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

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

A CASE STUDY ON IMPLEMENTATION AT A 3X1 COMBINED CYCLE FACILITY (ARTICLE 1 OF 3) 

By:  Kane Riggenbauch 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

BASIS FOR MONITORING
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.

HRSG DAMAGE TRACKING
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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Structural Integrity Associates | News and Views, Volume 51 | Pitting Corrosion in Conventional Fossil Boilers and Combined Cycle:HRSGs

News & Views, Volume 51 | Materials Lab Featured Damage Mechanism

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PITTING CORROSION IN CONVENTIONAL FOSSIL BOILERS AND COMBINED CYCLE/HRSGS

By:  Wendy Weiss

Pitting is a localized corrosion phenomenon in which a relatively small loss of metal can result in the catastrophic failure of a tube. Pitting can also be the precursor to other damage mechanisms, including corrosion fatigue and stress corrosion cracking. Pits often are small and may be filled with corrosion products or oxide, so that identification of the severity of pitting attack by visual examination can be difficult. 

Figure 1. Severe pitting in a tube from a package boiler

Mechanism 

Pitting is a localized corrosion attack involving dissolution of the tube metal surface in a small and well-defined area. Pitting corrosion can occur in any component in contact with water under stagnant oxygenated conditions. Pitting in economizer tubing is typically the result of poor shutdown practices that allow contact with highly-oxygenated, stagnant water. Pitting also may occur in waterwall tubing as a result of acidic attack stemming from an unsatisfactory chemical cleaning or acidic contamination. 

Pits that are associated with low pH conditions tend to be numerous and spaced fairly close together. The pits tend to be deep-walled compared to the length of the defect. A breakdown of the passive metal surface initiates the pitting process under stagnant oxygenated conditions. A large potential difference develops between the small area of the initiated active pit (anode) and the passive area around the pit (cathode). The pit will grow in the presence of a concentrated salt or acidic species. The metal ion salt (M+A-) combines with water and forms a metal hydroxide and a corresponding free acid (e.g., hydrochloric acid when chloride is present). Oxygen reduction at the cathode suppresses the corrosion around the edges of the pit, but inside the pit the rate of attack increases as the local environment within the pit becomes more acidic. In the event that the surfaces along the walls of the pit are not repassivated, the rate of pit growth will continue to increase since the reaction is no longer governed by the bulk fluid environment. Pitting is frequently encountered in stagnant conditions that allow the site initiation and concentration, allowing the attack to continue. 

The most common cause of pitting in steam touched tubing results from oxygen rich stagnant condensate formed during shutdown. Forced cooling and / or improper draining and venting of assemblies may result in the presence of excess moisture. The interface between the liquid and air is the area of highest susceptibility. Pitting can also be accelerated if conditions allow deposition of salts such as sodium sulfate that combine with moisture during shutdown. Volatile carryover is a function of drum pressure, while mechanical carryover can increase when operating with a high drum level or holes in the drum separators. Pitting due to the effects of sodium sulfate may occur in the reheater sections of conventional and HRSG units because the sulfate is less soluble and deposits on the internal surfaces. During shutdowns the moisture that forms then is more acidic. 

Figure 2. Pitting on the ID surface of a waterwall tube

Typical Locations

In conventional units, pitting occurs in areas where condensate can form and remain as liquid during shutdown if the assemblies are not properly vented, drained, or flushed out with air or inert gas. These areas include horizontal economizer tubes and at the bottom of pendant bends or at low points in sagging horizontal tubes in steam touched tubes. 

In HRSGs, damage occurs on surfaces of any component that is intentionally maintained wet during idle periods or is subject to either water retention due to incomplete draining or condensation during idle periods. 

Attack from improper chemical cleaning activities is typically intensified at weld heat affected zones or where deposits may have survived the cleaning. 

Features

Pits often are small in size and may be filled with corrosion products or oxide, so that identification of the severity of pitting attack by visual examination can be difficult. 

Damage to affected surfaces tends to be deep relative to pit width, such that the aspect ratio is a distinguishing feature. 

Root Causes

Figure 3. Pitting on the ID surface of an economizer tube

The primary factor that promotes pitting in boiler tubing is related to poor shutdown practices that allow the formation and persistence of stagnant, oxygenated water with no protective environment. Confirming the presence of stagnant water includes: 

  1. analysis of the corrosion products in and around the pit; 
  2. tube sampling in affected areas to determine the presence of localized corrosion; and 
  3. evaluation of shutdown procedures to verify that conditions promoting stagnant water exist. 

Carryover of sodium sulfate and deposition in the reheater may result in the formation of acidic solutions during unprotected shutdown and can result in pitting attack. Similarly flyash may be pulled into reheater tubing under vacuum and form an acidic environment.

