Mid-Wall Temperature in an Eroded Section of an Austenitic Superheater/Reheater Tube

2001 ◽  
Vol 123 (3) ◽  
pp. 334-337 ◽  
Author(s):  
Khosrow Zarrabi ◽  
Ian Rose
Keyword(s):  
Wall Temperature ◽  
Creep Damage ◽  
Metal Temperature ◽  
Financial Loss ◽  
Creep Life ◽  
Nondimensional Parameter

Superheater and reheater tubes in a fossil-fuelled boiler are subjected to erosion and corrosion that cause the tubes to lose their thickness in a localized manner. To avoid unscheduled tube failures due to creep damage and hence prevent large financial loss because of boiler shutdown and tube repairs, it is important to estimate creep life of these tubes. Creep life is very sensitive to metal temperature. This paper describes the development of a nondimensional parameter coined TM1*. It is shown that TM1* can be used to estimate the mid-wall metal temperature in the eroded/corroded section of tube.

scholarly journals Creep Damage Repair of a Nickel-Based Single Crystal Superalloy Based on Heat Treatment

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 623
Author(s):  
Xiaoyan Wang ◽  
Meng Li ◽  
Yuansheng Wang ◽  
Chengjiang Zhang ◽  
Zhixun Wen
Keyword(s):  
Heat Treatment ◽  
Single Crystal ◽  
Creep Damage ◽  
Primary Creep ◽  
Single Crystal Superalloy ◽  
Secondary Creep ◽  
Creep Life ◽  
Phase Coarsening ◽  
Damage Repair ◽  
Creep Time

Taking nickel-based single crystal superalloy DD6 as the research object, different degrees of creep damage were prefabricated by creep interruption tests, and then the creep damage was repaired by the restoration heat treatment system of solid solution heat treatment and two-stage aging heat treatment. The results show that with the creep time increasing, the alloy underwent microstructure evolution including γ′ phase coarsening, N-type rafting and de-rafting. After the restoration heat treatment, the coarse rafted γ′ phase of creep damaged specimens dissolved, precipitated, grew up, and became cubic again. Except for the specimens with creep interruption of 100 h, the γ′ phase can basically achieve the same arrangement as the γ′ phase of the original sample. The comparison of the secondary creep test shows that the steady-state creep stage of the test piece after the restoration heat treatment is relatively increased, and the total creep life can reach the same level as the primary creep life. The high temperature creep properties of the tested alloy are basically recovered, and the restoration heat treatment effect is good.

Creep Damage Evaluation of Fine-Grained HAZ in Mod. 9Cr Ferritic Heat-Resistant Steel Weldments

2007 ◽  
Author(s):  
N. Yoneyama ◽  
K. Kubushiro ◽  
H. Yoshizawa
Keyword(s):  
Creep Damage ◽  
Life Time ◽  
Creep Life ◽  
Creep Tests ◽  
Boundary Density ◽  
Fine Grained ◽  
Type Iv ◽  
Fine Grain ◽  
Type Iv Cracking ◽  
Rupture Mechanism

9Cr steel weldments are concerned with evaluation of creep life time and creep rupture mechanism. In fine grain HAZ (FG-HAZ) of weldments, TYPE IV cracking and creep voids occurred at lower stress than rupture stress level of base metal. In the crept specimen, FG-HAZ sometime has large coarsening grains near creep voids. These recovery phenomena are localized in FG-HAZ, and recovered microstructures are dependent on heat input of welding. In this study, creep tests are examined in two types of weldments, and relations between creep life time and coarsened sub-grains or grains have been studied by microstructural changing with EBSP analysis. In crept specimens, boundaries are moved and boundary density is decreasing in the fine-grained HAZ. Maximum grain size and creep life time have linear function, and EBSP can evaluate creep life time of 9Cr weldments. These microstructural changing are considered by morphology of precipitates in the several crept specimens.

