Industrial steam turbine/generators are used globally in chemical and petrochemical plants, refineries, pulp & paper mills, and mining operations. They are also used in biomass and waste-to-energy facilities, combined heat and power plants, geothermal and concentrated solar power installations, and desalination operations, including many others.

Ongoing operation of these units ensures stable, reliable use of proven technologies to convert the expansive power of steam into useful mechanical work. The processes are both fundamental and critical as the world exploits all available resources to meet its present and future needs for heat and power.

The professionals at MD&A are uniquely qualified to serve these needs by applying their deep and time-tested experience with steam turbine/generators, regardless of OEM.

For this particular industrial unit, onsite work was performed by MD&A’s Outage Services division, Generator division and our Turbine & Generator Controls division. All valves were sent to MD&A’s Turbine-Generator Repair Facility in St. Louis, MO for inspection and repair. MD&A’s Bearing, Seals and Hydraulics Division in Euclid, OH, inspected bearing assemblies, thrust pads and oil deflectors.

ST-660 Industrial Steam Turbine Major Inspection

After mobilizing, MD&A’s experts removed the upper-half shell and turbine rotor, then performed blast cleaning for complete non-destructive examination. The rotor, packing carriers and blade carriers were aligned to OEM specifications. The nozzles were blast cleaned and NDE’d in place.

Inspection revealed evidence of steam cutting that was photographed and recorded, as well as some deformed bolts. Various other specifics were recorded in the Recommendations Report.

Upper half and lower half shells were also cleaned and inspected.

A key benefit of MD&A’s inspections is written and photographic documentation of lessons learned that can assist the owner/operator in future outages. One lesson learned was on the rotor lift. For this inspection, the turnbuckles were removed and chain falls were used in their place. For future outages, two 15-ton and two 10-ton chain falls should be on hand due to minimal lift clearances.

This recording would benefit both owner/operator and contractors involved in future work.

In-depth inspections then proceeded. This included axial and radial blade clearances, rotor radial runout checks, nut rotation and tightening, thrust bearing clearances, and complete visual and NDE inspections (general, HP impulse wheel, and all 36 rotor stages).

Generator

For the Siemens® conventionally air-cooled generator (71.18 MVA), the coolers were cleaned, visually inspected and pressure tested. The field was removed and generator inspection and testing were performed.

MD&A completed major inspections of both the generator field and stator including visual, borescope and electrical testing. Minor contamination was found on the field turn windings beneath the retaining ring. Signs of field turn migration were also identified and addressed.

One field ground detection bolt was found already removed prior to the MD&A Generator Team’s arrival. It was reinstalled according to OEM specifications. To complete electrical testing, the field winding was isolated from the brushless excitation components. Testing then proceeded on the generator field (IR with PI, DLRO and AC Impedance), rotating armature and rectifier wheel, stationary field, and stator.

At completion, field windings were reconnected to the shaft-mounted brushless excitation equipment and a final IR test was performed.

Conductive paint was applied to the affected partial discharge areas to reduce sparking effect and increase stator bar life.

With testing complete, MD&A issued a recommendation for power factor testing at yearly outage intervals to monitor health of the insulation system.

Brushless Exciter

The brushless exciter was cleaned, inspected, and realigned. The ABB Unitrol 6000 Exciter Regulator Cabinet was also cleaned and inspected.

Steam Turbine Valves

MD&A’s facility in St. Louis disassembled, cleaned and inspected the control valve, main stop valve and other valves. The emergency stop valve was also disassembled, cleaned and inspected during the outage.

For all, a final blue check was performed, 100% blue contact was achieved. New rope packing, supplied by MD&A, was installed during valve reassembly.

Other Key Elements

All turbine bearings were replaced due to wear. Generator bearings were NDE’d and reused. Replacement thrust bearings were installed at reassembly due to wear, New RTDs were installed at MD&A’s Bearing, Seals and Hydraulics facility.

Auxiliary system work included the lube oil tank which was drained and cleaned under MD&A supervision. MD&A performed additional cleaning of the tank and baffle plates. Two lube oil coolers were unstacked, washed and disassembled.

