Tuesday, October 3, 2023

Building Utility Planned Outage Expertise

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EPRI works with member utilities to develop manuals and web applications to guide critical natural gas turbine inspections and repairs.

Tennessee Valley Authority (TVA) utilizes a rigorous planning process for planned maintenance outages. For years, TVA has started planning outages 18 months in advance and has a defined process for determining the budget, scope, and technology considerations involved with each outage.

The systematic approach to outage planning is understandable. For example, TVA’s fleet of generator units includes 32 GE 7EA gas turbines, and the typical cost associated with each 7EA hot gas path outage technical oversight is between $100,000 and $150,000. A 7EA hot gas path inspection (HGPI) inspection costs between $750,000 and $1 million. Besides the high cost, planned outages also pose significant financial, reliability, and safety risks.

For example, planned maintenance activities account for over 70 percent of gas turbine unit unavailability—in large part due to improper reassembly procedures and wrongly applied maintenance practices. Experience has demonstrated the critical importance of effective outages. At Enel’s Dock Sud natural gas power plant in Argentina, for instance, an improperly installed SEV Burner Balcony –part of the fuel nozzle that allows a gas turbine to burn more efficiently — disconnected and damaged turbine blades after an inspection and overhaul. The event prompted a forced outage that lasted six weeks and cost the company over $2 million in repair expenses.

A desire to ensure that GE 7EA and other gas turbine planned outages proceed efficiently and effectively led TVA to join with utilities like DTE Electric Company (DTE), Great River Energy (GRE), and Tri-State Generation and Transmission Association (Tri-State) to work with EPRI to develop the 7EA Hot Gas Path Outage Guide and an accompanying checklist to optimize each step of planned outages. For Clinton Lafferty, who worked as an outage engineer and eventually became outage manager responsible for all gas and steam turbine inspections across TVA’s gas turbine fleet, the rationale for helping to develop the guide and checklist was simple.

“One gap I saw was that we do not have a lot of gas turbine expertise internally within TVA,” said Lafferty, who is now senior program manager, project engineering, major projects for TVA. “There was a gap between what our less experienced gas turbine engineers knew about how machines come apart and go back together. The EPRI outage guide dovetails with the technical gap we have internally and helps guide site engineers and regional engineers to know what bolts to turn and what extra bolts to replace and all the details that go into an effective inspection and outage.”

The Need for Internal Outage Expertise

The need to close the expertise gap around planning and executing a gas turbine outage effectively and inspection is by no means limited to TVA. That is why EPRI has developed a series of outage manuals and checklists—applicable to GE 7EA hot gas path outages, Siemens 501F gas turbines, and Ansaldo/GE GT26 gas turbines—and a web application to help guide outage inspections.

It was important to comprehensively document how utilities should conduct or oversee gas turbine outages because many of the staffers responsible for conducting them are retiring. “We are finding that the industry is losing its expertise,” said Leonard Angello, an EPRI technical executive who leads the Gas Turbine Life Cycle Management program. “A lot of this know-how existed with experienced engineers who didn’t necessarily write that knowledge down to pass to the next generation of engineers. This is about providing a detailed framework for what a quality outage is and how to do it and helping transfer knowledge from one generation to the next.”

Another driver of this research is to equip utility staff with the knowledge they need to hold original equipment manufacturers (OEM) accountable when they lead turbine outages. Across the industry, utilities have reduced costs by entering into long-term service agreements with turbine OEMs to handle any inspections and repairs. These agreements aim to reduce risk and costs for utilities.

But outsourcing outages and inspections also means knowledge, especially about new gas turbines, stays with the OEM. “The only person who has the knowledge is the OEM because the utility is not directly involved with a lot of these maintenance activities,” Angello said. “For the utility, that means you have no knowledge about whether someone is doing the work correctly. These manuals and the web applications give inexperienced staff the knowledge and checklists to know if there is a deficiency in how the work is done.”

Equipping Workers for Today and the Future

Developing the manuals and web tools was a collaborative effort between EPRI and member utilities. For example, between 2016 and 2019, EPRI worked with member utilities Enel and Naturgy to document and demonstrate outage processes, procedures, and tools at natural gas plants in Spain and South America.

“The working process consisted of sharing with EPRI our experience in outage execution and control, analyzing different problems we had suffered in previous overhauls, and defining what should be done with new outage protocols, quality control forms, and outage quality, allowing our field engineers to perform the quality check,” said Tomás Alvarez, head of thermal maintenance, Iberia for Enel, whose company supported the idea of developing the manuals to provide internal direction about performing outages that went beyond what the OEM provided. One reason this was a need for Enel: The operations and maintenance (O&M) life cycle cost of a combined cycle gas turbine is more than double its initial cost.

The work resulted in a series of manuals that provide maintenance activity checklists and guidance for turbine disassembly, inspection, reassembly, and recommissioning of GT26 gas turbines during planned outages.

The collaborative fieldwork helped researchers identify risks involved with GT26 gas turbine overhauls and informed the manuals and tools that were developed. For example, during an inspection of Naturgy’s San Roque power plant in 2017, several challenges inhibited the completion of a planned outage. These included limited access to the objective acceptance criteria, expected dimensions, typical findings, and acceptable field repair methods. Objective acceptance criteria provide guidance about whether damaged plant components can continue to be used or need to be repaired or replaced. Expected dimensions refer to the minimum part specifications necessary for components to work properly. Typical findings are, as the name indicates, the condition one would expect equipment to be in after operating for a period of time. And acceptable field repair methods provide guidance about the actions necessary to correct any problems that are discovered.

Following the on-site visits to plants performing GT26 outages, EPRI worked with Naturgy and Enel to outline steps to improve planned outages. These steps are documented in the manuals and web tools, and include:

  • Comprehensive maintenance activity checklists that guide disassembly and reassembly hold points, verification points, and witness points with acceptance criteria.
  • Inspection techniques and quality control Inspection Assessment Data Sheet (IADS) forms for the rotating, stationary, combustion, and structural turbine components. Each data sheet includes a sketch or photo of the part, its expected dimensions, typical findings, and repair methods with acceptance criteria.
  • Field guidance for each of the data sheets, including recommendations for how to handle typical damages.

Once these best practice steps were identified, they were utilized at Enel’s Dock Sud plant and Naturgy’s Cartagena plant in Spain before being published in the manuals. A similarly collective approach was followed in developing the guide for GE 7EA turbine outages. For example, Lafferty and other utility engineers have extensive experience conducting outages for TVA’s 32 GE 7EA turbines.

“We contributed a lot of that knowledge and lessons learned to the manual and also reviewed and provided input to the document before it was published,” Lafferty said. “We had a lot of practical knowledge to provide, but we also wanted to make sure that the information in the manual was presented in an understandable way so that newer engineers would be able to follow it easily.” As was the case with the GT26 manuals, the procedures and tools highlighted in the GE 7EA manual were demonstrated in real-world environments before being published. For example, the guidance and methods were implemented at outages at TVA, Tri-State, and Great River Energy power plants in 2020 and 2021.

“This is all about making the actual outages, inspections, and repairs more effective,” Angello said. “But these are also tools that will continue to build turbine expertise within utilities so that companies have personnel that can either lead and complete outages themselves or confidently oversee OEMs and third-party consultants when they do the work.”

EPRI Technical Experts:

Leonard Angello, Bobby Noble
For more information, contact techexpert@eprijournal.com.