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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High Pressure Turbine

HP/IP – MD&A’s Outage Services Division disassembled and inspected the HP/IP rotor onsite, as well as reassembly. The HP/IP rotor, HP inner casing, nozzle, N1 and N3 packing cases, and all diaphragms were sent to the MD&A’s Turbine-Generator Repair Facility for inspection, testing, NDE, blast cleaning, and repair. MD&A’s technicians replaced the spill strips and shaft packing. They also drilled out and tapped all diaphragm elevation key screws and clearance key screws. The clearances were good radially and axially.

Bucket Replacements – The team also replaced both stage 6 and stage 7 buckets. Rotor NDE revealed concerning crack-like indications on two of the blades on stage 6, the last of the HP section. Excavation was attempted, but unsuccessful. A decision was made to replace the row of blades with new buckets, which were expeditiously manufactured during the outage. The replacements were produced by reverse engineering the existing ones, to help ensure proper functioning and fit. Once received, MD&A’s experts then machined and installed the new buckets.

Stage 7 buckets were replaced as part of the original scope of work for the planned outage. In addition to the buckets, new covers, axial lock keys, and grub screws were installed as well. The wheel dovetail showed minor mechanical damage in two locations, which were polished prior to installing the new buckets.

Diaphragms / Nozzle – Severe erosion was found on stage 7 at opening inspection. FOD was also noted.

At our Turbine-Generator Repair Facility, dimensional inspection revealed no major findings. NDE revealed some typical issues, such as impact damage, rubs and other relatively minor damage.

Other repairs included blending mechanical damage, removing impact damage, and resolving some indications. The team also machined the T1 and T2 journal surfaces.

MD&A’s Topless Laser Alignment (TLA) specialists aligned all diaphragms. Once complete, diaphragm clearance keys were measured and adjusted. The nozzle keys required significant scraping for contact. Large indentations were also noted and corrected. The nozzle clearance keys were adjusted to proper clearance, and the hold down bolt clearance was also adjusted. Minor repairs were performed on nozzle box components.

Alignment

Stationary component alignment for the HP/IP turbine section was conducted using our Topless Alignment® service. This method utilizes laser accuracy to eliminate the time-consuming and expensive process of reassembling a steam turbine for “Tops-On” alignment measurements, saving hundreds of man-hours labor per turbine section. Our alignment engineers have the expert knowledge needed to interpret the data. Coupling alignment was performed as well.

Outer Shells – Several issues were found on HP/IP outer shell as follows:

Severe dishing and indentation was noted on the steam inlet flanges, which were machined. Cracking in the reheat bowl was identified in the HP/LH casing crush pin appendage. These were drilled and mapped.

The blowdown pipe was found seized in the LH/HP casing. The seal rings were cracked locking rings and distorted seal rings and were replaced. The blowdown pipe was also machined to correct out of roundness.

The TC pipes were found to be severely bent during disassembly and were replaced with new pipes fabricated by MD&A’s Machining Services division.

Inner Shells – The HP inner shells were inspected at MD&A’s Turbine-Generator Repair facility. They performed visual and dimensional inspections, as well as NDE. The team prepared a report detailing observations and repair recommendations, and then conducted certain repairs.

On visual inspection, the HP inner shell, both lower half and upper half, revealed typical conditions including galling, scoring, dinging, fretting, thread damage, and the presence of raised material. The lower half blowdown seal rings were noted to be bound up and loaded to one end. No significant issues were otherwise noted.

Dimensional inspections were conducted on the snout pipe, blow down pipe, diaphragm grooves, and various critical fit widths. Dimensions were found to be mostly within range, except for a snout pipe diameter and float. Recommendations were made to remedy these issues.

MD&A performed repairs on the HP inner shells, including destructive removal of broken bolts & screws, stoning and blending of various indications and surfaces, and replacement of the blowdown seal rings.

Oil Deflectors – MD&A Bearings, Seals, and Hydraulics Division inspected and refurbished T1 and T2 oil deflectors. The team noticed that both were rubbed hard in the vertical plane. After evaluating the clearances with the customer, and previous experience with increased clearances in areas with 750 degree temperature potentials, T1 and T2 clearances were increased.

