501F and 501G Users Groups

Aftermarket competition

The annual meetings of the 501F and 501G Users Groups are among the best industry events for conducting due diligence on engine parts, services, and upgrades, and for purchasing decision-making. The reason is simple: Two major OEMs, Siemens Energy Inc and Mitsubishi Power Systems Americas Inc (MPSA), participate and compete head-to-head to serve a global fleet of about 450 F-class engines. Both manufacturers get significant podium time at the conference and by listening carefully to each you can decide on questions to ask the other. No machine is perfect and competitors generally are willing to share what they believe is wrong with the other company’s equipment.

PSM also is highly visible at the meeting, offering both parts and services for the F fleet. The leading third-party repair shops are there as well—including ACT Independent Turbo Services, Allied Power Group, and Sulzer Turbo Services—competing against the OEMs and PSM. The competitive battle focuses on business associated with the early 501F models—up to and including the 501FD2.

The Mitsubishi team annually updates attendees on the company’s infrastructure and capabilities before discussing the specific modifications and upgrades it recommends to improve durability, reliability, availability, etc, of the 501F engine. At the 2013 meeting, the first slide traced the company’s North American commitment from 2001 ($40 million, seven employees) through 2012 ($550 million, 1700 employees). Facilities installed during that period included the Outage and Resource Center in Houston, Power Generation Services in Orlando, MPSA Headquarters in Lake Mary, Fla, and the Savannah Machinery Works in Georgia. Profiles of each are available online.

Milestones in the development of the 501F was another segment of the presentation and of particular interest to industry newcomers. Here are the highlights:

• 1984. Mitsubishi and Westinghouse Electric Corp agree to co-develop the 501F with a 1350C (2462F) firing temperature.
• 1985. Mitsubishi takes over the manufacture of large gas turbines for Westinghouse, which later closes its Lester (Pa) GT manufacturing facility.
• 1993. First 501Fs begin commercial operation at Florida Power & Light Co’s Lauderdale Generating Station.
• 1998. Siemens acquires Westinghouse and the technology alliance between Westinghouse and Mitsubishi is terminated. Mitsubishi begins implementation of materials changes, structural modifications, and cooling enhancements to improve component durability at high firing temperatures.

The upgraded parts developed by Mitsubishi were installed in its M501F3 and later offered for the W501FD2. Company engineers presenting at the 2013 meeting focused first on the exhaust system issues experienced by many owner/operators in the room—such as cracking of the outer diffuser, strut shields, and struts. They believe at least some of the cracking can be traced to the design of the strut shield, which is welded to the casing, inner diffuser, and outer diffuser—and does not allow for thermal growth between the casing and diffusers (Fig 9).

The Mitsubishi speakers also pointed to the relatively sharp weld connections at the intersection of inner and outer diffusers and the strut shield, suggesting that smooth fillets would have been a better choice. Regarding materials, it was said that after the two OEMs went their separate ways, Westinghouse embraced the use of Hastelloy X for its outer and inner diffusers. One of its advantages was ease of welding. However, that material becomes brittle with age at F-class GT temperatures.

Mitsubishi stayed with stainless steel for the exhaust diffuser and increased its thickness in 2002. Plus, the flexible support system (strut shield is welded to the outer diffuser, not the casing, as shown in Fig 10), sealing off of the dead air space, and active cooling of the struts (an advancement based on G-fleet experience) all contributed to exhaust-system reliability and durability.

Modifications to the M501F two-piece exhaust cylinder to allow its use in W501F gas turbines were underway at the time of the last meeting with expectations that the first unit would be delivered in fall 2013. The Mitsubishi two-piece exhaust can be retrofitted into a Westinghouse machine during a typical major inspection plus three days.

Significant presentation time was devoted to the design features of individual 501F components developed by Mitsubishi that can be used in Siemens engines. Example: Mitsubishi uses assembled-type diaphragms rather than welded. Advantage is that mechanical fasteners increase vibration damping. First use was 1999, now well over 2 million hours of operating experience. Thicker airfoils were first used in a W501FD2 in 2008 in Rows 1-3 to increase structural rigidity; in 2010, in Rows 4-6. No evidence of hookfit wear has been identified to date. Come to Rancho Mirage and get an update.

