Fitness-for-Service of Longitudinal Seam Welds

2010 ◽  
Author(s):  
Dwight D. Agan ◽  
Marvin J. Cohn ◽  
Henry D. Vaillancourt
Keyword(s):  
Operating Temperature ◽  
High Energy ◽  
Management Program ◽  
Piping System ◽  
Operating Pressure ◽  
Seam Weld ◽  
Piping Systems ◽  
Average Operating ◽  
Operating Temperatures ◽  
Longitudinal Seam

A high energy piping (HEP) asset integrity management program is important for the safety of power plant personnel and reliability of the generating units. Hot reheat (HRH) longitudinal seam weld failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. The HRH piping system is one of the most critical HEP systems. Since high temperature creep is a typical failure mechanism for longitudinal seam welds, the probability of failure increases with unit operating hours. This paper concludes that some seam welded spools in this specific HRH piping system are more likely to fail earlier than other spools, depending on their actual wall thicknesses and operating temperatures. In this case study, the HRH piping system has operated over 200,000 hours and experienced about 400 starts since commercial operation. There are two separate HRH lines, Lines A and B, for this piping system. The 36-inch OD pipe has a specified minimum wall thickness (MWT) of 1.984 inches. Pipe wall thicknesses were measured in 57 spools. The measured spool MWT values varied from 1.981 to 2.122 inches. On average, Line A operated about 8°F higher than Line B. A comparative risk assessment was performed using the estimated average temperatures and pressures throughout the life of this HRH piping system. Data associated with the reported failures or near failures of seam welded Grade 22 piping systems were plotted as log σHoop versus the Larson Miller Parameter (LMP). The range of log σHoop and LMP values for this unique piping system was also plotted, based on the average operating pressure and the range in the average operating temperatures and the measured spool MWT values. The Line A (with a higher average operating temperature) seamed spool having the lowest measured MWT fell slightly above the threshold line of reported seam weld pipe failures. The Line B (with a lower average operating temperature) seamed spool having the lowest MWT is about 10 operating years from reaching the threshold of reported seam weld pipe failures. The Line A seamed spool having the highest measured MWT is about 8 operating years from reaching the threshold of reported seam weld pipe failures. The Line B seamed spool having the highest measured MWT is more than 18 operating years from reaching the threshold of historical seam weld pipe failures.

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.

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.

Creep Relaxation Behavior of High-Energy Piping

2000 ◽  
Vol 122 (4) ◽  
pp. 488-493 ◽  
Author(s):  
Raymond K. Yee ◽  
Marvin J. Cohn
Keyword(s):  
Stress Relaxation ◽  
Thermal Loading ◽  
Elevated Temperatures ◽  
Three Dimensional ◽  
Creep Damage ◽  
High Energy ◽  
External Loading ◽  
Piping System ◽  
Dead Weight ◽  
Piping Systems

The analysis of the elastic stresses in high-energy piping systems is a routine calculation in the power and petrochemical industries. The American Society of Mechanical Engineers (ASME) B31.1 Power Piping Code was developed for safe design and construction of pressure piping. Postconstruction issues, such as stress relaxation effects and selection of maximum expected creep damage locations, are not addressed in the Code. It has been expensive and time consuming to evaluate creep relaxation stresses in high energy piping systems, such as main steam and hot reheat piping. After prolonged operation of high-energy piping systems at elevated temperatures, it is very difficult to evaluate the redistribution of stresses due to dead weight, pressure, external loading, and thermal loading. The evaluation of stress relaxation and redistribution is especially important when nonideal conditions, such as bottomed-out or topped-out hangers, exist in piping systems. This paper uses three-dimensional four-node quadrilateral shell elements in the ABAQUS finite element code to evaluate the time for relaxation and the nominal relaxation stress values for a portion of a typical high-energy piping system subject to an ideally loaded hanger or to an overloaded hanger. The stress relaxation results are evaluated to suggest an approximation using elastic stress analysis results. [S0094-9930(00)01304-4]

