scholarly journals Aging Phenomena during In-Service Creep Exposure of Heat-Resistant Steels

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 800 ◽  
Author(s):  
G. N. Haidemenopoulos ◽  
K. Polychronopoulou ◽  
A. D. Zervaki ◽  
H. Kamoutsi ◽  
S. I. Alkhoori ◽  
...  
Keyword(s):  
Morphological Changes ◽  
Tensile Elongation ◽  
Creep Damage ◽  
M23c6 Carbide ◽  
High Exposure ◽  
Exposure Temperature ◽  
Reformer Tubes ◽  
Aging Phenomena ◽  
Heat Resistant Steels ◽  
Creep Exposure

An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable M23C6 carbide takes place at high exposure temperature (910 °C and above). The primary MC carbides transform to the Ni-Nb silicide or G-phase during creep exposure. The presence of Ti in the steel prevented the transformation of MC carbides to the G-phase. Morphological changes like needle to globular transitions, rounding of carbide edges, and carbide coarsening take place during creep exposure. The room-temperature tensile elongation and ultimate tensile strength are significantly reduced during creep exposure. The above aging phenomena are precursors to creep damage.

Role of Long Term Ageing on the Creep Life of Type 316H Austenitic Stainless Steel Bifurcation Weldments

2016 ◽  
Author(s):  
Ana I. Martinez-Ubeda ◽  
Ian Griffiths ◽  
Oliver D. Payton ◽  
Charles M. Younes ◽  
Tom B. Scott ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Creep Damage ◽  
M23c6 Carbide ◽  
Boiler Tube ◽  
Boundary Length

Intergranular creep cracks have been observed in the heat affected zone of the 316H austenitic stainless steel superheater boiler tube bifurcation weldments after long term service at temperature of ∼550°C. The cracking mechanism is believed to be creep dominated. Moreover, chemical composition of defective material compared with similar uncracked components suggests that composition influences susceptibility to creep cracking. A systematic characterization of ratios number of creep cavities/grain boundary length and inter-granular precipitation length/grain boundary length has been undertaken in HAZ of three samples extracted from plants with different specific compositions. Here, the role of precipitation on creep deformation and fracture is explored. Precipitates of both ferrite and M23C6 carbide arising from long term service and associated creep cavitation have been identified using transmission electron microscopy. The creep damage and cracking, and therefore overall service life creep, is discussed by consideration of susceptibility of creep cavity nucleation and subsequently growth arising from specific differences in the chemical composition of the three boiler tube bifurcations.

Microstructural Characterization and Property Evaluation of Service Exposed Reformer Tubes

2019 ◽  
Vol 795 ◽  
pp. 239-245
Author(s):  
Zhi Yuan Han ◽  
Guo Hao Sun ◽  
Guo Shan Xie ◽  
Luo Wei Cao ◽  
Zhen Jie Li
Keyword(s):  
Residual Life ◽  
Tensile Elongation ◽  
Ultrasonic Inspection ◽  
Stress Rupture ◽  
Microstructural Characterization ◽  
Tensile Tests ◽  
Optical Observations ◽  
Property Evaluation ◽  
Reformer Tubes ◽  
High Temperature Tensile

This study investigated the microstructural characteristics and property degradation of service-exposed reformer tubes. The reformer tubes were graded into three damage levels based on on-site ultrasonic testing. The microstructural and mechanical experiments were carried out included optical observations, scanning electron microscope (SEM) observations, room temperature tensile tests, high temperature tensile tests, and stress rupture tests. The results showed that the coarsen of carbides occurred during service. A decrease of tensile elongation was observed. The mechanical properties and rupture behaviours of reformer tubes for different inspection levels were also obtained. The results showed that the ultrasonic inspection levels of tubes could be significantly influenced by carbide morphology of tube materials. A residual life of 8.3 years was estimated for these tubes.

Elastic properties of heat resistant steels after long-term creep exposure

2008 ◽  
Vol 25 (3) ◽  
pp. 179-185
Author(s):  
K. Sawada ◽  
T. Ohmura ◽  
T. Ohba ◽  
K. Tsuzaki ◽  
F. Abe ◽  
...  
Keyword(s):  
Elastic Properties ◽  
Heat Resistant ◽  
Term Creep ◽  
Heat Resistant Steels ◽  
Creep Exposure

Application of a Creep-Damage Constitutive Model for the Rotor of a 1000 MW Ultrasupercritical Steam Turbine

