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.

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.

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.

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.

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.

Fitness for Service of Degraded Grade 91 Pipe

2012 ◽  
Author(s):  
Marvin J. Cohn ◽  
Steve R. Paterson
Keyword(s):  
Power Plants ◽  
Thermal Stresses ◽  
Creep Rupture ◽  
Piping System ◽  
Principal Stresses ◽  
Support Costs ◽  
Material Creep ◽  
History Of ◽  
Grade 91 ◽  
Life Consumption

The use of creep strength enhanced ferritic alloys such as Grade 91 in fossil power plants has become popular for high temperature piping applications. Since Grade 91 has higher stress allowables than Grade 22, a designer can specify thinner component wall thicknesses, resulting in lower through-wall thermal stresses during transient events and lower material and piping support costs. During the past two decades, Grade 91 has been used successfully in fossil power plants. However, this alloy has had some incidents of non-optimal weldment microstructure. In this case study, Brinell hardness tests of an ASME A182 Grade F91 (F91) wye block, including upstream and downstream F91 spools, revealed several readings of soft material, as low as 168HB. A study of creep rupture tests of degraded Grade 91 specimens revealed that the lower bound creep rupture curve of the degraded Grade 91 material is above the average creep rupture curve of Grade 22 material for the range of the specific piping operating stresses. Based on the empirical evidence that the average Grade 22 material creep rupture curve is conservative for the creep rupture of degraded Grade 91 material, a life consumption evaluation was performed for the degraded Grade 91 weldments using Grade 22 creep rupture properties. A life fraction analysis was performed considering the redistributed maximum principal stresses, based on simulation of piping displacements obtained from the hot and cold walkdowns. This study also considered the recent history of the specific piping system operating pressures and temperatures. This study also considered dissimilar metal welds, from ASME A182 Grade F91 (F91) to ASME A335 Grade P22 (P22) materials. It was determined that the Grades F91-to-F91 weldments had about 30% life consumption and the remaining lives were at least 7 years. The Grades F91-to-P22 weldments had less than 40% life consumption and the remaining lives were at least 15 years.

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.

Evaluation of Creep Strength Reduction Factors for Welded Joints of Grade 122 Steel

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Yukio Takahashi ◽  
Masaaki Tabuchi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Thermal Power ◽  
Strength Reduction ◽  
Creep Rupture ◽  
Piping System ◽  
Type Iv ◽  
Rupture Data

HCM12A (ASME Grade 122) is used for boiler components in thermal power plants because of its high creep strength. However, a type IV creep damage formed in the heat-affected zone can cause a considerable decrease in the creep strength of the weldment and a failure of large diameter piping due to this damage took place recently in a thermal power plant. In order to update the design method and develop life estimation method for this kind of piping system with axial weld, the creep rupture data of base metal and welded joints have been collected and analyzed by the Strength of High-Chromium Steel Committee in Japan. In the present paper, the creep rupture data of over 400 points for welded joint specimens of HCM12A offered from six Japanese organizations are analyzed. These data clearly indicate that the long-term creep strength of the welded joints becomes weaker than that of the base metal at above 600°C due to the type IV fracture in the fine grain heat-affected zone. After the discussions on the effects of product form, welding procedure, specimen sampling procedure, etc., on the creep strength, the master creep life equation for the welded joints is developed. The so-called region decomposition technique was adopted to fit the data in both high and low stress regimes with a reasonable accuracy. The creep strength reduction factor obtained from 100,000 h creep strength of the welded joints and the base metal is given as a function of temperature.

Quantification of Creep Cavitation in Welded Joint and Evaluation of Material Characteristics of Simulated Heat-Affected Zone in X 20 CrMoV 12 1 Steel

2000 ◽  
Vol 123 (1) ◽  
pp. 112-117 ◽  
Author(s):  
Yong-Keun Chung ◽  
Cheol-Hong Joo ◽  
Jong-Jin Park ◽  
Ik-Man Park ◽  
Hyo-Jin Kim
Keyword(s):  
Base Metal ◽  
Heat Affected Zone ◽  
Power Plants ◽  
Welded Joint ◽  
Charpy Impact ◽  
Creep Damage ◽  
Average Diameter ◽  
Damage Mechanism ◽  
Creep Rupture ◽  
Creep Cavitation

