MSV/CV Replacement

Replacement of the combined main stop / control valve (MSV/CV) was requested by the customer in response to a technical memo issued by the OEM relating to a material deficiency. The valve’s original body was a casting, which is prone to stress fatigue and cracking. As a result, the OEM recommended that the valve be replaced with one that has a forged body.

MD&A’s experts completely replaced the combined main stop and control valve assembly. The team provided engineering services for the MSV/CV replacement and outlet pipe modification work to accommodate the new valve assembly.

A new monorail beam was installed to facilitate future CV actuator removal.

After installation, MD&A’s technicians performed several tests and inspections on both main stop and control valves to verify proper installation and assembly.  They also performed HP shell arm loading tests before and after the valve assembly was replaced. Radiography inspections were also conducted after the valve casing was installed, revealing some deficiencies that were remedied immediately.

LP Rotor Inspection, Bucket Replacement, and Related Repairs

As part of planned work for this outage, MD&A’s experts removed and shipped the steam turbine LP rotor to MD&A’s Turbine-Generator Repair Facility for inspection and bucket replacement (which had been previously recommended by MD&A’s major inspection of the unit in 2020). The team performed visual inspection, blast cleaning, dimensional inspections, and NDE inspection of the entire rotor. The rotor was found to be in very good condition overall. Steampath inspection revealed minor FOD, minor moisture erosion, and minor rubs on packing seal lands.

MD&A’s experts installed new buckets for rows L-1 and L-0 rows, according to the moment weight chart provided with the buckets. They required replacement due to wet steam erosion and OEM TIL recommendations.

Rather than replacing them with conventional components, our Advanced Continuous Cover Blades (CCB) were utilized. These blades are constructed using a mono-block blade structure, leaving fewer locations for corrosive deposits. They are less susceptible to stress corrosion cracking and demonstrate excellent vibration characteristics. These long blades provide up to 8% stage efficiency increase, without requiring diaphragm replacement. As part of their installation, MD&A’s technicians reamed all dovetail pinholes, and installed new pins.

After installation, covers for both stages were final machined as required to meet the stated requirements. The team also conducted minor repairs for stages 13 TE & GE to resolve FOD/impact airfoil damage.

Upon completion of the work, a high-speed balance of the rotor was performed at our Repairs Facility.

Once the LP inner casing was removed, NDE inspection was performed on the struts located in the center flow area to verify the strut repairs from a previous outage. The LP inner casing horizontal joint was also inspected, and minor erosion was found on the upper half. During reassembly, high temperature sealant was used in the eroded area.

IP & LP Admission Control and Stop Valves were also disassembled and inspected during the outage.

Lastly, at startup, a vibration analysis was performed and the vibration levels were found to be low and met the requirements for acceptable operation.

CV and IP Admission Actuator Repairs

As part of the planned outage, MD&A’s team removed one Rexroth® Extraction CV actuator, two Mafag® IP admission valve actuators, and two Mafag® LP admission valve actuators.  They were shipped to MD&A’s Bearing, Seals and Hydraulics facility for disassembly, inspection, repair, reassembly, and testing.

For the CV actuator, our experts rebuilt the servo, and tested, flushed, reinstalled the poppets, and replaced shaft seals and O-rings. All other main components of the actuator were found to be in good condition and reused.

For the IP and LP admission valve actuators, our technicians performed various repairs including chroming and grounding two of the shafts, polishing two of the cylinders, replacing a poppet valve on one unit, and installed new RVDT and packing glands on all.

Upon completion of reassembly, all actuators were tested and found to be properly functioning and free of leaks. The actuators were pressure tested at 110% and stroked and tripped several times.

Bearing, Seals and Hydraulics experts also repaired the T4 bearing because onsite the upper half bearing showed indications of lack of babbitt bonding at the horizontal joint. They blended some babbitt and additional PT was performed with no indications found.

