News & Views, Volume 52 | Online Monitoring of HRSG with SIIQ™

Figure 1. Typical components that are monitored with the pertinent damage mechanisms in mind.


By:  Kane Riggenbach and Ben Ruchte

SI has successfully implemented a real-time, online, damage monitoring system for the Heat Recovery Steam Generators (HRSGs) at a combined cycle plant with a 3×1 configuration (3 HRSGs providing steam to a single steam turbine).  The system is configured to quantify and monitor the life limiting effects of creep and fatigue at select locations on each of the HRSGs (e.g. attemperators, headers, and drums – see Figure 1).  The brand name for this system is SIIQ™, which exists as a monitoring solution for high energy piping (HEP) systems and/or HRSG pressure-part components.  SIIQ™ utilizes off-the-shelf sensors (e.g. surface-mounted thermocouples) and existing instrumentation (e.g. thermowells, pressure taps, flow transmitters, etc.) via secure access to the data historian.  The incorporation of this data into SI’s damage accumulation algorithms generates results that are then displayed within the online monitoring module of SI’s PlantTrack™ data management system (example of the dashboard display shown in Figure 2).  

Figure 2. Example dashboard of the health status and ‘action’ date for a variety of components.

This article will be part of a series discussing items such as the background for monitoring, implementation/monitoring location selection, and future results for the 3×1 combined cycle plant.  

  • Article 1 (current):  Introduction to SIIQ™ with common locations for monitoring within HRSGs (and sections of HEP systems)
  • Article 2: Process of SIIQ™ implementation for the 3×1 facility with a discussion of the technical foundation for damage tracking
  • Article 3: Presentation of results from at least 6+ months, or another appropriate timeframe, of online monitoring data

The owner of the plant implemented the system with the desire of optimizing operations and maintenance expenses by reducing inspections or at least focusing inspections on the highest risk locations.  The system has been in place for a few months now and is continuously updating risk ranking of the equipment and ‘action’ intervals.  The ‘action’ recommended may be operational review, further analysis, or inspections.  This information is now being used to determine the optimum scope of work for the next maintenance outage based on the damage accumulated.  Like many combined cycle plants, attemperators are typically a problem area.  Through monitoring, however, it can be determined when temperature differential events occur and to what magnitude.  Armed with this information aides in root cause investigation but also, if no damage is recorded, may extend the inspection interval.

Many HRSG systems are susceptible to damage due to high temperatures and pressures as well as fluctuations and imbalances.  Attemperators have been a leading cause of damage accumulation (fatigue) through improper design/operation of the spray water stations (Figure 5).  In addition, periods of steady operation can result in accumulation of creep damage in header components (Figure 6) and unit cycling increases fatigue and creep-fatigue damage in stub/ terminal tubes and header ligaments (Figure 7).  Monitoring the damage allows equipment owners to be proactive in mitigating or avoiding further damage.

Traditionally, periodic nondestructive examinations (NDE) would be used to determine the extent of damage, but in HRSGs this can be challenging due to access restraints and, in the case of the creep strength enhanced ferritic (CSEF) materials such as Grade 91, damage detection sensitivity is somewhat limited until near end of life.  Continuous online monitoring and calculations of damage based on unit-specific finite element (FE) models (sometimes referred to as a ‘digital twin’) with live data addresses this issue.

Figure 4. Examples of damage observed by SI on attemperators.

Reliable life consumption estimates are made by applying SI’s algorithms for real-time creep and fatigue damage tracking, which use operating data, available information on material conditions, and actual component geometry.

Figure 5. Examples of creep damage observed by SI on header link pipe connections (olets).

SIIQ tracks trends in damage accumulation to intelligently guide life management decisions, such as the need for targeted inspections, or more detailed “off-line” analysis of anomalous conditions. This marks a quantum leap forward from decision making based on a schedule rather than on actual asset condition. 

Figure 6. Examples of creep/fatigue damage observed by SI at tube-to-header connections.

Figure 7. Examples of online monitoring alerts generated from SIIQ

SIIQ can be configured to provide email alerts (Figure 7) when certain absolute damage levels are reached, or when a certain damage accumulation over a defined time frame is exceeded. In this way, the system can run hands-off in the background, and notify maintenance personnel when action might be required.

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News & Views, Volume 52 | An SIIQ™ Primer


SI’s technology differs from most systems by focusing on MODELING OF DAMAGE MECHANISMS (e.g. damage initiation and subsequent rate of accumulation) affecting components that, if a failure were to occur, would impact safety and reliability.

Figure 1. Typical architecture for connection to data historian.

SIIQ™ is part of the next-generation approach for managing assets through online monitoring and diagnostic (M&D) systems. The advancements in sensor technology, signal transmission (wired or wireless), data storage, and computing power allow for ever more cost-efficient collection and analysis of ‘Big Data.’ 