The Effects of Cooling Holes on the Creep Life in a Modeling Specimen of Single Crystal Air-Cooled Turbine Blade

2011 ◽  
Vol 284-286 ◽  
pp. 1678-1683 ◽  
Author(s):  
Da Shun Liu ◽  
Bai Zhi Wang ◽  
Zhi Xun Wen ◽  
Zhu Feng Yue
Keyword(s):  
Single Crystal ◽  
Turbine Blade ◽  
Damage Model ◽  
Creep Damage ◽  
Creep Life ◽  
Damage Development ◽  
User Subroutine ◽  
Initial Rupture ◽  
Creep Deformations ◽  
Sem Analyses

This paper presents the study of the influences of cooling holes on the creep life behavior in the modeling specimen of single crystal cooling turbine blade at high temperature. Thin-walled cylindrical specimens with holes are tested to model the air-cooled turbine blade. Specimens without holes are also studied to make comparisons. Experimental results show that at 900°C, the creep lives of specimens with holes are longer than those of specimens without holes. Scanning Electron Microscopy (SEM) analyses reveal that creep deformations occur firstly around the cooling holes and finally rupture at the region with low stress and strain. Finite element analyses are used to study the creep damage development by a K-R damage model which has been implemented into the Abaqus user subroutine (UMAT). Simulation results show that stress concentration and redistribution occur around the cooling holes during the creep development. It is also shown that the maximum strain and stress are around the cooling holes which are the initial rupture region in the experiments.

The Significance of Thermo-Mechanical Fabrication on Long Term Creep Life of Type 316H Austenitic Stainless Steel Components

2016 ◽  
Vol 853 ◽  
pp. 384-388
Author(s):  
Ana Isabel Martinez-Ubeda ◽  
Alexander D. Warren ◽  
Ian Griffiths ◽  
Peter E.J. Flewitt
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Nuclear Power ◽  
Energy Dispersive Spectrometer ◽  
Creep Damage ◽  
Ion Milling ◽  
Creep Life ◽  
Thin Foils ◽  
The Impact

The UK’s Advanced Gas Cooled Reactor (AGR) nuclear power generating plant operates at temperatures up to 550 °C, where creep life is important. We consider Type 316H austenitic stainless steel headers and tubes with thermo-mechanical fabrication histories that result in significantly different initial microstructures. The heat affected zone of weldments, in these thick section headers and thin walled boiler tubes, have been found to be susceptible to creep damage leading to cracking during service. In this work we explore these differences in the long term service aged microstructure and the link to overall creep life of these components. To achieve this, samples containing weldments have been removed from plant after extended periods of service. Specifically parent and HAZ regions have been examined to determine the types of precipitates arising from the long term ageing. In particular, thin foils have been examined in a JEOL ARM transmission electron microscope operating at 200KeV fitted with an Oxford Instruments energy dispersive spectrometer to allow comparison between high resolution images and chemical composition. The thin foils were removed from predetermined locations using gallium ion milling and finally thinned using a low ion current to minimise ion damage. Differences between the distributions and types of precipitates are considered in the context of the initial microstructure arising from the thermo-mechanical history on the loss of creep strength and initiation of creep cavities at grain boundaries. The impact on overall service life is addressed.

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 damage and expected creep life for welded 9–11% Cr steels

2007 ◽  
Vol 84 (1-2) ◽  
pp. 69-74 ◽  
Author(s):  
P. Auerkari ◽  
S. Holmström ◽  
J. Veivo ◽  
J. Salonen
Keyword(s):  
Creep Damage ◽  
Creep Life ◽  
Cr Steels

Effect of High-Temperature Corrosion on the Service Life of P91 Piping in Biomass Co-firing

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
C. P. O'Hagan ◽  
R. A. Barrett ◽  
S. B. Leen ◽  
R. F. D. Monaghan
Keyword(s):  
Tube Wall ◽  
Thermal Power ◽  
Creep Damage ◽  
High Temperature Corrosion ◽  
Corrosion Mechanism ◽  
Creep Life ◽  
Sem Images ◽  
X Ray ◽  
Superheater Tube ◽  
Wall Loss

