Main Steam Piping Girth Weldment Stresses and Life Consumption Considering Malfunctioning Supports

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Stress Analysis ◽  
Principal Stress ◽  
Hoop Stress ◽  
High Energy ◽  
Operating Conditions ◽  
Piping System ◽  
Life Management ◽  
System Integrity ◽  
Creep Fatigue ◽  
Main Steam

A high energy piping (HEP) program is important for the safety of plant personnel and reliability of the generating units. HEP weldment failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. Since creep/fatigue is a typical failure mechanism, the probability of HEP failures increases with unit age. The main steam (MS) piping system is one of the most critical HEP systems. Weldment failures are typically due to a combination of high temperature creep and fatigue. Industry best practices include (1) the evaluation of historical operating conditions; (2) examinations of critical weldments to reveal nondestructive examination (NDE) indications, microstructural material damage, and detailed geometry data; (3) hot and cold walkdowns to document the field piping system behavior and anomalies; (4) simulation of as-found piping displacements to estimate actual stresses; (5) ranking of critical weldments; (6) recommendations for support repairs and adjustments; (7) recommendations for future examinations; and (8) remaining life estimates at critical weldments. Appropriate examinations, condition assessments, and recommendations for corrective actions are provided as a cost-effective life management process to maintain the piping system integrity. This paper provides examples demonstrating that the girth welds ranked below the top five to six welds are subject to significantly less applied stress and have substantially more creep/fatigue life than the top ranked welds. Hanger adjustments, along with selective identification, NDE, and possible repairs of top ranked welds provide substantially greater life to MS piping systems. Some fitness-for-service and risk-based programs for MS piping system girth weldments recommend a stress evaluation using typical pressure vessel or boiler tube calculations, in which the hoop stress is the principal stress. In some cases, the effective weldment stresses can be more than 50% above the hoop stress, resulting in the estimated remaining lives less than 15% of the life estimates using the hoop stress methodology. Some HEP life management programs may vaguely discuss using the principal stress based on a finite element analysis of the piping system. These principal stress values may be based on a conventional as-designed piping stress analysis. In the majority of the as-found piping stress analyses performed by the author, the maximum as-found stresses are substantially greater than the maximum conventional as-designed piping stresses. In the example case study, the maximum effective weldment stress was more than three times greater than the estimated as-designed piping stress at the same location. This paper illustrates than an as-designed piping stress analysis will typically overestimate the life of an HEP system and typically not predict the locations of maximum creep/fatigue damage.

Main Steam Piping Girth Weldment Stresses and Life Consumption Considering Malfunctioning Supports

2009 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Stress Analysis ◽  
Principal Stress ◽  
Hoop Stress ◽  
High Energy ◽  
Operating Conditions ◽  
Piping System ◽  
Life Management ◽  
System Integrity ◽  
Creep Fatigue ◽  
Main Steam

A high energy piping (HEP) program is important for the safety of plant personnel and reliability of the generating units. HEP weldment failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. Since creep/fatigue is a typical failure mechanism, the probability of HEP failures increases with unit age. The main steam (MS) piping system is one of the most critical HEP systems. Weldment failures are typically due to a combination of high temperature creep and fatigue. Industry best practices include (1) the evaluation of historical operating conditions, (2) examinations of critical weldments to reveal NDE indications, microstructural material damage, and detailed geometry data, (3) hot and cold walkdowns to document the field piping system behavior and anomalies, (4) simulation of as-found piping displacements to estimate actual stresses, (5) ranking of critical weldments, (6) recommendations for support repairs and adjustments, (7) recommendations for future examinations, and (8) remaining life estimates at critical weldments. Appropriate examinations, condition assessments, and recommendations for corrective actions are provided as a cost-effective life management process to maintain the piping system integrity. This paper provides examples demonstrating that the girth welds ranked below the top five to six welds are subject to significantly less applied stress and have substantially more creep/fatigue life than the top ranked welds. Hanger adjustments, along with selective identification, NDE, and possible repairs of top ranked welds provide substantially greater life to MS piping systems. Some fitness-for-service and risk-based programs for MS piping system girth weldments recommend a stress evaluation using typical pressure vessel or boiler tube calculations, in which the hoop stress is the principal stress. In some cases, the effective weldment stresses can be more than 50 percent above the hoop stress, resulting in the estimated remaining lives less than 15 percent of the life estimates using the hoop stress methodology. Some HEP life management programs may vaguely discuss using the principal stress based on a finite element analysis of the piping system. These principal stress values may be based on a conventional as-designed piping stress analysis. In the majority of the as-found piping stress analyses performed by the author, the maximum as-found stresses are substantially greater than the maximum conventional as-designed piping stresses. Consequently, an as-designed piping stress analysis will typically underestimate the life of an HEP system and typically not predict the locations of maximum creep/fatigue damage.

