News and Views Archives

News & Views, Volume 44 | The Impact of the ASCE 7-16 Standard on Seismic Design and Certification of Equipment

April 27, 2018/in News and Views, Seismic, Structural Assessments, TRU Compliance/by Structural Integrity

By: Matt Tobolski

Things change, that’s just a fact of life. But when it comes to engineering codes and standards, change can be confusing, frustrating and expensive. As it relates to seismic design and certification of equipment, it is beneficial to understand the impact of code changes early to begin incorporating requirements in new equipment design, product updates and in the certification process.

One of the main structural design codes used in the United States and abroad, American Society of Civil Engineering (ASCE) 7, undergoes revisions on a five-year cycle. These revisions are based on input from committee members, building officials, interested parties and academia with the goal of ensuring specific performance objectives are achieved as well as incorporating lessons learned from practice. With the increase in enforcement of seismic certification provisions over the past 10 years, there has been a noticeable increase in industry lessons learned. The updates to the seismic provisions in ASCE 7-16 relating to equipment design and certification can primarily be attributed to these lessons learned.

News & Views, Volume 43 | In-Line Inspection – An Improvement Over Pressure Testing for Pipeline Integrity Management

October 5, 2017/in News and Views, Non-Destructive Evaluation, Oil and Gas Pipeline/by Structural Integrity

By: Scott Riccardella, Dilip Dedhia, and Peter Riccardella

Structural Integrity recently performed probabilistic fracture mechanics (PFM) analysis of a gas transmission pipeline for a major U.S. operator. The analysis yielded interesting insights in several areas:

Pressure Testing versus In-Line Inspection
Pressure testing has long been considered the gold standard for assuring pipeline integrity. By testing at a factor (e.g., 1.25x or 1.5x) above the Maximum Allowable Operating Pressure (MAOP), any size critical flaws in the line would fail at this pressure level and are thus removed prior to future service. Subcritical flaws that remain after the test will be smaller than the critical flaw sizes during operation, and thus can be assumed to have some margin for growth before they become critical in service. Flaw growth rates can be calculated based on operational and environmental factors to establish a reassessment interval for future testing or inspections.

News & View, Volume 43 | Perforation, Scabbing, and Reinforcement Optimization in an Aircraft Impact Analysis (AIA)

News & Views, Volume 43 | Perforation, Scabbing, and Reinforcement Optimization in an Aircraft Impact Analysis (AIA)

October 5, 2017/in Complex Loadings, Critical Structures, Eric Kjolsing, News and Views/by Structural Integrity

By: Eric Kjolsing

Background
A 2016 project utilized a variety of Structural Integrity competencies to analyze a beyond design basis threat at an overseas nuclear power plant. The client was assessing a plant design and approached Structural Integrity to investigate local perforation and scabbing of a reinforced concrete wall due to hard missile impact. Perforation occurs when a missile fully penetrates and passes through a target while scabbing occurs when material is ejected from the back face of a target, potentially striking personnel and equipment inside the facility. The client also sought to reduce the volume of wall reinforcement, a potentially large cost savings, while still meeting the facility’s strict design criteria. The project is best described in four stages and took advantage of our AIA experience, finite element (FE) modeling expertise, and proprietary concrete constitutive model ANACAP.

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

October 5, 2017/in Combined Cycle, Fossil Power, Heat Recovery Steam Generator (HRSG), Monitoring, News and Views/by Structural Integrity

By: Fred DeGrooth and Ulrich Woerz

Attemperators (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.

News & Views, Volume 43 | Wind Project Continued Operation Beyond Designed Life

October 5, 2017/in News and Views, Wind Power/by Structural Integrity

By: Ceci Wilson

With the increase of renewable energy into the power generation market, aggressive state renewable targets, and recently renewed production tax credit (PTC), wind power generation demand is positioned to increase significantly. This is good news not only for new wind projects but also for existing wind power infrastructure.

As the wind energy market and demand has grown quickly, so has the technology – better turbine controls, more efficient drivetrains, longer and lighter blade designs, and taller towers. Figure 1 shows that in 2000 wind turbines had an average nameplate capacity of slightly less then 1 MW and 30% capacity factors, while the average nameplate capacity in 2016 was 2.15 MW ^[1], with capacity factors near 40%. Blade lengths of 25 meters in 2000 are dwarfed by the more recent 50 meter blades (see Figure 2). Longer blades at higher hub heights and more efficient controls means that new wind projects can achieve more power generation capacity with half (or less) the number of turbines compared to 10-year-old projects.