Boiler Feed Pump Turbine

MD&A’s experts at our Turbine-Generator Repair Facility removed and inspected boiler feed pump turbine (BFPT) A and B valves. For BFPT A, the LP SV stem was found and replaced. The team refurbished the LP SV disc and replaced the seat. The HP SV and CV were both replaced, and the HP SV strainer basket was repaired.

For BFPT B, MD&A’s experts refurbished the LP SV disc. Bushings on the LP SV rack were noted as oversized and had severe wear. The bosses were refurbished so OEM bushings could be installed. The HP SV was replaced, and the Machine Services team repaired the HP SV strainer basket. They also machined the bonnet to resolve excessive clearance.

Conclusion

Impressively, all of this was completed three days ahead of schedule! This is despite the challenge of resolving the unforeseen bucket replacement, which included manufacturing.

Several of MDA’s divisions participated including Outage Services, Generator, Steampath, Machining Services, Bearings Seals & Hydraulics division, Topless Laser Alignment, High Speed balance and Turbine & Generator Controls Division. This engagement underscores MD&A’s extremely diverse range of turbine inspection and repair capabilities, in-house expertise, and the ability to get the job done on time.

These are exactly the reasons why operators worldwide rely on MD&A for exceptional steam turbine inspection and repair services as a full-service, OEM-alternative. Call us at (518) 399-3616 today or use our contact form.

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Since standard documentation was lacking and this was an atypical configuration, the bucket replacement process began by developing a new assembly procedure specific to this unique configuration. MD&A’s team worked closely with the customer to acknowledge and overcome this challenge with open communication being at the forefront.

HP/IP Rotor Inspection

The process began with blast cleaning and inspection of the rotor by MD&A’s experts.  Visual, dimensional, and magnetic particle inspections (periphery and axial headshot) were performed prior to assessing any required repairs.

Several issues were found during the inspection. It was noted that airfoil HVOF (High-Velocity Oxygen Fuel) coating had visible lines, which were later determined to be acceptable. Incoming rotor runout measurements were collected. No major findings were discovered on the control shaft or packing lands. It was noted that the T1 journal had scratch marks, taper and diameter were assessed, and found to be within acceptable tolerances. The T2 journal, however, demonstrated deep grooves, a .004” taper, and a diameter deviation. As such, MD&A suggested that the journal be skim cut.

Prior to blast cleaning, stage 10 buckets were removed: both foreign object damage and solid particle erosion. Inspection revealed that there was foreign object damage (FOD) at every stage. On stage 1, damage was noted on the covers, roots, and tenons, while other stages had FOD primarily on the leading edges and some on the covers. Several stages had HVOF coating to the airfoils, while debris remained after blast cleaning beneath stage 11 and 12 covers. Raised material was noted on stage 14.

HP/IP Bucket Replacement

Bucket replacement was conducted at MD&A’s Turbine-Generator Repair Facility in St. Louis, MO. MD&A’s technicians replaced 90 standard buckets supplied by the customer, in addition to one auxiliary bucket, and a two-piece lock bucket.

Five D-keys were supplied along with 2 special keys for the last bucket. These keys fit between the bucket root and the rotor groove and serve to fix the buckets axially. The removed D-keys had mechanical damage and needed to be replaced, however none were in stock. As this was a time sensitive job, MD&A’s machinists fabricated 82 standard D-keys in the shop. Reverse engineering measurements were then taken in preparation for the overhaul. New buckets were scanned to record geometry, and hand measurements were taken.

The process involved fitting new buckets with an interference fit, necessitating the tightening of bucket groups by MD&A’s technicians using heavy-duty straps. Rubber protection was employed to safeguard trailing edges during this process. The last 5 buckets were secured axially with twist-locks. The twist locks were secured by bending over the tabs. The 2-piece lock bucket also had a special key installed to fix the airfoil axially.

Shims were inserted post-bucket installation, before cover machining. Following machining, shims were removed. A low-speed balance was then performed with the control shaft installed. After completing these repairs, the rotor was cleaned, coated with lubricant, and plastic wrapped.

Minor Bucket Repairs

In addition to the major bucket repair for stage 10, several other repair and maintenance tasks were executed in response to the inspection findings and recommendation detailed earlier. Raised and loose material was removed off the covers, root, and tenons on stage 1. For stage 2 and 11, loose material was removed from the airfoils. For stage 3-9,12, and 13, foreign object damage was removed from the leading edges. Debris was removed from underneath the covers for stages 11 and 12, while raised material was removed off the rubbed root axial seal on stage 14. The T2 journal was skim cut.