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Structural Integrity Associates | Wireless Sensor Node Featured Image

High Energy Piping Monitoring

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High Energy Piping Monitoring

SI moves beyond the pilot application of a High Energy Piping monitoring program designed to reduce operational risk and optimize maintenance activities.

Structural Integrity Associates | Wireless Sensor Node 6.17ESI has successfully implemented the initial application of an integrated monitoring solution that provides insight into damage evolution and operational risk using real-time data and automated engineering intelligence. This solution will assist in the optimization of maintenance activities and downtime, helping utilities get the most out of their O&M budgets.  “This is a decisive step toward a more modern asset management approach that will lower O&M cost for our clients,” said Steve Gressler, Vice President, SI Energy Services Group, a division of Structural Integrity Associates, Inc. (SI) focused on power plant asset integrity.

Informed by decades of material performance knowledge, the SI team has refined a proprietary risk-ranking method to optimize sensor placement and deliver a high-value monitoring platform supported by the PlantTrack™ asset data management platform.  The integration of monitoring information into the platform further enhances equipment asset integrity data to simplify stakeholder decision making.   The SI solution incorporates various sensors working on a distributed wireless network to feed real-time data to SI’s state-of-the-art algorithms and is also capable of integrating with existing plant data historians to pull in other valuable operational data. The outcome is a cost-effective damage monitoring approach to focus resources and the timing of comprehensive field inspections.

“The architecture enables asset managers to obtain real-time feedback, alerts, and trends that clearly link actual operating conditions to the lifecycle of critical components.,” said Jason Van Velsor, Director of Integrated Monitoring Technology at SI.

“We have supported clients with asset integrity insights for decades and now offer enhanced monitoring technology that will help automate risk management for high energy piping and help obtain the most value out of field inspection and other maintenance activities during outages.”

Unique Features of the SI Solution include:

  • Design and application of a monitoring program that focuses on safety and reliability and is consistent with guidance contained in the ASME B31.1 regulatory code.
  • Expert assessment (or Gap Analysis) to optimize monitoring including health checkups to validate optimum monitoring for plant operation.
  • Decades of material analysis insights as algorithms to expertly inform decision making.
  • Customized automated alerts to notify operators of abnormal or undesirable operating conditions affecting the life of high-energy components.

Contact Steve or Jason to learn more (info@structint.com)

News and Views Volume 49, Attemperator Monitoring with Wireless Sensors 02

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News and Views Volume 49, Attemperator Monitoring with Wireless Sensors

NEWS August 19 - HRSG Forum Major Cycle Chemistry Aspects for HRS copy

HRSG Forum: Major Cycle Chemistry Aspects for HRSGs

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‘SI is proud to have SI Expert and Senior Associate, Dr. Barry Dooley presenting at the HRSG Forum on August 19that 11 am (EST).  

TOPIC:  Introduction to the Key Cycle Chemistry Features for HRSG Reliability

HRSG ForumThe basic rules for providing optimum cycle chemistry control for HRSGs will be outlined. The latest statistics from over 100 HRSG plants worldwide will show how the lack of basic cycle chemistry controls leads to the major failure/damage mechanisms. The following two presentations will provide information on what is acceptable for the two top situations involving monitoring iron and continuous instrumentation.

Click here for more information

News & Views, Volume 49 | Materials Lab Featured Damage Mechanism - Soot Blower Erosion

News & Views, Volume 49 | Materials Lab Featured Damage Mechanism: Soot Blower Erosion

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News & Views, Volume 49 | Materials Lab Featured Damage Mechanism - Soot Blower ErosionBy:  Wendy Weiss

Soot blower erosion (SBE) is caused by mechanical removal of tube material due to the impingement on the tube wall of particles entrained in the “wet” blower steam. As the erosion becomes more severe, the tube wall thickness is reduced and eventually internal pressure causes the tube rupture.

Mechanism

SBE is due to the loss of tube material caused by the impingement of ash particles entrained in the blowing steam on the tube OD surface.  In addition to the direct loss of material by the mechanical erosion, SBE also removes the protective fireside oxide. (Where the erosion only affects the protective oxide layer on the fireside surface, the damage is more properly characterized as erosion-corrosion.) Due to the parabolic nature of the oxidation process, the fireside oxidation rate of the freshly exposed metal is increased. The rate of damage caused by the steam is related to the velocity and physical properties of the ash, the velocity of the particles and the approach or impact angle. While the damage sustained by the tube is a function of its resistance to erosion, its composition, and its operating temperature, the properties of the impinging particles are more influential in determining the rate of wall loss.

