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Fossil & Combined Cycle

Maintaining plant safety and reliability with proven asset lifecycle services

Structural Integrity is uniquely positioned to help power plant owners and operators meet the lifecycle challenges that face coal or gas fired plants, and combined cycle plants. We provide engineering and condition assessment services to the fossil power industry with more than thirty years’ experience tackling some of the biggest industry challenges such as seam welded piping, dissimilar metal welds, turbine bore cracking, and creep strength enhanced ferritic steels.  Our success is rooted in an integrated, multidisciplinary approach that combines engineering analysis, advanced nondestructive examination, and materials evaluation combined with state-of-the-art digital solutions, to provide targeted and scalable asset lifecycle management solutions for fossil plant owners and operators.

Boilers

In conventional coal and gas fired fossil plants, boilers are the most likely source of for a forced outage due to the plethora of damage mechanism that affect tubes, headers and piping. Because of this, Structural Integrity has well-defined techniques to optimize reliability through condition assessment and lifecycle management of various boiler components.

Most conventional fossil-powered generating stations have hundreds of thousands of operating hours and were originally designed for baseload duty. Today, these plants operate flexibly, experiencing load cycling, low load operation, start-stop cycles, and fast ramp rates which drive damage mechanisms that may not have been seen in the past. Superimposed on this are financial and resource constraints - reduced maintenance budgets, staff reductions, and fewer, shorter outages. Modern ultrasupercritical plants must endure higher operating temperatures and are constructed from newer materials with complex metallurgy that can result in challenges such as premature creep failures and oxide exfoliation which can occur even early in life.

Our comprehensive, integrated approach to boiler lifecycle management includes risk-based activities such as cycle chemistry review, inspections, fitness-for-service and metallurgical analysis that allows owners to operate with greater reliability, availability, and safety.

Boilers

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Boilers

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Avoided Costly Superheater Replacement

A coal fired plant in the US Midwest had plans to replace their entire finishing superheater based on what they considered a long service life, even though no failures had occurred. Structural Integrity's Materials Science Center examined four tube samples, looking at the microstructure and measuring the hardness, dimensions, and internal oxide. The results were fed into our proprietary boiler tube life model and determined that the tubes had been operating at lower temperatures than expected, and therefore had a significant remaining useful life yet. The plant was able to cancel the costly replacement, resulting in significant savings.

Multi-disciplined Approach Allows Plant to Avoid Being Offline Due to DMWs

A boiler in operation more than 50 years with hundreds of dissimilar metal welds in the Superheater had experienced several failures. Structural Integrity performed a field inspection that found a few DMWs inside the furnace were at end of life and needed repair, but also noticed most of the Penthouse DMWs had questionable indications. With the plant facing the expensive prospect of extending the outage to repair all the penthouse DMWs, we examined samples in our metallurgical lab and determined those indications were due to welding flaws rather than creep damage. Analysis showed sufficient remaining life to postpone repairs until the next planned outage, allowing the plant to get back online as scheduled and avoiding the costly outage extension.

Risk-Based Inspections of Boiler Components for Planning

An aging coal plant in the US was challenged to produce a 10 year plan for capital improvements, but realized past inspections did not provide a clear picture of the remaining useful life of boiler and piping components. Structural Integrity was called to apply its health, consequence, and confidence methodology to benchmark the health of these systems. The output was a set of ‘component assessment snapshots' that provided a relative risk ranking. The highest risk components were then inspected, and their health re-assessed to determine the remaining useful life. The plant now plans to continuously update the component assessment snapshots to guide future outage and budgets.

Solving the

Challenges

facing modern ultra-supercritical plants

Boilers

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Heat Recovery Steam Generators

The Heat Recovery Steam Generator (HRSG) is a vital part of a Combined Cycle (CC) plant, capturing the exhaust heat from the combustion turbine and converting that into steam. Being sandwiched between the combustion turbine and steam turbine puts the HRSG in a unique position having to accommodate requirements imposed by both those turbines. As a result, HRSGs experience significant thermal transients, operate under wide range of loads, and experience high steam temperatures and pressures. The HRSG is commonly provides all the feedwater heating, and frequently incorporates multiple pressure evaporators. Consequently, the HRSG can experience a huge range of damage mechanisms. To compound this, many HRSGs were originally intended for base-load operation and are now required to cycle. Modern HRSGs, now feature steam temperatures in excess of 1100F and utilize a number of modern alloys, which bring their own set of challenges. Fortunately, we have solutions to help you with life management of your HRSG.

We offer HRSG operational dependability assessments, creep and fatigue evaluations, component failure root cause analysis, water chemistry evaluations and training, P91/CSEF testing and assessment, design life analyses, and many other services to ensure more reliable HRSG operation.