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Jishen Jiang ◽  
Weizhe Wang ◽  
Nailong Zhao ◽  
Peng Wang ◽  
Yingzheng Liu ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Steam Turbine ◽  
Creep Damage ◽  
Turbine Rotor ◽  
Creep Analysis ◽  
Wide Range ◽  
Damage Constitutive Model ◽  
Creep Constitutive Model ◽  
Basic Features ◽  
Heat Resistant Steels

A damage-based creep constitutive model for a wide stress range is applied to the creep analysis of a 1000 MW ultrasupercritical steam turbine, the inlet steam of which reaches 600 °C and 35 MPa. In this model, the effect of complex multiaxial stress and the nonlinear evolution of damage are considered. To this end, the model was implemented into the commercial software abaqus using a user-defined material subroutine code. The temperature-dependent material constants were identified from the experimental data of advanced heat resistant steels using curve fitting approaches. A comparison of the simulated and the measured results showed that they reached an acceptable agreement. The results of the creep analysis illustrated that the proposed approach explains the basic features of stress redistribution and the damage evolution in the steam turbine rotor over a wide range of stresses and temperatures.

Microcontroller-Based Reformer Tube Internal Diameter Data Acquisition

2011 ◽  
Author(s):  
Liqiong Tang ◽  
Morio Fukuoka ◽  
Peter Tait
Keyword(s):  
Data Acquisition ◽  
Creep Damage ◽  
Cost Effective ◽  
Internal Diameter ◽  
Wireless Data ◽  
Process Industries ◽  
Industrial Companies ◽  
Wireless Data Acquisition ◽  
Reformer Tubes ◽  
Reformer Tube

Reformer tubes are high cost components in process industries. The service life of the reformer tubes is primarily ended by creep damage, which is caused by operation at high pressure and temperature. As a result of the creep damage, the geometry of reformer tubes changes especially the diameter. Therefore, monitoring the diametric changes of the reformer tubes is able to help to judge the degree of creep —damage. Different sensors, methodologies and techniques are proposed to obtain and monitor the diametric data of the reformer tubes. However, the cost of the dominant systems available is hard for majority of the industrial companies to afford. This paper presents a novel design of a microcontroller-based, wireless data acquisition system for obtaining reformer tube internal diameter data. The system focused on using cost effective components and methodologies. Tests made on the prototype showed that the system is able to reliably transmit reformer tube internal diametric data to a computer located on top of the reformer tube in real time.

Creep-damage assessment of high chromium heat resistant steels and weldments

2009 ◽  
Vol 510-511 ◽  
pp. 195-201 ◽  
Author(s):  
Kazunari Fujiyama ◽  
Keita Mori ◽  
Takahide Matsunaga ◽  
Hirohisa Kimachi ◽  
Takashi Saito ◽  
...  
Keyword(s):  
Damage Assessment ◽  
Creep Damage ◽  
High Chromium ◽  
Heat Resistant ◽  
Heat Resistant Steels

Remnant Life Assessment and Microstructural Studies on Service Exposed Primary Reformer Tubes of a Catalytic Converter of an Ammonia Plant

2012 ◽  
Vol 31 (6) ◽  
pp. 759-767 ◽  
Author(s):  
Krishna Guguloth ◽  
Jaganathan Swaminathan ◽  
Sumanta Bagui ◽  
Ashok Kumar Ray
Keyword(s):  
Catalytic Converter ◽  
Niobium Carbide ◽  
Microstructural Analysis ◽  
Stress Rupture ◽  
Creep Damage ◽  
Life Assessment ◽  
Tube Material ◽  
Service Exposure ◽  
Reformer Tubes ◽  
Primary Carbides

Abstract13.5 year service exposed (SE) catalyst primary reformer tube material made of H39WM micro-paralloy grade used in feritilizer plant was assessed for remaining life. The investigation includes mechanical properties evaluation; microstructural analysis and accelerated stress rupture tests. Failed tube portions showed coarsening primary carbides of Chromium and Niobium along the grain boundaries. Degradation of Niobium carbide (NbC) into Ni-Nb-Si phase and partial conversion this phase back to NbC was observed. Secondary carbides within grains were almost absent. Degradation in tensile strength for a range of temperature from 1123 to 1223 K was also observed but they were within the specified limits. Premature failures within 3–5 years service exposure are more common in reformer tubes. The failure was attributed to localized overheating leading to creep damage. The cast tube material may undergo microstructural changes during service exposure which is the main cause of degradation in strength and hardness changes. Accelerated stress rupture tests were performed in the range of 1173–1248 K on samples machined from 13.5 years at 1191 K and 15.4 MPa exposed reformer steel tubing, did not reveal any degradation of rupture behavior compared to that of the virgin alloy. An additional life of at least 10.6 years is predicted at the operating stress-temperature conditions.

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