Boiler-Condition-Assessment-Guide-Final-Report-4th-Ed-jun2006

This Guideline, and the more detailed guidelines referenced in it, provide a systematic approach to help managers: • Prioritize condition assessment expenditures • Estimate the remainin

Technical Report

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EPRI Project Manager

R Tilley

Final Report, June 2006

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CITATIONS

This report was prepared by

EPRI Charlotte Office

This report describes research sponsored by the Electric Power Research Institute (EPRI)

The report is a corporate document that should be cited in the literature in the following manner:

Boiler Condition Assessment Guideline: Fourth Edition EPRI, Palo Alto, CA, 2006 1010620

REPORT SUMMARY

Because boiler component failures are the most common cause of unplanned outages in fossil steam plants, a cost-effective condition assessment program is an important element of any operation plan that considers use of demanding operating modes Condition assessment involves determining which components are most vulnerable, inspecting these components, estimating their remaining life, making a run-repair-replace decision, and choosing an optimal re-inspection interval This report provides an overview of guidelines developed by EPRI to help power plant operators cost-effectively determine extent of degradation and predict the remaining life of key boiler components

Background

EPRI published the first edition of the Boiler Condition Assessment Guideline in 1998

Subsequent updates of the Guideline further addressed a number of issues, including

considerations for safely extending outage intervals, cycling, low-NOX operation, and firing low grade and off-design fuels The current revision updates and refines the third edition, adding recent research results and guidance on boiler components not explicitly addressed in previous versions, namely deaerators, feedwater heaters, and superheater crossover piping Increased emphasis is placed on identifying and mitigating root causes before damage occurs or progresses For many fossil plants, today’s market-driven operating practices expose boiler components to conditions not anticipated in their design Competitive markets value a plant’s ability to change output quickly to match load with demand Plants must maintain high reliability and availability while using operating modes, such as load-following and nighttime turndown to very low loads, that introduce rapid and cyclic temperature and furnace chemistry changes that can exacerbate damage mechanisms Lengthened intervals between major maintenance outages provide less opportunity to inspect and repair or replace damaged components At the same time, budgetary pressure continues to force plants to do more with less

assessment programs for specific boiler components, based on boiler type, history, and modes of

operation The Guideline features the EPRI-recommended three-level approach to condition

assessment The iterative character of this approach allows plants to match the level of condition

assessment efforts with their need and value The Guideline is organized by major boiler

component It covers tubing, high-temperature headers, drums, economizer headers, piping, valves and attemperators, and feedwater heaters, deaerators, and blowdown vessels Each chapter begins with discussion the relationship between damage mechanisms and specific design details and operating conditions for the subject component A generic or component-specific “roadmap” shows the connections between recommended condition assessment activities based on EPRI’s three-level approach Tables provide key supporting information References to EPRI’s detailed guidelines are provided in each chapter and in the appendices

This Guideline, and the more detailed guidelines referenced in it, provide a systematic approach

to help managers:

• Prioritize condition assessment expenditures

• Estimate the remaining life of damaged components

• Make better run-repair-replace decisions

• Establish cost-effective maintenance re-inspection intervals

• Make unit deployment decisions that more accurately consider maintenance impacts of

different operating modes

EPRI Perspective

This Guideline provides an overview of remaining life estimation procedures used to support

maintenance decisions, preserve asset value, and guide deployment decisions It serves as an entrée to a family of EPRI reports that provide detailed background and procedures for damage

characterizations and inspection recommendations for key boiler components In addition, the Guideline identifies actions that can mitigate or prevent future damage from occurring in boiler

components This approach has been successfully demonstrated in past EPRI programs on boiler tube failures

ABSTRACT

This report (Boiler Condition Assessment Guideline) provides a concise overview of procedures

developed by EPRI to help power plant operators cost-effectively determine the extent of

degradation and remaining life of key boiler components The Guideline draws from EPRI’s

detailed area-specific guidelines, which in turn are based on extensive research findings by

EPRI, member companies, and other organizations This Guideline offers a starting point for

power plant personnel to develop condition assessment programs for specific boiler components

The Guideline is organized by major boiler component It covers tubing, high-temperature

headers, drums, economizer headers, piping, valves, attemperators, and low-temperature vessels and piping

The Guideline reviews the relationship between damage mechanisms and design details and operating conditions for each major boiler component and provides a “roadmap” of

recommended condition assessment activities based on EPRI’s three-level approach to condition assessment This approach allows plant personnel to match the level of condition assessment efforts with their need and value

Additional information on typical damage mechanisms for each component type, suitable

nondestructive evaluation techniques, life assessment software, and damage prevention is

provided to support the roadmaps

References are provided to more detailed guidelines and source material for specific

components, failure modes, and condition assessment tools and practices

ACKNOWLEDGMENTS

Rich Tilley of EPRI provided essential material for the technical updates embodied in this fourth

edition of the Boiler Condition Assessment Guideline

CONTENTS

1 OVERVIEW AND STRATEGY FOR BOILER CONDITION ASSESSMENT 1-1

1.1 Introduction 1-1 Approach 1-1 Industry Environment 1-1 1.2 Condition Assessment Fundamentals 1-2 1.3 The Condition Assessment Program Plan 1-6 1.4 Impact of Operational Trends 1-7 Cycling 1-8 Low-NOX Operation 1-8 Off-Design and Low-Grade Fuels 1-9 Considerations for Extending Outage Intervals 1-9 1.5 Evaluation and Repair Technology 1-10 NDE Inspection and Monitoring Tools 1-10 Analysis Tools 1-11 Repair Tools 1-11 1.6 Life Optimization by Design 1-12 Design for Condition Assessment 1-12 Inherently Reliable Design 1-12 1.7 Structure of this Guideline 1-13 1.8 Resources and References Overview 1-15

