Elevated-Temperature Life Assessment

2021 ◽  
pp. 146-166
Author(s):  
Arun Sreeranganathan ◽  
Douglas L. Marriott
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Stress Relaxation ◽  
Damage Mechanics ◽  
Elevated Temperatures ◽  
Constitutive Models ◽  
Life Assessment ◽  
Remaining Life ◽  
High Temperature Components ◽  
Remaining Life Assessment

Abstract This article provides some new developments in elevated-temperature and life assessments. It is aimed at providing an overview of the damage mechanisms of concern, with a focus on creep, and the methodologies for design and in-service assessment of components operating at elevated temperatures. The article describes the stages of the creep curve, discusses processes involved in the extrapolation of creep data, and summarizes notable creep constitutive models and continuum damage mechanics models. It demonstrates the effects of stress relaxation and redistribution on the remaining life and discusses the Monkman-Grant relationship and multiaxiality. The article further provides information on high-temperature metallurgical changes and high-temperature hydrogen attack and the steps involved in the remaining-life prediction of high-temperature components. It presents case studies on heater tube creep testing and remaining-life assessment, and pressure vessel time-dependent stress analysis showing the effect of stress relaxation at hot spots.

scholarly journals The thermal history and stress state of a fresh steam-pipeline influencing its remaining service life

2011 ◽  
Vol 15 (3) ◽  
pp. 691-704 ◽  
Author(s):  
Gordana Bakic ◽  
Vera Sijacki-Zeravcic ◽  
Milos Djukic ◽  
Stevan Maksimovic ◽  
Dusan Plesinac ◽  
...  
Keyword(s):  
Service Life ◽  
Elevated Temperatures ◽  
Operating Temperature ◽  
Life Assessment ◽  
Temperature History ◽  
Significant Variable ◽  
Remaining Life ◽  
Pipe Bend ◽  
Steam Pipeline ◽  
Remaining Life Assessment

The service life of thick-walled power plant components exposed to creep, as is the case with pipelines of fresh- and re-heated steam, depend on the exhaustion rate of the material. Plant operation at elevated temperatures and at temperatures below designed temperatures all relates to the material exhaustion rate, thus complicating remaining life assessment, whereas the operating temperature variation is a most common cause in the mismatching of real service- and design life. Apart from temperature, the tube wall stress is a significant variable for remaining life assessment, whose calculation depends on the selected procedure, due to the complex pipeline configuration. In this paper, a remaining life assessment is performed according to the Larson-Miller parametric relation for a ?324?36 pipe bend element of a fresh steam-pipeline, made of steel class 1Cr0.3Mo0.25V, after 160 000 hours of operation. The temperature history of the pipeline, altogether with the pipe bend, is determined based on continuous temperature monitoring records. Compared results of remaining life assessment are displayed for monitored temperature records and for designed operating temperature in the same time period. The stress calculation in the pipe bend wall is performed by three methods that are usually applied so to emphasize the differences in the obtained results of remaining life assessment.

A Remaining Life Assessment of Autofrettaged Tubes From an LDPE Facility

2014 ◽  
Author(s):  
Jeffrey D. Cochran ◽  
Charles H. Panzarella
Keyword(s):  
Residual Stress ◽  
Stress Relaxation ◽  
Brittle Fracture ◽  
Creep Damage ◽  
Limit Load ◽  
Life Assessment ◽  
Creep Model ◽  
Normal Operation ◽  
Remaining Life ◽  
Remaining Life Assessment

The manufacture of low density polyethylene by radical polymerization regularly subjects components to extreme pressures exceeding 20 ksi and, possibly, to runaway reactions with fluid temperatures exceeding 2000 °F and pressures above 30 ksi. Components are often treated with autofrettage to induce a beneficial residual stress distribution that retards crack growth and increases fatigue life. This paper presents a case-study remaining life assessment of two autofrettaged tubes in accordance with API 579-1/ASME FFS-1. Measurements of the remaining residual stress after 40+ years in service agree with FEA predictions of the initial residual stress, indicating no significant stress relaxation over this time. Nevertheless, the MPC Omega creep model is calibrated to the tube material and used to estimate the potential for stress-relaxation due to creep. The model correctly predicts no stress relaxation for over 40 years of normal operation, but creep damage and stress relaxation are predicted for temperature excursions as low as 900 °F for 10.8 s. ASME FFS-1 procedures for assessing brittle fracture, fatigue, plastic collapse, and creep damage are then adapted for autofrettaged components. It is found that autofrettage increases resistance to brittle fracture and fatigue, does not affect limit load analyses, and alters creep damage distributions.

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