501F&G users benefit from presentations by non-OEM equipment/services providers (1 of 2)

The 501F and 501G Users Groups integrate more suppliers into their formal presentation program than any other user organization serving gas-turbine owner/operators. When the steering committees first encouraged widespread vendor participation in 2011, one could not have predicted the high degree of success the Vendorama segment of the annual meeting would achieve virtually overnight. Users do want to hear from vendors about their technologies, but they want to have a choice in what to listen to; Vendorama provides that flexibility.

On Day One of the 2014 meeting at the Westin Mission Hills Resort & Spa in Rancho Mirage, Calif, February 16-20, there were 42 vendor presentations—six conducted in parallel in each of seven time slots, beginning at 10:30 a.m. Speakers had 30 minutes to speak and take questions. The presentations were vetted by the steering committees to assure content of value to owner/operators and to eliminate any promotional material. At least one committee member attended each session to assure a timely start and end to the proceedings.

Below are short content summaries of several presentations selected by the editors; more will appear in the second CCJ ONsite dedicated to the 501F and 501G meetings.

AAF International. Bill Hale provided attendees sufficient information to help them communicate to their management the value proposition for HEPA filters. He began with a review of AAF’s long history in filtration and more than 15 years of HEPA experience  and then offered the following technical benefits of cleaner gas-turbine inlet air:

    • Greater machine availability and reliability.

    • High initial power output is maintained.

    • Increased fuel efficiency.

    • Longer hot-end component life.

    • Eliminates the need for water washing (Fig 1).

    • Reduces emissions.

1. Condition of compressors serving two gas turbines of the exact same type is compared after 8000 hours of operation with MERV 14/F8 filters in the air inlet house (left) and with E12 HEPA filters (right). No online or offline water washes were performed on the unit with the E12 filters

1. Condition of compressors serving two gas turbines of the exact same type is compared after 8000 hours of operation with MERV 14/F8 filters in the air inlet house (left) and with E12 HEPA filters (right). No online or offline water washes were performed on the unit with the E12 filters

The commercial upside offered by improved performance:

    • Increased plant revenue.

    • Higher power production.

    • Reduced fuel use and, therefore, cost.

    • Decreased emissions.

Hale’s slides contained tables and charts with information supporting the points made above, including pressure-drop data for different filtration schemes. He presented scenarios for a hybrid upgrade for an existing filter house as well as a complete retrofit filter house with three-stage static filtration. Regarding the latter, removal of salt is assured to eliminate the possibility of hot-gas-path corrosion.

Allied Power Group was one of at least six companies presenting at the conference on compressor diaphragms—repairs, design features, upgrades, etc. Alan Lovelace, PE, began with a historical review of diaphragm designs and manufacturing processes, and moved quickly into guidelines for repairs. He then addressed the blending of minor indications at the edges of the diaphragm airfoils, which Lovelace said, should be done using the 8:1 ratio rule. This means the length of the blended surface along the edge of the airfoil should be eight times the width of the airfoil at the bottom of the defect.  

For minor/medium indications, he continued, it is possible to use Inconel 82 weld wire for repairs; no heat treatment is required (Fig 2). But Lovelace cautioned that it is not recommended for any W501FD diaphragms because the airfoils are of marginal thickness by design. Major indications require Type 410 stainless steel weld wire for repairs, with stress relief (Fig 3). The repair expert strongly recommended inspection and dimensional restoration of anti-rotation lands at each repair.

2. Top-quality diaphragm fixturing is critical to repair success

2. Top-quality diaphragm fixturing is critical to repair success

3. W501FD R13 diaphragm in fixture, weld repair in progress

3. W501FD R13 diaphragm in fixture, weld repair in progress

Lovelace commented on possible mods and upgrades—such as replacing labyrinth-style seals with honeycomb seals—before closing with the following remarks:

    • The majority of diaphragm repairs are in the minor and medium categories.

    • W501F compressors typically have an operating lifetime of more than 80,000 hours.

    • The W501FD suffers from harmonics issues, which are conducive to hookfit wear, especially in Rows 1-3. Diaphragms for these engines manufactured before 2000 using the laser welding process should be inspected thoroughly and regularly, Rows 1-3 in particular. Concentrate on inner and outer shroud tenon welds, Lovelace said: Make a good visual inspection, tap test, red dye check if possible.