2 BOILER TUBING 2-1

2.1 Programmatic Approach 2-1 2.2 Condition Assessment Roadmap for Boiler Tubing 2-2 2.3 Example Case Actions for Corrosion-Fatigue 2-4

Action 6: Implement Long-Term Actions to Prevent Repeat Failures 2-8 Action 7: Determine Possible Ramifications or Ancillary Problems 2-9 2.4 Waterwall Tubing 2-10 Damage Mechanisms for Waterwall Tubing 2-10 NDE and Sample Evaluation Options for Waterwall Tubing 2-26 Analysis and Disposition for Waterwall Tubing 2-29 Preventive Actions for Waterwall Tubing 2-31 2.5 Superheater/Reheater (SH/RH) Tubing 2-37 Damage Mechanisms for SH/RH Tubing 2-38 NDE and Sample Evaluation Options for SH/RH Tubing 2-63 Analysis and Disposition for SH/RH Tubing 2-65 Preventive Actions for SH/RH Tubing 2-68 2.6 Economizer Tubing 2-75 Damage Mechanisms for Economizer Tubing 2-76 NDE and Sample Evaluation Options for Economizer Tubing 2-88 Analysis and Disposition for Economizer Tubing 2-90 Preventive Actions for Economizer Tubing 2-92 2.7 References for Boiler Tubing 2-96

3 HIGH-TEMPERATURE STEAM HEADERS 3-1

3.1 Damage Mechanisms for High-Temperature Steam Headers 3-2 3.2 Condition Assessment Roadmap for High-Temperature Headers 3-4 3.3 NDE and Sample Testing for High-Temperature Headers 3-10 3.4 Analysis and Disposition for High-Temperature Headers 3-13 Using BLESS for Creep and Fatigue Crack Growth Prediction 3-14 3.5 Preventive Actions for High-Temperature Steam Headers 3-15 3.6 References for High-Temperature Steam Headers 3-17

5 ECONOMIZER HEADERS 5-1

5.1 Damage Mechanisms for Economizer Headers 5-1 5.2 Condition Assessment Roadmap for Economizer Headers 5-4 5.3 NDE Options for Economizer Headers 5-7 5.4 Analysis and Disposition for Economizer Headers 5-10 5.5 Preventive Actions for Economizer Headers 5-12 5.6 References for Economizer Headers 5-14

6 MAIN STEAM AND HOT REHEAT PIPING 6-1

6.1 Damage Mechanisms for High-Energy Piping 6-2 6.2 Condition Assessment Roadmap for High-Energy Piping 6-5 6.3 Inspection Techniques – NDE and Sample Testing 6-10 6.4 NDE Monitoring Techniques 6-14 6.5 Analysis and Disposition for High-Energy Piping 6-15 Using BLESS for Crack Growth Prediction and Remaining Life Analysis 6-15 6.6 Preventive Actions for High-Energy Piping 6-17 6.7 References for Main Steam and Hot Reheat Piping 6-18

7 COLD REHEAT AND SUPERHEATER CROSSOVER PIPING 7-1

7.1 System Evaluation Approach for CRH and SHXO Piping 7-2 7.2 Damage Mechanisms for CRH and SHXO Piping 7-3 7.3 Application of Three-Level Condition Assessment Approach 7-6 Level I Evaluation – Pre-Outage 7-9 Level II Evaluation – On-Pipe Inspections During Outage 7-16 Level III Evaluation – Enhanced NDE and Sampling 7-19 7.4 NDE Options for CRH and SHXO Piping 7-22 7.5 Preventive Actions for CRH and SHXO Piping 7-23 7.6 References for CRH and SHXO Piping 7-24

8 ATTEMPERATORS (DESUPERHEATERS) 8-1

8.6 Preventive Actions for Attemperators and Adjacent Components 8-13 8.7 References for Attemperator Systems 8-15

9 VALVES 9-1

9.1 Damage Mechanisms Involving Valves 9-2 9.2 Condition Assessment Roadmap for Valves 9-5 9.3 NDE Options for Valve Components 9-8 9.4 Analysis and Disposition for Valves 9-10 9.5 Preventive Actions for Valves and Adjacent Components 9-12 9.6 References for Valves 9-14

10 DEAERATORS, FEEDWATER HEATERS, AND BLOWDOWN VESSELS 10-1

10.1 Damage Mechanisms for Low-Temperature Vessels and Piping 10-2 Deaerators 10-2 Feedwater Heaters 10-3 Feedwater and Attemperator Supply Piping 10-3 Drain Piping, Vent Piping, and Blowdown Vessels 10-3 Extraction Steam Piping 10-3 10.2 Roadmap for Low-Temperature Vessels and Piping 10-6 10.3 NDE Options for Low-Temperature Vessels and Piping 10-8 10.4 Analysis and Disposition for Low-Temperature Vessels and Piping 10-11 10.5 Preventive Actions for Low-Temperature Vessels and Piping 10-13 10.6 References for Low-Temperature Vessels and Piping 10-15

A DAMAGE MECHANISM ABSTRACTS A-1

Corrosion (General) A-1 Gas-Side Mechanisms A-2 Fireside Corrosion A-2 Waterwall Wastage with Low-NO Combustion A-3

