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

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

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 & Views, Volume 49 | Hydroelectric Penstock Inspection - Field NDE Services

News & Views, Volume 49 | Hydroelectric Penstock Inspection: Field NDE Services

News & Views, Volume 49 | Hydroelectric Penstock Inspection - Field NDE ServicesBy:  Jason Van Velsor and Jeff Milligan

Our talented experts, using the latest technology and methods, deliver unmatched value, actionable information, and engineering knowledge for the management of your most critical assets.

Many of the penstocks used in the hydroelectric power industry have been in service for over 50 years.  Often with older components, historical documents like, as-built drawings and proof of material composition no longer exist.  This information is critical for inspection, repair and replacement decisions.  SI has the expertise to assist hydro clients with everything from material verification, inspection, and fitness-for-service analysis to keep penstock assets in-service for many more years to come.

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News & Views, Volume 48 | Metallurgical Lab Case Study – Grade 91 Elbows Cracked Before Installation

By:  Wendy Weiss and Terry Totemeier

News & View, Volume 48 | Metallurgical Lab Case Study - Grade 91 Elbows Cracked Before InstallationStructural Integrity (SI) personnel visited a power plant construction site to examine four Grade 91 elbows (ASTM A234-WP91 20-inch OD Sch. 60) that were found to contain axially oriented surface indications. The elbows had not yet been installed. The indications were initially noticed during magnetic particle testing (MT) after one end of an elbow was field welded to a straight section and post weld heat treated (PWHT). Subsequently, three additional similarly welded elbows were inspected and indications were found at both the welded (inlet) and open (outlet) ends of three elbows. The elbow with the most significant indications was selected for SI’s on-site examinations. Figure 1 shows the inlet and outlet ends of the selected elbow.

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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

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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News & View, Volume 47 | Metallurgical Lab Case Study- Corrosion Fatigue in WaterWall Tubes Increasingly A Safety Concern as Coal Plants Cycle

News & Views, Volume 47 | Metallurgical Lab Case Study: Corrosion Fatigue in WaterWall Tubes Increasingly A Safety Concern as Coal Plants Cycle

By:  Ben RuchteNews & View, Volume 47 | Metallurgical Lab Case Study- Corrosion Fatigue in WaterWall Tubes Increasingly A Safety Concern as Coal Plants Cycle

It is well known that conventional coal-fired utility boilers are cycling more today than they ever have.  As these units have shifted to more of an ‘on-call’ demand they experience many more cycles (start-ups and shutdowns, and/or significant load swings) making other damage mechanisms such as fatigue or other related mechanisms a concern. 

The most recent short-term energy outlook provided by the U.S. Energy Information Administration (EIA) indicates the share of electricity generation from coal will average 25% in 2019 and 23% in 2020, down from 27% in 2018.  While the industry shifts towards new construction of flexible operating units, some of the safety issues that have been prevalent in the past are fading from memory.  The inherent risks  of aging seam-welded failures and waterwall tube cold-side corrosion fatigue failures are a case in point.   It is well known that conventional coal-fired utility boilers are cycling more today than they ever have.  As these units have shifted to more of an ‘on-call’ demand they experience many more cycles (start-ups and shutdowns, and/or significant load swings) making other damage mechanisms such as fatigue or other related mechanisms a concern.  The following case study highlights this point by investigating a cold-side waterwall failure that experienced Corrosion Fatigue.  While this failure did not lead to any injuries, it must be stressed that the potential for injuries is significant if the failure occurs on the cold-side of the tubes (towards the furnace wall).

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News & View, Volume 46 | Cross-Weld Creep-Rupture Testing for Seam Weld Life Management

News & Views, Volume 46 | Cross-Weld Creep-Rupture Testing for Seam Weld Life Management

By:  Jonnathan Warwick, Terry Totemeier, and Brian Chambers, Duke Energy

News & View, Volume 46 | Cross-Weld Creep-Rupture Testing for Seam Weld Life ManagementLongitudinal seam-welded hot-reheat steam piping operating in the creep regime is a continuing life-management challenge for many older fossil-fired power plants.  In response to catastrophic seam-welded piping failures in the 1980’s, the Electric Power Research Institute (EPRI) developed a comprehensive inspection protocol to insure continued safe operation of these piping systems [1]. The protocol requires full inspection of seam-welded hot-reheat pipe once a threshold of service exposure (calculated creep life consumption) has been reached, and re-inspection at intervals after the initial inspection depending on the inspection results.  Inspection for sub-surface cracking using ultrasonic testing (conventional or advanced) is strongly recommended, in combination with checking for surface cracking using wet fluorescent magnetic particle testing (WFMT).  Initial inspection and re-inspection of these piping systems represents a large maintenance cost for utilities, especially as older plants remain in service due to the changing economics of power generation.

