To Retrofit or Not to Retrofit – 7 Questions to Help you Decide

One of the challenges of maintaining infrastructure is deciding how best to keep the operational costs in check while delivering the highest amount of service. This is especially true for aging equipment. One option is to replace the equipment with a newer version entirely, continue to maintain the existing machine, or a third option, retrofit the current machine with updated features.

Retrofitting is a term used in the manufacturing industry to describe how new or updated parts are fitted to old or outdated assemblies to improve function, efficiency or additional features unavailable in the earlier versions.

steam turbine in repair process, machinery, pipes, tubes, at power plant
steam turbine in repair process, machinery, pipes, tubes, at a power plant

Retrofitting, like any investment of capital requires careful thought.  SoftInWay’s Manage ring Director, Abdul Nassar has put together a simple list of questions to ask yourself before committing to a retrofit project.  Answering these seven questions before you start can save you considerable time and effort.

1. When should this machine go for a retrofit?

After a long period of maintenance, there comes a phase when engineers face a challenging compromise between efficiency and investment. At this point, the decision must be made of whether to replace deteriorated blades, or to perform total retrofitting of the flow path, and receive efficiency and capacity benefits, for that renewed flow path. The most significant redesign and retrofitting variants are:

  1. Minimal. Blades and nozzles replacement are performed, while casing and rotor are preserved.
  2. Intermediate. Retrofitting changes the number of stages, while keeping the existing meridional and axial dimensions. Casing is also preserved; rotor may be replaced or modified based on remaining life estimated on the rotor.
  3. Maximal. Complete redesign, with change of stage meridional dimensions, without fixing them in existing casing. The foundations and overall footprint is preserved to benefit the exiting foundations and civil structures.
2. How can the power plant owners who has no experience in design/retrofits make that decision?

Normally, power plant owners hire consultants or EPC’s to perform a feasibility study in order to identify possible improvements and economic viability of retrofitting machines. The consultants perform steam path audits and invite the original equipment manufacturer (OEM’s) or third parties to offer solutions. The OEM’s generally are not very keen on redesigning the existing machinery, and would offer a best compromise from their existing product lines. Third parties would reverse engineer the blades and try to restore the machine back to the original state. However, there is a  third option, which is not usually explored. The EPC’s or even power plant owners themselves can do the engineering activities and provide the owners the most appropriate solutions based on which decision can be made.

Large thermal power machine

3. Can EPC’s or engineering teams from utility companies take up this task?

There is a great opportunity for the engineering team from utilities to take on this task and help determine the best course of action for their budgets. The first step is to perform a quick study by analyzing the existing power plant and seeing if the current plant is in-line with the existing state-of-the-art power plants. The plants considered for retrofitting are typically older with 20+ years of operation. The technologies used at that time and presently have changed. The engineering team can start by performing a feasibility study to help take the right decision. Performing an existing design analysis and redesigning the existing machines can be done using the AxSTREAM® platform (even for engineering who have minimal expertise on turbomachinery).

Thanks to its advanced preliminary design module, AxSTREAM® offers versatile opportunities in retrofitting. The inverse task solver of AxSTREAM®, finds the most efficient flow path, for a number of restrictions given as a range of acceptable values. These restrictions can be in terms of specific diameter for hub, mean, or tip, in terms of number of stages, axial length, blades height or even in terms of stator and rotor angles ranges. Later during detailed design, the obtained design can be further analyzed and optimized which can be done by experts or OEM’s.  Completing these preliminary studies and designs can save considerable amounts of time and money.

Preliminary Design
AxSTREAM® Preliminary Design Solver
4. Are OEM’s the only option for such retrofits?

Not necessarily. Retrofits using third parties often offers more flexibility, while OEM’s with readily available new state-of-the-art equipment prefer to place aging equipment as it is more suitable for them from a commercial standpoint. However, with the remaining life civil structure, casing and rotor of the existing equipment, it may be wiser to retain those components and not replace the equipment with new machine. By retrofitting the existing machine, the flowpath can be upgraded to meet the state-of-the-art performance and stay competitive in terms of both performance, and reliability.

5. How is remaining life estimated?

The main factor, determining the lifetime of steam turbines, is the strength and reliability of their high temperature design components. They can fail due to excessive deformations, or burst in, as a result of long-term influence of pressure or centrifugal force. Cracking can also occur, under pure creep, or creep-fatigue conditions.  As the initially assessed lifetime of a turbine nears its end, a possibility of its further extension needs to be determined individually. This is done, based on inspection of the state of the turbine’s major design elements. Such an inspection allows estimating the actual wear of their metal, and assessing their residual lifetime, by means of non-destructive examination.  New calculations can be performed then, taking into consideration, the actual history of the turbine’s operating conditions. This includes actual duration of operation, at the diverse levels of steam temperatures and loads, as well as, the number and characteristics of start-ups, load discharges, and other types of the transients.

This information can be found in the power plant’s archives, in the form of stored computer data and recorder tapes.  The more detailed the data, the more definite and trustworthy the assessments will be. Once these calculations are performed, the remaining life can be estimated and decisions about replacing vs retrofitting can be made.

6. Can a retrofitted machine have comparable performance?

Yes. In the last few years, significant developments have been made in blading technology, sealing, materials, etc. These have resulted in highly efficient steam turbines. The principle reason for carrying out retrofitting or uprating, is not just because of aging, but also to improve plant performance. It increases efficiencies and reliability, while reducing emissions. Due to this, the plant remains competitive in the market.  Moreover, it makes perfect sense, and is even more economical, to extend life of the equipment, rather than retiring the plant.

Today, in addition to addressing the aging fleet issue, utilities are also looking for the competitive technological edge, that additional capacity and better performance through retrofitting will provide.  Other factors that enter into the economic model, are the desire for sustained performance, with minimal degradation over period of at least ten years, and the desire to extend time between major overhauls, to at least ten years.

7. What are the options for retrofitting?

Power plants can have many different retrofit needs.  Many power plants perform these retrofits to address common issues. The first option is to convert the steam turbines, for usage in a combined cycle. Another option is to get a turbine rerating, to increase capacity, or to get cycle upgrades, with change of extraction and induction conditions or parameters. Also, replacement of blading, seals etc. can be a good way to increase turbine performance. Retrofitting can be performed to obtain the highest performance, with, or without, change to inlet and outlet conditions.

Whichever retrofit you consider, an evaluation of material life for each different components, like casing, rotor etc., needs to be done before the decision is made.

Meet an Expert!

Abdul Nassar is the Managing Director at SoftInWay, with over 23 years’ of industrial, academic and research experience. He has substantial expertise in designing and retrofitting turbomachinery and currently oversees many projects related to development of turbines, compressors, and pumps. In addition, he has delivered a number of courses on steam and gas turbine design throughout Europe and Asia. The author of more than 22 technical publications, Mr. Nassar is currently leading multiple projects for SoftInWay in India.

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