Controls

MD&A’s technicians performed a wiring inventory of the DEHC and distributed IO channels. Several observations were made including old wiring that should have previously been removed, and issues with wiring that was not wired to the manufacturer’s documented specifications. The shields for four RVDT position feedback triad cables were also not landed at the EHC cabinet. MD&A’s technicians worked with the on-site electrician to resolve these issues.

The team also noted that the CV junction box did not have a properly connected ground cable. Further, LVDT jumper settings in the EHC cabinet were found in to be in “as-shipped configuration”, and therefore not properly configured. MD&A’s team resolved the issues by adjusting the settings to match the manufacturer’s drawings.

Summary

The extensive scope and successful completion of this engagement demonstrate MD&A’s ability to provide expert service on a wide range of steam turbine systems and components. From inspection and routine repairs, to more extensive work, such as Main Stop Control Valve and Bucket Replacements, MD&A’s technicians completed the work on time and to the customer’s satisfaction. This case perfectly demonstrates why MD&A is respected as a full-service, one-stop source for turbine operators worldwide. Call our us at (518) 399-3616 or use our Contact Form.

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An exhaust temperature spread refers to a high differential in readings between the thermocouples placed radially around the exhaust of a gas turbine. The worst exhaust temperature spreads occur when the hottest- and coldest exhaust thermocouple readings are grouped very closely (adjacent). Most exhaust temperature spreads are the result of combustion section problems that can lead (very quickly in some cases) to premature turbine blade (“bucket”) failures. In other words, exhaust temperature spreads are indicative of combustion troubles that can lead to catastrophic failure.

Most heavy duty gas turbines employ multiple combustors, called ‘can annular combustors,’ each of which produce high temperature gases that are “funneled” to the first stage nozzles of the turbine section where they are expanded to produce torque. Ideally, each one of these combustors should be receiving equal amounts of fuel and air which should result in relatively uniform hot combustion gas temperatures from each of the combustors entering the first stage turbine nozzles.

The turbine buckets rotate past each combustor at very high rates—from 50 times per second for a 3000 RPM machine, to as many as 85 times per second for a 5100 RPM machine.

It surprises most people to learn that there are no temperature sensors monitoring the hot combustion gas temperatures as they leave the combustors and enter the first stage turbine nozzles. There are many reasons for this, but the four most important ones are:

1. the currently available sensors are very expensive;
2. the currently available sensors are prone to fail quickly requiring frequent replacement;
3. a failed sensor could result in pieces entering the turbine section and causing catastrophic damage;
4. there is too much stratification of the gases flowing into first stage turbine nozzle making it impossible for one sensor to adequately sense the temperatures under all conditions.

So, how are these combustion problems detected by the exhaust thermocouples? It also surprises most people to learn that as hot combustion gases flow through the turbine stages there is very little mixing. Hot combustion gases from a combustor don’t travel axially straight through the turbine section (a phenomenon known as “swirl”), but they mix very little with the gases from adjacent combustors before they enter the gas turbine exhaust. It’s this fact (that very little mixing occurs as the hot gases pass through the turbine section) that allows the exhaust temperature thermocouples to be used to sense cold or hot spots in the gas turbine exhaust which are indicative of unequal fuel- and or air flows into individual combustors.

So, what causes most exhaust temperature spreads? Far and away, most exhaust temperature spreads are the result of mechanical issues. Plugged fuel nozzle orifices, enlarged fuel nozzle orifices and fuel nozzle assembly problems (loose components; worn components) are the most common causes of unequal fuel flow-rates. MD&A has In-Situ Air Flow Test stand capabilities that allow for immediate and conclusive data on gas turbine nozzle performance.

On liquid fuel-fired machines, liquid fuel flow divider issues can cause unequal fuel flow-rates, as can leaking liquid fuel purge air check valves. Failed liquid fuel check valves can also cause incomplete combustion and high exhaust temperature spreads. Severe problems can even result in loss of flame in one or more combustors (combustors with or without flame detectors) which can cause very high exhaust temperature spreads/trips. Low, high or uneven atomizing air flows can result in incomplete combustion and even loss of flame. Primary zone re-ignition or flashbacks in DLN combustors can cause high exhaust temperature spreads. Cracked or broken combustion liners or transition pieces, hula seal problems, and leaking transition piece side seals can result in high exhaust temperature spreads.

