An Estimator for the Influence of Service Temperature on Creep Rupture Life

2004 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Rupture Life ◽  
Safety Margin ◽  
Creep Damage ◽  
Creep Rupture ◽  
Accelerated Life ◽  
Approximate Relationship ◽  
Accelerated Creep ◽  
Technical Basis ◽  
Relationship Of ◽  
The Relationship

The 2001 ASME B31.1 Code (Code) has a warning to the piping designer regarding materials susceptible to creep damage. However, the Code does not prescribe a methodology to determine the accelerated life reduction for a component due to events resulting in operating temperatures in excess of the design temperature. In general, the quantitative evaluation of the service life of a component subject to creep damage is very complex. Nevertheless, the amount of accelerated creep damage due to increased temperature can be approximately estimated. This paper is the technical basis for a recent modification to the Code. It provides an approximate relationship of operating temperature and time for equivalent creep damage of typical power piping materials. Piping designers, plant operators, and plant engineers may use this information as a rough idea of the relationship of temperature and time to maintain an equivalent safety margin on creep rupture life. This evaluation includes a discussion of tolerance to temperature increase for some low chrome ferritic, intermediate chrome martensitic, and austenitic stainless steel alloys.

Fitting Creep-Rupture Life Distribution Using Accelerated Life Testing Data

2000 ◽  
Vol 122 (4) ◽  
pp. 482-487 ◽  
Author(s):  
M. Zuo ◽  
S. Chiovelli ◽  
Y. Nonaka
Keyword(s):  
Least Squares ◽  
Least Squares Method ◽  
Rupture Life ◽  
Creep Rupture ◽  
Accelerated Life Testing ◽  
Likelihood Method ◽  
Linear Regression Method ◽  
Life Distribution ◽  
Accelerated Life ◽  
Life Distributions

This paper comments on using the Larson-Miller parameter to fit the creep-rupture life distribution as a function of temperature and stress. The commonly used least-squares linear regression method assumes that the creep-rupture life follows the lognormal distribution. Most engineering literature does not discuss the validity of this assumption. In this paper, we outline the procedure for validating two critical assumptions when the least-squares method is used. The maximum likelihood method is suggested as an alternative and more powerful method for fitting creep-rupture life distributions. Examples are given to demonstrate the use of these two methods using Microsoft Excel and the LIFEREG procedure in SAS. [S0094-9930(00)00504-7]

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 Observed relationships between protein heterozygosity and protein genetic distance and comparisons with neutral expectations

1985 ◽  
Vol 45 (3) ◽  
pp. 315-340 ◽  
Author(s):  
R. D. Ward ◽  
D. O. F. Skibinski
Keyword(s):  
Genetic Distance ◽  
Neutral Theory ◽  
Frequency Data ◽  
Vertebrate Species ◽  
Empirical Relationships ◽  
Allele Frequency Data ◽  
Approximate Relationship ◽  
Neutral Models ◽  
Relationship Of ◽  
The Relationship

SummaryRelationships between protein genetic distance (D) and protein heterozygosity (H) were studied using allele frequency data for 42 proteins derived from multilocus electrophoretic surveys of genetic variation in over 200 invertebrate and over 300 vertebrate species. D¯ and H¯ values for the different proteins (mostly enzymes) were calculated, and large and significant correlations between D¯ and H¯ were found in comparisons of both intraspecific and interspecific populations. Empirical relationships between D¯ and H¯ were compared with neutral expectations under the stepwise model of neutral mutation with the assumption that populations are in equilibrium with respect to the effects of mutation and genetic drift.At low divergence levels, a linear relationship of D¯ on H¯ was observed, but at high levels of divergence D tended towards an asymptote at high H¯. The results at high divergence cannot be explained using the approximate relationship D = 2ut (where u = mutation rate, t = time). However, computer simulations of neutral models showed that changes of this nature in the relationship between D¯ and H¯ were to be expected as divergence increases, the equation D = 2ut being a poor approximation at high D We therefore conclude that the observed relationships between D¯ and H¯ are, in fact, compatible with equilibrium neutral theory.

