News and Views Archives

News & Views, Volume 45 | Interval Relief from RPV Threads in Flange Examination Requirements

January 1, 2019/in News and Views, Nuclear Asset Integrity, Nuclear Energy, Reactor, Scott Chesworth/by Structural Integrity

By: Scott Chesworth

ASME Code Section XI requires that the RPV Threads in Flange component (Category B-G-1, Item Number B6.40, see Figure 1) be inspected each inspection Interval using volumetric examination. However, there is general agreement that the inspection does not contribute to the overall safety of the RPV. Industry experience indicates that these examinations have not been identifying service-induced degradation and that they have negative impacts on worker exposure, personnel safety, and outage critical path time. Savings from the elimination of this inspection can be applied to other more meaningful inspections of other more risk-significant plant components.

EPRI Report 3002007626 (March 2016) provides the basis for eliminating the RPV Threads in Flange examination requirement. This report includes the results of an industry survey in which 168 units provided the status of their RPV Threads in Flange examination, as well as insight into the impacts of conducting these examinations.

News & Views, Volume 45 | Gas Pipeline Safety Regulation Update

January 1, 2019/in Bruce Paskett, Eric Fisette, Mega-Rule, News and Views, Oil and Gas Pipeline, Scott Riccardella/by Structural Integrity

By: Scott Riccardella. Erica Fisette, and Bruce Paskett

Update on the Safety of Gas Transmission and Gathering Pipelines Rulemaking (known as the Mega-Rule)
Structural Integrity (SI) personnel have had significant involvement in the Gas Pipeline Advisory Group (GPAC) meetings focused on consideration of the proposed pipeline safety rule titled “Safety of Gas Transmission and Gathering Pipelines” (Notice of Proposed Rule Making April 8, 2016). The meetings produced several recommendations to the Pipeline and Hazardous Materials Safety Administration (PHMSA) that are likely to be included in the Final Rule. A key outcome of these meetings was that PHMSA has decided the Final Rule will be split into three sub-rule packages that will all be final rules to facilitate the rulemaking process:

Maximum Allowable Operating Pressure (MAOP) reconfirmation, Material Verification, Expansion of Integrity Management Assessments Outside of High Consequence Areas (HCAs) and other related issues,
Repair Criteria, Inspections Following Extreme Weather Events, Corrosion Control improvements, Management of Change; and
Expansion of Part 192 regulations to include additional Gas Gathering Lines.

News & Views, Volume 45 | Latitude™ Delivers – Highlights from the First Field Deployments

January 1, 2019/in Jason Van Velsor, LATITUDE, News and Views, Non-Destructive Evaluation, Nuclear Asset Integrity/by Structural Integrity

By: Jason Van Velsor, Dave Anthony, Joe Agnew, and Michael Lashley

Introduction
For the past 2 ½ years, Structural Integrity Associates (SI) has been working diligently to develop, qualify and deliver the nuclear industry’s first-of-a-kind manually acquired encoded phased array UT (PAUT) examination for Section XI dissimilar metal welds (DMWs). Development of the encoding technology behind this effort, the LATITUDE^TM non-mechanized encoding system, was completed in 2017, with our application-specific inspection procedure completed and qualified through the industry’s Performance Demonstration Program (PDI) in the Spring of 2018. Now, with much enthusiasm, we are proud to report that we have successfully completed the first field deployments of the LATITUDE technology and DMW procedure during the Fall 2018 outage season.

News & Views, Volume 45 | Life Management for High Energy Piping (HEP)

January 1, 2019/in Combined Cycle, Fossil Power, Heat Recovery Steam Generator (HRSG), High Energy Piping (HEP), Matt Freeman, News and Views/by Structural Integrity

By: Matt Freeman

High Energy Piping systems, including main steam and hot reheat piping, are typically very reliable and can often operate trouble-free for decades. However, due to the combination of pressure and temperature at which such systems operate, a failure can have catastrophic consequences from a safety perspective and in terms of equipment loss. Because of this and the requirements of the ASME B31.1 Power Piping code, HEP programs – or as defined by Code, Covered Piping Systems (CPS) – are established to ensure that the integrity of the system is maintained throughout their lifecycle. This article discusses the steps required to implement an HEP / CPS life management program.

A Life Management Program is not synonymous with an inspection program. Inspections are an important part of an overall program but should be complimentary to the use of analytical tools, real-time monitoring, and laboratory examinations

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

January 1, 2019/in Materials Laboratory, News and Views, Wendy Weiss/by Structural Integrity

By: Wendy Weiss

Structural 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.

News & Views, Volume 45 | Metallurgical Lab Featured Damage Mechanism – Acid Dewpoint Corrosion in Conventional Fossil Boilers and Combined Cycle HRSGs

January 1, 2019/in Materials Laboratory, News and Views, Wendy Weiss/by Structural Integrity

By: Wendy Weiss

Acid dewpoint corrosion can occur in conventional and HRSG units in locations where temperatures fall below the sulfuric acid dewpoint temperature. This can occur when either the tube metal temperatures are below the acid dewpoint so that condensate forms on the metal surface, or when flue gas temperatures are below the acid dewpoint, so that the condensate will form on fly ash particles.

Mechanism
This type of fire-side damage occurs when sulfur dioxide (SO²) in the flue gas oxidizes to sulfur trioxide (SO³) and the SO³ combines with moisture to form sulfuric acid. If the temperatures are at or below the acid dewpoint, so that the sulfuric acid condenses, then tube metal corrosion occurs. The temperature at which condensate first forms depends on a number of factors, including the partial pressures of SO³ and water vapor in the flue gas, but is usually around 250 to 300°F.

