Enhanced Creep Life Evaluations for Grade 91 Circumferential Weldments

2017 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Applied Stress ◽  
Hoop Stress ◽  
Axial Stress ◽  
Creep Damage ◽  
Creep Rupture ◽  
Piping System ◽  
Remaining Life ◽  
Creep Life ◽  
Rupture Properties ◽  
Applied Stresses

The basic power piping creep life calculations consider the important variables of time, temperature and stress for the creep rupture properties of the unique material. Some engineering evaluations of remaining life estimate the applied stress as the design stress obtained from a conventional piping stress analysis. Other remaining life evaluations may assume that a conservative estimate of the applied stress is no greater than the hoop stress due to pressure. The creep rupture properties of the unique material are usually obtained from the base material creep rupture properties. The typical methodologies to estimate remaining life do not consider the actual applied stress due to malfunctioning supports, multiaxial stress effects, axial and through-wall creep redistribution, time-dependent material-specific weldment creep rupture properties, residual welding stresses, and actual operating temperatures and pressures. It has been determined that the initiation and propagation of Grade 91 creep damage is a function of stress to about the power of 9 at higher applied stresses. There have been many examples of malfunctioning piping supports creating unintended high stresses. When the axial stress is nearly as high as the hoop stress, the applicable corresponding uniaxial stress for creep rupture life is increased about 30%. Multiaxial stress effects in circumferential weldments (e.g., when the axial stress is nearly as high as the hoop stress) can reduce the weldment creep life to less than 1/6th of the predicted life assuming a uniaxial stress or hoop stress due to pressure only. Since 2012, the ASME B31.1 Code has required that significant piping displacement variations from the expected design displacements shall be considered to assess the piping system’s integrity [1]. This paper discusses a strategy for an enhanced creep life evaluation of power piping circumferential weldments. Piping stresses can vary by a factor greater than 2.0. Consequently, the range of circumferential weldment creep rupture lives for a single piping system may vary by a factor as high as 40. Although there is uncertainty in the operating times at temperatures and pressures, all of the weldments within the piping system have the same time, temperatures, and pressures, so the corresponding uncertainties for these three attributes are normalized within the same piping system. Since the applied stresses are the most important weld-to-weld variable within a piping system, it is necessary to have an accurate evaluation of the applied stresses to properly rank the creep rupture lives of the circumferential weldments. This methodology has been successfully used to select the lead-the-fleet creep damage in circumferential weldments over the past 15 years.

Creep Life Evaluations of ASME B31.1 Allowance for Variation From Normal Operations: 11 Materials

2019 ◽  
Author(s):  
Marvin J. Cohn ◽  
Ron Haupt
Keyword(s):  
Base Metal ◽  
Rupture Life ◽  
Creep Damage ◽  
Creep Rupture ◽  
Creep Life ◽  
Material Creep ◽  
Metal Creep ◽  
Life Consumption ◽  
Rupture Properties ◽  
Design Pressure

Abstract The ASME B31.1-2018 Power Piping Code (Code) paras. 102.2.4, 102.3.3, and 104.8.2 provide an allowance regarding operating above the design temperature and design pressure for short time periods. The concept of allowing occasional operation for short periods of time at higher than the design pressure or design temperature has been in the Code since 1967. These 1967 Code para. 102.2.4 limitations were based on engineering judgment that can now be quantitatively evaluated for the additional creep life consumption (creep rupture damage accumulation). This study primarily is a quantitative estimate of the permitted increased life consumption, considering minimum creep rupture properties, associated with the 2018 Code operating allowances for piping materials operating in the creep range. Eleven base metal materials are considered in this paper — low carbon steel, 1.25Cr 0.5Mo, 2.25Cr 1Mo, 9Cr 1 Mo V, Type 304 SS, Type 316 SS, Type 316L SS, Type 321 SS, Type 321H SS, Type 347 SS, and Type 347H SS. Results of this evaluation may be used to improve the ASME B31.1 Code, including a technical basis for a possible revision to para. 102.2.4. Previous studies have revealed that Grade P22 base metal creep damage is slightly more sensitive to stress than Grade P11 material creep rupture damage, and Grade P91 base metal creep damage is substantially more sensitive to stress than Grade P22 material creep rupture damage. Therefore, the allowable pressure and temperature variations result in a range of increased creep life consumption for different materials. The intent of this study was to modify the two Code allowance criteria so that the permitted increased creep life consumption (considering the minimum creep rupture properties of the material) of Allowance B is about the same amount as the increased creep life consumption result of Allowance A for the same material. Consequently, this study was performed to realign the allowable increased creep rupture life consumption of Allowance B to be approximately equivalent to the allowable increased creep life consumption of Allowance A. If the Allowance B event duration is increased from 80 hours per year to 400 hours per year, the Allowance B increased creep life consumption is slightly less than the Allowance A life consumption for each of these materials.