Chemical Cleaning Damage A-6 Hydrogen Damage A-6 Pitting A-7 Fatigue A-8 Corrosion-fatigue A-8 Thermal Fatigue A-8 Fireside Erosion and Wear A-9 Coal Particle Erosion A-9 Fly Ash Erosion A-9 Rubbing/Fretting A-10 Sootblower Erosion A-10 Microstructural Damage A-11 Graphitization A-11 Fabrication Flaws A-12 Material Flaws A-12 Welding Flaws A-12 Overheating A-13 Creep (Long-Term Overheating) A-13 Short-Term Overheating A-13 Supercritical Waterwall Cracking A-14

B NDE AND SAMPLING METHOD ABSTRACTS B-1

B-1 NDE Techniques B-1 Acoustic Emission B-4 Eddy Current Testing B-4 EMAT (Electromagnetic Acoustic Transducer) B-4 Magnetic Particle Testing (MT) B-5 Liquid Penetrant Testing (PT) B-5 Replication B-5 Radiographic Testing (RT) B-6

C RESOURCES AND REFERENCES C-1

C-1 EPRI Software for Condition Assessment C-1 C-2 EPRI Program Support C-2 C-3 EPRI Reports C-3 Boiler Condition Assessment and Component Life Management C-3 Boiler Tube Failures C-3 Cycle Chemistry, Corrosion, and Deposition C-5 Materials, Damage Mechanisms, Welding, and Repair Techniques C-6 Nondestructive Evaluation, Sample Testing, and Analysis C-8 Operations, Maintenance, and Design Considerations C-9 C-4 Other References C-11

LIST OF FIGURES

Figure 1-1 General Procedure for Boiler Component Life Assessment 1-5 Figure 2-1 General Condition Assessment Roadmap for Identifying, Evaluating, and

Anticipating BTF 2-3 Figure 3-1 Condition Assessment Screening Questions for High-Temperature Steam

Headers 3-5 Figure 3-2 Level I Life Assessment Roadmap for Fatigue in High-Temperature Steam

Headers 3-6 Figure 3-3 Level I Life Assessment Roadmap for Creep in High-Temperature Steam

Headers 3-7 Figure 3-4 Level II Life Assessment Roadmap for High-Temperature Steam Headers 3-8 Figure 3-5 Level III Life Assessment Roadmap for High-Temperature Steam Headers 3-9 Figure 4-1 Condition Assessment Roadmap for Steam Drums and Lower Drums 4-4 Figure 5-1 Condition Assessment Roadmap for Economizer Headers 5-5 Figure 5-2 Details of Action 7 – Serviceability Evaluation for Economizer Headers 5-6 Figure 5-3 Details of Action 10 – Addressing Operating Impacts on Economizer Headers 5-7 Figure 6-1 Roadmap for Main Steam and Hot Reheat Piping System Evaluation 6-6 Figure 6-2 Level I Roadmap—Creep Life Expenditure Analysis for Seam Welds 6-7 Figure 6-3 Level II Life Assessment Roadmap—Inspection Process for Seam Welds 6-8 Figure 6-4 Level III-a Roadmap—Implications of Flaw and Cavitation Findings 6-9 Figure 6-5 Level III-b Roadmap—Determining RL through Creep Crack Growth Analysis 6-10 Figure 7-1 Roadmap for Evaluation of Cold Reheat and Superheater Crossover Piping 7-8 Figure 7-2 Details of Step 1 of the Roadmap 7-9 Figure 7-3 Details of Roadmap Steps 2A and 4A 7-11 Figure 7-4 Details of Step 4B of the Roadmap: On-Pipe Seam Weld Examination 7-17 Figure 7-5 Details of Step 5 of the Roadmap: Interpret Findings for Level II 7-18 Figure 7-6 Details of Step 6 of the Roadmap: Level III Inspections 7-19 Figure 7-7 Details of Step 7 of the Roadmap: Interpreting Level III Evaluation 7-20 Figure 8-1 Condition Assessment Roadmap for Attemperator Systems 8-7 Figure 9-1 Condition Assessment Roadmap for Valves 9-7

LIST OF TABLES

Table 1-1 Data Requirements for the Multi-Level Life Assessment Approach 1-4 Table 1-2 Key Boiler Components and Applicable Classes of Damage 1-14 Table 2-1 Action 1A – Initial Evaluation for Corrosion-Fatigue 2-4 Table 2-2 Action 1B – Steps to Follow with Corrosion-Fatigue Precursor 2-4 Table 2-3 Action 2 – Steps Confirming Corrosion-Fatigue 2-5 Table 2-4 Action 3 – Steps for Determining Root Cause of Corrosion-Fatigue 2-6 Table 2-5 Action 4 – Steps for Determining Extent of Corrosion-Fatigue 2-7 Table 2-6 Action 5 – Steps for Immediate Actions for Corrosion-Fatigue 2-8 Table 2-7 Action 6 – Long-Term Actions for Corrosion-Fatigue 2-9 Table 2-8 Action 7 – Determining Ramifications or Ancillary Problems 2-9 Table 2-9 Precursors for Waterwall Tubing Damage 2-11 Table 2-10 Screening Table for Waterwall Tubing Failures 2-20 Table 2-11 NDE Options for Waterwall Tubing 2-28 Table 2-12 Analysis and Disposition for Waterwall Tubing 2-29 Table 2-13 Preventive Actions for Waterwall Tubing Damage 2-31 Table 2-14 Precursors for Superheater and Reheater Tubing Damage 2-39 Table 2-15 Screening Table for SH/RH Tubing Failures 2-54 Table 2-16 NDE Options for SH/RH Tubing 2-64 Table 2-17 Analysis and Disposition for SH/RH Tubing 2-66 Table 2-18 Preventive Actions for SH/RH Tubing Damage 2-68 Table 2-19 Precursors for Economizer Tubing Damage 2-76 Table 2-20 Screening Table for Economizer Tubing Failures 2-85 Table 2-21 NDE Options for Economizer Tubing 2-89 Table 2-22 Analysis and Disposition for Economizer Tubing 2-90 Table 2-23 Preventive Actions for Economizer Tubing Damage 2-92 Table 3-1 Damage Mechanisms for High-Temperature Steam Headers 3-3 Table 3-2 NDE and Sample Testing Options for High-Temperature Steam Headers 3-11 Table 3-3 Analysis and Disposition for High-Temperature Steam Headers 3-14