Life Management of Main Steam and Hot Reheat Piping Systems: Part 2

2006 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Data Collection ◽  
Fatigue Damage ◽  
Terminal Point ◽  
Piping System ◽  
Material Damage ◽  
Life Management ◽  
Piping Systems ◽  
Creep Fatigue ◽  
Girth Welds ◽  
Main Steam

Since there have been several instances of weldment failures in main steam (MS) and hot reheat (HRH) piping systems, most utilities have developed programs to examine their most critical welds. Many utilities select their MS and HRH critical girth welds for examination by consideration of some combination of the ASME B31.1 Code [1] (Code) highest sustained stresses, highest thermal expansion stresses, terminal point locations, and fitting weldments. This paper suggests the use of an alternative life management methodology to prioritize material damage locations based on realistic stresses and applicable damage mechanisms. This methodology is customized to each piping system, considering applicable affects, such as operating history, measured weldment wall thicknesses, observed support anomalies, actual piping thermal displacements, and more realistic time-dependent multiaxial stresses. The high energy piping life consumption (HEPLC) methodology for MS and HRH critical girth welds may be considered as a rational approach to determine critical weldment locations for examinations and to determine appropriate reexamination intervals as a risk-based evaluation technique. The HEPLC methodology has been implemented over the past 15 years to provide more realistic estimates of actual displacements, stresses, and material damage based on the evaluation of field conditions. This HEPLC methodology can be described as having three basic phases: data collection, evaluation, and recommendations. The data collection phase includes obtaining design and post construction piping and supports information. The effects of current piping loads and anomalies are evaluated for potential creep/fatigue damage at the most critical weldments. The top ranked weldments of the HEPLC study are than selected as the highest priority examination locations. The author has completed many HEPLC studies of MS and HRH piping systems. The previous paper (Part 1) provided examples of data collection results and documentation of observed piping system anomalies. This paper will provide examples of evaluation results and recommendations, including a few case histories that have correctly ranked and predicted locations of significant creep/fatigue damage.

Ranking of Creep Damage in Main Steam Piping System Girth Welds Considering Multiaxial Stress Ranges

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Marvin J. Cohn ◽  
Fatma G. Faham ◽  
Dipak Patel
Keyword(s):  
Creep Damage ◽  
High Energy ◽  
Sustained Load ◽  
Piping System ◽  
Multiaxial Stress ◽  
Analysis Model ◽  
Principal Stresses ◽  
Piping Systems ◽  
Girth Welds ◽  
Main Steam

A high-energy piping (HEP) asset integrity management program is important for the safety of plant personnel and reliability of the fossil plant generating unit. HEP weldment failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. The main steam (MS) piping system is one of the most critical HEP systems. Creep damage assessment in MS piping systems should include the evaluation of multiaxial stresses associated with field conditions and significant anomalies, such as malfunctioning supports and significant displacement interferences. This paper presents empirical data illustrating that the most critical girth welds of MS piping systems have creep failures which can be successfully ranked by a multiaxial stress parameter, such as maximum principal stress. Inelastic (redistributed) stresses at the piping outside diameter (OD) surface were evaluated for the base metal of three MS piping systems at the piping analysis model nodes. The range of piping system stresses at the piping nodes for each piping system was determined for the redistributed creep stress condition. The range of piping stresses was subsequently included on a Larson–Miller parameter (LMP) plot for the grade P22 material, revealing the few critical (lead-the-fleet) girth welds selected for nondestructive examination (NDE). In the three MS piping systems, the stress ranges varied from 55% to 80%, with only a few locations at stresses beyond the 65 percentile of the range. By including evaluations of significant field anomalies and the redistributed multiaxial stresses on the outside surface, it was shown that there is a good correlation of the ranked redistributed multiaxial stresses to the observed creep damage. This process also revealed that a large number of MS piping girth welds have insufficient applied stresses to develop substantial creep damage within the expected unit lifetime (assuming no major fabrication defects). This study also provided a comparison of the results of a conventional American Society of Mechanical Engineers (ASME) B31.1 Code as-designed sustained stress analysis versus the redistributed maximum principal stresses in the as-found (current) condition for a complete set of MS piping system nodes. The evaluations of redistributed maximum principal stresses in the as-found condition were useful in selecting high priority ranked girth weldment creep damage locations. The evaluations of B31.1 Code as-designed sustained load stresses were not useful in selecting high priority creep damage locations.