Some exhaust temperature spreads have been caused by insulation found to be blocking the air flow across the thermocouple. Improperly inserted- or terminated exhaust thermocouples can cause high exhaust temperature spreads immediately after a maintenance outage.

Finally, failed, failing or intermittent exhaust thermocouples can cause false exhaust temperature spreads and even trips. While commonly suspected at the first hint of exhaust temperature spread problems on running units, instrumentation problems are not usually to blame for exhaust temperature spreads unless wiring is damaged by heat or other causes. One way to quickly eliminate instrumentation issues is to change load appreciably. If the highest and/or lowest exhaust thermocouple readings do not move with load changes—meaning the position of the coldest (or hottest) exhaust thermocouple will change (“move”)—the cause may be attributed to failed or intermittent instrumentation. As was mentioned before, due to the swirl phenomenon a true exhaust temperature spread will appear to move (rotate; change position) as load changes; if the problem is one or two failed or failing exhaust thermocouples the position of the hottest/coldest thermocouple will not change with load.

MD&A Turbine and Generator Controls Division maintains a staff of OEM experienced field engineers who provide installation, technical support, advanced troubleshooting, training, and consulting services for gas turbine controls, generator excitation, and turbine auxiliary systems.

Call our MD&A Turbine and Generator Controls Division today at +1 (970) 224-2223 or use our Contact form.

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Mechanical Dynamics & Analysis (MD&A) Turbine and Generator Controls Division can recommission legacy gas turbine power generation control systems at a fraction of the cost of system replacement and can enhance these systems with a modern human-machine interface (HMI).

This recommissioning process can alert owner/operators to safety concerns, detect current and future nuisances or erroneous alarms, and build renewed confidence in asset operation through optimized control systems, alarms, and indications.

Recommissioning services and calibrations were recently completed, for example, on two GE^® Frame 7EA heavy-duty gas turbines with DLN-1 combustors, burning natural gas and used for peaking service. Both units utilize the Mark V turbine control system. Calibration check line-item pass/fail listings on these units showed device failure ratios of up to 30 percent.

The key to such work is focused precision along with full knowledge of the OEM system’s operations, hardware, and components.

Primary tasks are I/O loop-checking, function testing, and running checks while investigating all field devices, connections, and operating conditions. Improper equipment is either recalibrated or replaced.

Plant personnel offer input into the recommissioning and both their experience, efficiency, and safety are of utmost concern to MD&A. In a recent example, personnel expressed concerns over high turbine compartment temperatures. During recommissioning, MD&A’s investigators found non-working gravity-operated dampers and potentially high temperatures in the accessory compartment and around the turbine.

Both site personnel and MD&A also noticed loud buzzing in the 125 VDC battery chargers, indicating possible problems with the output filter capacitors and/or the main transformer. Loop-checking also uncovered numerous junction box issues that could severely impact the fire protection system.

This was in addition to the background that site personnel offered on nuisance and false alarms. Some field devices were found to be non-working and were replaced or readjusted, several inputs had not been originally connected to the Mark system, and general issues and long-term concerns were uncovered regarding conduits and circuit connections. Selected incorrect wiring was also discovered.

The key descriptors for MD&A’s Recommissioning Legacy Turbine Control Systems are meticulous attention to detail, pinpoint examination, in-depth problem solving, precise record-keeping and reporting, and full use of MD&A’s gas turbine knowledge and experience. And as a result, any alarms articulated during startup and operation should be reduced to only those that require attention.

MD&A recommissioning projects can be completed for as little as 10 percent of the cost of new or retrofit equipment with significantly less site and downtime and are available for any unit capable of being operated on cooldown, cranking, and starting and loading.