A typical wind turbine is designed for 20-year operation. In 2017, most of the US wind turbine fleet is less than 10 years old, with 20% of the fleet between 10 and 16 years of age. As wind turbines age and near their design life of 20 years, owners should start assessing their future options for continued operation:

Partial repowering: Would it be beneficial to invest in upgrades that take advantage of new technology to increase power generation and/or turbine life?
Repowering: Given technology development, is it better to replace existing wind turbines with new ones?
Life extension: Can the operating wind turbines continue operating past 20 years as-is (or with minor adjustments)?

The answers to these questions are project and site specific.

News & Views, Volume 43 | Managing Fatigue-Challenged Components in SLR

October 5, 2017/in News and Views, SI:FatiguePro/by Structural Integrity

By: Jennifer Correa

Subsequent License Renewal (SLR) will require a shift in the approach for managing plant components for thermal fatigue. The components are older and will have experienced more fatigue damage. As time goes on, more components will become fatigue-challenged, meaning that they will require more management to demonstrate serviceability.

There are several approaches that can be taken to manage fatigue-challenged components in SLR.

Refining the design fatigue analyses is one approach that has been widely used in License Renewal (LR), and will remain useful in SLR. Components that were previously managed through cycle counting alone may still be managed through cycle counting if a refined analysis results in fatigue and environmentally-assisted fatigue (EAF) cumulative fatigue usage values below 1.0.

Another useful approach is to revisit assumptions made about plant operation earlier in life. Conservative assumptions were made about early plant operation for many components. This was often done for expediency and may have been sufficient for LR, but as the components age, those assumptions may prove too conservative. Revisiting these assumptions can help lower the overall fatigue usage for components.

News & Views, Volume 43 | Advanced Structural Analysis

October 5, 2017/in Complex Loadings, Critical Structures, Eric Kjolsing, Hydroelectric Power, News and Views, Structural Assessments/by Structural Integrity

By: Eric Kjolsing & Philip Voegtle

The sophistication of structural analysis has evolved side-by-side with computing and graphics technology. Structural engineers have at their fingertips very powerful software analysis tools that assist them in evaluating very large and complex structures for stability, suitability, and code adequacy. The tools themselves vary in complexity in proportion with the engineering analysis required of them – the most complex and unique engineering problems requiring the most advanced analysis tools. Structural Integrity is a leader in advanced structural analysis (ASA), utilizing state-of-the-art software and material science expertise to solve an array of structural and mechanical problems.

Structural analysis, in its most basic definition, is the prediction of the structural performance of a given structure, system, or component to prescribed loads, displacements, and changes in temperature. Common performance characteristics include material stresses, strains, forces, moments, displacements and support reactions. The results from a structural analysis are typically compared to acceptable values found in design codes. Meeting the design code acceptance criteria ensures a design that protects the public’s health, safety, and welfare.

ASA extends this basic definition of structural analysis to one-of-a-kind problems where the acceptance criteria may not be well defined. Since loads, material behavior, or the structure itself can go beyond the scope of basic design codes, ASA requires an in-depth understanding of modeling techniques, software limitations, and non-linear material behavior. In ASA, sophisticated finite element analysis solvers are utilized to gain a detailed understanding of a system’s non-linear mechanical behavior, providing a full three-dimensional view of the critical stresses and strains in a loaded system.

News & Views, Volume 43 | A Strategic Approach for Completing Engineering Critical Assessments of Oil and Gas Transmission Pipelines

October 5, 2017/in News and Views, Oil and Gas Pipeline, Scott Riccardella, Steven Biles/by Structural Integrity

By: Scott Riccardella and Steven Biles

Regulatory Overview
In January 2012, the Pipeline Safety, Regulatory Certainty, and Job Creation Act of 2011 was signed into law directing PHMSA to take steps to further assure the safety of pipeline infrastructure. PHMSA issued the related Notice of Proposed Rulemaking (NPRM) for Safety of Gas Transmission and Gathering Pipelines on April 8, 2016. Included in the NPRM were significant mandates regarding:

Verification of Pipeline Material (§192.607); and
Maximum Allowable Operating Pressure (MAOP) Verification or “Determination” (§192.624)

The NPRM proposes requirements for operators to verify the MAOP of a gas transmission pipeline when:

The pipeline has experienced an in-service incident (as defined by §191.3) due to select causes¹ in a High Consequence Area (HCA), “piggable” Moderate Consequence Area (MCA), or Class 3 or 4 location since its last successful pressure test
The pipeline lacks Traceable, Verifiable, and Complete pressure test records for HCAs or Class 3 or 4 locations
The pipeline MAOP was established by the grandfather clause (§192.619 (a)(3)) for HCAs, “piggable” MCAs, or Class 3 or 4 locations.