Creep Life Evaluations of ASME B31.1 Allowance for Variation From Normal Operation

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Base Metal ◽  
Creep Damage ◽  
Creep Rupture ◽  
Normal Operation ◽  
Piping System ◽  
Creep Life ◽  
Stress Increase ◽  
Material Creep ◽  
Metal Creep ◽  
Life Consumption

The ASME B31.1-2012 Power Piping Code (Code) paras. 102.2.4, 102.3.3, and 104.8.2 provide an allowance regarding operating above the design temperature and internal pressure for short time periods. This study is a quantitative evaluation of the permitted increased life consumption associated with the 2012 Code operating allowances for piping materials operating in the creep range. Three base metal materials are considered in this paper—ASTM A335 Grades P11, P22, and P91. Results of this evaluation could be used to improve the ASME B31.1 Code, including a technical basis for a recommended revision. The para. 102.2.4 allowables were evaluated: (A) 15% stress increase for 10% of the operating hours and (B) 20% stress increase for 1% of the operating hours. It was determined that these allowances increased the base metal creep rupture life consumption of Grade P11 material up to 8%, Grade P22 material up to 14%, and Grade P91 material up to 25%. Allowance A results in permitting significantly more creep life consumption than Allowance B. An evaluation was performed to realign the increased creep life consumption of Allowance B to be approximately equivalent to the increased creep life consumption of Allowance A. If Allowance B event duration is increased from 80 hrs per year to 400 hrs per year (from 1% to 5% of the operating hours per year), Allowance B increased the creep life consumption which is slightly less than Allowance A life consumption for Grades P11, P22, and P91 materials. Main steam (MS) and hot reheat (HRH) piping system typical operating temperatures and stresses were evaluated for these variation allowances. This study revealed that Grade P22 base metal creep damage is slightly more sensitive to stress than Grade P11 material creep rupture damage, and Grade P91 base metal creep damage is substantially more sensitive to stress than Grade P22 material creep rupture damage.

Fitness-for-Service Creep Life Evaluation of a Hot Reheat Piping System at 400,000 Operating Hours

2017 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Creep Damage ◽  
Creep Rupture ◽  
Piping System ◽  
High Confidence ◽  
Creep Life ◽  
Nondestructive Examination ◽  
Life Evaluation ◽  
Girth Welds ◽  
Stress Analyses

This paper discusses a fitness-for-service (FFS) evaluation of a hot reheat (HRH) piping system with about 400,000 hours of operation. It discusses significant differences between the as-designed and simulation as-found piping stress analyses. The significant range of stresses in the piping system illustrates that the few lead-the-fleet girth welds should have significant creep damage decades before many other girth welds. Since the weldment examination intervals will correspond to scheduled outages, the creep life uncertainties can be grouped into high, medium, and low priorities (e.g., 0–10 years, 10–20 years, and beyond 20 years) with high confidence of rankings among the selected groups. There are 14 girth welds in this HRH piping system. In this case study, only 2 girth welds were evaluated as high priority nondestructive examination (NDE) locations and 1 girth weld was evaluated as a medium priority location for the next set of NDE reexaminations. Many of the low priority girth welds have predicted creep rupture lives substantially beyond 1,000,000 operating hours.

Development of continuum damage in the creep rupture of notched bars

1984 ◽  
Vol 311 (1516) ◽  
pp. 103-129 ◽  
Keyword(s):  
New York ◽  
Damage Mechanics ◽  
Axial Stress ◽  
Numerical Procedure ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Constant Load ◽  
Creep Rupture ◽  
Continuum Damage ◽  
Discrete Crack