Heat Recovery Steam Generators

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Heat Recovery Steam Generators

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Eliminated Flow Accelerated Corrosion (FAC) in an HRSG

A combined cycle plant requested help with "an FAC problem" after a failure occurred at the top of the LP evaporator. The plant had planned to arrest the problem by raising the oxygen level, but a review by SI indicated the problem was two-phase FAC, which wouldn't be arrested by increasing oxygen. An assessment of the plant's cycle chemistry and a deterministic FAC analysis uncovered the feedwater operating at too low pH. Corrective actions including increased instrumentation, monitoring total iron in feedwater and drums, and gradually increasing the pH. The result is that the FAC has been arrested with no further failures.

Increased Cycling Rate Without Decreasing Life Expectation of Equipment

A combined cycle plant in the western US needed to increase ramp rate significantly faster than it had traditionally operated. Structural Integrity was asked to analyze the effects of faster ramp rates so reviewed the design and operational characteristics, performed calculations of fatigue and creep damage and assessed the thermal flexibility of connected sections. The attemperator system was the limiting factor, so the plant implemented a new attemperator design and is installing SI's Attemperator Damage Tracking App to be warned if any damage occurs. As a result, the plant is now able to ramp at a rate 67% faster than before.

Offering a wide variety of services to

Ensure

reliable HRSG operation

HP Drum Cracking Addressed Without Extending Outage

A 10-year-old combined cycle plant found indications/cracks at the toe of the HRSG HP drum downcomer nozzles in both of its HRSGs. With a short outage, dispositioning the damage and performing any repairs became the critical path so Structural Integrity was called to evaluate. The damage was corrosion-fatigue which, while common, still requires analysis and repair. With the recommended solution being to blend the welds to decrease the local stress concentration factor, calculations were performed to determine how much material could be safely removed. The quick turnaround allowed the repair to be done in confidence without having to extend the outage.

Heat Recovery Steam Generators

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High Energy Piping

High-energy piping (HEP) systems in power plants contain critical components that require careful maintenance and inspection. Structural Integrity offers plant owners and operators a full range of HEP services, including HEP program development based on ASME B31.1 guidance, advanced inspection methodologies, industry-leading expertise in piping engineering and materials evaluations, and critical input for run/repair/replace decisions.

Structural Integrity offers a range of services related to HEP Program development and implementation, including analyses using our Vulnerability Index (Vindex) for risk-based inspection and PlantTrack, our knowledge/data management system. These are cost-effective tools for maximizing the efficiency of lifecycle management budgets. We promote use of real-time monitoring, finite element modelling, fitness for service analysis, non-destructive examinations, and metallurgical lab analysis for a complete HEP program.

High Energy Piping

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High Energy Piping

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Development of B31.1 HEP Program

An attachment failure on the HP steam line at a combined-cycle plant raised questions on the effectiveness of the plant’s HEP life management program so Structural Integrity was called and performed a 'gap' analysis. With areas of improvement identified, SI was further engaged to enhance the program and implement a risk-based approach for inspections, analysis, and monitoring and to implement SI’s PlantTrack software for managing the program. This met ASME B31.1 requirement and addressed critical issues beyond the scope of the code. The plant now has a program that incorporates inspection, monitoring, and analysis to continually assess the condition of the HEP system.

Seam Weld Inspection and Analysis Gives Green Light for Continued Operation Following Repairs

A seam weld through wall leak on a steam line at a unit with over 250,000 operating hours was cause for concern for the plant and its owners. Structural Integrity was engaged and after a failure analysis, a stress analysis using finite element modeling, and performing NDE on the entire length of the pipe, SI was able to determine the remaining useful life of the pipe sections. Some areas were replaced while others were assigned a future inspection interval based on the lifing calculations. The unit was returned to service with the confidence that the HEP system would continue to function for many more years.

Creep-Redistributed Stress Analysis Enables Risk-Based Inspections

A large US utility wanted to reduce the cost of their High Energy Piping (HEP) inspections. Their previous approach used original design stress analysis to select inspection locations and re-inspect based on a fixed amount of time, which led to some welds inspected at a higher frequency than necessary. Structural Integrity was engaged to implement our Vindex risk-ranking of welds based on the stress (calculated using finite element modeling accounting for creep redistribution), and industry issues. Inspection scopes are now developed based on calculated risk allowing for inspections based on condition rather than simply time interval.