We are your full-service, OEM-alternative! MD&A Turbine and Generator Controls Division maintains a staff of OEM experienced field engineers who know and efficiently plan and execute the process, identify any issues and work with plant personnel on optimum resolutions. We provide installation, technical support, advanced troubleshooting, training, and consulting services globally for gas and steam turbine controls, generators, and auxiliary systems.

Contact our Turbine and Generator Controls Division to recommission your legacy turbine control systems at +1 (970) 224-2223 or use our contact form.

The post Recommissioning Legacy Turbine Control Systems for Enhanced Reliability appeared first on MDA Turbines.

The primary drivers for the project were the operator’s desire to increase the long-term maintainability and reliability by replacing the MHC components that had become more problematic as they reached their end of life. Secondary benefits of the retrofit were increased operability through enhanced remote control and on-line testing capabilities as well as the addition of automatic synchronization.

The MHC governor components in the turbine’s front standard were removed and replaced with a Woodward® Governor 505D electronic governor, mounted in a stand-alone cabinet in the unit’s control room.

The turbine speed feedback to the governor is supplied by a toothed wheel mounted on the end of the generator shaft and electronic speed pick-ups mounted on the generator’s collector assembly. The governor’s load control and speed regulation software combine with set points from the plant DCS to provide a position signal for the control valve actuator governing the steam flow through the turbine.

The low pressure hydraulic control valve actuator in the front standard has been removed and replaced with a REXA® high pressure, rotary electraulic™ actuator coupled directly to the control valve cam shaft. This rotary action and direct coupling eliminates lost motion and mechanical hysteresis inherent in the original system.

The actuator’s positioning electronics receive the desired position signal from the 505D governor and control the position of the rotary actuator. The electronic to hydraulic interface is provided by the REXA® skid mounted control module and accumulator assembly. The assemblies servo-motor, booster pump and motor, accumulator and trip solenoids provide control over the actuators normal motion, fast motion and trip closed functions respectively. The recommended maintenance cycle for the new actuator components is ten years.

The unit’s new electro-hydraulic trip system replaces the mechanical over speed device and trip system components that govern the operation of the unit’s main steam stop valve. The MD&A trip manifold, which is mounted on the unit’s front standard, has a two-out-of-three, de-energize to trip solenoid valve configuration which allows the manifold components to be fully testable with the turbine in operation.

Trip and reset of the solenoid valves is governed by signals from a Woodward® ProTech TPS electronic protections system which is mounted in the control cabinet with the 505D governor. The TPS has speed pick-up, pressure switch and relay inputs to provide a single source for all of the turbine’s protective functions including over speed, operational trips and generator protection trips.

The customer was satisfied and appreciative of this successful installation. The original installation plan was able to be modified “on the fly” to facilitate easier access to turbine hardware during maintenance outages and utilize the customer’s preferred pressure and temperature transmitter hardware.

MD&A’s Turbine and Generator Controls Division maintains a staff of OEM experienced field engineers who provide installation, technical support, advanced troubleshooting, training, and consulting services for gas and steam turbine controls, generator excitation, and auxiliary systems.

Call our MD&A Turbine and Generator Controls Division today at +1 (970) 224-2223 or use our Contact form.

The post Co-Gen Turbine Controls Retrofit appeared first on MDA Turbines.

First unit:  This was a major outage and generator test & inspection. In addition, this unit was retrofitted with a new rotor, bearings, and steam path components that required machining, including installing and fitting new nozzles. MD&A provided Project Management, Technical Direction, a Controls Engineer, and a Vibration Engineer for startup and balancing.

In order to maintain the outage’s schedule, MD&A worked closely with the OEM’s engineering team to ensure that the new retrofitted components were installed correctly and to resolve any technical or engineering issues quickly. MD&A’s knowledge, experience and our skilled project manager and technical adviser resulted in this successful outage.