The overspeed trip device was inspected and tested at our Bearings Seals and Hydraulics facility in Euclid, OH, leading our technicians to install new lock plates with the control shaft and overspeed trip device. The final runout was recorded and noted as within tolerance.

HP/IP Diaphragm Inspection and Repairs

MD&A experts performed minor repairs to the diaphragms and removed broken hardware.

This included corner weld repairs, bench backing of trailing edges, loose material removal, and straightening of trailing edges with foreign object damage (FOD). Localized weld repairs were also performed by MD&A’s technicians for damaged HJ bolt spot faces, NDE indications, and stage 3 HJ steam cut. Broken hardware, such as HJ bolts, packing screws, and spill strip retaining screws, were removed, and replaced as needed. Raised material was removed off steam seal faces and keyways, and the rubbed root radial seals were sharpened. Weld was also added to select crush pins and centering keyways. Ledge keys were destructively removed and replaced with MD&A’s stock components.

In Conclusion

What began as a stressful situation for our customer ended up being a success story for all involved. Our ability to overcome obstacles and be innovative demonstrated MD&A’s breadth and agility within the repair space. Our nine bucket technicians leveraged roughly 300 years’ worth of experience to successfully plan and execute this job. The team excelled at assessing the non-standard configuration, inspecting it, repairing, and maintaining the unit, and developed and provided detailed maintenance procedure documentation for future reference.

This case also serves as an excellent reminder for customers to form beneficial partnerships with their service providers. This teamwork approach, combined with open communication on both sides, leads to quick and thorough resolution of the customer’s challenges. As testament to the customer’s satisfaction, they called MD&A back to perform bucket replacement on a second unit (after the first unit)!

For all service and repair questions, and to discuss creative resourceful solutions, call MD&A today at +1 (518) 399-3616 or use our contact form.

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The inspection revealed severe damage to the Stage 1A airfoils necessitating replacement of buckets. The Stage3 buckets were also replaced. For both rows, bucket hardware was supplied by MD&A and bucket covers were final machined to restore geometry.

In addition, both the L-1 stage & L-0 stage buckets and covers were replaced using material supplied by the customer. Our experts inspected the customer supplied buckets, confirmed critical criteria were met, provided consultation on a material substitution, performed the necessary activities to ensure properly balanced rows and machined bucket covers to restore geometry.

Additional rotor work included supply of a newly manufactured shrunk-on thrust collar and machining of the T1 journal. The overspeed trip was removed and tested by MD&A’s Bearings, Seals & Hydraulics Division. Experts also polished the 11th stage bucket admission edges to remove foreign object debris.

Inspection of the stationary components of diaphragms and packing boxes found some with excessive pitting on the packing groove axial steam seal faces. The seal faces were skim cut and custom packing was installed for these diaphragms and packing boxes. New spill strips were installed and machined for these same diaphragms.

Several diaphragm horizontal joints were weld repaired and restored to address joint indications and erosion damage. The nozzle bolt hole peening grooves were weld repaired, stress relieved and re-machined. The nozzle admission face was weld repaired, stress relieved and machined to restore axial clearance.

Finally, an inspection of the Curtis ring discovered it was out of round. The Curtis ring peening grooves and seal grooves were weld repaired and re-machined. The Curtis ring was bolted to the nozzle discharge face and stress relieved after the weld repairs were completed. This re-rounded the Curtis ring to fit into the nozzle tongue and groove fit. The Curtis seals were replaced and machined on-site with a boring bar to restore design specifications.

These complex and intricate steps were accomplished in minimal time thanks to the skilled experts at our St. Louis Turbine-Generator Repair facility. Our customer’s turbine was back in use with a short downtime and running again at optimum efficiency.

Have MD&A look at your turbine rotor today! Call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

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Our Parts Division (formerly named Turbo Parts or TPL) is a premier worldwide supplier of replacement gas turbine parts and components. Through the breadth and depth of our engineers’ expertise, these master craftsmen can reverse engineer your components to exacting industry specifications.

View the video on our commitment to serving you for Gas Turbine Capital Parts. For additional information call MD&A’s Parts Division today at (518) 885-3199 or use our Contact form.

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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.

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