Integrity Evaluation of an Older Vintage ERW Pipeline

2002 ◽  
Author(s):  
Geoff B. Rogers ◽  
Steve C. Rapp ◽  
Garry M. Matocha
Keyword(s):  
Planning Process ◽  
Ultrasonic Inspection ◽  
Mechanical Damage ◽  
Project Planning ◽  
Operating Pressure ◽  
Seam Weld ◽  
Weld Defects ◽  
Natural Gas Pipeline ◽  
Longitudinal Seam ◽  
Future Project

As part of a program to increase the operating pressure of a 20” (508.0mm) natural gas pipeline, a careful plan was developed and executed to ensure the integrity of the pipeline. The pipeline was built in 1943 using linepipe produced having a DC ERW longitudinal seam weld and travels along a densely populated route in the suburbs of Philadelphia. The work plan included ILI inspection methods to detect corrosion (MFL tool), mechanical damage (geometry tool), and ERW seam weld defects (TFI MFL tool). After the anomalies were identified and the necessary pipe replacements were completed, the pipeline was hydrostatically tested prior to being returned to service at the newly established operating pressure. The paper will describe the project planning process used to ensure the fitness and reliability of the pipeline and provide a review of the ILI results, excavations, pipe replacements, and hydrostatic test experiences. Of particular interest were the capabilities and limitations of the TFI tool to detect, discriminate, and size ERW seam weld defects. Seam weld defects were evaluated using ILI inspection methods and in many cases field prove-up ultrasonic inspection methods. When an ERW defect was confirmed by field NDT prove-up, the pipe section was removed and metallographic work was conducted to characterize the ERW flaw size and nature. A correlation was then possible between the sizing capability of the TFI tool, the ultrasonic prove-up method, and the actual defect size. All this information is useful to establish a level of confidence in defect sizing for future project needs. The final validation of the pipeline fitness at the higher operating pressure was established through the successful hydrostatic test. A short summary will be given on how the pipeline fitness was qualified and demonstrated.

The Importance of High Energy Piping Support Maintenance to Enhance System Useful Life

2015 ◽  
Author(s):  
Samuel A. Huff ◽  
John P. Leach ◽  
Daniel S. Vail
Keyword(s):  
High Energy ◽  
Life Extension ◽  
Piping System ◽  
Support Design ◽  
Piping Systems ◽  
Proper Design ◽  
Useful Life ◽  
High Level ◽  
Extension Program

As part of the design basis of any piping system utilized to convey materials, pipe supports are required to ensure those pipes remain in their designed locations and do not overly expand or move due to sustained or occasional loads. These loads represent the total forces and moments in the piping components and as a result create stresses that affect the life of the component. Proper design and maintenance of these supports per the applicable codes and standards provide a reasonable life expectancy for the piping systems. This presentation will review the various codes and standards utilized for both pipe support design and maintenance. A high level overview of what information must be obtained to perform an analysis and meet ASME B31.1 Power Piping code requirements when modifying piping systems will be presented. Specific inputs to system design and computational software including material properties, stress intensification factors (SIF), thicknesses and tolerances, pressures, temperatures, insulation, coatings, the occasional loads, etc. will be discussed. Guidelines will be discussed for determining what piping modifications warrant a full pipe stress analysis to be performed. Recommendations for pipe support maintenance inspections will be provided to facilitate increased life expectancies of subject piping systems. The mandatory requirements of ASME B31.1 Chapter VII will be discussed, as well as recommendations from the non-mandatory appendix. Implementing maintenance programs at existing facilities will be discussed. Step by step recommendations for how to apply these guidelines within a long-term life extension program will be given. Tolerances and general guidelines associated with these programs will also be discussed. Finally, common pipe support failures, what they can affect, and how to look for early indicators of fatigue or failure will be covered.

