THE EPRI CYCLE CHEMISTRY PROGRAM

Availability and reliability are of paramount importance to the overall economic performance and profitability of fossil plant unit operations. Industry statistics have demonstrated the negative impacts of improper water chemistry on unit availability and reliability, as a consequence of chemistry-related failures and associated unscheduled outages. Plant assessments have shown how deficient chemistry practices reduce the efficiency and performance of fossil plant components in contact with water and steam. Further, non-optimum chemistry conditions can shorten the useful service life of fossil plant components, requiring that replacement projects begin sooner than normally required.

In recognition of these issues, the EPRI Cycle Chemistry Program was established in 1984. Initial efforts and activities addressed the most obvious and apparent needs within the fossil plant industry. The EPRI response to these needs included:

• Improving the recognition and understanding of the impacts on fossil plant equipment caused by deficient chemistry practices.

• Critically appraising the science of water and steam chemistry, and identifying specific data needs and other deficiencies.

• Establishing industry guidelines for cycle chemistry in all varieties of fossil plant units. • Through open communications, conferences and collaborative research efforts, creating a

worldwide network of cycle chemistry specialists, allowing appraisal of the science and technology on a global basis.

• Preparing publications and other products intended to facilitate technology transfer to fossil plants, designed to simplify application of good chemistry practices.

Over the nearly 20 years the program has been in existence, the understanding of chemistry influenced damage and the effects of deposits on unit performance has increased substantially. Unfortunately, there are still cases where the causes of damage and performance degradation are not properly identified, resulting in situations where the role of chemistry goes unrecognized, or damage and performance losses not involving chemistry are incorrectly determined to be

There are also many cases where the optimum cycle chemistry has not been selected and

continually validated, or where inadequate instrumentation was responsible for allowing units to operate with gross contamination. Deposits can also impair performance and have been

experienced in many areas of the steam-water cycle. Chemistry influenced component damage in fossil plant units is widespread and includes the following mechanisms.

• Condenser tubes: stress corrosion cracking, pitting, condensate grooving.

• Condenser structure: flow-accelerated corrosion of steam side shell, supports, headers and piping.

• Deaerators: flow-accelerated corrosion, pitting, corrosion fatigue, and stress corrosion cracking.

• Feedwater heaters and associated piping: general corrosion and pitting, corrosion fatigue, flow-accelerated corrosion, stress corrosion cracking, and deposits.

• Economizer tubes: pitting, flow-accelerated corrosion and corrosion fatigue.

• Boiler tubes: hydrogen damage, acid phosphate corrosion, caustic gouging, corrosion fatigue, pitting, and deposit induced overheating.

• Superheaters and reheaters: pitting corrosion, stress corrosion cracking and corrosion fatigue. • Turbines: corrosion fatigue, erosion and corrosion, stress corrosion cracking, crevice

corrosion, pitting, and deposits (reducing efficiency and capacity).

It should be noted that some of these damage mechanisms were unknown at the inception of the program. Others were not readily distinguished from superficially similar damage mechanisms, including some that are not influenced by chemistry. In other cases, the extent of components that were vulnerable to the damage mechanism was not fully appreciated. Today, there is a very good understanding of damage mechanisms, including the influence of chemistry on many of them. Permanent solutions, based on identification of the responsible root cause and initiation of action to “kill the mechanism” are generally available. Deficient chemistry is either a root cause or significant influencing factor in all chemistry influenced damage mechanisms.

Initial interim chemistry guidelines were issued in 1986.(1) Subsequent research findings, field experience with the interim guidelines, and worldwide cycle chemistry practices justified updates and revision activities. As a result, individual guidelines for phosphate, all-volatile, and

oxygenated treatments were issued in the 1990s.(2-4) Additionally, a document describing favorable international experience with caustic treatment of drum boilers was published.(5) This report represents the second in a series of “third generation” EPRI cycle chemistry guidelines for fossil plants which will be published between 2002 and 2004. The first of these revisions was for all-volatile treatment.(6)

This guideline introduced a couple of very important new concepts into the world of fossil plant cycle chemistry:

Decoupling of the steam and boiler limits, while providing unique protection for the steam turbine and the boiler.

Clear distinction between AVT(O) and AVT(R) for oxidizing and reducing conditions for all-ferrous and mixed-metallurgy feedwater systems respectively, and

Use of ORP as a core parameter for controlling feedwater chemistry with mixed-metallurgy feedwater systems operating on AVT(R).

This second guideline is for the solid alkali phosphate and caustic treatments. As such it introduces the concept of Phosphate Continuum (PC), which replaces the two treatments (EPT and PT) in the previous phosphate guideline.(2) In 2004, the OT Guideline will be revised.