News & Views, Volume 45 | Proving Performance – What Distinguishes an ISO-Compliant Product Certification Agency?

January 1, 2019/in Andy Coughlin, Critical Structures, News and Views, TRU Compliance/by Structural Integrity

By: Andy Coughlin

Whether it’s fair-trade coffee, sustain-ably harvested lumber, energy efficient appliances, or other certified products, consumers and companies look for products that have high standards of origin, production, and performance. Structural Integrity Associates’ TRU Compliance mark is no different. Our mark shows buyers a product has undergone rigorous assessment for seismic, wind, and blast performance to nationally recognized standards.

However, not all agencies conform to the internationally recognized set of standards that govern a product certification agency, allowing it to be impartial, objective, and accountable to the public. The standard ISO/IEC 17065 Conformity assessment — Requirements for bodies certifying products, processes and services spells out requirements that make agencies like TRU Compliance accountable to its clients and to the public. The requirements in TRU Compliance’s Certification Manual are broad, but they generally fall into the three categories below.

News & Views, Volume 45 | The Importance of HRSG HP Evaporator Tube Internal Deposit Evaluation

January 1, 2019/in Barry Dooley, Combined Cycle, Fossil Power, Heat Recovery Steam Generator (HRSG), News and Views/by Structural Integrity

By: Barry Dooley

Evaluation of High Pressure (HP) Evaporator Tube Deposits is important for several reasons:

Determining if flow-accelerated corrosion (FAC) might be occurring in the lower pressure circuits.
Regular evaluations can provide information on the internal deposit deposition rate, which is information necessary to help prevent under-deposit corrosion damage mechanisms.
Provides information necessary to develop an optimized cycle chemistry for HRSGs.
Can help determine if the HRSG needs to be chemically cleaned.

The leading heat recovery steam generator (HRSG) tube failure mechanisms are FAC, thermal and corrosion fatigue, and under-deposit corrosion (UDC) and pitting. The corrosion products released by the FAC mechanism are transported from the affected area (typically the feedwater or lower pressure systems) and can eventually reach the HP evaporator tubing, so understanding the deposition in the HP evaporator is an important step in determining if FAC might be occurring. Deposition on the inside of HP evaporator tubing is also a precursor to any of the under-deposit corrosion HRSG tube failure mechanisms.

News & Views, Volume 44 | Failed Grade 91 “Soft” Pipe Bend – A Case Study – Failure Occurred With Less Than 35,000 Operating Hours

April 27, 2018/in Materials Laboratory, News and Views, Tony Studer/by Structural Integrity

By: Kane Riggenbach and Tony Studer

Grade 91 steel is widely used in tubes, headers and piping of superheaters and reheaters because of its higher strength at elevated temperature compared to low alloy steels such as Grade 22. The improved strength is a result of a tempered martensitic microstructure with a fine distribution of carbonitride precipitates. This microstructure is achieved through careful heat treatment: normalizing, tempering, and subsequent forming and post weld heat treatments. If these heat treatments are not performed properly, then the strength of the material essentially reverts to that of a low alloy steel like Grade 22, and is usually accompanied by a reduction in hardness, leaving the Grade 91 material in a so-called “soft” condition.

This article summarizes a case study for Grade 91 material in the “soft” condition, which was responsible for a steam leak after only 5 years of operation, illustrating how this material condition can result in forced shutdowns and safety hazards. It is because of these consequences that it is recommended to have a Grade 91 life management program to understand if your plant may have such vulnerability.

This case study provides general background to the steam leak and describes the subsequent metallurgical evaluations performed to verify that mal-heat treatment of the Grade 91 steel was the root cause of the leak. A follow-on article (the next issue, Volume 45, of News and Views) will provide additional insight into local stresses and analytical prediction of such failures, as well as highlighting key aspects of a Grade 91 life management program. Suffice it to say if this plant had implemented such a program, the vulnerability of the affected spool would have been identified and mitigating actions could have been taken to avoid the leak.

News & View, Volume 44 | Weld Overlay Repair Mitigates Thermal Fatigue Flaw Growth

News & Views, Volume 44 | Weld Overlay Repair Mitigates Thermal Fatigue Flaw Growth

April 27, 2018/in David Segletes, News and Views, Nuclear Energy, Weld Overlay/by Structural Integrity

By: David Segletes

A circumferential flaw in a 14-inch diameter suction pipe-to-elbow stainless steel weld was identified in both units of a nuclear power plant as depicted in Figure 1. The two units are Westinghouse designed four-loop pressurized water reactor (PWR) plants and are mirror images of each other. The pipe-to-elbow weld is the first junction remote from the hot leg piping. The circumferential flaw at this location was first discovered on Unit 2 during the spring of 2016 and subsequently on Unit 1 in the spring of 2017. The flaws are located at comparable circumferential positions, given the two pipes are mirror images of each other and at the same distance from the RHR nozzle. Structural Integrity (SI) performed the flaw evaluation for each unit at the time of discovery. The flaws are ID connected and located at the weld heat affected zone (HAZ) on the pipe side. Although stress corrosion cracking has not be observed in the HAZ of austenitic stainless steel in PWR systems, the flaws were evaluated for both fatigue crack growth and stress corrosion crack growth. The flaw evaluations indicated there was life remaining for a short period of operation, with the appropriate safety margin, but not sufficient to allow the client to operate the plant until the end of the operating license for the given unit. Subsequently, a repair plan was developed to allow the units to operate to the end of the operating license.