Reliability of LBB Evaluation Considering Randomness in Design Parameters

2011 ◽  
Author(s):  
Arindam Chakraborty ◽  
Haiyang Qian ◽  
Angah Miessi
Keyword(s):  
Material Properties ◽  
Factor Of Safety ◽  
Leak Detection ◽  
High Energy ◽  
Design Parameters ◽  
Piping System ◽  
Operating Pressure ◽  
Detection Capability ◽  
Crack Morphology ◽  
Input Parameters

In US, definition of the Leak-Before-Break (LBB) approach and criteria for its use are provided in NUREG-1061. Volume 3 of NUREG-1061 defines LBB as “…the application of fracture mechanics technology to demonstrate that high energy fluid piping is very unlikely to experience double-ended ruptures or their equivalent as longitudinal or diagonal splits.” Current LBB evaluation uses a factor of safety of two (2) on critical flaw size and a factor of safety of ten (10) on detectable leakage to deterministically analyze, that for a given set of input those factors are achieved. Typical input for LBB evaluation consists of pipe geometry, material properties (both elastic and plastic), crack morphology, loads, and operating pressure and temperature. Since LBB has recently been applied for pipes with weld overlays (WOL), thickness, material properties, and crack morphology of WOL also becomes important. However, in real structure all the design parameters (input) for LBB evaluation are inherently random in nature. The current work includes randomness in the critical design input parameters for LBB evaluation. Based on the result of this study reliability (or its compliment, probability of failure) curves are obtained based on the randomness in the critical input parameters. A piping system is considered to fail the LBB evaluation if the actual leakage through the pipe is less than the required leak rate which is calculated as ten times the plant minimum leak detection capability. Separate reliability curves are obtained for various minimum plant leak detection capability piping (e.g.,…, 1, 0.5,…, 0.1 GPMs) and for various piping systems (large diameter pipes such as reactor coolant loop hot leg and cold leg; and small diameter pipes such as pressurizer surge line, etc.). The reliability curves give an insight into the likelihood for a deterministic design input based LBB evaluation to remain valid in view of the in-situ variations.

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.

High Energy Piping Walkdowns in Compliance With ASME B31.1

2021 ◽  
Author(s):  
Marvin J. Cohn ◽  
Robert J. Gialdini ◽  
Osborne B. Nye
Keyword(s):  
High Energy ◽  
Management Program ◽  
Piping System ◽  
Original Design ◽  
Structure Damage ◽  
Qualified Personnel ◽  
American Society ◽  
Position Indicator ◽  
Operating Company ◽  
Spring Support

Abstract This paper discusses high energy piping (HEP) system walkdown requirements and guidelines in compliance with the American Society of Mechanical Engineers (ASME) B31.1 Code. Chapter VII states that the Operating Company shall develop and implement a program requiring documentation of piping support readings and recorded piping system displacements. Guidelines for this program are provided in Nonmandatory Appendix V, para. V-7. The Code also requires that the Operating Company shall evaluate the effects of unexpected piping position changes, significant vibrations, and malfunctioning supports on the piping system’s integrity and safety. These requirements and guidelines have been developed for personnel safety and piping system reliability. The HEP system should be maintained to behave as expected in the original design analysis unless a field change is justified by qualified personnel. The walkdown program should be an integral part of an asset integrity management program, including observations, documentation, evaluations, corrective actions, and countermeasures. A thorough HEP system walkdown includes more than documented hanger readings. It should include visual assessments of possible sagging pipe, unusual pipe slopes, building structure damage, lagging/insulation damage, locked spring hangers, piping interferences, damaged spring coils, loose/missing support fasteners, unloaded rigid supports, bent struts, insufficient hydraulic fluid in snubbers, detached Teflon strips on sliding supports, and confirmation that the current supports are consistent with the original design specifications. If accessible, it should be confirmed that there are no gaps in the sliding supports. This paper illustrates that it is now possible to photographically document spring support position indicator readings from distances up to 30 feet (9.1 meters). Photographic documentation provides higher confidence in the position indicator readings and can resolve many visual documentation discrepancies, such as incorrect support readings, readings from opposite position indicator sides, and parallax issues. If accessible, closer inspections may confirm if a spring support is in fact internally bottomed-out or topped-out. Nonmandatory Appendix V provides recommended hot walkdown and cold walkdown forms. These forms provide additional space for applicable notes. Example photographs of many piping system anomalies and associated documentation are provided in this paper. ASME B31.1 requires that significant displacement variations from the expected design displacements shall be considered to assess the piping system’s integrity.