Alignment

Topless laser alignment was completed before startup. 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. This included horizontal joint measurements, bolt roundness checks, stationary component position verification, and side slip readings among others using laser equipment. Our alignment engineers have the expert knowledge needed to interpret the data.

Why MD&A?

The experts at MD&A are not only dedicated to the fundamentals of turbine and generator longevity. They apply their vast experience in all OEMs to understand and import precise lessons learned throughout the industry, then direct their knowledge and skills to the ongoing development of using steam effectively and efficiently for the long-term benefit of owner/operators throughout the world.

MD&A’s technical directors and service technicians bring decades of experience to each industrial and utility project regardless of OEM, a process now proven in more than 20 countries worldwide. Committed to both industrial and utility customers.

We invite you to discuss any industrial steam turbine major inspection or other steam turbine, generator or gas turbine issues with us today. Call us at (518) 399-3616 or use our Contact Form.

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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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Work was divided among MD&A’s teams including the Bearings, Seals & Hydraulics (BSH) team and the Valves Team of MD&A Machining Services Division and conducted as follows:

Valves

MD&A’s Valve Team performed inspection, replacement, and repair on various valves and related components. These included control, main stop, reheat stop and intercept valves, as well as a blowdown and a ventilator valve. Each valve was disassembled, blast cleaned, dimensionally checked and repaired as required. All valve work was completed at MD&A’s Turbine-Generator Repair Facility in St. Louis, Missouri.

Control Valves – All four control valves failed the incoming inner valve blue check which was corrected by lapping the pilot valve seats.  The team honed the bushings on valves #1 and #2 to correct stem to bushing clearance issues. They also replaced several components as needed, including the disc and balance chamber, anti-rotation screws, stems, bushings and pins. Disc to balance chamber clearance issues and out of tolerance run outs were noted on valves #3 and #4. Clearance was restored by hand working the blue blush from the balance chamber IDs and grinding the disc ODs. Several other clearance issues were found and resolved by honing, grinding, or lapping. MD&A supported vendor performed NDE, revealing indications on two valves, which were excavated and hand blended by the team.

Reheat Stop Valves – New stem nut pins were installed on both valves during reassembly. Further, the stems were machined, and backseats were lapped to achieve acceptable blue checks. The valve disc seating surfaces were ground and polished as well. MD&A’s valve technicians also replaced the stem, inner/outer bushings and back seat on the R/S valve.

Intercept Valves – The two intercept valves were found to have similar issues among them. Both had several clearance deficiencies, which were remedied by grinding, honing, or machining. Component replacements included the crosshead guide busing, as well as disc bolts on both valves. The stem on the L/S valve was machined, drilled, and pinned; while the R/S valve had the backseat machined and lapped to achieve acceptable blue checks.

Ventilator Valve – This valve required the stem OD to be lapped. To ensure proper contact, the main disc seating was ground and polished. MD&A’s Valve team replaced the air cylinder gasket, the balance chamber, and corrected the valve lift during reassembly.

Blowdown Valve – Our technicians reset the gap between the piston stem and valve stem and restored the inner valve lift. They also polished the pilot valve and lapped the valve seat in the main disc. The main disc seating surface was ground and polished. Replacements included the air cylinder gasket and piston rings, air cylinder fitting and the bushing.

Main Stop Valves – For both valves, the team cut the stem back seat and lapped the pressure seal head backseats to achieve a good blue check. They ground and polished the disc contact seating surfaces, skim cut the gasket faces and restored the disc cap peening lips. Further, on the R/S, the bypass valve and disc seat were skim cut, and the stem was replaced.  On the L/S, various clearances were restored as required.

Compression Rings

MD&A’s experts inspected and repaired two compression rings. Damage including corrosion was observed and remedied on both rings. The rings were oxide blast cleaned to bare metal.  The I.D. and O.D. of the lower face were then weld repaired. The rings were then machined.

EHC Actuators & Spring Cans 

MD&A’s Bearings, Seals & Hydraulics (BSH) team disassembled, inspected, repaired, and tested ten GE® EHC actuators and spring cans. The coil springs were shot peened, mag particle inspected, and painted. The spring cans had several components replaced including seals, bushings, and bearings. The cans were bead blasted and painted. The team tested the actuators to confirm they were functioning properly and leak-free prior to leaving our BSH repair facility.