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Turbine Generators

Structural Integrity provides comprehensive turbine and generator inspection and life assessment services for solid rotors, rotor bores, shrunk on disks, blade attachment dovetails, turbine blades, turbine main inlet sleeves and nozzle chambers, turbine and valve casings, generator rotor dovetails, retaining rings, coupling keyways, and other critical components. Our life assessment analytical services include EPRI®-licensed SAFER-PC© rotor analysis, EPRI LPRimLife© rotor disk rim dovetail analysis, EPRI RRingLife© generator retaining ring analysis, and finite-element stress analysis of shafts, turbine disks, blades, and other components. In the case of turbine failures, our metallurgical testing laboratory also offers a full range of testing services for rotor, disk, and blade failure analyses.

Our team brings an in-depth understanding of the complexities associated with turbine and generator operation and familiarity with industry issues, including known flaw locations and orientation in similar machines. This insight and experience leads to targeted inspections that maximize resources and minimize outage times.

Turbine Generators

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Turbine Generators

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Life Extension of Existing Steam Turbine Saves Cost of Replacement

Structural Integrity provided an independent assessment of a repowered vintage steam turbine, after the OEM had recommended replacement. Component assessment included critical welds, piping, valves, turbine rotors and casings. The assessment consisted of material sampling, nondestructive inspection, and life assessment. Material sampling activities provided critical material properties. The nondestructive inspection activities identified damage that was recorded and dispositioned. For life assessment, analytical tools were applied to quantify operating stresses, predict progression rates, and develop component life estimates. The independent assessment identified 20+ years of service life for all major components, with recommended re-inspection intervals of 5-20 years, dependent on component.

Avoided Expensive and Unnecessary Turbine Repair

A 1970's vintage Generator rotor was boresonic inspected by the OEM, after which the OEM recommended a bottlebore of a portion of the rotor bore, to remove indications that the OEM determined were life-limiting for continued operation of the rotor. Due to the cost involved, the owner wanted Structural Integrity's opinion. SI re-inspected and gathered material samples from the bore then performed an analysis of the rotor using the EPRI SAFER-PC code. SI's analysis indicated the rotor could continue to operate without a bottlebore and the owner was provided with a suitable re-inspection interval.

Turbine Generators

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PlantTrack Digital Twin

Minimizing risk and maximizing reliability are the key goals for an effective asset management program. An essential part of any effective program is a system that will warehouse the associated data. Simply storing the data is not sufficient, however. The data management system must be capable of mining and analyzing the data to transform that data into information which can be used to make informed and effective decisions. Through intuitive interaction with this information, knowledge is developed that helps you to proactively manage your plant. To that end, Structural Integrity has developed our data management program, PlantTrack™.

PlantTrack is a powerful, web-based software solution with features designed specifically for the power industry. PlantTrack helps utilities to manage all types of data related to power plant design, construction, operation, specifications, inspections, maintenance and repairs, and failure investigations. In addition to offline data management, online monitoring and engineering assessment capabilities can be added, providing an integrated solution for asset health management of stationary power plant components.

PlantTrack Digital Twin

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PlantTrack Digital Twin

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Plant Streamlines HEP Inspection Planning

A rural cooperative had an active HEP life management program but was struggling to manage the information used to support the program. As a solution, Structural Integrity's HEP PlantTrack Module was implemented. Since the program has been implemented, the process of planning for outages has been significantly streamlined. With the risk ranking and past history readily available and overlaid on drawings, the engineer/planner can quickly select the locations and generate a bid-package that includes the design information in short order. This has reduced the amount of time needed for planning outage inspections and ensured the work is focused on the most appropriate locations.

Plant With CSEF Steel Proactively Monitoring for Damage

A supercritical plant in the US wanted a robust life management program for the components made from Creep Strength Enhanced Ferritic (CSEF) steel. The plant chose to implement Structural Integrity's HEP Online Damage Tracking App to provide real-time indications of how much life has been consumed at various locations. Using the app, the plant and corporate engineers view both the up-to-date life consumption and the trend of how life consumption rate has varied during different operating regimes. This information is viewed alongside inspection data to give the best assessment of overall equipment health.

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Metallurgy & Failure Analyses

Structural Integrity is an industry leader in materials testing, condition assessment, and failure analysis. The metallurgical experts at our Materials Science Center in Austin, Texas, a state-of-the-art laboratory, are well-equipped to tackle the toughest industry problems related to material performance. Our services include characterizing the condition of existing materials, identifying damage mechanisms such as thermal degradation, creep, oxidation, corrosion, and fatigue, evaluating the root cause of failures, and providing useful information for the ongoing use of components and materials that remain in operation.