    • Pick your repair facility based on its tooling capability and people. Look for robust tooling/fixtures and experienced personnel.

    • Finally, always compare the incoming versus the outgoing dimensions. If there is a big difference, take steps to ensure the parts will fit back into your gas turbine.

Emerson Process Management. Dave Cicconi, a familiar face at user group meetings, covered a considerable amount of material in the half hour he had at the podium, integrating it into a coherent presentation that focused on the following requirements for a successful gas-turbine controls retrofit:

    • Vendor prequalification: proven hardware and experienced supplier.

    • Definition of scope, including system improvements beneficial to the bottom line and safety—such as conversion from mechanical to electronic overspeed trip protection.

    • Application-specific design.epm_cmyk_pc

    • Well-defined engineering deliverables.

    • Customer participation in design reviews.

    • Complete testing, including dynamic simulation.

    • Detailed outage planning.

    • Long-term support.

Cicconi’s slides, available here, contain useful checklists for planning purposes—such as what turbine control features you should consider including in your new system, considerations for vendor pre-selection, vibration monitoring and protection, project drivers for excitation replacement, etc. In closing, Cicconi pointed users to case histories of the company’s controls experience in generating facilities powered by gas turbines available via the CCJ Online Buyers Guide.

JASC, Jansen’s Aircraft Systems Controls Inc. Schuyler McElrath, known by many users for the successful JASC liquid-fuel-system valve solutions he has implementedJASC-Logo-White-on-Blue at their plants, was at the front of the room for another Vendorama presentation. Except this year the subject was not valves, but rather high-temperature metal-to-metal seals; more specifically, copper crush gaskets. They were developed by JASC back in 1996 to provide zero leakage between and fuel and purge-air housings of its three-way purge valve.

With technology borrowed from the 3WPV crush seal, JASC is developing a series of crush gaskets that can replace O-rings of various sizes. These seals are designed for field retrofit and for multiple make-and-breaks. Review McElrath’s slides for more information on this development.

PSM, an Alstom company. Hany Rizkalla, one of the company’s most senior combustion experts, presented an overview on the value of combustion dynamics monitoring (CDM): enhanced operational flexibility, emissions reduction, reliability improvement, etc. He reviewed the reasons for regular tuning, reminding attendees that over time, emissions and dynamics change because of the following:PSM-Logo_4C-10-2012a

    • Weather—specifically temperature and humidity.

    • Variations in fuel properties.

    • Hardware condition. Remember that engine and combustion-system components degrade as operating hours accumulate.

Rizkalla offered as an alternative to seasonal manual tuning, the company’s AutoTune system, which has gotten high marks from some owner/operators. It enables autonomous gas-turbine combustion tuning to maintain emissions and dynamics within limits under varying ambient conditions, changes in fuel composition, and engine deterioration. The system also incorporates features to optimize unit operation consistent with power-output requirements, Rizkalla said. AutoTune was developed for the 7FA DLN2.6 combustion system in 2009; it was expanded to 501F application in 2012.

PSM’s Kjalid Oumejjoud conducted a valuable primer on combustion operation theory, which included a chapter on CDM, at the fall 2013 meeting of CTOTF™. The CTOTF workshop was directed at plant O&M personnel, like Vendorama. Oumejjoud’s presentation, recommended for training purposes, is available to all GT owner/operators via the CTOTF’s Presentations Library.

Strategic Power Systems Inc. Senior VP Tom Christiansen explained to the 501F and 501G users why it’s virtually impossible to properly manage gas-turbine assets and operational risk without a robust methodology for tracking the lives of critical engine parts. SPS has been providing this service to the industry since 2005. Tracking initial installation is easy, he said, but life gets more interesting when the following business realities, among others, are factored into the equation:

    • Parts are changed out.

    • Parts are warehoused—repaired and unrepaired.

    • Parts are sent out for repair.

    • Blade and vane sets are modified.Strategic Power Systems Inc

    • Some parts are scrapped.

    • New parts are purchased.

    • Pre-owned parts are purchased.

    • Blade and vane sets are installed in different units.

