501D5-D5A users share major maintenance, repair experience

During the closed session at the recent 501D5-D5A Users Group meeting, discussion transitioned from engine vibration concerns to maintenance outages, experience with conventional and extended-life parts, repairs and coatings, etc—a cornucopia of subject matter. One attendee with a pending major inspection polled the group for experiences in using contractors for this work. Standard practice at his facility has been to perform maintenance outages with plant personnel under the direction of an OEM technical advisor. This has worked well over the years, but a multitude of projects would prevent staff from doing the work on the upcoming major. He was leaning toward hiring the OEM or Mitsubishi to perform the outage. What was the group’s experience?

Hands shot up in all directions. The majority of attendees had opinions, as you might imagine. Difficult to draw objective conclusions from such an exchange: The experience base of the commenters varied widely, plus the crew from Company X that did a good (or bad) job for you likely was not the same crew that did the bad (or good) job for the colleague disagreeing with your assessment.

Also obvious from the discussion: Performance may vary widely among repair shops, depending on the owner and key personnel at the time the work is scheduled to be done. Thorough due diligence of candidate repair shops was strongly suggested. A couple of participants stressed very objective evaluation of low-cost providers.

They said some service providers may not have the specific experience, or even qualified in-house procedures, for your work. Those shops may look to you to provide repair procedure. In sum, the users were in general agreement that there is no “right” answer on which way to go regarding repairs. You have to make decisions based on what “fits” at the time.

However, the value of the exchange definitely was positive. For those in the room who had experiences they wanted to forget, it was a welcome opportunity to vent; for those with good experiences, an opportunity to pass on to colleagues their good fortune with the hope that others might benefit as well. There seemed to be unanimity of opinion on two points:

• Leading aftermarket repair shops typically will scrap fewer parts, cost less, and have better turn times than an OEM.

• Owner/operators must have a shop presence to assure proper conduct of repair jobs, assess repair quality, evaluate parts the contractor wants to scrap, etc. If there’s no direct employee with the capability to perform these functions, use of third-party expert was highly recommended. Two oversights mentioned: Repaired transition pieces provided without cooling holes; a new vane row that included a refurbished vane.

As the discussion of overhaul experience continued, one user mentioned that his plant had essentially completed its major when the rotor being lifted for reinstallation in the casing was dropped. The lengthy exchange following this revelation left one with the impression that the owner must remain involved in transportation (Fig 1), rigging, lifting (Fig 2), and other such tasks contracted to others. It’s your unit that won’t be producing power when the unthinkable happens.

1. Over-the-road transport is not without risks. Heights of tunnels and intersecting highways on the chosen route must be checked and rechecked. Allowable bridge loadings also must be verified

1. Over-the-road transport is not without risks. Heights of tunnels and intersecting highways on the chosen route must be checked and rechecked. Allowable bridge loadings also must be verified

2. Crane collapsed while moving a very large generator. This accident involved a fatality

2. Crane collapsed while moving a very large generator. This accident involved a fatality

There have been several reported “drops” in the last year or so. This particularly disturbing fact might well point in the direction of inexperienced riggers. Rigging is both engineering and art and one must assume that some of the more talented people have retired—riggers get old, too—and that their replacements may not have been properly trained.

Another thread related to annual maintenance outages was started when the subject of contingency was brought to the floor. The question that stimulated the discussion went something like this: For a base-load D5A, how much contingency would you allow for a combustion inspection? First reply: “We aim for 8000 hours but will go to 10,000 or 10,500 if necessary.”

Next question: How far can you stretch out an inspection without incurring problems? A different user replied: You should not put off an HGP or major, although some believe 10% in hours is acceptable. It’s all about risk assessment, he said. The ductility of R1 and R2 turbine blades is the variable that should drive decision-making. For a base-load unit, material degradation is not as much of a concern as it would be for a peaking machine.

The user continued, saying it’s important to get critical hot parts into the shop for thermal rejuvenation. The life cycle of components comes into play here, he added. Is this the first cycle, the second, the third? The younger the component, and the fewer the thermal cycles, the more flexibility you have in scheduling—generally speaking.

Service agreements had a brief run in the open discussion session. Renegotiation and what should be included in the new arrangement were key talking points. A parts agreement was suggested in place of a service agreement. If you go that route, the group was told by a colleague that they have to consider who handles and stores the parts. In addition to tax implications, how will you confirm that all parts are of the quality level you believe they are? Recall the earlier comment on the reconditioned vane segment that was included in the new vane row.

One more thing the experienced user suggested: Specify in the contract that the customer has the right to have the service provider’s program manager replaced at its discretion. This is important in situations where the original manager approved by the customer is changed by the contractor or leaves its employ and the replacement is not to the customer’s liking.

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