MD&A performed a Full-Service Steam Turbine Major outage, which included the HP/IP inspection and repairs on a 610MW GE® G2 steam turbine. While keeping tight to the schedule deadline, several of MD&A’s divisions and teams worked closely together on this comprehensive engagement, both onsite and offsite. They performed an extensive scope of work ranging from visual and dimensional inspections, NDE, and machining, all the way through bucket replacement and repairs as follows:
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.
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.
T2 Oil Deflector
Boiler Feed Pump Turbine
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.
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