The online monitoring module of SI’s PlantTrack™ data management system can retrieve operating data from OSIsoft’s PI data historian (or other historians, for that matter – see above for typical architecture).  Access to data from the historian is critical for moving beyond the stage of detecting adverse temperature events from the local surface-mounted thermocouples.  Examination of pertinent data from select tags (as seen in Figure 3 of the article beginning page 29) is reviewed by SI experts to help derive a more optimal solution to mitigate further events.  The benefit of the real-time monitoring is to detect improper operation and diagnose prior to damage progressing to failure.  Continuously monitoring the condition allows for early remediation and potentially avoiding a failure that would result in loss of unit availability and possible personnel injury.  Further, if monitoring indicates no issues are occurring, it may justify deferring a costly inspection.

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Structural Integrity Associates | News and Views, Volume 51 | High Temperature Ultrasonic Thickness Monitoring

News & Views, Volume 51 | High Temperature Ultrasonic Thickness Monitoring


By:  Jason Van Velsor and Robert Chambers

Figure 1 – Photograph of an ultrasonic thick-film array for monitoring wall-thickness over a critical area of a component.

The ability to continuously monitor component thickness at high temperatures has many benefits in the power generation industry, as well as many other industries. Most significantly, it enables condition-based inspection and maintenance, as opposed to schedule-based, which assists plant management optimizing operations and maintenance budgets and streamlining outage schedules. Furthermore, it can assist with the early identification of potential issues, which may be used to further optimize plant operations and provides ample time for contingency and repair planning.

Over the last several years, Structural Integrity has been working on the development of a real-time thickness monitoring technology that utilizes robust, unobtrusive, ultrasonic thick-film sensor technology that is enabling continuous operation at temperatures up to 800°F. Figure 1 shows a photograph of an installed ultrasonic thick-film array, illustrating the low-profile, surface-conforming nature of the sensor technology. The current version of this sensor technology has been demonstrated to operate continuously for over two years at temperatures up to 800°F, as seen in the plot in Figure 2. These sensors are now offered as part of SI’s SIIQ™ intelligent monitoring system.


ultrasonic signal amplitude

Figure 2 – A plot of ultrasonic signal amplitude over time for a sensor operating continuously at an atmospheric and component temperature of 800°F.

In addition to significant laboratory testing, the installation, performance, and longevity of Structural Integrity’s thick-film ultrasonic sensor technology has been demonstrated in actual operating power plant conditions, as seen in the photograph in Figure 3, where the sensors have been installed on multiple high-temperature piping components that are susceptible to wall thinning from erosion. In this application, the sensors are fabricated directly on the external surface of the pipe, covered with a protective coating, and then covered with the original piping insulation. Following installation, data can either be collected and transferred automatically using an installed data acquisition instrument, or a connection panel can be installed that permits users to periodically acquire data using a traditional off-the-shelf ultrasonic instrument.

Figure 4 shows two sets of ultrasonic data that were acquired approximately eight months apart at an operating power plant. The first data set was acquired at the time of sensor installation and the second data set was acquired after approximately eight months of typical cycling, with temperatures reaching up to ~500°F. Based on the observed change in the time-of-flight between the multiple backwall echoes observed in the signals, it is possible to determine that there has been approximately 0.005 inches of wall loss over the 8-month period. Accurately quantifying such as small loss in wall thickness can often provide meaningful insight into plant operations and processes, can provide an early indication of possible issues, and is only possible when using installed sensors.

Other potential applications of Structural Integrity’s ultrasonic thick-film sensor technology include the following:

  • Real-time thickness monitoring
    • Flow Accelerated Corrosion (FAC)
    • Erosion / Corrosion
  • Crack Monitoring
    • Real-time PAUT
    • Full Matrix Capture
    • Critical Area Monitoring
  • Other Applications
    • Bolt Monitoring
    • Guided Wave Monitoring

In addition to novel sensor technologies to generate data, Structural Integrity offers customizable asset integrity management solutions, as part of the SIIQ platform, such as PlantTrackª, for storing and managing critical data. Many of these solutions are able to connect with plant historians to gather additional data that feed our engineering-based analytical algorithms, which assist in converting data into actionable information regarding plant assets. These algorithms are based on decades of engineering consulting and assessment experience in the power generation industry.

Reach out to one of our NDE experts to learn more about SI’s cutting-edge thick-film UT technology.

Figure 3 – Photograph showing Structural Integrity’s thick-film ultrasonic sensor technology installed on two high-temperature piping elbows that are susceptible to thinning from erosion.


Ultrasonic waveforms acquired approximately 8 months

Figure 4 – Ultrasonic waveforms acquired approximately 8 months apart showing 0.005 inches of wall loss at the sensor location over this period.


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News & Views, Volume 49 | Attemperator Monitoring with Wireless Sensors - Risk and Cost Reduction in Real Time

News & Views, Volume 49 | Attemperator Monitoring with Wireless Sensors: Risk and Cost Reduction in Real Time

News & Views, Volume 49 | Attemperator Monitoring with Wireless Sensors - Risk and Cost Reduction in Real TimeBy: Jason Van Velsor, Matt Freeman and Ben Ruchte

Installed sensors and continuous online monitoring are revolutionizing how power plants manage assets and risk by facilitating the transformation to condition-based maintenance routines. With access to near real-time data, condition assessments, and operating trends, operators have the opportunity to safely and intelligently reduce operations and maintenance costs and outage durations, maximize component lifecycles and uptime, and improve overall operating efficiency.