Table 5-2 NDE and Sample Testing Options for Economizer Headers 5-8 Table 5-3 Analysis and Disposition for Economizer Headers 5-10 Table 5-4 Preventive Actions for Economizer Headers 5-13 Table 6-1 Damage Mechanisms for Main Steam and Hot Reheat Piping 6-3 Table 6-2 NDE Options for Main Steam and Hot Reheat Piping 6-11 Table 6-3 Invasive Testing Options for Main Steam and Hot Reheat Piping 6-13 Table 6-4 Analysis and Disposition for Main Steam and Hot Reheat Piping 6-16 Table 6-5 Preventive Action for Main Steam and Hot Reheat Piping 6-17 Table 7-1 Common Damage Mechanisms for Cold Reheat Piping 7-4 Table 7-2 Common Damage Mechanisms for Superheater Crossover Piping 7-4 Table 7-3 Typical Damage Sites in CRH and SHXO Piping Systems 7-5 Table 7-4 Inspection Recommendations Based on Risk Self-Assessment Findings 7-12 Table 7-5 Analysis and Disposition for Thick-Walled Steam Piping 7-21 Table 7-6 NDE Options for Thick-Walled Steam Piping 7-22 Table 7-7 Preventive Actions for Thick-Walled Steam Piping 7-24 Table 8-1 Damage Mechanisms for Attemperator Systems 8-4 Table 8-2 NDE Options for Attemperator Systems 8-8 Table 8-3 Analysis and Disposition for Spray Attemperator Systems 8-11 Table 8-4 Preventive Actions for Attemperator Systems 8-13 Table 9-1 Damage Mechanisms for Valves 9-3 Table 9-2 NDE Options for Valves 9-9 Table 9-3 Analysis and Disposition for Valves 9-11 Table 9-4 Preventive Actions for Valves 9-13 Table 10-1 Damage Mechanisms for Low-Temperature Vessels and Piping 10-4 Table 10-2 NDE Options for Low-Temperature Vessels and Piping 10-8 Table 10-3 Analysis and Disposition for Low-Temperature Vessels and Piping 10-11 Table 10-4 Preventive Actions for Low-Temperature Vessels and Piping 10-13 Table B-1 NDE Methods Overview B-1 Table B-2 Sample Evaluation Methods Overview B-8

OVERVIEW AND STRATEGY FOR BOILER CONDITION ASSESSMENT

Boiler components command a major portion of maintenance activities and produce a majority

of operational outages for coal and other fossil fuel power plants For effective management of unit operations and maintenance, plant personnel must have trustworthy information on key

components This Boiler Condition Assessment Guideline was developed to aid utilities in

preparing and maintaining such information for coal-fired units Many sections are also relevant for oil and gas units

Approach

This Guideline is designed as a concise introduction and overview of boiler condition

assessment It summarizes information derived largely from the library of EPRI-sponsored work

on condition assessment of boiler components and impacts of operating strategies such as

cycling This material is generally presented in a streamlined format The intent is to quickly focus efforts on the required activities, and corresponding tools available, to perform boiler component condition assessments Key references are listed in each chapter, and a

comprehensive list of references is provided in Appendix C

Since its first publication, in 1998, the Boiler Condition Assessment Guideline has been updated

on a periodic basis to respond to industry trends, incorporate new additions to the EPRI

knowledge base, and refine the presentation to help make the reader better aware of available tools For this fourth edition, significant additions have been made to reflect knowledge gained from new studies and guidelines addressing “Flow-Accelerated Corrosion,” “Reliability Under Cycling Operation,” and “Cold Reheat Piping.” Other additions include new nondestructive evaluation (NDE) techniques and new repair techniques To further extend the reach of “lessons learned” in the work that led up to this guideline, candidate preventive actions include principles

of “design for condition assessment” and “inherently reliable design.”

Industry Environment

plant operators have implemented comprehensive condition assessment programs In many instances, programs are enhanced with continuous condition monitoring for high-risk

components

In practice, these challenges require the plant to maintain high reliability and availability,

avoiding forced outages and extending major maintenance outage intervals, while operating generating units in load-following, two-shifting, and other cyclic modes Extension of outage intervals allows fewer opportunities to inspect and repair (or replace) damaged components This can translate into greater risk of component failure Similarly, rapid load changes and cyclic operation can exacerbate certain damage mechanisms, such as fatigue and corrosion For many plants, maintenance challenges are greater at a time when staff and budgets have been reduced Plants must, increasingly, “do more with less.”