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News & View, Volume 49 | Piping Fabricated Branch Connections

News & Views, Volume 49 | Piping Fabricated Branch Connections

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By:  Ben Ruchte

Fabricated branch connections represent a common industry issue in combined cycle plants. Many are vulnerable to early damage development and have experienced failures.  Despite these challenges, a well-engineered approach exists to ensure that the baseline condition is fully documented and a life management plan is put in place to help reduce the overall risk to personnel and to help improve plant reliability.

Fabricated branch connections between large bore pipes (including headers and manifolds) are often fabricated with a reinforced branch commonly in the form of a “catalogue” (standard size) fitting, such as an ‘o-let’. These are more prevalent in today’s combined cycle environment as compared to conventional units that used forged blocks or nozzles rather than welded-on, integrally reinforced pipe fittings. The fittings are typically thicker than the pipes in which they are installed to provide compensating reinforcement for the piping run penetration. Full reinforcement is often not achieved as the current Code requirements place all of the reinforcement on the branch side of the weld joint.  As a result,  higher sustained stresses are generated and, particularly in the case of creep strength enhanced ferritic (CSEF) steels, early formation creep cracking in the weld heat-affected zone (HAZ) can occur (known as Type IV damage – see Figure 1). The well documented challenges of incorrect heat treatment of the o-let weld can also add to the likelihood of damage in CSEF components.  Damage is therefore most likely to occur in fabricated branches that operate with temperatures in the creep range.

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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

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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.

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News & View, Volume 48 | Bypass Line Spray Issues

News & Views, Volume 48 | Bypass Line Spray Issues

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News & View, Volume 48 | Bypass Line Spray IssuesBy:  Ben Ruchte and Kane Riggenbach

To provide operating flexibility, combined cycle plants are typically equipped with bypass systems (high pressure routing steam to cold reheat and hot reheat routing steam to the condenser).  These bypass systems include conditioning valves designed to reduce steam pressures followed by outlet desuperheaters which inject water to reduce steam temperatures.

This service environment exposes the downstream piping to a high frequency of temperature transients making these areas one of the most prominent ‘industry issues’.

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Structural Integrity Associates Announces the Appointment of Steve Gressler as Vice President, Fossil

Structural Integrity Associates Announces the Appointment of Steve Gressler as Vice President, Fossil

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Structural Integrity Associates | Steve Gressler, Vice President, FossilStructural Integrity Associates, Inc. (SI), a leader in engineering and technology in the power and oil & gas industries, today announced the appointment of Steve Gressler as Vice President of its Fossil business. Gressler will report to Mark Marano, SI President and Chief Executive Officer.

Mr. Gressler is a metallurgical engineer with over 30 years of experience in metallurgy, failure analysis, and the damage assessment of fossil power generation equipment and distributed heating and cooling systems with an emphasis on piping, boilers, headers, and balance of plant equipment. He is a principal contributor to engineering life cycle programs and procedures, risk assessments, analysis tools, and technologies to assess service degradation in low alloy and creep-strength enhanced ferritic steels.  His current work focuses on the development, integration, and deployment of nondestructive testing and damage tracking technology in addition to engineering consulting and materials assessments.

Since joining Structural Integrity Associates in 1997, Steve has been a principal contributor to the methodologies applied for life assessment of high temperature and critical piping components. This includes characterization of creep and fatigue damage in longitudinal seam welds, girth welds, and header ligaments.  It also extends to the engineering of data management systems used for aiding decision-making processes.

Marano noted, “Steve brings metallurgical leadership and technology development experience to the SI leadership team and is an integral part of our new customer focused strategy. Steve’s knowledge of the fossil business, tenure with SI, and relationships with our clients will accelerate our journey to create value for power and oil industry customers as a highly valued engineering and technology partner.”

Gressler received a Bachelor of Science in Metallurgical Engineering from the University of Pittsburgh and is a Registered Professional Engineer. Steve is also a prior recipient of the SI Riccardella Innovation Award for Prioritization Method for Fossil Plant Piping.

News & View, Volume 47 | Surface Preparation – A Pivotal Step in the Inspection Process

News & View, Volume 47 | Surface Preparation – A Pivotal Step in the Inspection Process

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By:  Ben Ruchte, Steve Gressler, and Clark McDonaldNews & View, Volume 47 | Surface Preparation – A Pivotal Step in the Inspection Process

Properly inspecting plant piping and components for service damage is an integral part of proper asset management.  High energy systems constructed in accordance with ASME codes require appropriate inspections that are based on established industry practices, such as implementation of complimentary and non-destructive examination (NDE) methods that are best suited for detecting the types of damage expected within the system.  In any instance where NDE is used to target service damage, it is desirable to perform high quality inspections while at the same time optimizing inspection efficiency in light of the need to return the unit to service.  This concept is universally applicable to high energy piping, tubing, headers, valves, turbines, and various other power and industrial systems and components.

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