Developing and Implementing Ch. VII O&M Programs at CCGT Plants: Case Studies

2021 ◽  
Author(s):  
Peter Jackson ◽  
Robert Rosario ◽  
Andreas Fabricius ◽  
Anita Johny ◽  
Alexandria Wholey
Keyword(s):  
High Temperature ◽  
High Energy ◽  
Piping System ◽  
Inspection Planning ◽  
Accelerated Corrosion ◽  
Advantages And Disadvantages ◽  
Effective Implementation ◽  
Creep Fatigue ◽  
The Usa ◽  
High Temperature Steam

Abstract We will present the results from several projects from the USA and other jurisdictions where ASME B31.1 Ch. VII O&M Covered Piping System (CPS) Programs have been implemented at several types of natural gas-fired CCGT plants. Common elements of programs for different plants will be summarized as well as plant-specific considerations for high energy piping condition assessment for newer plants. Pros and cons between a common program for a thermal fleet and plant-specific programs will be discussed including advantages and disadvantages of each approach. Effective implementation of parts of the Nonmandatory Appendix V guidance within the CPS Program will be described and recommendations for best practices. A brief overview of degradation-specific mechanisms for high energy piping and approaches for planninng/scheduling NDE inspections will be described. This overview will include: creep, fatigue, corrosion (erosion-corrosion - E/C and flow accelerated corrosion - FAC) as well as mechanisms that are commonly responsible for high energy piping leaks, failures and repairs including thermal quench cracking of HRSG interstage, terminal desuperheaters and turbine bypass attemperators. A brief summary of Gr. 91 inspection planning in Ch. VII O&M Programs will also be included as well as corrosion under insulation (CUI) and common inspection scopes for high temperature steam drains. Resolution of constant force and variable spring pipe supports on high pressure/high temperature piping that are not accommodating thermal expansion as per their engineering design can be evaluated using pre-outage pipe stress models and data obtained from field walkdowns to support rapid decisions for repair/replacement in the field. Finally, experiences with long term scheduling the need for adaptive management of the CPS Programs will be summarized with typical management oversight actions described for effective implementation.

The TransAlta High-Energy Piping Program—A Five-Year History

2000 ◽  
Vol 123 (1) ◽  
pp. 65-69 ◽  
Author(s):  
Marvin J. Cohn,
Keyword(s):  
Creep Damage ◽  
Analytical Techniques ◽  
High Energy ◽  
Management Plan ◽  
Piping System ◽  
Engineering Consulting ◽  
Piping Systems ◽  
Creep Fatigue ◽  
Sustained Loads ◽  
Selection Of

In 1995, the High-Energy Piping Strategic Management Plan (HEPSMP) was initiated at TransAlta Utilities Corporation (TAU) for the three generating facilities. At that time, it was recognized that several of the piping systems were exhibiting signs of creep relaxation, with some hangers bottomed or topped out online and/or offline. Previous hanger adjustment attempts were not always adequate. The program workscope included: 1) hot and cold piping system walkdowns, 2) selection of high-priority girth weld inspection locations, 3) examination of critical weldments, 4) weld repairs where necessary, 5) adjustments or modifications of malfunctioning steam line hangers, and 6) recommended work for future scheduled outages. Prior to 1996, examination locations were limited to the traditional locations of the terminal points at the boiler and turbine, with reexaminations occurring at arbitrary intervals. Since the terminal points are not necessarily the most highly stressed welds causing service-related creep damage, service damage may not occur first at the pre-1996 examined locations. There was a need to maximize the safety and integrity of these lines by ensuring that the highest risk welds were identified and given the highest priority for examination. An engineering consulting company was selected to prioritize the highest risk weldments for each piping system. This risk-based methodology included the prediction and evaluation of actual sustained loads, thermal expansion loads, operating loads, multiaxial stresses, creep relaxation, and cumulative creep life exhaustion. The technical process included detailed piping system walkdowns and application of advanced analytical techniques to predict and rank creep/fatigue damage for each piping system. TAU has concluded that the program has met its objective of successfully prioritizing inspection locations. The approach has also resulted in reducing the scope and cost of reexaminations. Phases 1 and 2 evaluations and examinations have been completed for all units. Results of some of the important aspects of this program are provided as case history studies.

