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.

The post Siemens ST-600 Industrial Steam Turbine Major Inspection appeared first on MDA Turbines.

View the video on the advantages of the main stop valve upgrade and for additional information call MD&A Parts Division today at (518) 885-3199 or use our Contact form.

Solid Particle Erosion (SPE) occurs where steam and solid particles at high velocities make an abrupt change in direction. SPE reduces component life and decreases valve reliability. A thorough investigation of stem and bypass valve erosion on main stop valves led to an engineering design study of these issues.

The evaluation resulted in the design of MD&A Parts Division Triplet Type Main Stop Valve upgrade as an effective countermeasure to the solid particle erosion seen in conventional designs. The main stop valve upgrade addresses these issues with a configuration that allows for high-velocity bypass steam to flow parallel to the stem, thus eliminating stem erosion issues.

MD&A Parts Division’s Engineering Manager, said:

“The triple bypass main stop valve upgrade significantly reduces solid particle erosion (SPE). The engineering experts at MD&A Parts Division design each valve to optimize the flow geometry and apply the latest materials and nanocoating technology to extend component life. The overall valve offering is a drop in replacement that reduces valve maintenance costs and increases the time between valve outages.”

MD&A Parts Division (MD&A) manufactures and supplies all parts for Triplet Type Bypass Main Stop Valve. MD&A’s Turbine-Generator Repair Facility in St. Louis performs the final valve assembly.

Advantages of Triplet Type Bypass Main Stop Valve:

• MD&A Triplet poppet valve geometry, contoured to gradually turn the steam flow parallel to stem
• Proprietary TiSiCN nanocoating applied to poppets for improved SPE resistance
• Flared conical diffuser shape of the bypass holes reduce particle velocity and improve direction
• Stellite shielded pressure seal head improves SPE resistance on forward facing steps
• Reduced valve maintenance
• Applicable to subcritical and supercritical plant applications
• 30+ Years of replacement experience (175 MW to 700 MW)
• 8” to 15” Valves

MD&A Parts Division (MD&A) manufactures and supplies all parts for Patented Triplet Type Bypass Main Stop Valve. MD&A’s Turbine-Generator Repair Facility in St. Louis performs the final valve assembly.

The post Triplet Type Main Stop Valve Upgrade appeared first on MDA Turbines.

Take the generating unit whose valve stand suffered an exceptionally deep crack in its inner bore caused by an improperly installed bushing. MD&A received the valve stand at its St. Louis repair facility not knowing just how extensive the crack was. Working with the utility customer, a repair program was designed that included excavating the crack, weld-repairing the stand, and installing new bushings. The repair was completed in three weeks and saved the utility from buying an entirely new valve stand.

At MD&A’s repair facility, a full set of readings were taken on the valve stand. Inspection revealed heavy galling on the bushing fit ODs, and measurements were taken to determine if there was enough stock for the proper interference fits.

NDE inspection revealed a crack extending some 14” into the valve stand bore. It began on one side of the bore, moved toward the valve’s outboard side, wrapped around the bore, and came back toward the inner bore.

The repair plan included machining the bushing bore to determine how deep the crack was, and removing an OEM modification that held the inner bushing fits. After removing ¾” on a side from the bore, MD&A determined that the crack persisted under the stud flange, so the repair was modified to hand grind the crack.

With the crack removed, the valve stand was pre-heated and MD&A technicians hand-welded deep pockets that were present on the valve stand to return those areas to the proper bore diameter.

Once the hand-ground area was welded and hand-worked, a second NDE was done to ensure no new cracks had formed. Seven layers of weld were added to the valve stand using an automated welder. After completing the post-weld heat treatment (PWHT), the stand was set up in a horizontal boring mill for rough machining to within .030” final size.

A final NDE was done to ensure no further cracking had occurred, and then the bore was machined to the final size. All bushings were machined, installed and the valve underwent a try bar check. As a final step, the valve was set between centers, the casing fit OD, and the gasket face was cut to design size.

For this critical valve stand repair, MD&A tapped its deep and experienced team of experts to complete the repair in a time frame that quickly returned the unit to full service versus replacing the valve stand which would have taken months.

Check out our video: Full-Service Valve Capabilities Video

Have MD&A inspect or repair your valves today, call our Turbine-Generator Repair Facility at (314) 880-3000, or use our Contact form.

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The HP valves were the first to be inspected in-shop. It took very little effort to liberate the stellite from these valves. In some cases, the entire inlay popped completely out of the valve seat, which indicated very little, if any, bonding to the parent metal. It is our valves project manager’s expert opinion that a butter pass of either Inco or 309L was not inlayed between the parent metal and the stellite inlay. It has also been his experience that the butter pass is a must to ensure proper bonding takes place.

This is the stellite inlay from one of the HP valves. Obviously there was a bonding issue, specifically a lack thereof. The lack of bonding was found to be worse on the HP valves than it was on the IPs. MD&A has experienced this issue on several occasions, and our preferred method of repair is to remove all of the stellite, along with an amount of parent metal, to excavate any of the material that may have migrated.

We then pre-heat and weld build up using for 410SS filler material. After a PWHT, the valve seats are then machined to the as found contour, and final lapped to achieve 100% blue contact with the associated disc. The method of welding is semi-automatic gas tungsten arc welding (GTAW). This is performed with a machine that was developed by MD&A and built in conjunction with an industry leader in the manufacture of semi-automatic welding equipment. Below is a picture of that machine mounted to the end of a valve body.

All valve seats were overlaid with 410SS, except the LS HP CV. The parent metal was full of porosity/trash and a solid overlay could not be produced. MD&A machined out enough parent metal to allow for the installation of a shrunk in seat insert that was made from 410SS forging.

It was then seal welded both in the bore and in the front face of the valve seat. That was done with a 500°F pre-heat, and no PWHT was performed. After machining, all seats were lapped and 100% blue check was achieved.

Below is a picture of a completely refurbished valve seat, showing the blue contacts from the disc to seat check.

MD&A also performs valve seat repair in-place or on-site, saving you time and money! A fabricated seat can be installed in the valve body and seal welded in lieu of a complete weld repair solution for the seating surface.

Have MD&A look at your valve seats today, call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

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