1.1.1 Program Goals and Objectives

The overall objectives of the program are to provide guidelines, technology and training materials, which together will assist in avoiding the major damage and failure mechanisms in fossil plants. By implementation of improved water chemistry, the following goals, which have been set for the EPRI program, are attainable by virtually all fossil plant units:

• No boiler tube failures influenced by cycle chemistry

• No turbine problems involving the cycle chemistry, specifically: – no corrosion fatigue in low pressure turbine components – no stress corrosion cracking in disks

– minimum deposits (no availability losses or performance concerns) • Optimized feedwater treatment to:

– eliminate serious flow-accelerated corrosion failures

– minimize iron and copper transport (each to less than 2 ppb in the feedwater) • Operational guidelines for all unit designs and operating conditions

– selected to protect boiler and turbine – customized for each unit

• Simple and reliable chemistry instrumentation and control

– minimum (“core”) levels of instrumentation for all units and treatments – continual chemistry surveillance, control and alarms for all units • Optimized procedures for unit shutdown and layup

• Eliminate unneeded chemical cleanings – appraise need to clean

– establish effective approaches and procedures

• Optimum managerial approach and support for cycle chemistry – training of staff

– benchmarking assessments of plant chemistry programs

– value and risk-based management tools for assessment of cycle chemistry improvements

• Cost effective cycle chemistry programs

There are already a number of world class utility organizations that enjoy the benefits of operating without chemistry-related boiler and turbine failures, with minimal rates of corrosion product transport, requiring few (if any) chemical cleanings, etc. Many others are working with EPRI to improve their chemistry programs and making measurable progress, with commensurate changes in unit availability and performance.

1.1.2 Program Philosophy

The overall philosophy of EPRI’s Cycle Chemistry Program for Fossil Plants is shown in Figure 1-1. Various projects, including state-of-knowledge assessments, technology appraisals, research and development programs, and relevant non-technical investigations are performed to improve the overall understanding of the science of water treatment technology and how to optimally apply it to working fossil plant units.

Figure 1-1

Overall Philosophy of EPRI’s Cycle Chemistry Program. CCIP is Cycle Chemistry Improvement Program, BTFR is Boiler Tube Failure Reduction, FAC is Flow-accelerated Corrosion, and CP is Condensate Polishing.

The results of these projects serve as critical input to development and products for use by plant personnel. As indicated in bold in the figure, the main products consist of cycle chemistry guidelines, a cycle chemistry advisor (ChemExpert), and various training programs that ensure proper technology transfer to plant staff for optimal understanding and application. By following this approach, it has been possible to continually refine the understanding of the underlying science while also making appropriate changes in the products utilized by plant personnel.

1.1.3 Key Cycle Chemistry Guidelines

In all, there are 10 essential cycle chemistry guideline documents that should be available for use by all utility personnel responsible for fossil plant cycle chemistry. Included are two operating guidelines(4,6) as well as this current document for PC and CT, four selection, process and transient guidelines,(7-10) and three cycle support guidelines.(11-13) Table 1-1 indicates the subject matter of these guideline publications, the year of publication, and the year in which publication of revised and updated guidelines is planned.

Table 1-1

Key Cycle Chemistry Guidelines*

Guideline Type/Subject Year Published Planned Updates

Operating Guidelines

•All-Volatile Treatment (AVT) 2002

•Oxygenated Treatment (OT) 1994 2004

•Phosphate Continuum (PC) and Caustic Treatment (CT)

2003

Selection, Process and Transient Guidelines

•Selection and Optimization 1994 +

•Flow-Accelerated Corrosion 1997 2004

•Cycling/Startup/Shutdown/Layup 1998 2004/2005

•Control of Copper in Fossil Plants 2000

Cycle Support Guidelines

•Makeup (Revision 1) 1999

•Chemical Cleaning (Revision 2) 2001

•Condensate Polishing 1996 2005

*See Appendix G for further information on these and other publications.

+

This report will be removed from circulation after publication of the revised OT Guidelines in 2004. The selection and optimization process in now included in each EPRI Guideline (see for example Section 2).

As shown in Figure 1-1, the chemistry guideline documents are integral to the content of the training programs and other tools developed for operations, maintenance, technical, and

management personnel. The updated guidelines are the initial conduit through which the findings of research and development efforts are transferred to the plants. However, the important new concepts introduced in the guidelines are subsequently integrated into training program materials and future versions of the expert system code (ChemExpert).

1.1.4 Program Vision and Future Plans

Utilities desiring optimum benefits from these and future cycle chemistry guidelines publications will derive the best results as follows:

• Perform initial benchmarking assessments of existing cycle chemistry and boiler tube failure reduction programs to establish worldwide rankings for each unit and to identify areas of deficiency. (EPRI’s approach to Cycle Chemistry Benchmarking is included as Appendix D.)

• Organizations desiring optimized chemistry should arrange for Boiler Tube Failure

Reduction/Cycle Chemistry Improvement Program (BTFR/CCIP) training to familiarize staff with: a) the controllable aspects of the key cycle chemistry program guidelines, b) the

importance of formalized, management supported, BTFR/CCIP Programs, and c) the importance of establishing customized chemistry treatment programs based on the