of well over 1000 LM/LMS engines worldwide—machines driving generators and pipeline compressors and others dedicated to ship propulsion. The group hosts an online forum at www.wtui.com, but questions often come directly to officers, directors, and the breakout session chairs. Contact information for these aero leaders is available on the website.

Atkisson collects the questions/comments/ideas sent to him during the year and uses them to drive discussion during the breakout sessions. Here are some of the topics he introduced to the floor during the meeting in Pasadena:

  • Passive case cooling system. A plant reported removing it, but losing very little power as a result. Risk mitigation was the reason: A part could wear from thermal stress and get into the LPT case.
  • Exhaust diffuser cracking. Several users’ engines experienced the issue, but success was elusive and the crack reappeared. Some owners are comfortable not repairing diffuser cracks because the repairs always seem to be temporary.
  • Gas-compressor lube oil carryover to the engine. User said the synthetic oil used even passed through coalescing filters. Addition of secondary coalescing filters appears to have solved the problem.
  • Exhaust-spread issues. Discussion was vibrant on the subject. Mention was made of the OEM’s “cheat sheet” for plotting exhaust temperature to the T48 thermocouples to help determine if excessive spread can be corrected by change-out of fuel nozzles.
  • Water washing. User varies rotor speed during water wash to improve cleaning effectiveness.
  • Running on AGC at low loads. One user reported operating at 7 MW and suffering the consequences—wear on first-stage blades, fuel nozzles, and VBV doors, etc.
  • NOx water valves received poor reviews from users. One user said he has changed valves twice in seven years of running and rated that part one of the most unreliable on the engine. The valve supplier just brushed off his findings of metal particles inside the valve and unraveling gaskets with a “dirty and harsh environment” excuse. Fed up, he changed from the OEM’s preferred supplier to an alternative supplier. Valves were more expensive, but operating problem-free.
  • After short discussions on the 11th-stage check valve, an HPC blade failure of the type no one could determine, and a CDP valve failure, IGB sludge became the topic of choice. Opening question: Is there anyone present who needs to do SB 225 and hasn’t yet? One hand raised.

An OEM rep cautioned, “If you see sludge, or have wear beyond the 10-mm limit, you have to do SB 225.” If you decide to keep running, the risk is that the spline shaft will be damaged and the spline won’t engage. Also, if you’re having problems, don’t keep hitting the start button. When an IGB spline disengages, things are still turning and generating heat which can damage IGB disks.

Some background on the issue may benefit new users. Prior to publication of SB 220, inadequate lubrication often was the cause of gearbox problems. Specifically, inadequate spline lubrication, and relative motion between the horizontal gear shaft and HPC spline adapter, caused wear that resulted in a core speed change or inability to restart. Wear can be identified by the presence of iron oxide sludge during a borescope inspection.

SBs 220 and 225 can prevent this problem. The first document, published six years ago, introduced an oil insert and new oil nozzle. The insert was selected based on successful experience on other GE engines.

SB 225 introduced a new spline adaptor that almost doubles the oil passage area to prevent wear particles from clogging the holes. It also made adjustments to reduce contact between spline teeth. At a Western Turbine meeting several years ago, users recommended fulfilling the requirements of SB 220 because SB 225 requires disassembly of the engine to the modular level. It was considered by users as cost-effective to implement only when related maintenance is required.

A package discussion closed out the LM6000 breakout for 2012. Balance-of-plant issues were included in this lively “ask anything that is on your mind” session. Topics included the following:

  • Conversion of belt-driven generator fans to direct drive.
  • Rusting air filters and alternatives to galvanized steel frames—stainless steel and plastic. Concern was the production of rust that blows into the engine.
  • How to avoid water in lube oil. Shut down the Sprint system (if installed) 10 to 15 min prior to engine shutdown and/or install coalescing filters that are more effective than the ones supplied with the engine.
  • Generator lube-oil issues.
  • Fuel-system problems during startup. OEM recommended that gas valves are covered during a water wash.
  • Flow testing of Sprint nozzles.
  • CO2 system permissives changed to prevent a unit start when the fire protection valve is closed.

 LMS100

Chairman and discussion leader for the LMS100 breakout sessions was Don Haines, facility manager, Panoche Energy Center, Firebaugh, Calif; session secretaries, Sal and Tripp DellaVilla of Strategic Power Systems.

