Safety, engine performance among highlights of Siemens’ 501D5-D5A presentations

Judging from the number of entries in CCJ’s annual Best Practices Awards program, worker safety came of age as a top priority at powerplants eight years ago. Three years later, the number of entries for safety best practices topped all other categories—including O&M. More recently, many plants have earned Star status in OSHA’s Voluntary Protection Program (VPP), typically acknowledged as the platinum standard in personnel safety.

A plant’s safety net extends beyond its staff to all contractors and site visitors. Any injury is a black eye. This means contractors must have their safety programs approved by plant management before they can do any work. Violations will stop jobs for a sit down and review of the offenses. Serious violations will get a contractor kicked offsite. This doesn’t happen often but it does happen.

So, it was not surprising that the first presentation by Siemens at the 501D5-D5A Users’ 2014 annual conference and vendor fair in Key Biscayne, Fla, would review the field-service organization’s enviable service record and stress its continual improvement in critical areas such as job-hazard analysis (JHA), proactive safety stand-downs, and personnel protective equipment (PPE).

Closely related to the JHA program is Siemens’ pre-job briefing requirements, which includes its two-minute drill to focus worker awareness before starting a task. Here’s how it works: A card issued to all personnel that fits in a shirt pocket or can be attached to a badge shouts out, “Before performing work, ask yourself. . . .” On the back of the card are 10 questions such as these two: Where could there be stored energy? What’s in or under my load path? You get the picture.

The speaker next discussed safety policies established by the Siemens service organization in the last year—such as special shrouded hoods, eyewear, and air-purifying respirators for welding and grinding activities. Most important, perhaps, was the work done by the OEM to further ensure safe rotor lifts.

Siemens engineers developed an improved rotor lifting process with designed-in checks and holds during the lift. The procedure stresses the requirement for individual accountability of all actions. Modifications to the lifting beam and rotor skid were part of the effort. More specifically, a bubble level was permanently installed on the lifting beam to guide those conducting the lift and a piece of neoprene sheet is located between the sling and the clean rotor to improve friction.

Plus, a special plate is installed on the turbine end of the rotor prior to the lift to eliminate the unlikely possibility of the sling sliding off the shaft during a lift. A coupling prevents that from happening at the other end of the spindle. The so-called “disaster plate” is removed after the lift is complete. For more information on this development, and on other topics discussed below, visit the company’s Customer Extranet Portal (CEP).

A fleet statistics update is part of every Siemens user-group presentation and it seems to be of interest to attendees judging from facial expressions. The OEM tracks fleet reliability, availability, and starting reliability. These percentages were mid to high 90s for both the D5 and D5A fleets, but the statistical base could be better. Example: only 26% of the D5 engines report operating data to the manufacturer, 49% of the D5As. By contrast, data are received from all units in the 501G fleet and from nearly three-quarters of the 501F engines.

This information is critical to the OEM to facilitate identification and prioritization of potential improvements. The user-group leadership understands the importance of the data acquisition program and it is working with Siemens to improve response. Making data entry easier is one initiative. Expectations are that later this year reporting of unit information will be done online via the CEP.

Turbine component sealing was the subject of a presentation encompassing more than a dozen slides. Minimizing leakage is important because of its negative impact on power output and fuel consumption. Seals should be checked seasonally during borescope inspections and replaced if damaged. At a minimum, replace seals during hot-gas-path inspections at 24,000 equivalent operating hours or 900 equivalent starts, the group was told. Interestingly, some D5s and D5As may never require an HGP inspection because they don’t start often and operate most years at a very small fraction of the period hours (2% or less).

The speaker said the seals on the inside and outside diameters of the R1 vane segments impact performance most. About half of the total performance loss caused by ineffective sealing occurs at these locations. Another 11% of the total loss occurs at the R1 ring segments and yet another 10% from leakage by static and ring seals. This means about three-quarters of the performance loss attributed to ineffective sealing typically occurs in Row 1. Here’s a summary of the material presented:

      • R1 vane seals reduce the loss of cooling air between vane segments thereby preventing distortion of the airfoils.

      • R1 static seals prevent ingestion of hot gas into the disc cavity, thereby minimizing the potential for rotor-disc damage.

      • R1 isolation ring seals reduce the leakage of cooling air between isolation right segments, helping to prevent blade-ring distortion.

      • R1 ring-segment seals reduce the flow of cooling air from between ring segments, thereby minimizing the potential for blade-ring distortion.

      • R1 seal pins prevent hot-gas ingestion into the blade shank cavity, minimizing the possibility of blade cracking.

      • R1 blade seal plate prevents hot-gas ingestion by the blade shank cavity to help prevent blade cracking.

The same seals in Row 2 have a relatively minor impact in performance loss when they leak—roughly one-fifth of the average R1 loss.

Strut and splitter-plate cracks in the compressor inlet manifold (both top and side entry) have been reported by some users. An inspection service bulletin available on the CEP was suggested reading. Corrective action likely will be based on strut features used on the company’s 501F.

Diaphragm retention screws prevent the diaphragms from rotating in their cases. A small number of screw-fracture incidents reported on W501FC units resulted in diaphragm rotation and related wear and disassembly issues. A durability retrofit mod was developed for the FC based on the W501FD. While no similar incidents have been reported on W501D5-D5A units, users requested a similar durability enhancement for these frames. An alternative suggested preventive measure: Replace screws at every major inspection.

Adjustable root springs for R4 turbine blades, which force airfoils radially outward when the unit is on turning gear (less than 125 rpm), are designed to reduce wear and tear on blade and disc fir trees as well as the potential for an unbalance issue caused by a shift in blade position. The latter can increase vibration on engine restart. Work on the development of springs for air-cooled blades in Rows 1 through 3 continues.

Spring installation in R4 is relatively easy because of access to the uncooled fourth-stage blades from the exhaust end of the unit. The springs are designed for long life with replacement expected only during HGP inspections. They can be tightened when necessary to compensate for creep. Heat treatment of springs after manufacture relaxes the metal and minimizes the potential for creep.

Rotor and casing inspection and evaluation, RCIE in Siemens lingo, reviewed the findings from inspection of 23 rotors—including coupling-hole galling, marriage-coupling spigot wear, unacceptable curvic-clutch findings, belly-band slot wear, and compressor journal scoring and pitting. The goal of the presentation was to show users that certain things could happen with their engines that likely would not be identified unless the units were disassembled.

The speaker’s suggestion was to thoroughly inspect the unit during the HGP prior to the second major to identify action items for the upcoming major and assure the necessary components would be available without adverse schedule impact.

Siemens modernization and upgrade products for extending scheduled inspection intervals, improving operational flexibility, and increasing the thermal performance of W501D5 and D5A gas turbines also were discussed. The presenter summarized experience with the following recent product introductions—all inspection-interval extension capable:

      • Si3D blading was successfully implemented for the first time on the D5 and met design expectations: GT power output increased by about 7.5 MW, heat rate improved by approximately 500 Btu/kWh.

      • A new bolted-design compressor rotor with improved vibratory response is capable of a fast start to full load.

      • Redesigned DF42 components have addressed durability concerns with D5A water-injected combustion systems. The new-style transitions are in service and meet design parameters. New-style baskets and WI nozzles are ready for their planned first installations.

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