Co-firing biomass with traditional fuels is becoming increasingly relevant to thermal power plant operators due to increasingly stringent regulations on greenhouse gas emissions. It has been found that when biomass is co-fired, an altered ash composition is formed, which leads to increased levels of corrosion of the superheater tube walls. Synthetic salt, which is representative of the ash formed in the co-firing of a 70% peat and 30% biomass mixture, has been produced and applied to samples of P91 at 540 °C for up to 28 days. This paper presents results for oxide layer thickness and loss of substrate from testing. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDX) element maps are obtained and presented in order to gain an understanding of the complex corrosion mechanism which occurs. A finite-element (FE) methodology is presented which combines corrosion effects with creep damage in pressurized tubes. The effects of corrosion tube wall loss and creep damage on tube stresses and creep life are investigated.

Models and Methods of Determining the Minimum Stack Metal Temperature During Sonic Blowdown of Natural Gas

2014 ◽  
Author(s):  
C. Hartloper ◽  
K. K. Botros ◽  
E. Abdalgawad ◽  
S. Reid
Keyword(s):  
Boundary Layer ◽  
Natural Gas ◽  
Wall Temperature ◽  
Steel Grade ◽  
Metal Temperature ◽  
Suitable Model ◽  
Gas Temperature ◽  
Flow Reynolds Number ◽  
Flow Through ◽  
Temperature Recovery

During a natural gas blowdown event, the flow through the blowdown stack is either sonic or supersonic at the stack exit. In this case, the temperature of the gas at the stack exit can drop significantly as the gas enthalpy is converted to kinetic energy. Depending on the initial pipeline temperature, it is possible for the gas temperature at the stack exit to drop below the minimum metal temperature specification of the stack steel grade. Traditionally in this case it is assumed that the blowdown-stack metal temperature follows the gas temperature; therefore, it would also drop below this minimum temperature. However, analogous to the decrease in the temperature of the gas as the velocity increases, the gas will increase in temperature as the velocity decreases near the wall of the stack due to the boundary layer. As such, the blowdown-stack wall temperature will not decrease to the same extent as the bulk gas temperature during the blowdown event. This phenomenon is referred to as wall temperature recovery. This paper describes the various models and methods for determining the extent of this temperature recovery via a parameter known as “recovery factor” which is a function of the flow Reynolds number, Prandtl number, Mach number, etc. These methods are evaluated and compared for several pipeline conditions, and the most suitable model is determined. It is recommended that fundamental blowdown testing on natural gas be conducted on well instrumented full-bore blowdown stack to validate the predictions by these methods.

An Investigation on Monitoring Methods of Creep Damage Using Ultrasonic Technique

2004 ◽  
Author(s):  
Yoshikazu Yokono ◽  
Yoshihiro Nagano
Keyword(s):  
Continuous Monitoring ◽  
Ultrasonic Method ◽  
Creep Damage ◽  
Ultrasonic Technique ◽  
Monitoring Methods ◽  
Material Degradation ◽  
Creep Life ◽  
Term Operation ◽  
Safety Operation ◽  
Life Fraction

The reliability of facilities under long-term operation, that is to prevent trouble or accident, is one of the most important matters in the field of petroleum and petrochemical plants. For this purpose, some kinds of non-destructive inspection methods are carried out periodically to detect damages or degradation of material. Moreover, to enrich the reliability of safety operation of the plants, continuous monitoring methods to detect material degradation without mistiming are required. Recently, ultrasonic method has been developed as a key technology to detect and evaluate the damage of materials. One of the advantages of ultrasonic technique is to obtain much information about microstructure change due to material degradation when ultrasounds travel through the material. Further, ultrasonic technique has also the potential ability to be applied for continuous monitoring methods. The objective of this study is to accomplish monitoring methods of creep damage using ultrasonic technique. A novel technique to acquire the ultrasonic data during uni-axial creep test is investigated as the first step of monitoring of creep damage. As a result, it is confirmed that the sound velocity in time domain decreases gradually in creep acceleration stage which starts at the creep life fraction of 0.6 and the gravity frequency in frequency domain begins to increase at the creep life fraction of 0.8. Therefore, the possibility to monitor the creep damage under continuous operation by ultrasonic technique is suggested.

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