Breakout session chairs invest a great deal of time throughout the year ensuring that Western Turbine members openly share O&M issues to benefit their respective user communities. Example: Haines prepared a detailed handout for all LMS100 attendees that both identified historical problems and described new findings and issues since the previous meeting. This refresher for seasoned participants and backgrounder for first-timers put everyone in the room on the same page at the start of the meeting.

Following Haines’ opening remarks, Sal DellaVilla presented on the value of user participation in the ORAP® system, which tracks and reports on the availability and reliability performance of the various LM fleets, consistent with WTUI’s mission of “advancing the operability and reliability of the GE line of aeroderivative gas turbines.” DellaVilla’s presentation is available at www.wtui.com; more detail on the Operational Reliability Analysis Program is available at www.spsinc.com.  

Currently, ORAP collects monthly operational, event, and counter data for 18 of the 26 LMS100s in the fleet. DellaVilla reported that only one unit is operating base-load, with the fleet average service factor at 18.4%. The majority of the time, the fleet is in a state of ready reserve. Simple-cycle availability and reliability from 2007 through 2011 was 88.4% and 94.1%, respectively. The OEM expects the fleet to grow to 50 engines by mid-2013, the group was told.

As of March 1, the fleet had accumulated 17,500 starts and nearly 110,000 fired hours with the high-time engine just north of 22,000 hours. There were 26 operating units at the time with six more being installed/commissioned (two in Australia, one in Venezuela, and two in California) and five others in transit to plant sites.

Two user presentations followed DellaVilla. Don Stahl, a WTUI board member and plant manager for Black Hills Corp’s Pueblo Airport Generating Station, discussed the design, commissioning, and early operating experience for his new plant. It features two 2 x 1 LM6000-powered combined cycles and two LMS100 peakers. For more, retrieve the article from 1Q/2012 CCJ.

Stahl was followed at the podium by Haines, who conducted a review of the historical issues at Panoche and encouraged the vibrant discussion session that ensued. Here’s a sampling of the issues Haines mentioned and how to deal with each one:

  • Eighth-stage anti-icing hose failure. Inspect annually prior to the winter run for cracks, etc. Put the unit on crank, use hands on outside to check for leaks. Remove the clamp on the HPC and conduct a visual inspection.
  • VSV loss of hydraulic pressure. A unit trip occurred at about 15 MW while loading. VSV hydraulic supply pressure was decreasing; would not follow demand as HPC pressure increased. Issue was found to be the hydraulic pressure regulator, consisting of two regulating valves and one PRV. The regulator was replaced.
  • HPC failure and possible FOD. Inspect unit prior to acceptance for debris, dirt, particles, etc, that can impinge on HPC surfaces.
  • Hydraulic pump suction spool installation. Don’t over-torque: Rubber spool will deteriorate and disintegrate, going downstream to the HP filter. There should be a visible gap in the flange; a tightly compressed flange is evidence of a problem.
  • Over-torqued compression fittings are conducive to miniature fractures which will result in leaks.
  • Detronics firmware upgraded to prevent spurious trips.

An OEM presentation reviewed 18 active development programs implemented to address fleet issues and the progress to date. Here’s a sample of procedures/processes developed to mitigate three of those issues:

  • IPT frame strut tubes. Fractures associated with the IPT frame are being addressed by implementing inspection processes to check for stress cracking.
  • Online water-wash procedure, if not performed properly, can result in water accumulation in the rotor system and lead to heavy rubbing. Users were reminded of procedures.
  • Second-stage tube fractures caused by stress on joint-IPT frame. SB 104 has developed to address this issue.

Other programs being conducted by the OEM and of interest to owner/operators, include the following:

  • Mid-span shroud pad wear on HPC first-stage blades. Recall that this blade row has an interlocking mid-span shroud with adjacent blades sharing a carboloy wear pad. The design is the same as that for the LM6000 blade—same PN in fact—but the wear pattern is different, with the LMS100 pad wearing at an accelerated rate. The OEM is working at figuring out what would drive different wear results.
  • Cracking of single annular combustors has been identified at various locations—primarily at the inner overhang. By the time of the meeting, nine combustors had been replaced in the field but there had been no downstream damage (HPT). Investigation is ongoing; the inspection interval has been reduced to monitor the condition going forward. One thought is that water-induced erosion hurts the coating and causes the cracks in and around the dilution holes. An alternative coating has been proposed.
  • Plugging issues with intercoolers has been traced to rusting of the carbon steel supply waterbox. Depending on water quality, exposure time, and other variables, the waterbox may rust and cause the blockage of some tubes. Inspect the waterbox periodically and paint if necessary; check tubes for fouling and clean if required.