Risk-Based Inspection Applied to Main Steam and Hot Reheat Piping Systems

2007 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Cost Effective ◽  
High Energy ◽  
Accurate Estimate ◽  
Terminal Point ◽  
Rational Approach ◽  
Piping System ◽  
Piping Systems ◽  
Risk Areas ◽  
Main Steam ◽  
Life Consumption

Many utilities select critical welds in their main steam (MS) and hot reheat (HRH) piping systems by considering some combination of design-based stresses, terminal point locations, and fitting weldments. The conventional methodology results in frequent inspections of many low risk areas and the neglect of some high risk areas. This paper discusses the use of a risk-based inspection (RBI) strategy to select the most critical inspection locations, determine appropriate reexamination intervals, and recommend the most important corrective actions for the piping systems. The high energy piping life consumption (HEPLC) strategy applies cost effective RBI principles to enhance inspection programs for MS and HRH piping systems. Using a top-down methodology, this strategy is customized to each piping system, considering applicable effects, such as expected damage mechanisms, previous inspection history, operating history, measured weldment wall thicknesses, observed support anomalies, and actual piping thermal displacements. This information can be used to provide more realistic estimates of actual time-dependent multiaxial stresses. Finally, the life consumption estimates are based on realistic weldment performance factors. Risk is defined as the product of probability and consequence. The HEPLC strategy considers a more quantitative probability assessment methodology as compared to most RBI approaches. Piping stress and life consumption evaluations, considering existing field conditions and inspection results, are enhanced to reduce the uncertainty in the quantitative probability of failure value for each particular location and to determine a more accurate estimate for future inspection intervals. Based on the results of many HEPLC projects, the author has determined that most of the risk (regarding failure of the pressure boundary) in MS and HRH piping systems is associated with a few high priority areas that should be examined at appropriate intervals. The author has performed many studies using RBI principles for MS and HRH piping systems over the past 15 years. This life management strategy for MS and HRH critical welds is a rational approach to determine critical weldment locations for examinations and to determine appropriate reexamination intervals as a risk-based evaluation technique. Both consequence of failure (COF) and likelihood of failure (LOF) are considered in this methodology. This paper also provides a few examples of the application of this methodology to MS and HRH piping systems.

Failure Investigation of a Low Chrome Long-Seam Weld in a High-Temperature Refinery Piping System

1995 ◽  
Vol 117 (3) ◽  
pp. 227-237 ◽  
Author(s):  
G. M. Buchheim ◽  
D. A. Osage ◽  
R. G. Brown ◽  
J. D. Dobis
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Stress Analysis ◽  
Hoop Stress ◽  
Weld Seam ◽  
Creep Damage ◽  
Piping System ◽  
Testing Program ◽  
Metallurgical Investigation ◽  
Fabrication Tolerances

The results of an investigation of a long-seam welded low chrome pipe that failed in a high-temperature refinery piping system are presented in this paper. Based upon the results of a metallurgical investigation, which included a creep testing program and a detailed finite element stress analysis, the cause of the failure has been attributed to creep damage at the weld seam. The metallurgical investigation and creep testing program indicated that the 1-1/4 Cr-1/2 Mo pipe material was normalized and exhibited greater than average creep strength and creep ductility. The results of a piping stress analysis indicated that all pressure, weight, and thermal stresses were in compliance with the ASME B31.3 Piping Code (ASME, 1993a). Nonetheless, the pipe failed after only 100,000 h at a nominal hoop stress of 6 ksi (41.4 MPa) with an operating temperature range of 970°F (521°C) to 1000°F (538°C). Results from subsequent detailed finite element stress analyses of the failed pipe indicated that very high localized bending stresses were present in the pipe due to peaking at the long-seam weld. These stresses partially relax by creep, but after 100,000 h they were still approximately 38 percent higher than the nominal hoop stress. The creep strains resulting from stress relaxation and those associated with the long-term value of the sustained stresses cause severe creep damage at the weld seam. As a result of this damage, cracks initiated at the inside of the pipe and primarily grew through the HAZ/fusion line until an 18-in. through-wall crack developed. The pipe was produced to ASTM A691, Grade 1-1/4 Cr, Class 41 (ASTM, 1989), and the peaked geometry was found to satisfy the fabrication tolerances of this standard. The need for the development of an acceptable tolerance for peaking in addition to the outside diameter and out-of-roundness fabrication tolerances currently included in this standard is highlighted for long-seam welded pipe that is to operate in the creep range.