Among the other components discussed were the following:

• Hybrid DLN combustor baskets, rated for 24,000 hours. The K-point DLN combustor was re-engineered; enhanced swirler mounting avoids swirler pin cracking. Ongoing work includes increasing flashback margin.
• Thick-wall transition piece introduced in 2002, now capable of 24,000-hr intervals. Increase in wall thickness and other design improvements reduced metal temperature and stress.
• R1 turbine blades. Changed material to directionally solidified MGA-1400, enhanced cooling to reduce oxidation loss, modified tip design. Looking to go beyond 50,000 hours.
• R2 turbine blades. Optimized cooling to reduce thermal fatigue, reduced stress concentration of cooling holes, increased fillet radius and trailing-edge thickness in platform, and new material all implemented in 2004 and meeting expectations.
• Turbine vanes. Moved away from cobalt-based alloy and Rows 1-3 now made from MGA-2400, which was said to have 100 times the creep strength of X-45. Also, cooling air optimized for R1.
• Root springs for use under R4 turbine blades eliminate blade rock in W501FC and FD2 units. Work continues on the development of a spring for R3.

You can’t be too safe

The 501G Users Group, chaired by Plant Manager Steve Bates, GDF Suez-Wise County Power Co LLC, is a close-knit organization. Unlike most other user groups, it has a low percentage of first-timers. Almost everyone in the meeting room either knows most everyone else present or knows someone from his or her plant. Another factoid that sets the 501G users apart from the pack: Each plant in the fleet sends an average of two or three employees to the meeting. Most other groups average about one or less.

At the last meeting, the safety discussion, led by Bates, was robust and beneficial to virtually all plants powered by gas turbines. Here are some of the takeaways:

• Scaffold up as the outage progresses. Be aware that protection can be momentary, because as you progress in the outage, railings, etc, have to be added.
• Install a cabling system for tie-offs; it’s tough to design a system flexible enough to accommodate several different engines and plant arrangements.
• Bear in mind that falls of even less than 6 ft can be lethal according to OSHA stats. Wearing a harness is a risk in itself because it can get tangled up, as can the tie line. Plus, workers can get tangled up in other’s lines.

  Have a scaffolding crew onsite while work is ongoing, to provide safe access as the need arises. To keep the scaffolding crew busy, use them as part-time helpers to clean bolts, etc.

• Always look to make the scaffolding and fall protection better as the outage proceeds; be sure to take pictures and notes on what works/what doesn’t to make the next outage safer. Verify that tie-offs to beams and piping are rated for the shock load. One user installed a supplemental beam system with full-column support to ground just for tie-offs.
• If you pull a harness from a bin, it must be certified before each use. If you issue harnesses to individuals, as most plants do, annual inspection and documentation is satisfactory. Identify harnesses by their serial numbers.
• Fire watch. The insurance company for at least one user requires a three-hour fire watch (periodic inspection) after hot work. Users agreed that they generally do it for 30 minutes, but for that duty, there’s a watchman with no other duties except fire watch.
• Enclosure test for CO2. If you lift the roof to check for proper sealing, run a fan test. Tough to pass the first time; the second time you do a better job of fit-up and sealing. A CO2 dump test can cost upwards of $50,000, so most do not want to do that. Another suggestion: Put cameras in the enclosure to see if there’s a fire inside before you enter.
• Evap-cooler doors can be difficult to open when need be. A pressure drop of 3 in. H2O can be challenging. You can get that if a fog bank passes or if snow fouls the head end. Consider installing windows in the evap-cooler section so you can see what’s going on in case you can’t get inside. Also, put big grips on the doors because the standard chrome handle may not give you the necessary leverage. And be sure to install hold-open kick latches at the bottom of the doors.
• Confined space. Hire the local fire department for confined-space rescue standby when a plant is more than about 10 minutes away from emergency response personnel. Two benefits: Helps familiarize fire-department personnel with the plant and provides the FD another source of revenue.
• Every time job requirements change, reverify lock-out/tag-out requirements. CCJ