Special technical presentations

The six special technical presentations conducted Tuesday afternoon in two time slots meant Western Turbine attendees could attend a maximum of two. That was unfortunate because each of the presentations got two thumbs up from the editors.

One, presented by Rob McMahon of Alliance Pipeline, which detailed his company’s experience with hydrophobic HEPA inlet air filters, was summarized in an earlier issue. It is of value to owner/operators of all makes and models of gas turbines.

Two of the six presentations—“User-Generated Package Improvements,” conducted by WTUI Directors Brad Hans and Ed Jackson, and “Peaker versus Base Load Operations and Maintenance,” by Dale Reed, president, Reed Services Inc—have greatest value to the LM community and are summarized here.

“Tools for Optimizing Gas Turbine SCR Performance,” by Larry Muzio and Tom Martz of Fossil Energy Research Corp, is of interest to all power producers controlling NOx emissions by way of selective catalytic reduction (SCR). This feature article based on their work in the field was published in CCJ  2Q/2012 (2012 Outage Handbook).

“Greenhouse Gas (GHG) Impacts of California AB32 and Federal Regs,” presented by Jackie Ferlita, director, Element Markets, Huntington Beach, Calif, obviously was of greatest interest to California power producers, but it likely sent a shiver up the spines of attendees from out-of-state electric generators.

Before the Enron fiasco, other states blindly followed California’s lead on energy policy and legislation, and while that probably is no longer true, it is worthwhile having an understanding of the carbon market in the nation’s most populous state as it prepares to implement an economy-wide cap-and-trade program in 2013.

California’s GHG cap-and-trade program is a central element of the state’ s Global Warming Solutions Act (AB32) and covers major sources of GHG emissions in the state—such as refineries, powerplants, and industrial facilities. The regulation includes an enforceable GHG cap that will decline over time.

Goal is to reduce GHG emissions to 1990 levels by 2020 and ultimately achieve an 80% reduction from 1990 levels by 2050. An overall limit on GHG emissions from capped sectors will be established by the cap-and-trade program, and facilities subject to the cap will be able to trade permits (allowances) to emit GHGs.

White papers and implementation guidelines for the program, which is said to have started Jan 1, 2012, had not been released by the California Air Resources Board (ARB) at the time of the Western Turbine meeting. An enforceable compliance obligation begins with 2013 GHG emissions. Ferlita said that the cap will begin at around 2% below 2012 emissions and will decline by 2%-3% annually until 2020. 

Power generating facilities governed by the program are those emitting more than 25,000 metric tons/yr (an obligated entity). Merchant power producers must offset actual emissions 1:1 by obtaining allowances at quarterly auctions or arranging for carbon offsets from the Climate Action Reserve (urban forestry initiatives, for example).

The editors asked representatives from a couple of California power producers in the audience what the 25,000 t/yr meant to owners of gas-fired LM engines in terms of operating hours. Back of the envelope calculations, assuming between 2% and 3% of CO2 per lb of exhaust gas during normal operation, translates to between 1667 and 2500 hours for an LM6000 and between 2500 and 3750 hours for an LM2500.

Ferlita said that the majority of allowances will be given freely to utilities and industrial companies in the early years of the program, with a higher percentage of allowances being auctioned over time. Beginning in 2015, the regulations will include all importers of electricity, liquid fuel suppliers, and suppliers of natural gas with GHG emissions greater than 25,000 t/yr. To learn more about the California program, a good place to start is the ARB website at www.arb.ca.gov.

“NERC Audit Interpretation Management,” by Chris Siplin of Wood Group GTS Power Plant Services, was a presentation with follow-on discussion of value to all power producers subject to NERC audits. Siplin’s prepared remarks were relatively short; his goal was to share with less-experienced colleagues in an open forum, pitfalls to avoid in the audit process.

He began his prepared remarks with the formal audit notification process and how plants are supposed to respond, which includes the preparation of documentation that must be submitted to the audit team. Typically, three or four auditors—including the team leader—will be involved, Siplin said.

Documentation of everything is critical, he told the group; answer all questions with the required detail. Stick to a standard’s literal translation, he suggested, and be able to explain your interpretation using the language of NERC as presented in the organization’s Glossary of Terms.