The creep rupture of circumferentially notched, circular tension bars which are subjected to constant load for long periods at constant temperature is studied both experimentally and by using a time-iterative numerical procedure which describes the formation and growth of creep damage as a field quantity. The procedure models the development of failed or cracked regions of material due to the growth and linkage of grain boundary defects. Close agreement is shown between experimental and theoretical values of the representative rupture stress, of the zones of creep damage and of the development of cracks for circular (Bridgman, Studies in large plastic flow and fracture , New York: McGraw-Hill (1952)) and British Standard notched specimens (B.S. no. 3500 (1969)). The minimum section of the circular notch is shown to be subjected to relatively uniform states of multi-axial stress and damage while the B.S. notch is shown to be subjected to non-uniform stress and damage fields in which single cracks grow through relatively undamaged material. The latter situation is shown to be analogous to the growth of a discrete crack in a lightly damaged continuum. The continuum damage mechanics theory presented here is shown to be capable of accurately predicting these extreme types of behaviour.

scholarly journals Creep rupture properties of bare and coated polycrystalline nickel-based superalloy Rene®80

2021 ◽  
pp. 36-36
Author(s):  
M.M. Barjesteh ◽  
S.M. Abbasi ◽  
K.Z. Madar ◽  
K. Shirvani
Keyword(s):  
Elevated Temperatures ◽  
Life Time ◽  
Creep Rupture ◽  
Polycrystalline Nickel ◽  
Creep Life ◽  
Nickel Based Superalloy ◽  
Platinum Aluminide ◽  
Rupture Properties ◽  
Low Activity ◽  
Rupture Behavior

Creep deformation is one of the life time limiting reasons for gas turbine parts that are subjected to stresses at elevated temperatures. In this study, creep rupture behavior of uncoated and platinum-aluminide coated Rene?80 has been determined at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 Mpa in air. For this purpose, an initial layer of platinum with a thickness of 6?m was applied on the creep specimens. Subsequently, the aluminizing were formed in the conventional pack cementation method via the Low Temperature-High Activity (LTHA) and High Temperature-Low Activity (HTLA) processes. Results of creep-rupture tests showed a decrease in resistance to creep rupture of coated specimen, compared to the uncoated ones. The reductions in rupture lives in LTHA and HTLA methods at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 MPa were almost (26% and 41.8%), (27.6% and 38.5%) and (22.4% and 40.3%), respectively as compared to the uncoated ones. However, the HTLA aluminizing method showed an intense reduction in creep life. Results of fractographic studies on coated and uncoated specimens indicated a combination of ductile and brittle failure mechanisms for all samples. Although, the base failure mode in substrate was grain boundary voids, cracks initiated from coating at 760?C/657MPa and 871?C/343. No cracking in the coating was observed at 982?C/190MPa.

Creep Life Simulation and Assessment of High Temperature Piping Systems and Components

2012 ◽  
Author(s):  
Brian Rose ◽  
James Widrig
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
High Temperature ◽  
Creep Behavior ◽  
Material Behavior ◽  
Piping System ◽  
Remaining Life ◽  
Creep Life ◽  
Element Analysis ◽  
Piping Systems

High temperature piping systems and associated components, elbows and bellows in particular, are vulnerable to damage from creep. The creep behavior of the system is simulated using finite element analysis (FEA). Material behavior and damage is characterized using the MPC Omega law, which captures creep embrittlement. Elbow elements provide rapid yet accurate modeling of pinching of piping, which consumes a major portion of the creep life. The simulation is used to estimate the remaining life of the piping system, evaluate the adequacy of existing bellows and spring can supports and explore remediation options.

Optimization of NDE Reexamination Locations and Intervals for Grade 91 Piping System Girth Welds

2015 ◽  
Author(s):  
Marvin J. Cohn ◽  
Michael T. Cronin ◽  
Fatma G. Faham ◽  
David A. Bosko ◽  
Erick Liebl
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Creep Rupture ◽  
Piping System ◽  
Creep Life ◽  
Stress Increase ◽  
Creep Crack ◽  
Grade 91 ◽  
Girth Welds ◽  
Stress Analyses