Reliable condition assessments are crucial for managing units dedicated to load following, two shifting, and other cycling modes Knowledge of component condition and expected remaining life is similarly critical to success when efforts are made to extend major maintenance outage intervals to reduce costs and improve availability

When units designed for baseload operation are cycled, they often experience accelerated

component degradation The large number of startups and rapid load changes that cycling entails add substantial thermal stress to many boiler components, thereby contributing to fatigue

Cycling also makes water chemistry more difficult to control, promoting corrosion and other material degradation phenomena This situation is aggravated when condensation occurs in steam piping during startup, shutdown, and reduced load conditions

Many baseloaded and cycled units now operate in off-design combustion modes to limit NOXformation This may entail low excess air, rich or lean recalibration of individual burners or burner elevations, shut-off of selected burners, recirculation of a flue gas slipstream back to the combustion zone, and/or increased overfire air These operating modes often create local

oxygen-starved areas (i.e., reducing conditions), which can dramatically accelerate corrosion, especially when alternating with oxidizing conditions during cyclic operation

Finally, in response to economic factors and emissions control mandates, many units now fire off-design fuels and/or switch fuels more frequently This changes furnace heat absorption profiles, slag rates and composition, fly ash properties, and more

the end of their respective topical chapter and in Appendix C

In the chapters that follow, specific processes are identified for acquiring and evaluating these three pieces of data for key boiler components These processes are organized around a

condition assessment roadmap that:

• develops background information on component design and operational history

• estimates risk of component damage based on available knowledge

• provides decision points with follow-up actions based on assessment of risk

• suggests increasingly stringent evaluation techniques to confirm or reduce the known level of

risk

Background, information, which may be gathered and used for a one-time assessment or as part

of a comprehensive condition management program, includes the following:

• design and fabrication records for the component

• operating and maintenance history for the plant and component

• operating and maintenance history for similar components at plants of similar design

• the operating plan (including desired service life) for the component and the plant

The condition assessment process develops additional information through:

• nondestructive evaluation tools

• material removal and testing

• stress analysis

• fracture mechanics analysis

• other software tools for predicting damage progression and risk

Damage prevention options are included as a subset of the damage accumulation category Generally, the most cost-effective life management approach entails addressing the root cause(s)

of component damage and eliminating the vulnerability to future damage Much of EPRI’s successful program to reduce boiler tube failures (BTF) is based on this approach and is

described in Chapter 2, “Boiler Tubing.”

The condition assessment approach recommended by EPRI uses a multi-level structure in which component evaluations become progressively more detailed as needed (see Figure 1-1)

This iterative approach allows engineers to balance the costs of obtaining additional data against the value of those data Table 1-1 illustrates the increasing levels of sophistication required in

progressing through Level I, II, and III life assessments In the chapters that follow, specific activities, such as inspections, are categorized as Level II or Level III A Level III

component-assessment is typically recommended when the highest confidence in the RL of a particular

component is required

Table 1-1

Data Requirements for the Multi-Level Life Assessment Approach

Failure History Plant records Plant Records Plant Records

Plant Records, EPRI Guidelines and Reports, EPRI CA Database, Peer Contacts s

Plant Records, EPRI Guidelines and Reports, EPRI CA Database, Peer Contacts

Dimensions Design or Nominal Measured or Nominal Measured

Condition Records or Nominal Inspection Detailed Inspection

Temperature and

Pressure Design or operational

Operational or

Stresses Design or operational Simple Calculation Refined Analysis

Material Samples

More rigorous assessment -Æ

More accurate operation data required -Æ

More accurate estimate of equipment RL -Æ

YES Is key information missing?

and/or re-inspection period

or install condition monitoring system

Experience with the successful EPRI BTF reduction program indicates that a successful

condition assessment program requires several key elements beyond the technical guidance provided in this guideline and the referenced EPRI reports These elements include:

• management commitment of support

• cross-functional teaming of maintenance, operations, and engineering personnel

• attention to long-term solutions to the root cause(s) of problems

• training

• documentation of results and periodic review

The condition assessment program should capture as much data as practical on the unit’s

operating history Of particular importance are records of operation at conditions in excess of design values Data gathered should include:

• unit operating hours

• number of starts, by type (cold, warm, hot), and applicable ramp rates

• steamside “indicators,” such as steam temperature, pressure, pressure drop, mass flow, and

attemperator spray cycle timing, mass flow rate, and temperatures

• gas-side indicators, such as boiler furnace and convective section exit temperatures (with

detailed temperature distribution, if available), mass flow, excess oxygen level, economizer outlet temperature, draft loss, and soot-blowing timing and process

• water chemistry control indicators (e.g., iron and copper levels, pH, oxygen)

• detailed records of excursion incidents such as over-temperature, water hammer, etc

• relationships (concurrence) between the various data values

Boiler condition assessment efforts should produce a document that fully captures the condition assessment results and provides a clear basis for O&M decision-making The document should include the following types of information:

• date the assessment was performed

• summary of assessment activities, such as inspections, material tests, and results

• estimate of component RL, summary of basis, and reference to calculations and other

supporting documents for the estimate and basis

Some plant owners/managers augment condition assessment programs with investment in

condition monitoring systems, such as arrays of acoustic emission receptors that can be used to screen for creep and fatigue damage locations in high-energy piping and high-temperature

headers Use of these systems can decrease the amount of corrective maintenance and associated cost and downtime By providing more confidence when balancing equipment failure risks with economic goals, real-time condition information helps extend outage intervals while reducing the number or frequency of time-based preventive maintenance tasks