An Experimental Study of Small Sized Reactors Containment Heat Transfer Phenomena Under MSLB Accident

2016 ◽  
Author(s):  
YeYun Wang ◽  
ShengFei Wang
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Ambient Pressure ◽  
High Energy ◽  
Operating Conditions ◽  
Normal Operation ◽  
Working Fluid ◽  
Steel Shell ◽  
Measuring Point ◽  
Main Steam

Main Steam Line Break (MSLB) accident will lead to the release of high-energy steam inside the containment, then cause the pressure and temperature of containment rise, which threatening containment integrity and the normal operation of the containment equipment. Containment equipment layout will affect the flow of steam, while the break position, steam temperature and other factors also affect the temperature distribution inside the containment. Test bench was reconstructed on the original foundation, but analogs of Pressure Vessel and CMT have not been arranged in the simulated reactor containment at this stage. Experiments with steam as the working fluid were carried out at ambient pressure environment. Steam injected into the containment and after reaching steady state data acquisition card got temperature values of each measuring point. The main purpose of this work is to study the temperature distribution inside containment and heat transfer phenomenon of steel shell in MSLB accident. Experimental results show that the temperature stratification appears in the containment, although the temperature distribution in the shell is different under different operating conditions.

A Quantitative Approach to a Risk-Based Inspection Methodology of Main Steam and Hot Reheat Piping Systems

2008 ◽  
Author(s):  
Marvin J. Cohn ◽  
Jeffrey T. Fong ◽  
Philip M. Besuner
Keyword(s):  
Failure Probability ◽  
High Energy ◽  
Quantitative Approach ◽  
Life Management ◽  
Probability Estimates ◽  
Richter Scale ◽  
Inspection Strategy ◽  
Piping Systems ◽  
Definition Of ◽  
Main Steam

This paper presents an evaluation of the failure probability and cost of high energy piping (HEP) failures. Using a conventional definition of risk as the product of failure probability and failure consequence, we propose in this paper a dollar value of consequence in order to develop a quantitative approach to risk-based inspection (RBI) methodology. A 16-year historical database of probability and consequence was evaluated as an RBI methodology for devising a life management strategy for welds in main steam and hot reheat piping systems. This evaluation provides us the raw data necessary for producing a concrete example of this new Richter-scale-like approach. Uncertainty in consequence and probability estimates is also provided in plotting (a) a static consequence vs. likelihood diagram at a specific time for comparing the relative severity of a variety of potential failures, and (b) a dynamic risk vs. time diagram for a specific hardware under continuous monitoring where the effect of life management decisions over a period of time is quantitatively displayed. Significance of this new approach to risk-based inspection strategy for advancing the state-of-the-art of managing aging structures is discussed.

Analysis on Energy-Saving Reconstruction of Jinshan Water Pumping Station in Zhenjiang

2018 ◽  
Author(s):  
Yin Luo ◽  
Bo Gong ◽  
Shouqi Yuan ◽  
Hui Sun ◽  
Zhixiang Xiong
Keyword(s):  
Energy Saving ◽  
High Energy ◽  
Operating Conditions ◽  
Piping System ◽  
Suction Pump ◽  
Pumping Station ◽  
Pump Station ◽  
Manufacturing Testing ◽  
Low Efficiency ◽  
The Cost

For the reason that current pump performance parameters and its piping system do not match, a new plan was proposed in this study to improve the low efficiency and reduce the high-energy consumption of Zhenjiang water intake pump station. According to the measured data in the field and the design information of the pumping station system, the simulation model of the pumping station is established with the help of commercial software Flowmaster. Based on this model, the simulation of various operating conditions is carried out. Considering the running condition of the pump station in the past years, the design condition spectrum of the new pump station is finally formed. On the purposes of optimizing the scheduling and decreasing the reconstruction cost, the implementation plan of pump station reconstruction was determined. Under the guidance of the plan, the work of design, manufacturing, testing, installation and debugging of a new type of double suction pump are completed in combination with the actual situation. The results show that the cost of electricity can be saved by 35,000 dollars and the cost of reconstruction can be recovered in less than one year. This study realizes energy-saving in the pumping station operation.

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