Additional Components

The BSH team also inspected and repaired several additional components including the overspeed trip, two tilt pad bearings, eight journal bearings, eleven oil deflectors, four hydrogen seal bronze assemblies, and two hydrogen seal housings.

Overspeed Trip was disassembled, cleaned, and inspected. Several components were replaced including the spindle, upper and lower bushings, eccentric ring, and lock plates. Weld repairs were performed on the body, spring seat, and spring shim. Trip speed was set and the unit was test.

Tilt Pad Bearings were in acceptable condition. Babbitt pads were cast and bored. New seal teeth were installed and also bored. One bearing required boring on several anti-rotation pin holes.

Journal Bearings underwent centrifugal cast repair. The inspection revealed that several dowels were no longer acceptable, and were replaced. Bearing T8’s body bolts were also not acceptable, and re-fit.

Oil Deflectors – all units received new teeth. One deflector required modification to accommodate insert-style teeth. Several required new body bolts.

Hydrogen Seal Bronze Components were machined to be within manufacturer’s specifications.  As for the housings, the dowels were replaced on one unit, while the other required bolt replacement.

Conclusion

The extensive range of work and complexity involved in this project highlights one of MD&A’s greatest strengths: being a dependable one-stop solution for virtually any power-generation repair need. The scope demanded the expertise of two teams of experienced engineers and technicians, who performed quickly and properly, to the customer’s satisfaction.  As the go-to service provider for power generation asset owners across the globe, call MD&A today at +1 (518) 399-3616 or use our contact form to learn more about MD&A’s steam turbine control component repair services.

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MD&A experts arrived in Abu Dhabi and immediately established all support systems and protocols necessary for an efficient state-of-the-art response.

Initial assessment and engineering analysis showed heavy scale buildup but no significant rub on the covers. Runouts of the steam turbine rotor showed a total indicator runout reading (TIR) of 0.0324 in., confirming that the rotor was bowed and must be straightened.

All options, including rotor machining, thermal straightening, and mechanical straightening, were considered and discussed with the owner/operator in detail. MD&A’s technical expertise, experience, and recommendations were critical factors in the final decision.

The selected solution was the thermal process known as thermal straightening, viewed globally as one of the most successful and least damaging long-term steam turbine rotor straightening techniques. This thermal straightening technology, properly applied, would produce the desired immediate and long-term results while preserving the integrity of the rotor’s original structure and geometry.

The decision was made to keep the rotor horizontal throughout the entire process. Thermocouples, heating pads and insulation were prepared. Scaffolding was erected for electric wire control. A custom fixture was designed to check rotor location during turning.

The rotor was first inspected (including non-destructive examination), cleaned and prepared for initial stress relief to remove any stresses imposed by the bending. Initial post-stress-relief runouts showed the TIR now reduced to 0.0247 in., improved but not sufficient for full-service, long-term operation.

Controlled and precise thermal applications at well-defined points would follow.

A series of thermal straightening, runouts and stress relief followed. Progress was monitored as hot spots were applied and stress relieved.

Three iterations of thermal straightening would be applied along with runouts, blast cleaning and NDE/hardness testing, and axial measurements.

After the third iteration of thermal straightening and stress relief, MD&A experts determined the maximum TIR to be 0.009 in. Then, in consultation with the owner/operator and with careful review of data from a companion unit, all parties agreed to terminate the hot spotting. MD&A confirmed that limiting the number of hot spotting iterations and thus reducing the metallurgical impact is the ideal goal in any steam turbine rotor thermal straightening project. With this agreement, the rotor was again cleaned and inspected, and prepared for proper low-speed balance.

With the TIR measurement greatly reduced and low speed balance achieved, the unit was successfully placed back in full operation.