MD&A’s Repairs Division personnel performed onsite final machining of the nozzle plates and their associated shell locations. Our repair technicians also performed on-site diaphragm repairs.

MD&A also provided a packing installation specialist to install and final machine new upgraded packing.

To support the major outage schedule and expedite the on-site work, MD&A sourced equipment locally to overcome the time required to get the specialty tooling and equipment trailers through Colombian customs.

This unit was started up without incident and has been operational since.

Another unit: MD&A provided Project Management and Technical Direction on a Steam Turbine Generator (STG) major inspection and performed Generator testing and inspection. MD&A also provided a balance engineer, Topless Alignment®, and start-up commissioning support through our Turbine and Generator Controls Division.

The steam turbine had not been inspected for 23 years. Using MD&A’s pre-outage planning processes and experience, the execution team immediately started working to identify & mitigate potential project risks. One example was special tooling, which needed to be located and prepared for use.

After the balancing work was performed, the machine was started up smoothly, synchronized, and brought to full load. This unit has been operational without issue since this start up, after 23 years without maintenance.

Another unit: MD&A worked this unit and the one above in parallel to minimize the impacts on schedule caused by the emergent work.  MD&A provided Project Management, Technical Direction, and balance support at start up for this valve, bearing, and turning gear inspection.  MD&A also supported conversion of the Mechanical Hydraulic Controls (MHC) to Electro-Hydraulic Controls (EHC) (with the exception of the mechanical overspeed trip, which was retained).

This unit was started up without incident and has been operational ever since.

Last unit:  This major outage was similar to the other unit’s scope including valve, bearings, and turning gear, but was expanded to include generator bearings and coupling alignment. As was the case for all units, a lube oil flush was performed. For this start up, vibration data was analyzed remotely by MD&A, saving the customer the mobilization cost for the vibration specialist.

This unit was also started up without incident and has been operational ever since.

Epilogue: These successful outages demonstrate the full-service capability, responsiveness, and flexibility that MD&A can provide. The customer was very appreciative of our flexibility and our ability to adjust our execution plan as required to support the overall outage plan.

Throughout the U.S. and around the globe, MD&A provides responsive support, thorough communication, and excellent execution, making MD&A the service provider of choice for numerous power generation asset owners who desire a one-stop solution for all of their turbine-generator needs.

Call MD&A today at +1 (518) 399-3616 or use our Contact form.

Also be sure to sign up for our MD&A Insight e-newsletter delivered quarterly.  Fill in sign up form on the left-hand side and hit SUBSCRIBE!

The post Global Multiyear Major Outages appeared first on MDA Turbines.

Because the nature of the forced outage was not fully known when the job was awarded, the scope of work initially was incomplete. Despite the uncertainties, MD&A’s experienced technical team quickly evaluated the damage and designed a comprehensive scope of work.

As part of its work, MD&A’s gas turbine maintenance team both opened and closed the gas turbine. In addition, the team removed the original rotor and shipped it off-site for refurbishment and high-speed balance.

As well, MD&A removed the generator field and sent it to our St. Louis facility for a complete test and inspection, and high-speed balance before being returned to site.

The scope of work included:

Site Work Services

• GT Major Inspection & Rotor Removal
• Generator Major Inspection and test & inspection – the insulation was repaired, flux probes installed and completely re-painted inside
• Stage 9 Stator Hook Fit Mod- removal of Upper & Lower Compressor Casings
• Installed New Electronic Gas Valves – removal of old Hydraulic Gas Valves
• Remove Existing Liquid Fuel System, and associated support systems, such as Atomizing Air and Water Injection – A Controls Software Upgrade to eliminate these control sections
• Accessory and Load Gear Refurbishments
• Exhaust Frame Repairs

Shop Work Repairs

• Gas Turbine Rotor Inspection
• Remove and Inspect 1st stage buckets – Apply coating for excessive rock and repair Aft Angel Wings
• Replace out 2nd stage buckets
• Compressor Blending
• Refurbish HGP Components, Combustion Hardware
• Generator Field Rings Off Inspection, test & inspect, and high-speed balance
• Gas Turbine rotor high-speed balance

