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Planning for the next maintenance outage
Perform a proactive analysis before planning the maintenance efforts for the upcoming outage. Then compare the information uncovered against the operating experiences since that outage. During that comparison, ask the following questions:
- During the previous outage, was damage detected where it was anticipated? If so, was the extent of damage greater or less than expected?
- Were there failures since the outage? If so, is the cause of the failures understood? Were the causes eliminated? If not, can the cause of the failures be corrected during the upcoming outage?
- Have the stewardship boundary conditions changed since the last outage? Are the units still operating with the same fuel? Are the units still operating in the same mode or manner? Has the outage duration or operating interval changed?
- Has the outage budget changed?
From this comparison, the appropriate variations from prior maintenance actions can be determined, and the outage can be planned. While
Plan how to respond to outage findings
The next consideration should be with regard to the actions needed if the outage examinations identify issues. With predetermined acceptance criteria, decisions on the necessary repair actions can be made quickly. One source for developing appropriate acceptance criteria is the ASME Guideline FFS-1, “Fitness for Service,” developed jointly by API and the ASME. Acceptance criteria are damage mechanism dependant. As such, the acceptance criteria should be based on the anticipated damage mechanism(s), based on the stewardship boundary conditions.
The development of acceptance criteria intended to support examining feedwater supply tubes for ID-initiated corrosion fatigue cracking was presented at the ASME POWER-2010 conference in a paper by Peters and Jones, POWER2010-272255, “A Case Study on Generation of Acceptance Criteria in Feedwater Supply Tube Bends.” That paper discusses the use of fracture mechanics to determine acceptance criteria associated with (potential) flaws in downcomer piping. The maximum allowable flaw size was calculated so that the appropriate mitigation steps can be developed depending on the inspection findings. With these criteria, run/repair/replace decisions can be made in a timely fashion to minimize any impact on the outage schedule.
Maintenance planning is an instrumental part of good stewardship. The appropriate areas of concern can be best determined through an unbiased review of the operating and maintenance history of the equipment, in conjunction with an understanding of the recent operating history and intended future operating parameters. Then maintenance efforts can be applied to evaluate those areas in a timely manner with predetermined acceptance criteria, and any undesirable findings addressed appropriately. In the end, these maintenance efforts allow the engineer to do right and achieve the goals of safe, reliable and efficient power generation, even when faced with the daunting challenges of cyclic operation, new fuel sources, increased operating time between outages, reduced outage times, decreases in the maintenance budget and an aging steam generator. ~
John Arnold has been helping utilities manage aging fossil plant assets for more than 20 years through the development of comprehensive assessment programs, field engineering evaluations and laboratory metallurgical testing. His work is mainly focused on boilers and the evaluation of water and steam-touched tubing and the heavy-wall pressure parts. He has worked with Structural Integrity Associates since 2005 in its Fossil Plant Services group, focusing on the nondestructive testing and lifing of boiler tubing. Arnold has a master’s degree in Metallurgy and Materials Engineering from the University of Connecticut, and is a member of ASME’s Steam Generators and Auxiliaries Committee.
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