Successful condition monitoring and component life management require the appointment of a recognized program coordinator and the development of guidelines and procedures that provide clear programmatic direction and indicate the persons responsible for key elements Boiler condition monitoring is a data-intensive activity that goes beyond such traditional predictive maintenance activities as vibration analysis, lube oil analysis, and infrared thermography

Additional on-line sensors and data acquisition equipment may be needed New or refined NDE methods will also be beneficial

Collected data can be analyzed by a growing range of software models, with varying degrees of sophistication At the high end, three-dimensional finite element analysis models, such as

EPRI’s Creep-FatiguePro, can be queried to produce up-to-date component damage

accumulation and remaining life estimates (after calibration using historic condition and

operating data and linkage to current operating data) Simplified software models, such as

EPRI’s Boiler Life Evaluation and Simulation System (BLESS) and Tube Life Probability

(TULIP) can often produce suitable results without the expense of creating geometrically

accurate finite element representations of key components

Company and plant engineers must decide, on a case-by-case basis, the appropriate degree and sophistication of condition monitoring required to optimize both costs and risks within a

component, a boiler system, a generation unit, or a family of similar units Depending on the rate of damage accumulation (and the level of existing damage), options include:

• periodic monitoring of components with off-line analysis to determine whether the rate of

damage has changed significantly from historic trends

• continuous monitoring plus automated off-line analysis

• continuous monitoring with automated off-line analysis and on-line “real-time”

display/alarming of component stress and accumulated damage

(and drained available capital budgets)

Comprehensive boiler condition assessment programs have helped many companies respond to the challenge, with their units performing at levels of availability beyond those once thought possible Still, these programs cannot completely negate the challenges to boiler component reliability and longevity imposed by age and by operating regimes including cycling, low-NOXcombustion, and the use of off-design or low-grade fuels Despite the appearance of success in

“doing more with less,” the rates of material damage accumulation and the subsequent failure risk have, in fact, increased in many units Under these conditions, condition assessment and component life management programs become even more crucial to boiler component reliability, plant longevity, and economic objectives

Cycling

Cycling can affect virtually all boiler components In particular, cycling promotes several key problems: (1) water/steamside chemical attack, because control of boiler cycle water chemistry is markedly more difficult, (2) thermal-stress-induced fatigue of thick-walled components, (3) creep-fatigue interactions, in which adverse synergies accelerate material damage, and (4)

corrosion-fatigue interactions Condensation and condensate pooling during cycling operation also increase risks of corrosion, corrosion/fatigue interactions and water hammer

To help limit damage due to cycling, many power companies are investing in better NDE

equipment, conducting more comprehensive inspections, and applying damage accumulation and life prediction models to better estimate failure probabilities In addition, some companies are supplementing condition assessment activities with condition monitoring systems

Combustion modifications to decrease NOX formation almost invariably affect the types and rates of damage experienced by boiler components, especially tubing Established corrective measures can also produce secondary problems Damage mechanisms of particular concern when using low- NOX burners or low excess air stoichiometries include:

• waterwall fireside corrosion and erosion

• alternation between reducing and oxidizing chemistry during cyclic operation, which has

been recognized as a major factor in waterwall wastage

Many units now fire fuels that differ from their original design coal or oil for reasons of SO2compliance and economics To take advantage of spot markets, a single unit also may now burn

a much broader range of fuels

Furnace dimensions and size, location, and operating temperature of different heat exchange surfaces are typically optimized for the combustion, slagging and ash properties of a single fuel Changes in slagging and fouling patterns will in turn affect the relative heat absorption rates of the waterwall and convective passes In oil-fired units, magnesium-based additives can coat waterwalls and boost convective pass temperatures

These relative heat absorption rates are also influenced by flame pattern and radiance differences between fuels Increased superheater and reheater temperatures accelerate creep damage,

increase demands on attemperators, and make tubing more susceptible to erosion and corrosion Corrosion and erosion in these and other components is also influenced by ash chemistry, fusion temperature, and abrasivity

Other observations related to specific coal properties include:

• the abrasive content in coals high in silica and iron pyrite causes higher erosion

• high-potassium and especially high-sodium content, including the contribution from thawing

salts, increases fouling in convective passes and promote corrosion

• low-sulfur coal with high chloride content (>0.3% Cl) can accelerate corrosion in boilers that

use overfire air for NOX control

• heavily slagging coals increase the need for sootblowing, which can accelerate erosion

• Powder River Basin coal tends to form more tenacious, insulating waterwall deposits and

sticky convective pass deposits than eastern bituminous coal

Considerations for Extending Outage Intervals

Many operators have improved unit availability and decreased maintenance costs by extending the intervals between major boiler inspection and maintenance outages They have achieved this, without compromising safety, through systematic efforts to collect component-specific data and operating history data Improved data and analysis reduces “material condition uncertainty” and thereby permits use of less conservative assumptions than are required when using

“component/material class” (statistical average) information Such efforts usually entail added investment in NDE and other techniques to estimate remaining life and failure probabilities This incremental expense can often be justified by the premiums earned through assured

availability at critical times in competitive power markets

system, data from other components can sometimes be used for analyzing the operating history

of target components

New approaches to unit operation and availability have recognized that some cracks can be tolerated, depending on location, size and other factors Use of improved data collection and analysis tools is key to making confident run/repair/replace decisions

The heart of a boiler condition assessment program is the assortment of inspection and analysis tools that are used to determine the condition of boiler components, determine root causes if damage is detected, and predict how long they can safely operate (i.e., determine remaining life)