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.

scholarly journals Study of Creep Damage in a 10.86% Cr Heat Resistant Steel using Synchrotron X-Ray Microtomography

2013 ◽  
Vol 794 ◽  
pp. 476-483
Author(s):  
C. Gupta ◽  
Hiroyuki Toda ◽  
C. Schlacher ◽  
Peter Mayr ◽  
Christof Sommitsch ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Rupture Life ◽  
Creep Damage ◽  
Void Volume Fraction ◽  
Resistant Steel ◽  
Heat Resistant Steel ◽  
X Ray ◽  
Heat Resistant ◽  
The Relationship ◽  
Fracture Specimens

Synchrotron X-ray microtomography(SR-μCT) scans have been carried out on sample coupons extracted from the fracture specimens of a 10.86% Cr heat resistant steel exposed to crep deformation at 873K over stresses of 120, 150, and 180 MPa. The 3D cavitation characteristics in terms of void volume fraction, numbwer density and size distribution as a function of the applied stress has been determined by quantitative analysis of the reconstructed tomograohy slice datasets. The relationship between heterogenous spatial distribution of creep voids and variation in rupture life has been exploited in terms of microstructural sites during the onset of creep embrittlement.

EFFECT OF BORON ON CREEP DUCTILITY AND CREEP RUPTURE LIFE IN 9CR-1.5MO STEEL

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2490-2495 ◽  
Author(s):  
BUMJOON KIM ◽  
JIWOO IM ◽  
MOON K. KIM ◽  
JONGHOON LEE ◽  
BYEONGSOO LIM
Keyword(s):  
Creep Test ◽  
Rupture Life ◽  
General Concept ◽  
Creep Rupture ◽  
Displacement Rate ◽  
Boron Addition ◽  
Creep Ductility ◽  
Small Punch ◽  
Uniaxial Creep ◽  
The Relationship

In this study, the relationship between the creep ductility and rupture life of 9 Cr -1.5 Mo steel with boron addition at 600°C was investigated by small punch (SP) creep test from the viewpoint of the modified Monkman-Grant relation. The amount of boron addition ranged from 0.0076wt% to 0.0196 wt%. The general concept of Monkman-Grant ductility for uniaxial creep was introduced and then particularly modified for the SP creep. The microstructure of the steel was observed to analyze the effect of boron addition on the creep ductility and rupture life. Based on the modified Monkman-Grant ductility for SP creep, it was found that the boron addition improved the creep ductility and rupture life of the 9 Cr -1.5 Mo steel. Also, the relationship between the minimum creep displacement rate and the amount of boron addition was analyzed.

Study on Creep Behaviors of T92 Steel under Multiaxial Stress State

2013 ◽  
Vol 860-863 ◽  
pp. 774-779
Author(s):  
Xue Ping Mao ◽  
Yang Yu ◽  
Chao Li ◽  
Sai Dong Huang ◽  
Hong Xu ◽  
...  
Keyword(s):  
Stress State ◽  
Rupture Life ◽  
Creep Damage ◽  
Creep Rupture ◽  
Failure Behavior ◽  
Multiaxial Stress ◽  
Creep Tests ◽  
Creep Ductility ◽  
Notched Specimen ◽  
Multiaxial Stress State

Creep tests for smooth specimens and notched specimens of T92 steel were carried out to study the effect of multiaxial stress state on creep rupture behaviors at 650°C. Creep rupture life was estimated by representative stress at multiaxial state of stress, the failure behavior of multiaxial creep was analyzed, and Kachanov creep damage formula was used to analyze the experimental data. The results show that the notch strengthens rupture life, multiaxial rupture behavior is controlled by mixed parameters, the creep ductility of the smooth and notched specimen decreases with rupture time, and damage factors of the smooth specimen and notched specimen are similar according to Kachanov formula.

The relationship of the scleractinian corals to the rugose corals

Paleobiology ◽  
1980 ◽  
Vol 6 (02) ◽  
pp. 146-160 ◽  
Author(s):  
William A. Oliver
Keyword(s):  
Critical Points ◽  
Scleractinian Corals ◽  
Convincing Evidence ◽  
Early Triassic ◽  
Rugose Corals ◽  
History Of ◽  
The Subject ◽  
Relationship Of ◽  
The Relationship ◽  
Biologic Factors

The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.

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