This project exemplifies many of the experience-based benefits brought to a project by MD&A:

• Responsive communications
• Solid in-depth analysis
• Strict attention to detail
• Ability to develop and perform “out of the box” repairs to support continued, reliable operation
• Project management skills and coordination of multi-disciplined operations
• Focus on the end goal
• Consideration for the owner/operator’s long-term use of the equipment
• MD&A’s commitment to steam equipment as part of our gas turbine/steam turbine/generator portfolio of expertise and experience
• Global commitment to the power industry

MD&A invites you to discuss any steam turbine, gas turbine or generator rotor issues with us today. Call our Turbine-Generator Repair Facility in the U.S. at (314) 880-3000 or use our Contact Form.

The post Steam Turbine Rotor Straightening in Abu Dhabi appeared first on MDA Turbines.

We were contracted to perform an inspection and any necessary Steam Turbine rotor repairs. After a thorough inspection, bucket and cover repair work was performed on the 1^st and 17^th stages of this rotor due to damage identified.  This rotor has a total of 19 stages, 12 high pressures and 7 reheat stages.

The 1^st stage buckets and covers were replaced with hardware supplied by the customer.  The new buckets were installed on-site, the notch bucket was driven and pinned and the new covers were peened into placed using gathered reverse engineering data.

The 17^th stage had the covers that were found partially liberated.  The tenons of those buckets that had liberated covers were welded up, and then new covers installed.

Both stages were machined to restore the proper clearance and required features.

Further inspection of the rotor showed that the underside of the bucket covers on the other stages had excessive debris build up, which was was removed and the entire rotor was then blast cleaned.

1st stage row restoration and machining completed

17th stage cover restoration and machining completed

1st stage admission side machined

Additionally, during the on-site inspection of the turbine first stage stationary blading (diaphragm) severe damage was found and MD&A was requested to repair this diaphragm.  The diaphragm was shipped to our Turbine-Generator Repair Facility in St. Louis MO. Upon inspection, it was discovered that the diaphragm exhibited significant Foreign Object Damage (FOD) and linear indications were detected in the partitions.

When the diaphragm was received, it was cleaned and given a complete Non-Destructive Examination.  Due to the extent of damage found on the blading in the steam path partitions, major repairs were required. After weld repair was performed, a post weld heat treatment was done to remove residual stresses.

Repair of the partition side wall, as well at the horizontal joint, were necessary due to extensive damage found. The steam seal face was machined, and an insert installed to restore the axial position of this diaphragm.

New diaphragm root radial seals, seal strips and horizontal joint keys were installed as well as the support bars for the diaphragm.

MD&A can be called upon to perform any technical evaluation anywhere and do the work needed for your rotating power generation equipment to get it back online safely and quickly.

For all steam turbine rotor repairs questions, and to discuss creative resourceful solutions, call MD&A today at +1 (518) 399-3616 or use our Contact form.

Steam seal face prior to insert installation

Extensive damage to the steampath

Final diaphragm repair finished and ready for shipment back to site.

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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.

The post Bucket Replacement for Non-Native Bucket appeared first on MDA Turbines.

The high-pressure (HP) section of a 320 MW Alstom® STF30 steam turbine was severely damaged. Over time, the rotor’s shaft end at the oil deflector area developed a groove approximately 0.58 in. (14.7 mm) deep. Either repair or rotor replacement was recommended by the OEM.

Full unit disassembly and rotor removal would be costly and time-consuming.

Experienced professionals at MD&A’s Machining Repairs Division devised the most efficient and robust long-term solution. The rotor would remain in place within the machine.

MD&A technicians would machine the shaft end to a smaller diameter, removing all damage while restoring the turbine end and generator end transition fillet radii. MD&A would also machine to restore the depth of the oil slinger groove.

MD&A’s scope included:

• Disassembly and reassembly of the unit front and mid standards.
• Machining repairs to the HP rotor at the mid standard.
• Borescope inspection of the HP section.
• Visual inspection of the LP section L-0 buckets.
• Repacking and seal replacement of the right-side control/stop valve.
• Design and supply of a modified oil deflector to match the new machined shaft.

MD&A mobilized to site with equipment, tooling, and dedicated experts to perform all work. The equipment was specifically designed and produced to perform work within the tight quarters of the mid-standard between the HP and IP turbine sections.

The Process

This Alstom® turbine is designed with a separate HP section, IP section, and double-flow LP section.