Deficient Materials in Hot Reheat Seam Welded High-Energy Piping

2017 ◽  
Author(s):  
Kent Coleman ◽  
Stan Rosinski ◽  
Jude Foulds
Keyword(s):  
Filler Metal ◽  
Damage Mechanism ◽  
High Energy ◽  
Management Program ◽  
Life Assessment ◽  
Thick Wall ◽  
Premature Failure ◽  
The World ◽  
Piping Systems ◽  
American Society

Although failures of seam welded high-energy piping date to about 1970, the utility industry concern about premature failure of longitudinal seam welded piping has been of the utmost importance since the mid 1980’s driven primarily by well publicized piping failures at that time. The major concern is with hot reheat piping, some of which failed catastrophically resulting in substantial costs and personnel injury. Many utilities manage their high energy piping integrity through a combination of engineering analysis and periodic inspections. At many utilities around the world, however, high energy piping has not received the attention that normally occurs after a major failure because the perception is that there have been few failures. EPRI has compiled a database of over 50 failures and large areas of damage in utility piping systems around the world and it does not include the entire utility experience but still demonstrates the need for a diligent high energy piping integrity management program. The investigation of a recent failure in a 42 in. (1066 mm) diameter, 2 in. (50.8 mm) thick wall, ASTM A155 (American Society of Testing and Materials) seam welded hot reheat pipe demonstrated a first of its kind damage mechanism which determined that inappropriate welding filler metal was utilized for at least some of the weld passes resulting in a weldment that was weak in creep. Due to the placement of the incorrect welding filler metal, the failure occurred as a leak instead of a rupture however, the damage on the inside surface of the pipe extended for over 9ft. (2743 mm). This paper presents the results of the failure analysis and life assessment work performed and provides guidance for the rest of the utility fleet.

Remaining Life of High-Energy Piping Systems Using Equivalent Stress

1990 ◽  
Vol 112 (3) ◽  
pp. 260-265 ◽  
Author(s):  
M. J. Cohn
Keyword(s):  
Equivalent Stress ◽  
Creep Damage ◽  
High Energy ◽  
Piping System ◽  
Term Operation ◽  
Flexibility Analysis ◽  
Multiaxial Stress State ◽  
Piping Systems ◽  
System Life ◽  
American Society

Fossil power plant high-energy piping systems operated at high temperatures are subject to creep damage, which is a time-dependent phenomenon. Traditional guidelines, such as the American Society of Mechanical Engineers (ASME) B31.1 Power Piping Code, were developed for plants having design lives in the 25–30 yr regime. Since many of these systems are being operated beyond 200,000 hr, it is important to reconsider the methodology of creep damage analysis to assure reliable long-term operation. Seven high-energy piping systems were evaluated in this study. The analysis of a minimum piping system life due to creep considered two approaches. The first approach used the traditional ASME B31.1 flexibility analysis guidelines. The second approach considered more detailed multiaxial stress state types of evaluations. The various equivalent stress methods used all six load components from the flexibility analysis. In nearly every case, the equivalent stress methods predicted significantly higher stresses. Consequently, the equivalent stress methodology results in 14 to 97 percent lower time to rupture values as compared to the values predicted using ASME B31.1 stresses.

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