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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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.

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