As operating trends impose new challenges, technology development is increasing the selection

of tools available to address them Run/repair/replace decisions are also influenced by new metallurgical choices and welding technologies that can extend component life and shorten maintenance outages

NDE Inspection and Monitoring Tools

Conventional ultrasonic, radiographic, dye, and magnetic particle techniques are well

established, but inadequate for the quality NDE required for high levels of confidence regarding the condition of boiler components Although many gaps remain, many new technologies are enabling faster and/or higher resolution location and characterization of flaws New inspection tools include:

• advanced ultrasonic techniques, some capable of identifying creep and fatigue damage prior

to the formation of cracks (i.e., “pre-crack damage”)

• non-intrusive tools for flow and temperature measurement

• smart pigs and robotic crawlers that permit faster inspections in locations unsafe or

inconvenient for human access

• robotic welding machines that improve weld quality and speed for shop and field repairs

ranging from boiler tube patches to high-temperature header spool replacement

• digital radiographic techniques that increase resolution while reducing source strength and

corresponding exclusion zones

Analysis Tools

EPRI and other organizations are continually working to develop new types of Level III

condition assessment and remaining life analyses tools to support the approaches presented in this guideline Available tools (described in more detail in Appendix C) include:

• EPRI’s Boiler Life Evaluation and Simulation System (BLESS) software for analyzing

cracks and predicting the rate of crack growth

• EPRI’s Boiler Overhaul Interval Optimization tool for prioritizing equipment screening and

repairs

• EPRI’s Creep-FatiguePro software for analyzing and predicting damage accumulation due to

creep and fatigue interactions in high-temperature thick-walled components

• EPRI’s Dissimilar Metal Weld Prediction of Damage In-Service (DMW-PODIS) software

for estimating damage accumulation and remaining life in dissimilar metal welds in

superheaters and reheaters

• EPRI’s Tube Life Probability (TULIP) software for estimating the remaining life of

superheater/reheater tubing

• accelerated creep and fatigue tests that use miniature specimens to gauge remaining life

• tools for quantifying the ability of weld repairs to provide adequate creep strength to safely

extend component life

• use of “small punch” tests to gauge a thick-walled component’s fracture appearance

transition temperature

• tools for determining the kinetics of the fine grain and coarse grain portions of weld

heat-affected zones (HAZ) and their role in Type IV cavity formation and growth

The specialized tools developed for boiler condition assessment are supplemented or enabled by advanced finite element analysis tools that decrease the cost and increase the speed and accuracy

of static and dynamic modeling of thermal, mechanical and fluid flow phenomena

1.6 Life Optimization by Design

The effectiveness of a boiler condition assessment program, in advancing the safe, reliable and economic life of the facility, is significantly affected by decisions made during the design and construction of the facility Existing plants can benefit from updated understanding of good design principles by implementing modifications incorporating “design for condition

assessment” and “inherently reliable design.” Such modifications may be pursued reactively, when damage accumulation or failure forces replacement, or proactively, when modification is justified by safety or economic benefits

Design for Condition Assessment

In many cases, the confidence level provided by condition assessment findings is limited by the ability to obtain complete and timely inspections of at-risk components “Design for Condition Assessment” adjusts design parameters and incorporates design details to improve on-line monitoring and to improve inspection access during outages For example, inspection access may be improved by:

• increasing the number of RT test ports and making them large enough to accept video probes

• incorporating inspection windows during the installation or reinstallation of insulation

• using removable panels instead of cast-in-place refractory

• considering NDE probe size when selecting tube spacing

• ensuring that pipe routing and support spacing do not hamper inspection access

On-line monitoring may be improved by:

• installing thermocouples and high-temperature strain gages to provide better information on

thermal and stress transients during cycling

• installing permanent wave guides for acoustic emissions monitoring

• installing travel indicators and load cells or strain gages on key supports

• installing sight windows for laser and thermographic monitoring

• installing access ports and allowing space on the cold side of waterwalls for NDE probes

mounted on robotic arms or crawlers

• recirculation pumps and piping as well as low flow warm-up bypasses around main valves

that help avoid thermal shock and thermal stress during startup and shutdown

• well located and properly sized drains for steam piping and reheater/superheater passes

• erosion resistant severe duty valves, with multi-stage pressure drop and tight shut-off, to

provide long-term accurate throttling and prevent leakage than can lead to pooling, corrosion, thermal shock, and water/steam hammer

• continuously adjustable flow control for spray attemperators, to allow gradual temperature

adjustment and prevent thermal shock and fatigue

• pipe routing and support design with adequate leeway to ensure reliable condensate drainage

for the life of the facility

• condenser and feedwater heater metallurgy that allows use of oxygenated treatment and

avoids flow-accelerated corrosion

This guideline contains a series of chapters that address damage mechanisms and provide

condition assessment roadmaps for specific types of major boiler component Table 1-2 provides

a map of boiler components and their major in-service damage mechanisms

A series of appendices provide more detailed descriptions of damage mechanisms and

assessment tools, and provide listings of EPRI publications and other reference material

The component-specific chapters each begin with discussion of component and system

characteristics, damage mechanisms, damage precursors, and other conditions relevant to that type of component Key information is tabulated for quick reference This background material

is followed by presentation of a generic or component-specific “roadmap” of recommended condition assessment activities for the class of components These roadmaps have been

developed to reflect damage mechanisms and degradation timeframes as the key drivers to performing specific condition assessment activities