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News & View, Volume 46 | Turnkey Rapid-Response Plant Support Disposition of Wall Thinning in Standby Service Water Piping

News & Views, Volume 46 | Turnkey Rapid-Response Plant Support Disposition of Wall Thinning in Standby Service Water Piping

By:  Jason Van Velsor, Roger Royer, and Eric Houston

News & View, Volume 46 | Turnkey Rapid-Response Plant Support Disposition of Wall Thinning in Standby Service Water PipingStructural Integrity recently had the opportunity to support a client’s emergent needs when their Standby Service Water (SSW) piping system experienced a pinhole leak just downstream of a valve. Concerned about other locations in the piping system with similar configurations, the site asked SI to assist with the expedited development of assessment and disposition plans for these other components. In response, SI was able to lean on our core competencies in failure analysis, advanced NDE inspection, and flaw evaluation to develop and deploy a comprehensive solution that met our client’s expedited timeline and helped them to mitigate the threat of future unplanned outages. The following sections outline how SI utilized our in-depth knowledge, cutting-edge technology, and world-class engineering to meet our client’s needs.

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News & View, Volume 46 | Metallurgical Lab Case Study- Cracking of Grade 23 Steel Furnace Wall Tubes

News & Views, Volume 46 | Metallurgical Lab Case Study: Cracking of Grade 23 Steel Furnace Wall Tubes

By: Terry Totemeier

News & View, Volume 46 | Metallurgical Lab Case Study- Cracking of Grade 23 Steel Furnace Wall TubesGrade 23 is a creep strength enhanced ferritic (CSEF) steel that was designed to offer similar creep strength to Grade 91 but with lower Cr content and, in the original concept, fabrication without pre- and post-weld heat treatment making the material attractive for the furnace wall tubes of ultra-supercritical coal plants where T12 has insufficient strength and T91 would be too complex to fabricate. Experience gained with T23 has shown that pre-heat is necessary and that post-weld heat treatment should also be performed when the material is employed in “high restraint” applications such as furnace wall tubes. Like other CSEF steels, T23 is very sensitive to heat treatment, and care must be taken to ensure that hard, brittle microstructures do not enter service – particularly in high restraint applications such as furnace wall tubes.

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News & View, Volume 46 | Metallurgical Lab Featured Damage Mechanism- Waterwall Fireside Corrosion (WFSC) in Conventional Boilers

News & Views, Volume 46 | Metallurgical Lab Featured Damage Mechanism: Waterwall Fireside Corrosion (WFSC) in Conventional Boilers

By: Wendy Weiss

News & View, Volume 46 | Metallurgical Lab Featured Damage Mechanism- Waterwall Fireside Corrosion (WFSC) in Conventional BoilersIndustry experience shows that waterwall tubing in conventional boilers can be susceptible to fireside corrosion, depending on fuel type, firing practice, etc. In boilers where fireside corrosion has been identified as a maintenance issue, wastage rates of 5 to 25 mils/year are not uncommon. Since the mid 1990s, the installation of low NOx burner systems designed to lower NOx emissions has significantly increased the wastage rates in some boilers. Operators of subcritical boilers have reported wastage rates as high as 30 mils/year, while those operating supercritical boilers have reported rates exceeding 100 mils/year in the worst cases. These higher damage rates have resulted in an increase in tube failures, and operators have struggled to accurately define the extent of the damage and install the appropriate mitigating technologies.

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News & View, Volume 45 | Metallurgical Lab- Case Study – Thermowell Failure Analysis

News & Views, Volume 45 | Metallurgical Lab: Case Study – Thermowell Failure Analysis

By:  Wendy Weiss

News & View, Volume 45 | Metallurgical Lab- Case Study – Thermowell Failure AnalysisStructural Integrity (SI) was recently asked to examine a fractured thermowell and determine the damage mechanism.  The thermowell had been removed from bypass line piping in a heat-recovery steam generator (HRSG) that ran from the High Pressure (HP) bypass valve to the cold reheat section, and sent to the SI Materials Science Center. As reported by plant personnel, the fracture was located within the pipe wall. The pipe material was specified as ASME SA-335, Grade P22, and the thermowell was specified to be ASME SA-182, Grade F22.

Examination Procedure and Results

The fractured thermowell sections were visually examined and photographed in the as-received condition, as shown in Figure 1. The thermowell was comprised of two pieces: the thermowell housing itself which protruded into the steam stream, and a fitting connection to the pipe into which the thermowell housing was inserted.

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