If you’ve never experienced paying for a multi-million-dollar, power-generating turbine before, then there’s always a sticker shock—especially when you include the amount required for parts over a normal maintenance cycle. The frequency with which those parts must be replaced can also be unexpected for the uninitiated; to some it can seem as if the cycle of parts planning and acquisition is never-ending.
Dale Grace, senior project manager for combustion turbines at the Electric Power Research Institute (EPRI), uses “incendiary” words to describe the dynamics: “Turbines essentially burn up their parts,” which necessitates constantly buying new or refurbished ones or repairing them.
Maintenance intervals come relatively quickly with these plants, whether the engines are turning on and off constantly in stressfully cyclic mode, spinning in continuous operation, or driving a combined heat and power application—although smaller turbines, Grace notes, “are probably not as sensitive to cycling-wear as larger frame ones.”
EPRI provides clients with a turbine analytical service, which his office packaged in 2006, to provide a roadmap for decision-making about maintenance, economic analysis, reliability, and durability issues. One key research insight: The cost of maintenance over a 25- to 30-year life comes to about triple the cost of the initial turbine investment, assuming near-continuous operation and nominal inflation.
“For aero-derivatives, [it’s] probably even more intense, because capital cost per kilowatt is less,” he adds.
A few rare analyses show it comes out as high as five times. All of which has spurred the development of a niche for value-added, upgraded, durable, higher-performing parts, coatings, and monitoring and maintenance services; and many of which are sold at a better price-point than the original equipment manufacturer (OEM) price. All of this makes for an interesting competitive shopping experience. When you think about it, the task of corralling and containing three- to five-fold maintenance costs is the management challenge which, dollar-wise, makes or breaks project success.
It’s also a vendor sweet spot and a lucrative niche; someone has coined the acronym “OOEM,” or “other OEM,” for them, to connote the higher status they enjoy above simply “replacement parts makers.”
How to Best Handle Parts and Maintenance
Grace outlines three basic strategies for proceeding them. Owners usually opt for when maintenance is required:
- “Self directed with third-party parts,” meaning doing it in-house and canvassing the OOEM and aftermarket to acquire discounted parts and major overhauls
- Buying an OEM service agreement
- Doing maintenance in-house and buying parts at OEM list
In deciding upon the path that fits best, he says, the organization will usually consider: the model of engine they have; the length of commitment to the project; available labor, skills background, and experience; and “their comfort level” about the thought of managing the work.
Opting for either a long-term OEM contract or one signed with a third-party vendor, he notes, “shifts a fair amount of the responsibility for engine maintenance over to that provider over a longer period of time—say, six to 10 years,” and basically lets that OEM or vendor have all the maintenance headaches. For doing so, the turbine owner pays a substantial premium.
Alternatively, if saving money is the priority, “often times they’ll hire a contract labor to perform the hot gas path or major interval, and they’ll procure parts and procure services on a bid basis,” says Grace.
As for parts acquisition itself: Depending on the type of turbine, greater or lesser competitive dynamics may or may not be available from sources. “As an engine model has been out and serviced,” he explains, “then you get more expertise in that area and that model, and you get more independent people branching out and offering services as well”—all to the buyer’s benefit. Conversely, “If it’s a more advanced technology, then only the OEM is a provider of those parts.” You are more likely to get jacked up, a bit, in the billings.
Repair services likewise may be available from multiple qualified providers, who can be managed advantageously; or, again, repair/refurbishing may be quite specialized, and shopping options are limited.
Next, assuming multiple after-market parts and repair services are out there, “Going to the next level—and actually qualifying people—that is where some further technical expertise is required,” says Grace. This piece can prove “fairly difficult;” EPRI provides guidelines to assist in procurement and repair, either from OEMs or third parties.
Condition- Versus Interval-Based Maintenance
Buying a replacement part at the “optimal” moment, from the standpoint of squeezing the greatest value from it, often comes down to choosing the right point in that equipment’s life to take it out, inspect it, and refurbish it.
One common mistake is to assume that the OEM’s life estimate is an absolute.
In fact, the recommended intervals are often based on conservative norms that do not apply broadly to all situations. And if you simply obey recommended specs, you risk replacing parts too often, incurring needless added expense (i.e., with big turbines, well into six figures or more). On the other hand, running the part beyond its capacity can also cause trouble. You could cause additional problems that undermine efficiency. Ultimately, you will get more life out of your equipment by discerning the moment when a part should be removed for refurbishing. Every part runs in a unique environment. By using diagnostics intelligently, the user can tell whether the particular part under consideration truly has some more effective life left in it or not.