   Siplin stressed becoming familiar with the Compliance Application Notice (CAN) process, which is vital to responding to any disagreements you may have with the audit team’s findings. You will find it detailed under “Compliance Application Notices Processes and Tools” at www.nerc.com and includes five appendices:

  • To submit potential issues.
  • To prioritize issues.
  • To submit comments.
  • To submit suggestions to standards.
  • To request a high-level review.

One of Siplin’s recommendations to anyone responding to a question from the audit team by phone is to follow that up with an email clarifying your response. This will help prevent misinterpretation. Paper trails are critical to success.

Remarks by owner/operators during the open discussion session made it clear that the audits were anything but predictable. While audit teams follow a common set of guidelines their interpretations may be different, so responses that might have been accepted at your last plant might not be accepted at your current one. Also, there are regional differences in rules and interpretations much like there are for the federal court system.

An attendee with familiarity of Texas audits said they are extremely tough—perhaps the most difficult in the country. One audit that he was familiar with generated 120 follow-up items and questions—each requiring the plant to defend itself against a possible violation.

User-generated package improvements

The one-hour session on package improvements made by users, chaired by WTUI Directors Brad Hans  and Ed Jackson, two seasoned aero users, could have gone on for hours more. This, the best-attended of the three concurrent sessions conducted from 3:30 to 4:30 pm, was designed as an open discussion forum to share ideas among owner/operators.

The co-chairs put up a list of about a dozen and a half topics, introduced each with a slide, said a few words about their experience with a given improvement and encouraged audience participation. It didn’t take much encouragement: Discussion was virtually continuous for the hour allocated. When interest in a given topic began to wane, the discussion leaders moved quickly to the next subject.

Below are some of the discussion topics compiled by Hans and Jackson that enabled many users to return home with affordable and proven solutions for improving equipment operability and maintainability, efficiency, safety, etc. This session alone made the trip worthwhile for many attendees and the benefits gained offset the cost of attendance for most of those users.  

Maintenance platforms  may not be provided with the package to assure easy access to generator and turbine enclosure fans, chiller-coil drains, etc. In some cases where they are provided, the access path is not customized to the site and personnel hazards are created inadvertently.

After the constructor leaves the site, it’s up to the plant to make necessary safety improvements. One solution offered was platforms mounted to the package roof with safe access (Figs 1, 2). They were engineered and installed by a local company, which prefabricated sections to expedite installation. In Fig 3, a trip/fall hazard is avoided by modifying the marginal ground-level access to an important cabinet.

Generator-fan lifting device.  For a situation where fan maintenance created an unsafe working environment, plant personnel came up with the idea of a lifting device that mounts in the generator-compartment air intake to remove the belt-driven fan. Engineered and installed by a local company, it consists of three pieces that bolt together, two of which are made of aluminum for ease of handling (Fig 4).

Redundant fire sensors.  The generator compartment, as installed, had one sensor for fire detection. It’s failure or spurious activation, possibly caused by electronic noise, could lead to an unnecessary dump of the CO2 system and a unit shutdown. Plant personnel decided to add a sensor with the goal of reducing nuisance trips (Fig 5). It did that, at minimal cost. Additional coverage of the compartment for early detection was another benefit.

Oil-drains box.  Tell-tale drains as originally configured made isolating a problem time-consuming. The drains box shown in Fig 6, designed and installed by Reed Services Inc, makes troubleshooting and identification of leaking seals quick and easy.

Cycle tracking is very important today. Get the details in the Western Turbine article that appeared in  CCJ 1Q/2012.

“Hands off auto” switches  supplied with the unit were failing to make contact when going from “off” back to “auto.” Problem can be misinterpreted as a flow switch failure. Replacing with a premium product eliminated vent-fan fail alarms and increased fan reliability.

 Chiller coil drains  for winter lay-up may have limited accessibility, depending on the manufacturer. One user avoids removal of the drain pan to gain access by connecting flexible hoses to the intermediate-header drains and routing them to an accessible location (Fig 7). The benefits: coil freeze prevention and personnel safety.

Generator-fan exhaust hood. Package orientation was such that the exhaust hood for the generator fan faced north. Cold air would cause loss-of-start permissive because stators would get too cold. The OEM solution was mechanical louvers; the user solution was a fabricated cover over the exhaust hood that prevented cold air from blowing directly into the compartment (Fig 8). The less-expensive alternative stabilized stator temperatures and avoided the maintenance requirements associated with mechanical louvers.