The specific shaft area of damage was at the mid-standard between the shaft end steam packing gland and the inboard thrust collar, on the turbine-end side of the oil seal housing.

To perform this work, the upper half of the generator exciter bearing was removed for manual lubrication of the lower half bearing. The mid-standard upper half housing and turning gear assemblies were removed for direct access and machining equipment installation. The front standard cover and upper half oil deflector were removed to install a temporary shaft train rolling device to support machining of the damage shaft in the bearings. FME measures, blanks, and filter screens were also installed in the mid-standard supply and oil return lines to eliminate possible contamination.

The main lubrication oil tank was drained for installation of lift oil system jumpers. This allowed the unit to be rolled on lift oil during the machining operation without the main lubricating oil supply. Not having lift oil capabilities, the HP turbine T1 bearing and the generator exciter bearing had their upper halves removed to allow manual oiling during rotating of the shaft train for the work.

Casted molds were made of the damaged area, reverse engineering of the original geometry was performed, and all required measurements were taken. The area was prepared for machining.

The shaft end was then machined to remove all damage. Shaft diameter rough machining was completed, followed by both fillet transition radii. Final machining and shaft polishing to achieve the required surface finish followed. Shaft diameter was reduced by ~0.6165” per side to a diameter of 8.610 in. (218.69 mm). The distance between axial faces and the transition radii geometry remained the same.

The new final machined geometry was measured, final non-destructive testing performed, and final runout taken of the shaft showing a maximum TIR of only 0.5 mil (0.0005 in.).

At the completion of repairs, the jumper lines were removed, the main oil tank was cleaned, and the lubricating oil system restored.

During the site work, MD&A experts dimensionally reverse-engineered and manufactured a new oil deflector/oil seal housing, installed new seal strips, and precisely machined to achieve the required clearance to the new shaft diameter.

Borescope and Visual

Right side stop and control valves were removed for borescope inspection of the HP section by MDA’s Steam Path Division. MD&A also performed a visual through-the-hood inspection of the L-0 buckets.

Additional visual inspections were performed to look for any signs of damage to the exhaust hood struts, hood sprays, and ID casing wall above the bucket tips.

No significant issues were found in the inspections.

With the valves disassembled, new stem packing was installed, and MD&A specialists performed a visual inspection of the seats and discs. New gaskets, seals, and lock plates were installed at reassembly. Also, stop and control valve seal head lock plates were installed and all stem packing and seal bolting was retightened to OEM specifications.

MD&A’s Outage Services Division also provided support for the setup and breakdown of equipment necessary for the post machining cleaning/flushing of the main oil tank and lube oil system.

All components and systems were reassembled, and the steam turbine returned to service.

Full-Scope Repair

The on-site work of the HP Rotor In-Place Machining by the dedicated MD&A experts completed all tasks on time. All inspection findings were positive, and there were no reportable issues during startup.

Specific and comprehensive recommendations to the customer from MD&A should ensure that this type of damage does not occur again.

MD&A routinely rallies its best people from multiple divisions for critical on-site work to save both cost and time for its customers. Creative solutions like in-place machining are key examples of our commitment to our customers, the power generation industry, and its many systems regardless of the original equipment manufacturer.

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.

The post Innovation Allows Efficient and Successful HP Rotor In-Place Machining appeared first on MDA Turbines.

For Hermiston Generating Plant in Oregon, Mechanical Dynamics & Analysis (MD&A) completed a complex, multiple-component combined-cycle major inspection and overhaul project that successfully brought both turbines and both generators back to full and reliable operations.

The 474 MW combined-cycle plant was depending on the complete and efficient renewal of its Unit 2 system.

This major project demonstrates the full capabilities and product knowledge of MD&A personnel, and the organization’s commitment as a premier, fully integrated non-OEM supplier to the turbine/generator community.

It began with a full major inspection of a late 1990s vintage 170 MW GE® 7FA gas turbine and included the 7FH2 generator robotic inspection work. The GE® A-10 steam turbine and 7A6 generator would also be fully inspected and refurbished by MD&A in the same outage.