Taking the assessment topic further, Alan Lovelace, who is engineering manager for Allied Power Group (formerly Turbine Blade Repair Specialists) of Houston, TX, advises that using diagnostics, including the gamut of vibration analysis, testing, and planning, actually “saves a lot of money,” for several reasons.
First, as already noted, obviously the cost of parts is such that, on bigger turbines, tens and hundreds of thousands of dollars in savings can be racked up by accurately gauging the parts’ remaining life. Here, not only is money lost by replacing prematurely, but in the larger turbines, thousands of dollars may be squandered merely by taking them out for assessment. This is because the coatings must be stripped, then reapplied—after discovering that the part “wasn’t even that worn anyway,” notes Lovelace, whose organization specializes in repairs on larger GE and Westinghouse frame turbines.
Doing the highest-quality assessments without incurring such costs is a rare skill, often requiring high-end equipment and proprietary toolkits or phenomenal troubleshooting technology—e.g., “ultrasonically checking blades in place ... measuring blade tip clearances while engine is running … weird stuff like that,” says Lovelace. Only OEMs typically have these, he says.
Old-style borescopes are still adequate tools, though, as they’ve steadily evolved over the years. Some independent borescope specialists “are really good at it,” says Lovelace, and give results that may be less biased than those of self-interested OEMs.
On smaller turbines, depending on the make and size, the cost of inspections may be superfluous and can be avoided; a depleted part “can just be unbolted, and new module put on,” he says, following the OEM’s recommendations.
Metallurgical Analysis
Selecting some worn component for lab study is advised by one repair specialist, who, due to confidentiality agreements with OEMs and clients, asked not to be identified. “See what the problems and what the degradation modes really are,” he suggests. The turbine operator can usually gather the sample selection(s) himself.
Testing is highly specialized and not widely available, he notes: “I would say there are very few groups out there capable of doing it,” numbering perhaps three in North America.
“You’re looking for someone, outside the OEM, who has experience with high-temperature materials and coatings,” he says. OEMs tend to adopt a more conservative opinion regarding remaining part life.
Based on assessment results, the next step is to obtain uniform quotes from service shops, comparing these to the OEM rates, using specs that typically cover coatings, the heat treatments, the blending, and weld repair.
The amount of money you stand to save on a repair, by doing a good analysis to prepare these specs, can easily run into the mid-six figures for large turbines, he adds. “Yes, it is definitely worth obtaining an independent assessment.
“On littler ones, parts are much cheaper, so you will buy new rather than try to refurbish,” he continues. The respective parts strategies with large versus small turbines are “totally different” throughout.
Acquiring Parts: OEM or Third-Party?
With a need determined, the search begins for purchase options.
A first stop will be the OEM of course, but, depending on the engine and region, competitors offering better price, delivery, and, even, quality may be available, Lovelace says.
Example: Choosing an OEM to refurbish a first-stage nozzle or vane of a certain prominent turbine will cost perhaps $250,000–$275,000, but a good specialty shop may bid 30–40% less. And, while the OEM may require 24 to 40 weeks for delivery, an eager aftermarket shop may do it in only 12.
What drives these opportunities is, again, the number of shops that have plunged in by tooling-up for particular engines; so, the more widely used the equipment in question, and the longer it’s been out there, the likelier a base of providers exists.
As for aftermarket parts’ quality and performance: In several instances these have actually surpassed the OEMs.’ A couple of experts point out that flaws (which are not uncommon in original components) have likely been fixed by ambitious competitors, and higher-performing premium components are also routinely brought to market, even matched against stable parts. In truth, often the component (rather than the entire engine) is something of a lemon, and the equipment-maker knows it, but the word is getting out only slowly. One vendor collected a “ little book of pictures” shot from plants around the Power-Gen market, showing what happens to certain notorious rapidly wearing components; it’s an effective selling tool.
Dodging and denial “is really not anything new,” reports the consulting engineer who earlier asked not be identified. He says candidly, “There’s always something that goes wrong” with turbines. OEMs will then issue statements to customers, similar to consumer product recalls, “saying that they should replace the row-one compressor blades at the next scheduled maintenance, with ones less prone to cracking, or whatever.”
Aftermarket vendors are only too happy to fix them, “or help by locating replacement parts … kind of specializing in changing them out. “This doesn’t mean that the OEMs have been sitting idly without improving their parts as well,” he adds.
Lovelace agrees that, while some aftermarket innovations are superior, this certainly cannot be applied as any kind of broad rule. “I’ve seen third-party cast blades that I wouldn’t put on my kid’s bicycle much less inside a gas turbine,” he says.