Damper actuators were continually sticking or failing, resulting in loss of anti-icing capability in cold weather. The practical user removed the actuator and replaced it with a manual operator (Fig 9). Result: Increased winter reliability.

Inlet volute drain. A build-up of water in the inlet volute during crank washes was problematic for one user. If the drain check valve failed, a slug of water could enter the engine. Solution was to install a manual drain valve for the volute upstream of the check valve. A union was installed to facilitate maintenance.

Bird screens. Pigeons roosting in drain collection trays and inlet houses would clog condensate drains and overflow the inlet. Pigeons also would get into Higgot Kane penetrations and tear up the inlet filters. Simple solution: bird screens (Fig 10).

Package base insulation. Interestingly, package sidewalls and roof are insulated but not the base. Despite the package heaters, the bottom of the enclosure remains cold when ambient temperatures are low. Another simple solution: Insulate the base structural members to minimize heat loss and reduce winter freeze-up issues (Fig 11). 

Peaker vs base-load O&M

Aero maintenance expert Dale Reed is a frequent presenter at industry technical meetings, WTUI in particular. During his time at the podium between 4:30 and 5:30 Tuesday afternoon, Reed focused on several known areas of LM engine wear and how maintenance requirements differed dramatically between engines operating base load and those in peaking service. Among the wear areas Reed addressed were the following:

  • External GT components
    • VBV door and actuation components.
    • VSV bushings.
    • Starter clutch and seal wear.
  • Internal GT components
    • HPT nozzles (vanes).
  • Package components
    • AC lube-oil pump.

Referring to Fig 12, Reed discussed VBV hinge wear first. He noted three stages of distress:

  • Stage 1. Nylon bushings develop cracks.
  • Stage 2. Sections of bushings liberate and increase the clearance between the steel bushing and hinge.
  • Stage 3. Contact between the hinge and door is in evidence. This continues with more wear on the steel bushing, hinge, and door.

Such deterioration can be found in less than 800 hr on peakers, Reed said, but might not be seen on base-load units in the first 8000 hr of service.

In the experience of Reed Services Inc (RSI), a bent and broken rod end bearing always is found in conjunction with worn hinge bushings and bellcrank bearings. On peakers, expect to see this at the 10,000-hr mark; base-load units should run about 35,000 hr before this occurs.

Bellcrank wear typically is found on the door at the clevis end of the device. The OEM limit on axial and radial movement is zero (0.000 in.). A Stage 1 condition means wear between zero and 0.004 in. or less and that you should consider maintenance; Stage 2 (up to 9 mils of wear), schedule maintenance; a Stage 3 condition (above 10 mils of wear) warrants a shut down. You can expect the onset of these conditions in less than 10,000 hr on a peaking machine; upwards of 35,000 hr when operating base-load.

The OEM recommends replacement of VSV bushings in 12,500 hours. Reed said both peaking and base-load units should make the recommended replacement interval. However, wear can be expected in less than 4000 hours for peakers, while base-load machines should run about 8000 hours before distress is evident.

Inspect the starter clutch for internal wear every 18,000 hours on peaking engines, every 40,000 hours on base-load GTs. Clean carbon steel every 35,000 hours (2300 starts) on peakers; every 40,000 on base-load units.

HPT wear is cycles-based—the more cycles, the more wear and tear. Whether the GT is in peaking or base-load service doesn’t seem to matter. Reed also said there does not seem to be a correlation between new or overhauled parts in terms of wear.

The aero expert then flashed a series of slides on the screen to illustrate the types of erosion and other damage you can expect over time on S2 nozzles. One of those was Fig 12, which shows distress on the outer platform trailing edge. It started as a crack in the parent metal (right). Erosion then moved forward and exposed the shroud leading edge at the left.

The preliminary stages of heat distress, Reed continued, are evidenced by leopard spots on the convex side of the vanes; coating distress and erosion on the concave side. As shown in Fig 14, vane trailing-edge erosion starts as coating oxidation, then the parent metal is eroded. The condition is easiest to recognize on the convex side of the airfoil.

Regarding the ac lube-oil pump, Reed stressed the need to follow both the manufacturer’s installation instructions and good pipe-fitting practices to assure reliable operation and expected life. He did indicate that engine 10-min starts take their toll on these pumps. One example is the reduction in the life of Magnaloy couplings. CCJ