But not all data is created equal and determining what to monitor, where to monitor, selecting appropriate sensors, and determining data frequency are all critical decisions that impact data value. Furthermore, sensor procurement, installation services, data historian/storage, and data analysis are often provided by separate entities, which can lead to implementation challenges and disruptions to efficient data flow.


News & View, Volume 44 | Strategic Internal Corrosion Monitoring for Gas Pipelines

News & Views, Volume 44 | Strategic Internal Corrosion Monitoring for Gas Pipelines

By:  Lance Barton and Tom Pickthall (EnhanceCo)

News & View, Volume 44 | Strategic Internal Corrosion Monitoring for Gas PipelinesA March 16, 2017, advisory bulletin (Docket No. PHMSA-2016-0131 – “Pipeline Safety: Deactivation of Threats”) gave guidance on the deactivation of pipeline threats, including the threat of internal corrosion.  On April 8, 2016, PHMSA issued a Notice of Proposed Rulemaking (NPRM) entitled “Safety of Gas Transmission and Gathering Pipelines”. Section §192.478 “Internal Corrosion Control: Onshore transmission monitoring and mitigation” of the NPRM would increase the scrutiny and requirements for monitoring and mitigating the threat of internal corrosion for the gas industry.

This bulletin and NPRM reinforce the requirements of CFR part 192-subpart O, Section 192.937, requiring gas pipeline operators to continuously assess their pipelines for the threat of internal corrosion as part of their overall integrity management program.  One of the requirements is to determine if the gas entering the system is corrosive or not corrosive.  The optimal way to prove that the gas is not corrosive is to build a thorough continuous monitoring program that considers guidance from the NPRM and the advisory bulletin.


News & View, Volume 44 | Real-Time Damage Tracking with SI Technology and GP Strategies’ EtaPro Expanding Capabilities in Condition-based Pressure-part Integrity Management

News & Views, Volume 44 | Real-Time Damage Tracking with SI Technology and GP Strategies’ EtaPro

By:  Matt Freeman

Expanding Capabilities in Condition-based Pressure-part Integrity Management

News & View, Volume 44 | Real-Time Damage Tracking with SI Technology and GP Strategies’ EtaPro Expanding Capabilities in Condition-based Pressure-part Integrity ManagementStructural Integrity and GP Strategies recently announced an agreement to bring SI’s technology for calculating, tracking, and trending life consumption of piping and boiler components to GP Strategies EtaPRO real-time monitoring platform (Press release here).  SI has a long history with creep and fatigue damage monitoring applications, most recently with the suite of applications available as part of SI’s PlantTrack platform.  The partnership with GP Strategies brings that technology to EtaPRO, which is used worldwide by power-generating organizations to monitor the performance and reliability of their generation assets.

EtaPRO users will benefit from easy integration of SI’s leading-edge Boiler and Piping Component Reliability (BPCR) modules to quantify damage to high-pressure, high-temperature components such as tubing, piping, headers, and desuperheaters. The BPCR modules track and trend accumulated creep and fatigue damage in real time using SI’s proprietary algorithms that combine actual operating data and material condition with a plant’s specific configuration. Plant operators can use the resulting life consumption estimates to guide asset management decisions, such as changes in operating procedures, targeted inspections, or off-line analysis of anomalous conditions.


News & View, Volume 43 | Attemperator Damage Prevention A Case Study Using Online Monitoring

News & Views, Volume 43 | Attemperator Damage Prevention A Case Study Using Online Monitoring

By:  Fred DeGrooth and Ulrich Woerz

News & View, Volume 43 | Attemperator Damage Prevention A Case Study Using Online MonitoringAttemperators (aka desuperheaters) are used in fossil and combined cycle plants to protect boiler/HRSG components and steam turbines from temperature transients that occur during startup or load changes. The attemperator sprays water droplets into the superheated steam to ensure that the downstream, mixed, steam temperature will not adversely affect downstream components.  While there are a number of attemperator designs and configurations (Figure 1 shows a schematic of a typical arrangement), all of them are potentially vulnerable to damage, making attemperators one of the most problematic components – particularly in combined cycle plants. If the causes of damage are not identified (and addressed) early, then cracking and steam leaks can occur leading to costly repairs and replacements. 

The frequent cycling and wide operating range of combined cycle plants impose particular demands on attemperator functionality.  Spraywater demand to the attemperator can fluctuate greatly within a startup where heat input to the boiler and steam flow are changing rapidly.  At part load operation spraywater may be required continuously to moderate steam temperatures because of high exhaust gas temperature from the combustion turbine.  Spraywater may also be demanded when duct burners are fired.