7FA Gas Turbine

MD&A mobilized and completed the disassembly process utilizing a two-shift operation. Detailed visual inspections began, coupled with detailed NDE, followed by the recommended refurbishments.

In the turbine section, first-, second-, and third-stage buckets were replaced due to rubbing wear and thermal barrier coating (TBC) loss.

First-, second-, and third-stage nozzles were also replaced due to foreign object damage, evidence of cracking, and coating loss. Inspections and similar indications revealed the need to also replace the shrouds.

In the combustion section, liners and transition pieces were replaced with refurbished sets due to TBC loss. New inner crossfire tubes and retainers were installed due to wear and outer crossfire tube packing was replaced at reinstallation.

Although no abnormal visible wear was found, forward combustion cans and fuel nozzles were replaced with customer-provided refurbished sets. Flow sleeves also showed no wear, but the flow sleeve piston rings were replaced.

Liner caps were replaced with refurbished, and transition piece bullhorn brackets were found worn and replaced with new.

For the compressor section inlet guide vanes, MD&A replaced gears, rack, inner and outer bushings, and spacers. Inlet guide vane blades themselves will need to be replaced at the next major inspection.

Rotating and stationary blades showed no damage. R-0 inlet compressor blades were replaced with a refurbished set and shims were added to stages 14, 15, and 16. The casing and rotor showed no need for immediate action, but the discharge casing retention bars were replaced.

The inactive thrust bearing showed heavy scoring and the T-1 & T-2 bearings revealed pitting and scoring, which were subsequently replaced with refurbished bearings. The active thrust bearing was cleared for service.

7FH2 Generator

For the generator, the initial scope of work was visual inspection, robotic wedge map analysis, electromagnetic core imperfection detection (ELCID), and a full battery of electrical testing.

The borescope inspection showed substantial widespread greasing and several areas that had loose hardware. The field was recommended to be removed for a more comprehensive stator investigation. After field removal, a core wedge map was performed that showed approximately 90% of the wedge system was loose and/or hollow, not meeting MD&A criteria. A full stator re-wedge, replacement of greasing blocking/ties, and axial support tightening was recommended and performed.

MD&A also provided and installed an improved the wedge design.

Prior to re-wedging, a significant amount of time was expended cleaning the core. All slots were cleaned including dovetails.

New filler material and top ripple springs were installed during the re-wedge. A modification was made to the end wedges to improve mechanical strength. The original flux probe was installed without issue, and a final ELCID was performed with acceptable values.

Based on modal bump testing, MD&A recommended that the entire collector and turbine ends have series blocking installed to reduce resonant frequency response. Saturated felt and ties were added to dampen the response.

New axial support hardware was installed, replacing the loose axial supports and hardware found during initial inspections. Locking epoxy was applied on all hardware to ensure no complications during operation.

H2 seals were replaced with new, and field collector rings were ground.

Successful electrical testing was performed at the completion of all work performed.

A-10 Steam Turbine

MD&A performed a major inspection and overhaul of the 81MW GE® A-10 steam turbine, generator stator, and field installed in 1996.

The main steam valves were also removed by MD&A and sent to MD&A’s St. Louis Repairs Facility for inspection and repairs.

MD&A specialists performed a complete steam path structural audit of the A10 steam turbine.

Although many minor diaphragm indications could be repaired by MD&A onsite, ILP diaphragms 9, 10, 11, and 13 were shipped to MD&A’s repair facility for major repairs. Stages 10 and 11 would also have inserts installed on the steam seal face due to dishing.

HP and ILP rotors remained coupled and were removed for sand blasting and NDE. Minor bucket repairs were performed on site to correct impact damage and moderate solid particle erosion.

On reassembly, MD&A performed a Topless Alignment®, and MD&A On-Site Seal Services fit and installed new diaphragm and gland steam packing.

7A6 Generator

The 7A6 air-cooled generator was disassembled and the field removed. The generator field was shipped to MD&A’s St. Louis Facility for a full rewind. In addition, MD&A’s Generator Division mobilized onsite to perform a full stator rewind.

The combined HP stop and control valve was disassembled and the cores were shipped to MD&A’s St. Louis Repair Facility for inspection and repairs. The Steam Turbine Repairs Division also received two reheat stop valve and two intercept valve cores for inspection and repair.