Metallurgy & Failure Analyses

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Metallurgy & Failure Analyses

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Grade 91 Drain Tube Failure

An elbow from a Grade 91 high pressure steam drain line failed, resulting in a need for immediate repair/replacement. SI was asked to perform metallurgical testing to identify the failure mode and to provide information in support of the overall failure investigation. The elbow was found to have an abnormal internal shape, which was attributed to the original manufacturing process, and the failure was attributed to internal erosion along the extrados of the elbow. In addition to the localized erosion and wall thinning, incipient cracks were identified at the internal corners created by the abnormal shape, although these features were not directly related to the failure.

Results of Failure Analysis of Finned Tubes Leads to 'Seasoning' Replacements

Structural Integrity was asked to analyze multiple failures of finned, 90Cu10Ni heat exchanger tubes that occurred shortly after an in-kind replacement. The previous tubes had reportedly lasted for more than twenty years. Examination and testing revealed that the tubes failed due to ID pitting corrosion primarily at locations where surface deposits were present. Tubes of this type rely on a passivated surface layer to prevent localized corrosive attack, and this protective layer was not present on the new (replacement) tubes. In the course of analyzing and identifying the failure mechanism, SI was able to provide information to potentially guide the client in "seasoning" the new tubes in order to reduce the chance for ongoing failures.

Analysis Determines Stress Corrosion Cracking of Check Valve

Structural Integrity was asked to perform metallurgical testing of a failed, high pressure, austenitic stainless steel check valve component. The analyses performed on the submitted valve component included fractography, metallography, hardness testing, chemical composition analysis, and energy dispersive spectroscopy. The failure mode was identified as stress corrosion cracking (initiation region) with propagation via environmentally assisted cracking (corrosion fatigue). Elongated inclusions identified within the austenitic microstructure were oriented parallel to the crack and likely affected the crack propagation process. In addition, smeared metal on the inner surface of the component was associated with machining processes during the original manufacture of the valve component.

Our metallurgical experts at the

Materials Science Center

tackle the toughest industry problems related to material performance

Metallurgy & Failure Analyses

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Cycle Chemistry

Cycle chemistry in fossil and combined cycle plants plays an under-appreciated, but critical role in plant reliability. Although cycle chemistry is often out of the spotlight, water and steam cycle products and practices have a very strong influence on component damage accumulation. Because the water and steam touch virtually all components within a power plant, non-optimized practices result in unintended (and often avoidable) damage in boiler and HRSG tubes, condenser tubes and feedwater tubes and piping, and steam turbines.

Structural Integrity has knowledgeable chemists and engineers that can help clients take control of complicated plant cycle chemistry, optimize plant performance, and promote long-term savings. Services include review of cycle chemistry programs, optimization of feedwater and boiler water treatment, optimization of HRSG cycle chemistry, elimination of flow-accelerated corrosion (FAC), elimination of steam turbine phase-transition zone damage, instrumentation consulting, and plant personnel training. If a component failure occurs, Structural Integrity has extensive experience with metallurgical testing and failure analysis to identify causative factors to prevent future or recurring failures.

Cycle Chemistry

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Steam Turbine Problems Exacerbated by Cycle Chemistry Issues

During an inspection of a low pressure (LP) steam turbine, cracks were found emanating from the L-0 blade attachment areas. SI's metallurgical investigation revealed stress corrosion cracking and extensive pitting on phase transition zone (PTZ) surfaces with all the cracks initiating at pits. The chemistry assessment of the plant revealed: a) frequent condenser leaks of the brackish water above the plants shutdown limits, b) no measurements of drum carryover, and c) no shutdown protection for the LP turbine using dehumidified air. Cycle chemistry influenced failure and damage in the PTZ of the LP steam turbine include stress corrosion cracking and corrosion fatigue. Such failures are less frequent than boiler tube failures, but the damage resulting can be enormous. SI suggested that these deficiencies should be corrected and that a chemistry manual should be developed.

Eliminated Flow Accelerated Corrosion (FAC) in an HRSG

An east coast US triple-pressure combined cycle plant requested help with "an FAC problem" in the low pressure (LP) evaporator. They reported that the failure and damage was at the top of the evaporator close to the outlet header downstream of a bend in the tube and they were planning to arrest the problem by raising the oxygen level. A quick review by SI of the internal surface of the failure and other similarly positioned tubes indicated that the problem was two-phase FAC, which wouldn't be arrested by increasing oxygen. The field findings of two-phase FAC were later verified by examining tube samples at SI's Material Science Center. A two-day comprehensive assessment was conducted of the plant's cycle chemistry and a deterministic FAC analysis performed which uncovered the cause of the FAC being the feedwater operating at too low pH. Several corrective actions were taken including increased instrumentation, development of a program to monitor total iron in feedwater and drums, conducting a baseline chemistry monitoring, and gradually increasing the pH. The result is that the FAC has been arrested with no further failures.

Cycle Chemistry

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