It has become apparent with the development of creep strength enhanced ferritic steels, the mandatory ASME B31.1 Chapter VII and the non-mandatory ASME B31.1 Appendix V guidelines require a more rigorous method to manage the Grade 91 piping integrity at Genesee Unit 3. Given the relatively young age of Genesee Unit 3, three questions have been asked: 1) when do the examinations start, 2) what locations should be examined first, and 3) how often should the same location be reexamined? To ensure that the best value is obtained from the reexamination budget, a five-step process can be effectively used to define and categorize the scope of each set of reexaminations in the girth weld integrity management program. The five processes are performing the following analyses: 1) an evaluation of the historical information, 2) piping system hot and cold walkdowns, 3) as-designed and as-found piping stress analyses, 4) creep life consumption evaluations, including elastic and inelastic axial and radial stress redistributions, and 5) creep crack growth curve analyses. Reexaminations of the few critical lead-the-fleet weldments are performed with lower examination costs and higher confidence. Evaluations of the Genesee Unit 3 main steam (MS) piping system revealed that the applicable weldment stress is probably the most significant parameter in determining the Grade 91 girth weld critical reexamination locations and intervals. ASME B31.1 piping stress analyses of the MS piping system have sustained load stress variations of more than 100% among the girth welds. The lower bound American Petroleum Institute (API) 579 creep rupture equation for Grade 91 operating at 1,060°F (571°C) indicates that the creep life is a function of stress to the power of 8.9; consequently, a 15% stress increase results in about 2/3 reduction of creep rupture life. Creep crack growth analyses of several of the MS piping system weldments revealed that the creep crack growth time to grow from 1/8 inch to through-wall is a function of stress to the power of 8.8; consequently, a 15% stress increase results in about 2/3 reduction of time for a 1/8-inch crack to grow through-wall. This evaluation reveals that a few critical lead-the-fleet locations should be reexamined most frequently and justification can be provided for much longer reexamination intervals of the remaining girth welds with much lower applied stresses.

Creep Life Evaluations of ASME B31.1 Allowance for Variation From Normal Operation

2014 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Base Metal ◽  
Rupture Life ◽  
Creep Damage ◽  
Creep Rupture ◽  
Normal Operation ◽  
Piping System ◽  
Stress Increase ◽  
Material Creep ◽  
Metal Creep ◽  
Life Consumption

The ASME B31.1-2012 Power Piping Code (Code) paras. 102.2.4, 102.3.3, and 104.8.2 provide an allowance regarding operating above the design temperature and internal pressure for short time periods. This study is an evaluation of the permitted increased life consumption associated with the above Code operating allowances for piping materials operating in the creep range. Three base metal materials are considered in this study, ASTM A335 Grades P11, P22, and P91. Two case studies were evaluated, A) 15% stress increase for 10% of the operating hours, and B) 20% stress increase for 1% of the operating hours. It was determined that these allowances increased the base metal creep rupture life consumption of Grade P11 material up to 8%, Grade P22 material up to 14%, and Grade P91 material up to 25%. Allowance A results in permitting significantly more creep damage life consumption than Allowance B. Main steam and hot reheat piping system typical operating temperatures and stresses were evaluated for these variation allowances. This study revealed that Grade P22 base metal creep damage is slightly more sensitive to stress than Grade P11 material creep rupture damage, and Grade P91 base metal creep damage is substantially more sensitive to stress than Grade P22 material creep rupture damage.

scholarly journals Experimental Investigation and Modeling of Damage Accumulation of EN-AW 2024 Aluminum Alloy under Creep Condition at Elevated Temperature

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 404
Author(s):  
Adam Tomczyk ◽  
Andrzej Seweryn
Keyword(s):  
Damage Accumulation ◽  
Axial Stress ◽  
Axial Strain ◽  
Creep Condition ◽  
Creep Damage ◽  
Creep Rupture ◽  
Uniaxial Tensile ◽  
Creep Tests ◽  
Damage State ◽  
2024 Aluminum Alloy

The paper is focused on creep-rupture tests of samples made of the 2024 alloy in the T3511 temper under uniaxial tensile stress conditions. The basic characteristics of the material at the temperatures of 100, 200 and 300 °C were determined, such as the Young’s modulus E, yield point σy, ultimate tensile strength σc and parameters K and n of the Ramberg–Osgood equation. Creep tests were performed for several different levels of nominal axial stress (load) at each temperature. It was observed that in the process of creep to failure at 200 and 300 °C, as the stress decreases, the creep time increases and, at the same time, the strain at rupture increases. However, such a regularity is maintained until a certain transition stress value σt is reached. Reducing the stress below this value results in a decreased value of the strain at rupture. A simple model of creep damage accumulation was proposed for the stress range above the transient value. In this model, the increase in the isotropic damage state variable was made dependent on the value of axial stress and the increase in plastic axial strain. Using the results of experimental creep-rupture tests and the failure condition, the parameters of the proposed model were determined. The surface of fractures obtained in the creep tests with the use of SEM technology was also analyzed.

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.

Sign in / Sign up

Export Citation Format

Share Document