For each component, additional information on NDE techniques, life assessment calculations, and damage prevention is introduced, briefly, and presented in tabular form This supporting information is linked to the component life assessment roadmap, with Level I, II, and III

designations provided as appropriate

Key Boiler Components and Applicable Classes of Damage

Creep Fatigue

Corro-sion

Internal Erosion / FAC

External Erosion / Corr’n

Thermal / Mech’l Deform’n

each chapter Appendix A provides descriptions of individual damage mechanisms while

Appendix B provides descriptions of NDE techniques Appendix C provides an expanded list of references and other resources

EPRI has produced a number of comprehensive technical reports to assist member companies with implementing comprehensive condition assessment programs and performing equipment-specific activities A series of “guideline” reports assembles and organizes information from numerous EPRI reports and other references into a single document addressing a particular group

of related boiler components Key reports include:

Boiler Tube Failures: Theory and Practice EPRI: 1996 Report TR-105261, Vols 1-3

Damage to Power Plants Due to Cycling EPRI: 2001 Report 1001507

Guidelines for the Evaluation of Cold Reheat Piping EPRI: 2005 Report 1009863

Guidelines for the Evaluation of Seam-Welded High-Energy Piping EPRI: 2003 Report

1004329

Guidelines for Controlling Flow-Accelerated Corrosion in Fossil and Combined Cycle Plants,

EPRI: 2005 Report 1008082

Header and Drum Damage: Theory and Practice: Volume 1: Information Common to All

Damage Types EPRI 2003 Report 1004313-V1

Header and Drum Damage: Theory and Practice: Volume 2: Mechanisms EPRI: 2003 Report

1004313-V2

Impact of Operating Factors on Boiler Availability EPRI: 2000 Report 1000560

Inherently Reliable Boiler Component Design EPRI: 2003 Report 1004324

Life Assessment of Boiler Pressure Parts EPRI: 2000 Report 1000311

NDE Guidelines for Fossil Power Plants EPRI: 1997 Report TR-108450 and CD-ROM

CD-108450

BOILER TUBING

Boiler tube failure (BTF) continues to be the most frequent cause of fossil plant forced outages The large variety of damage mechanisms seen with boiler tubing corresponds to a similarly large variety of relatively harsh operating conditions to which different tubing is exposed and therefore must be designed Similarly, the sheer number of welds and separate pieces of tubing, and the challenges in selecting materials and configuration, present ample opportunity for vulnerabilities related to flaws in design and fabrication

This chapter emphasizes processes for determining boiler tube damage mechanisms and their root causes, and for implementing long-term, corrective actions to minimize or prevent future damage The material in the following sections highlights the scope of effort and required

actions for determining the condition of boiler tubing components The tables on nondestructive evaluation options update a key area in which technology continues to evolve

Recommendations on when to use which “level” of NDE techniques aim to help a

cross-functional team execute a BTF reduction program cost-effectively

Formal implementation of the EPRI program on BTF reduction is recommended for all fossil steam plant operators as part of their boiler condition assessment activities Experience with this program has shown that much of the damage sustained by boiler tubing is avoidable Utilities participating in the BTF program have achieved significant reductions in BTF and corresponding increases in unit availability and average boiler tube life

EPRI’s three-volume publication, Boiler Tube Failures: Theory and Practice (1996, Report

TR-105261) still serves as the comprehensive reference for implementing a BTF reduction program More recent work, with benchmarking tools to help utilities evaluate the strength of their

programs, shows that many facilities can make great gains with better use of current tools Even the best performers have not yet reduced BTF to a non-significant level Toward this end, EPRI and others are continuing work to develop better techniques to detect damage and to implement durable repairs in locations that are subject to harsh conditions and/or difficult access

As noted, a comprehensive BTF reduction program is the key to addressing the most significant cause of lost production in most power plants To be carried out effectively, this programmatic effort must:

condition assessment program

• include action plans for addressing root causes of repeat failures

Other features of the most successful programs generally include:

• formalized goals and objectives for the BTF failure reduction program

• record keeping and analysis to determine the equivalent availability loss (EAL) due to BTF

• a ranking of damage mechanisms within plants and systems by EAL, lost MWh, or costs

• proactive plans to inspect superheater (SH) and reheater (RH) tubes and perform remaining

creep life calculations prior to the first failure incidents

• formalized action plans to address damaged tubing and BTF forced outages, including

assessment of neighboring and similarly positioned tubing

• maximizing use of opportunities for additional inspection, especially during BTF forced

outages and by extending outages at times of low-demand/revenue

The EPRI approach to BTF reduction is summarized in the roadmap of actions shown in Figure 2-1 The process begins with identification of actual tube failure mechanisms of concern

EPRI has cataloged 33 separate damage mechanisms Each damage mechanism can be related to factors such as materials, design, fuel, NOX controls, and plant operations and maintenance practices Each boiler tube section in any given power plant will generally only be susceptible to

a few of these mechanisms

The EPRI BTF reduction program recognizes this situation and advocates that a cross-functional team, composed of representatives from maintenance, operations, and engineering, jointly

undertake the steps in the Figure 2-1 roadmap

The process shown in Figure 2-1 is illustrated by an example case on corrosion-fatigue damage

in waterwall tubing in Section 2.3 Tables 2-1 through 2-8 provide the details for fatigue corresponding to the action steps in the general roadmap As noted, the focus is root cause identification and implementation of damage-limiting or damage-preventing actions

corrosion-Sections 2.4 through 2.6 are arranged by major boiler tube section: waterwalls, superheaters and