To verify the MAOP of a pipeline, the NPRM provides the following options:

Method 1: Pressure Test
Method 2: Pressure Reduction
Method 3: Engineering Critical Assessment (ECA)
Method 4: Pipe Replacement
Method 5: Pressure Reduction for segments with small potential impact radius (PIR) & diameter
Method 6: Use Alternative Technology

The ECA Approach
Per the NPRM, Method 3 (ECA) is defined as an analysis, based on fracture mechanics principles, material properties, operating history, operational environment, in-service degradation, possible failure mechanisms, initial and final defect sizes, and usage of future operating and maintenance procedures to determine maximum tolerable sizes for imperfections.

News & Views, Volume 43 | LATITUDE™ Innovating the NDE Data Acquisition Process

October 5, 2017/in Jason Van Velsor, LATITUDE, News and Views, Non-Destructive Evaluation/by Structural Integrity

By: Jason Van Velsor

From the creation of the first simple stone tools to the invention of the world wide web, technological innovation has been the undercurrent that has carried the human species from our primitive survivalist ways to our present-day complexity of modern conveniences. We innovate from necessity, competition, or from a desire for an improved quality of life. Innovation has been and remains key to our survival and proliferation.

In business, it is no different and innovation has been a mainstay at Structural Integrity and part of our core values since our inception in 1983. We are constantly developing and applying innovative practices and technologies to meet our clients’ toughest challenges and to provide best-in-value solutions. In this spirit, we are excited to announce one of our most recent innovations, LATITUDE^TM.

LATITUDE is a non-mechanized position and orientation encoding technology designed for use with nondestructive evaluation (NDE) equipment. Simply stated, LATITUDE enables an operator to manipulate a probe by hand while maintaining a digital record of the position and orientation of the probe at all times. For many applications, LATITUDE can be thought of as a fast and compact alternative to cumbersome and complicated automated inspection equipment.

News & Views, Volume 43 | Using Falcon to Develop RIA Pellet-Cladding Mechanical Interaction (PCMI) Failure Criteria

October 5, 2017/in John Alvis, News and Views, Nuclear Fuel, Reactor/by Structural Integrity

By: John Alvis

Introduction
The goal to achieve higher fuel rod burnup levels has produced considerable interest in the transient response of high burnup nuclear fuel. Several experimental programs have been initiated to generate data on the behavior of high burnup fuel under transient conditions representative of Reactivity Initiated Accidents (RIAs). A RIA is an important postulated accident for the design of Light Water Reactors (LWRs). It is considered the bounding accident for uncontrolled reactivity insertions.

The initial results from RIA-simulation tests on fuel rod segments with burnup levels above 50 GWd/tU, namely CABRI REP Na-1 (conducted in 1993) and NSRR HBO-1 (conducted in 1994), raised concerns that the licensing criteria defined in the Standard Review Plan (NUREG-0800) may be inappropriate beyond a certain level of burnup. Figure 1 is an example of a typical high burnup fuel cladding showing the oxidized and hydrided cladding of higher burnup fuel rods. Figure 2 shows the typical radial crack path in oxidized and hydrided cladding, subjected to RIA simulation tests. As a consequence of these findings, EPRI with the assistance of the Structural Integrity’s Nuclear Fuel Technology Division (formally ANATECH) and other nuclear industry members conducted an extensive review and assessment of the observed behavior of high burnup fuel under RIA conditions. The objective was to conduct a detailed analysis of the data obtained from RIA-simulation experiments and to evaluate the applicability of the data to commercial LWR fuel behavior during a Rod Ejection Accident (REA) or Control Rod Drop Accident (CRDA). The assessment included a review of the fuel segments used in the tests, the test procedures, in-pile instrumentation measurements, post-test examination results, and a detailed analytical evaluation of several key RIA-simulation tests.