    • Parts are exchanged.

    • Plant personnel change.

    • Plant ownership changes.

Christiansen urged the users to establish a formal, consistent process for life management of critical parts. This effort, he said, begins with written documentation and project definition. Can individual plants/companies do this? Of course, but very few, if any, do it well for several reasons:

    • Data collection is a tedious, thankless task.

    • Spreadsheets are prone to error.

    • Responsibility is assigned to an individual, who has no backup for verifying data accuracy, who might transfer to another position within the company or outside of it, who is not properly supervised, etc.

    • Lifing algorithms grow more sophisticated as more is learned about how and why parts fail. Plus, a changing O&M paradigm may require a different algorithm. Who in your organization would know about this?

    • The life management effort is more than an inventory; you’re managing the life history of each part.

    • Rigor is required in data collection and entry. Accuracy is paramount because multi-million-dollar business decisions are made based on these data.

As fleet-wide asset management, versus plant-level asset management, grows in importance regarding financial success, the outsourcing of critical-parts life tracking makes more sense than ever. Access Christiansen’s presentation here to dig deeper.

Sulzer. Matt Walton, PE, one of six presenters at the 501F and 501G on compressor diaphragm repairs, covered common wear mechanisms and failure modes, inspection, and repairs in a well-organized and well-illustrated presentation. The primary failure modes, he said, were solid particle erosion and foreign object damage (FOD, Fig 4), seal rubs (Fig 5), fretting and contact stress, distortion, and high-cycle-fatigue (HCF) cracking. Fretting damage often is found at the outer hook fit and can be expected to extend 6 in. from the split lines and at the bottom quadrant (Fig 6).

Sulzer 1

4. FOD (left) and solid particle erosion (right) often are found in compressor diaphragms sent to repair shops

Sulzer 2

5. Seal rubs also are relatively common

Sulzer 3

6. Fretting can be expected at the outer hook fit at these locations

Sulzer 4

7. New seals are peened after installation

Distortion of diaphragms may be caused by pressure loads in the early stages of the compressor, heat in the latter stages; and also by millwrights during disassembly. HCF, which is not common, can be caused by cyclic aerodynamic loading.

Inspection begins with an overall visual review of components, Walton continued. A fixture fit typically is next, followed by verification of critical dimensions (hook-fit thickness, twist, roundness, seal diameters, etc). Disassembly, cleaning, and NDE are next; a tap test is common.

Repairs are rated either minor or major. In the former group are the following tasks:

    • Straighten, blend, and weld repair airfoils.

    • Seal tooth straightening and deburring.

    • NDE.

    • Recoating.

    • Reassembly.

    • Fixture check and dimensional inspections

Major repairs typically are initiated by hook welding or other nonstandard requirements. They include all of the tasks identified above adjusted for the degree of damage, plus:

    • Plating.

    • Undercutting and welding of hookfits.

Seal replacement is possible, Walton said, noting that angled seals have to be specially made. Seals are removed by machine, new seals installed and peened (Fig 7).

Logo-Vogt_72dpi_rgbVogt Power International. Deron Johnston and Chelsey Beals were a change of pace for the 501F and 501G users attending Vendorama, most of the presentations being focused on gas turbines. Their message was clear: F-class combined cycles operating on 1800-psig/1050F main steam typically take 1.5 to 2.5 hours to go from cold iron to base load, but this doesn’t have to be. It is possible to decrease the start-up time, while also reducing life consumption.

One example they gave was for a 2 x 1 combined cycle powerws by two 7F engines and having an HP drum operating pressure of about 1500 psig. Plant averaged two starts weekly so warm starts were a rarity. Average start time a couple of years ago was 3.5 hours; today it is 2 hours.

Critical to the dramatic reduction in start time was to minimize HP drum pressure/temperature loss between starts by closing steam vents and drains, stack damper, and IGVs quickly after shutdown. They stressed verifying leak-tightness of drains to avoid filling the drum with cold feedwater.

More solutions for reducing startup times with conventional heat-recovery steam generators can be found in How to design, retrofit drum-type HRSGs to cycle, start faster.

Posted in 501 F&G Users Group |

Leave a Reply

Your email address will not be published.