What’s most critical in determining a part-marker’s competence is “the technical backup behind the people who came up with this part. The question you have to ask is, ‘Do they have technical intellectual property to perform the repairs that you want as a customer?’
He also advises: “Go look at the tooling that this third-party repair shop has.”
Welding and Repair Innovations
As for repairs, as opposed to refurbished parts, the same anonymous consultant offers nearly the opposite opinion of aftermarket competitiveness.
Although “third-party repairs are always cheaper” and often quite attractively priced, he says, they’re usually not as skillfully done, “especially on sophisticated turbine systems using advanced coatings full of cooling holes.” With simpler turbines, this is not a make-or-break consideration, but with higher-end coated ones, welding precision may be much more critical.
Abandoning the OEM, to buy repairs elsewhere, risks inherent “pitfalls,” he says. “You have to assure your own quality—it’s a ‘buyer beware’ market.”
Although the lowball price may look like a worthwhile gamble, “some people do not understand the risks,” he’s found. Also, the newest thing in repairs is something, which tends to give OEMs a big leg up: automation. OEMs, he says, “have set it up, basically, to do higher-volume production levels, with much more automated welding and coating systems, for refurbishing hot-section components.”
Results tend to produce impressive, high-precision finished repairs, with better quality control and—due to the automation—often a lower price.
Automated welding “is far less prone to cracking,” he adds, because “it replaces … having guys sitting there grinding on things and on the same spot every time,” which, of course, weakens the metal.
After the automated weld is done, “You have all the levels of sophistication there for applying the coatings on top of it,” and finessing the many cooling holes—again, with much greater precision and speed than on a manual operation.
OEMs, with their capital resources, are much farther along in developing the automation game than are regional independent shops, he adds. And most buyers of repairs remain clueless about what goes on, and the growing roll of automation.
Lovelace finds that manual shop welding skills are pretty much a given, and adequate, quality-wise—“but not everybody can fixture-check [a repair properly] and hold it where it belongs while they're welding it,” he believes. In fact, “The third-party repair is going to ‘die’ on the fact that the fixture-check is not dimensionally back where it belongs to fit in the engine.
“So, the fixtures are the absolute key,” he sums up.
A turbine-owner searching for a great repair, he says, needs to “go look at the shops fixtures. [Ask:] what dimensions are they going to take? How are they going to guarantee that the part that’s being sent back will fit in his engine?”
A fairly new trend, too, is a shift to brazing instead of straight welding. In this somewhat-exotic process, powered metal is applied on a surface, and the part is run through a vacuum furnace, diffusing and combining it into the base metal.
Braze repairs are more automated than manual welding, less costly, and the results are excellent, he adds.
Among aeroderivative turbine repairs, brazing is now the preferred method, and the demand is drawing lots of service-providers. Brazing for industrial turbines has come along, too, quite recently, he adds.
Lovelace ends by offering “all-purpose” turbine repair tips:
- Spend more to maintain a baseload rather than peaking turbine. “If you can save just a quarter of a percent on some seal leakage,” and the machine is running more than 300 days a year—“this can add up to a big dollar value in fuel costs,” he says.
Conversely, with a peaking machine that runs few hours, “You typically want just a fast, reliable start every time, without a rub;” so, optimize that. Beyond this, though, “You don't really want to spend much to tighten all the clearances to get every ounce of horsepower.”
- Settle for a cheaper coating. Parts engineers “are applying these bad-to-the-bone coatings that are absolutely phenomenal for durability, resistance to heat damage, and to keep cracking minimal,” he says. They’re terrific—“until you have to take them off to repair the part.” In the process of stripping the coat, “you’re killing the part.”
Also, the top-end coatings are often a waste, because they may outlast the part itself. The price difference between a 50,000-hour coating and a 25,000-hour one might come out at $35,000 versus $18,000. But, “the part is only dimensionally stable for 20,000 hours anyway,” so why invest in a costlier one that will be stripped off?
“Go with the cheaper coating,” he recommends.
Lastly, maybe his best tip:
- For great starting efficiency, reset fuel nozzle tolerances to ±1% max. Ignore OEM specs that call for ±3%, 5%, or more—“That’s too wide and results in inefficient starting,” he says.
“It doesn’t cost that much more to get nozzles flow-checked” and adjusted down to get ±1%, adds Lovelace. “Good fuel-nozzle shops can do this while a turbine is in for its normal service or repair—and the starting efficiency will go way up.”