X 20 CrMoV 12 1(DIN 17 175) steel has been used for components subjected to high temperature in power plants and chemical and petroleum industries. Therefore, extensive studies have been made on this steel. However, these studies focused mainly on the base metal, and few studies on the welded joint have been reported. Actually, a large number of failures have occurred at the welded joint, so there is increasing need to investigate the characteristics of X 20 CrMoV 12 1 weldment. In this study, the interrupted and creep rupture tests were carried out and quantification of the creep damage was attempted for the X 20 CrMoV 12 1 welded joint. The interrupted and creep rupture tests were performed at four conditions\M650-60, 600-100, 600-120, and 575-150(|SDC-MPa)\Mon the X 20 CrMoV 12 1 welded joint specimens, respectively. It was revealed from the experimental results that creep damage mechanism of a welded joint was mainly creep cavitation, and that the intensively damaged area by creep cavitations was the transition region from fine-grained heat-affected zone (HAZ) to unaffected base metal, namely intercritical HAZ. For both the interrupted and ruptured specimens, quantification of creep damage was attempted by evaluating cavitated area fraction, average diameter, and the number of cavities with creep life fraction. In addition, on the basis of the heat input during the welding, microstructure, microhardness, and grain size of the actual intercritical HAZ, simulated HAZ was made in order to evaluate its material properties. For the simulated HAZ specimens, tensile, charpy impact, and creep rupture tests were carried out. As a result, yield, tensile strength, and elongation of simulated HAZ were similar to those of base metal, respectively, and impact property of simulated HAZ was slightly above base metal. Also, it was found that creep strength of simulated HAZ was inferior to that of the base metal.

Evaluation of Creep Strength Reduction Factors for Welded Joints of HCM12A (P122)

2006 ◽  
Author(s):  
Yukio Takahashi ◽  
Masaaki Tabuchi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Thermal Power ◽  
Strength Reduction ◽  
Creep Rupture ◽  
Piping System ◽  
Type Iv ◽  
Rupture Data

HCM12A (ASME Grade 122) is used for boiler components in thermal power plants because of its high creep strength. However, type IV creep damage formed in heat affected zone brings about considerable decrease in creep strength of the weldment and a failure of large diameter piping in a thermal power plant due to this damage took place recently. In order to update the design method and develop life estimation method for this kind of piping system with axial weld, creep rupture data of base metal and welded joints has been collected and analyzed in the SHC (Strength of High-Chromium Steel) committee in Japan since 2004. In the present paper, the creep rupture data of over 400 points for welded joint specimens of HCM12A offered from six Japanese organizations were analyzed. These data clearly indicated that the long-term creep strength of welded joints becomes weaker than that of base metal at above 600C due to Type IV fracture in fine grain heat-affected zone. After discussing the effects of product form, welding procedure and specimen sampling etc. on the creep strength, the master creep life equation for the welded joints was developed. So-called region decomposition technique was adopted to fit the data both in high and low stress regimes with a reasonable accuracy. The creep strength reduction factor obtained from 100,000 hours creep strength of welded joints and base metal was given as a function of temperature.

Creep Life Prediction of HR3C Steel Using Creep Damage Models

2017 ◽  
Author(s):  
Hoomin Lee ◽  
Seok-Jun Kang ◽  
Jae-Boong Choi ◽  
Moon-Ki Kim
Keyword(s):  
Life Prediction ◽  
Power Plants ◽  
Creep Damage ◽  
Creep Rupture ◽  
Creep Life ◽  
Damage Models ◽  
Creep Life Prediction ◽  
Uniaxial Creep ◽  
Term Creep

The world’s energy market demands more efficient power plants, hence, the operating conditions become severe. For thermal plants, Ultra Super Critical (USC) conditions were employed with an operating temperature above 600°C. In such conditions, the main failure mechanism is creep rupture behavior. Thus, the accurate creep life prediction of high temperature components in operation has a great importance in structural integrity evaluation of USC power plants. Many creep damage models have been developed based on continuum damage mechanics and implemented through finite element analysis. The material constants in these damage models are derived from several accelerated uniaxial creep experiments in high stress conditions. In this study, the target material, HR3C, is an austenitic heat resistant steel which is used in reheater/superheater tubes of an USC power plant built in South Korea. Its creep life was predicted by extrapolating the creep rupture times derived from three different creep damage models. Several accelerated uniaxial creep tests have been conducted in various stress conditions in order to obtain the material constants. Kachanov-Rabotnov, Liu-Murakami and the Wen creep damage models were implemented. A comparative assessment on these three creep damage models were performed for predicting the creep life of HR3C steel. Each models require a single variable to fit the creep test curves. An optimization error function were suggested by the authors to quantify the best fit value. To predict the long term creep life of metallic materials, the Monkman-Grant model and creep rupture property diagrams were plotted and then extrapolated over an extended range. Finally, it is expected that one can assess the remaining lifetime of UCS power plants with such a valid estimation of long-term creep life.

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