Structural Integrity Associates | News and Views, Volume 51 | Turbine Unit Trip and Event

News & Views, Volume 51 | Turbine Unit Trip and Event

Recovery Best Practices

By:  Dan Tragresser

When a unit trips or experiences an event, the site will incur costs associated with the loss in production, regulatory penalties, and, if applicable, outage scope, hardware replacement, and the purchase of make-up power.  These costs can drive the priority of returning to service to quickly become the only priority.

Structural Integrity Associates | News and Views, Volume 51 | Turbine Unit Trip and EventWith the reduction in staffing at power plants over the past 2 decades, many traditionally routine engineering and maintenance tasks have fallen by the wayside.  With limited resources, operations and engineering personnel must focus their time and efforts based on priority.  Quite often, keeping a unit online or quickly returning a unit to service will take priority over continuous improvement actions such as investigations and root cause analysis.

When a unit trips or experiences an event, the site will incur costs associated with the loss in production, regulatory penalties, and, if applicable, outage scope, hardware replacement, and the purchase of make-up power.  These costs can drive the priority of returning to service to quickly become the only priority.  Unfortunately, the review of event operational data, event precursors, and the collecting evidence through the unit disassembly very often fall below the priority of returning to service.  Collecting or re-creating evidence after the fact is nearly impossible.  This lack of priority often results in a lack of understanding of the root cause of the trip or event.  

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Structural Integrity Associates | News and Views, Volume 51 | Combustion Turbine Compressor Hygiene Component Longevity

News & Views, Volume 51 | Combustion Turbine Compressor Hygiene

COMPONENT LONGEVITY

By:  John Molloy

Introduction

Structural Integrity Associates | News and Views, Volume 51 | Combustion Turbine Compressor Hygiene Component LongevityAn industrial combustion turbine can ingest over 1000lbs of air per hour of operation.  Entrained within the air is a spectrum of mineral, salt, moisture, and VOC, and other compounds that are present in the local atmosphere.  Locally high concentrations of potentially corrosive species may also be present due to surrounding industries or even effluent from the power plant itself, such as cooling tower drift, evaporation cooler deposits, or water treatment effluent.

In addition to disrupting the flow path area of the compressor blades and vanes, with a consequential drop in compressor efficiency, these contaminants can also serve as sites for under-deposit corrosion cells that have implications for component life as well as risk for catastrophic failures.  Compressor waterwashing with detergents has been utilized with some success by utilities as a method for mitigating the effects of deposit accumulation.  Nevertheless, tenacious deposits can accumulate over time.  The presence of moisture in the deposit can also result in activation of a corrosion cell that can corrode the typical stainless steels used for blade and vane construction.  Higher strength PH stainless steel blades and vanes suffer a larger loss in fatigue endurance limit from pitting, and tend to suffer more airfoil liberations due to cracking initiated at pitting.

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News & View, Volume 48 | Considerations of Pin Cracking in Finger Pin Turbine Blade Attachments

News & Views, Volume 48 | Considerations of Pin Cracking in Finger Pin Turbine Blade Attachments

By:  Cliff Lange and Matt Freeman

OEMs recommend periodic inspection of pinned finger turbine blade attachments for detection of service-induced damage as part of ongoing rotor maintenance activity. 

This article provides an example where ultrasonic inspection detected cracking in several pins of finger attachments and outlines an engineering assessment to support continued operation and identify a re-inspection interval.  This approach can be applied to other pinned finger blade attachments to determine suitability for service.

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News & View, Volume 46 | NDE Best Practices for Generator Rotors

News & Views, Volume 46 | NDE Best Practices for Generator Rotors

By: Paul Zayicek News & View, Volume 46 | NDE Best Practices for Generator Rotors

Three factors typically drive inspection intervals of generator rotors:

  1. a timeframe recommended by the insurance carrier or OEM
  2. an engineering evaluation that supports a different inspection interval due to service operation events or existing rotor damage
  3. industry best practices

Drivers from the OEM include issues defined in service bulletins or technical information letters that pertain to the entire fleet or some subset of the population. Intervals based on engineering evaluations can be derived from an identified damage mechanism with the rotor or with a critical component. An engineering evaluation can also provide for extended inspection intervals in situations where the generator has no inherent material issues, has a clean inspection record, and sees limited operational stress such as in a base-load unit.

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