Stator

Concurrent with the major steam turbine inspection, an elevated workspace onsite was constructed to support the generator division for stator disassembly and reassembly work. A baseline ELCID was performed to determine integrity of the current stator core iron. No shorted laminations were noted.

The wedge system was removed, then the flex probe was carefully set aside for reassembly.

With wedges and series loop connections removed, bar removal began. Inner axial supports were left in place and prepared for the reassembly. Connection pieces were cleaned for reuse.

The stator was thoroughly cleaned to remove any contaminants from the wedge/bar removal process. A post wedge/bar removal ELCID indicated no core iron damage during wedge and bar removal.

Each core slot was cleaned, and a detailed inspection of any abnormalities was conducted. The core compression flange and all exposed areas where the end windings sit were painted with an epoxy paint for a uniform color on the compression flange.

After a thorough cleaning, the rewind began.

Bar boxes were moved to the scaffolding deck with an innovative safety-conscious method of disassembling the scaffolding roof and flying the boxes to the deck with a crane following completion of a detailed lift plan.

Each of the six circuit rings were acceptance tested, and the outside binding bands were installed.

A tapered gauge from the bar manufacturer was used to ensure concentricity was achieved on the four binding bands. Concentricity of each band is a vital step that will properly align each bar and subsequentially the end winding basket once the rewind is completed.

Two top and two bottom bars were installed to ensure alignment. Bars were fit into a shoe on the collector end and carefully transferred through the bore to the turbine end. All 72 bottom bars were installed, blocked, and tied. All 72 top bars were then installed, blocked, and tied, along with 12 new resistance temperature detectors (RTD’s).

After all bottom bars were installed, a Hipot test was performed using a high potential voltage to ensure no bar armor insulation damage. Another Hipot was performed on all top & bottom bars at the completion of top bar installation.

Wedges were then installed, and filler was adjusted at each wedge for proper radial compressive force. Axial locking pins were installed, followed by a final ELCID and brazing. The existing circuit ring copper connection pieces were re-used and brazed to respective top and bottom phase connections.

Upon completion of all rewind activities, final electrical testing consisted of winding copper resistance, insulation resistance, and a final Hipot of each respective phase. Each phase produced satisfactory resistance values.

The stator rewind activities progressed as expected throughout this project. The consistent bar shapes and robust bar design aided in completing the project without incident.

Field

The 7A6 generator field was sent to MD&A in St. Louis for testing, disassembly, coil removal, cleaning, further testing, re-assembly, and high-speed balance.

During initial electrical testing of the heavily dished collector rings, collector studs, and bore copper, the collector studs failed high potential testing. This resulted in the replacement of the collector rings which included removing the old collector rings, manufacturing new collector rings, new collector ring insulation, and reinsulating of the collector studs.

Coils were removed and sent off-site for cleaning. They were then returned and checked by MD&A.

After reinstallation, each coil received AC Hi-Pot and turn-to-turn testing.

Also, during the rewind process, the blocking was upgraded to the MD&A standard block and tie design. Turn insulation was coated, requiring a rotor bake cycle.

Electrical testing, high-speed balance, acceptance testing, and shipping followed.

Post-Outage GT Performance Analysis

MD&A issued a report that calculates the relative change in output and heat rate after the gas turbine outage. Operating data from pre and post-outage was used for the analysis.

Full-Scope MD&A

MD&A provided startup and balance support of the unit.

Our team provided full recommendations of what to look for or replace at the next outage.

This combined-cycle inspection and overhaul clearly reveal MD&A’s total service capability and non-OEM commitment with deep and focused product knowledge and experience. The precision of all MD&A divisions in support of a common goal merged into a powerful, comprehensive response, returning the facility to full and long-term operations.

With this project, MD&A has added to its impressive project resume as a holistic provider of services to all makes and models of turbines and generators, returning them to and above their original standards.

MD&A is a one-stop shop! Call MD&A about your next outage today at (518) 399-3616

The post MD&A Completes Significant Combined-Cycle Inspection and Overhaul appeared first on MDA Turbines.