New Parts

• 2nd Stage Buckets
• 2nd Stage Shroud Blocks
• Consumables & Hardware
• Auxiliaries
• Exhaust Plenum

MD&A also performed major repairs on the turbines accessory system, such as refurbishment of Accessory & Load Gears, replacement of turbine compartment vent fans, rebuilding of Exhaust Ducting, replacement of Exhaust Expansion Joints, as well as removal of hydraulic overspeed bolt and replacement with redundant electronic overspeed protection.

MD&A’s specialized services range from Combustion, Hot Gas Path and Major Inspections, as well as, Compressor & Turbine Rotor Repairs to Plant Performance Testing and Analysis. We also provide turbine internal alignment to your gas turbine, along with vibration analysis and balance (low-speed & high-speed.)

Call our Gas Turbine Services at (518) 399-3616 or use our Contact form.

Read the Combined Cycle Journal (CCJ) article.

The post Gas Turbine Major and Generator Test & Balance appeared first on MDA Turbines.

DETAIL
Many Hydraulic Power Unit (HPU) pump motors have been observed to be running with excessive current while the turbine is at steady-state operating conditions. This condition may also be accompanied by an inability to hold normal operating pressure of 1600 psi with one pump running and/or unusually high-pressure swings during valve testing or other transient operation conditions. High fluid temperatures with normal cooling water flow through the coolers may also be observed.

Pump flow and motor current are directly related, except in cases where the pump is worn, so if a high motor current condition persists on pumps that are known to be in good condition, excessive flow should be suspected. Long-term operation in this condition can cause rapid pump wear and, if uncorrected, eventually lead to pump or motor failure.

Recent investigations have shown that improperly set relief valves, which should begin to relieve at 2000 PSIG of pump discharge pressure, have been a frequent cause of excessive flow conditions. Many portions of the hydraulic system can be responsible for leakage, but the HPU relief valves, which are located just downstream of the pump discharge, are capable of passing far more flow than most other portions of the system. Valves found to be improperly set were typically either bench set at lower than normal operating temperatures or were set in place with both pumping loops in operation.

It is possible to ascertain whether a relief valve is improperly set by adjusting the HPU manifold pressure to 1600 to 1700 PSIG and checking the temperature of the vertical pipe below the relief valve. If this pipe, which carries the relief flow to the reservoir, is approximately the same temperature as the discharge line from the pump, an improper relief valve setting should be suspected. Whether or not this test is conclusive the possibility can be eliminated by following the procedure given below.

SOLUTION
Prior to setting the HPU relief valves, the following initial conditions should be obtained:
A. Only the pumping loop being worked on should be running as the system check valves do not seal positively at low differential pressures. (The other pumping loop should be left in standby, not locked out.)
B. The hydraulic fluid should be at normal operating temperatures of 110 to 120
degrees F.
C. Ensure that fluid accumulators are properly charged per the manufacturer’s instructions.
D. The turbine should be reset, if possible, to approximate normal system flow.

Be sure to have an MD&A Turbine and Generator Controls Division representative on hand to guide the calibration.  To properly set a relief valve proceed as follows: (Repeat for both pumping loops.)

1. Raise the pump discharge pressure to 2000 to 2050 PSIG with the compensator on the fluid pump. (Raise the relief valve setting with CW adjustments as required. Adjust the compensator in 50 to 100 PSIG steps allowing the pressure to stabilize after each increase. Do not exceed 2050 PSIG.)
2. Reduce the relief valve setting (CCW adjustment) until the pump discharge pressure is 2000 PSIG and lock the adjusting stem with the lock nut.
3. Reduce the pump discharge pressure with the compensator adjustment until the HPU manifold pressure is 1600 PSIG and lock the compensator adjustment in place.

For more information, please contact MD&A Turbine and Generator Controls Division at 970-224-2223.

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