Creep Damage Simulation Elevated Temperature Plant Test and Creep Life Assessment System for Components (original) (raw)
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Creep life assessment of an overheated 9Cr-1Mo steel tube
Crude oil heater 9Cre1Mo steel tubes from a refinery plant were studied, after 24 years of service at nominally 650 C and 27 MPa, to predict their remanent lives. The investigation included dimensional, hardness and tensile measurements in addition to accelerated stress rupture tests between 650 C and 700 C and microstructural examination. Tube specimens were taken from two sections, the overheated side and the side which only saw the nominal operating temperature. The method employed involved the prediction of the increase in temperature with increasing sediment deposition during the operating life times using an FEM model. In addition the predicted temperatures are used to derive appropriate creep properties at relevant temperatures in a 3D pipe FEM creep analysis to predict the pipe deformation rate. All compare well with the actual service exposed pipe measurements and layer deposition. The overheated side revealed a small loss of creep strength in a stress rupture test. A layer of sediment (appr. 10 mm thickness) consisting basically of sintered carbon (coke) spread over the inside of the tube was acting as a thermal barrier causing the temperature to rise above 650 C. Analysis for the overheated side predicted an upper bound temperature of z800 C and a life of about 50 h suggesting that failure by creep rupture could occur rapidly in the sediment region.
2011
One of the most common failure modes for elevated temperature piping working in the creep conditions is initiation, growth of cracks in pipe bends that finally leads to the failure. Failure of bends is much more dangerous than appearance of cracks in the piping joint welds or tees due to size of affected areas. It is known that for pipe bends, working in creep range, attention must be paid to imperfections of the cross-section, such as out-of-roundness and different wall-thickness, and their interaction with the internal pressure as well as bending and torsion moments. FE analyses of different bend configuration have been performed to investigate effect of the above factors on the creep damage of this element. It was recognized that out-of-roundness and bending moments are significant contributors to the stress state of pipe bends and hence in the creep cumulative damage. Neglecting of these factors could lead to big uncertainties in the remaining life prediction.
Creep Characteristics of Engineering Materials [Working Title]
2019
The assessment of suitability for further service of the basic material and circumferential welded joints of primary steam pipelines made of 14MoV6-3 steel was made based on the determined characteristics of their mechanical properties and structure. The tests were carried out on materials after service significantly exceeding the design time and 200,000 h. The mechanical properties with respect to the determined class of structure for the basic and welded joint material were compared to the determined class of damage in accordance with the Institute for Ferrous Metallurgy's own classification of the condition of materials after service under creep conditions. The residual life and disposable residual life were determined based on short-term creep tests and referred to the class of existing structure and the class of damage. The assessment of the suitability of the basic and circumferential welded joint material for further service was made.
Materials Science and Engineering: A, 2007
Superheater and reheater 2.25Cr-1Mo steel boiler tubes from a thermal power plant after 17 year of service at nominally 540 • C and 40 MPa were studied to predict their remnant life. The investigation included dimensional, hardness and tensile measurements in addition to accelerated stress rupture tests between 625 and 700 • C and microstructural examination. The microstructure of the service-exposed alloy was free from any signs of deterioration, and the hardness was within the expected ranges; however, tensile testing revealed an apparent loss of strength from room temperature to 600 • C. Accelerated rupture testing, on the other hand, did not reveal any degradation of rupture behaviour compared to that of the virgin alloy. Analysis of the stress rupture data predicted that the 17 years exposed superheater and reheater tubes could remain in continued service for at least 12 more years at the current stress-temperature conditions.
Accelerated Creep Life Assessment of In-Service Power Plant Components
MATEC Web of Conferences
Structural metals used in plant components are subject to aging from a combination of fatigue, creep, and corrosion. Exposure to elevated temperatures promotes creep. Aged metals lose toughness, or the ability to absorb energy at stress above the yield point and cannot endure an occasional high load without fracturing. Creep is one of the most critical factors for determining the structural integrity of components. The main objective of the current study is to assess the remaining creep life of various 20-year old power plant engineering components such as the high temperature fasteners. Due to time constraints, the approach followed in this study was to utilize the accelerated high temperature creep testing in addition to Scanning Electron Microscopy (SEM) analysis to assess the remaining life of 4 different samples. The accelerated high temperature creep tests were conducted at a stress level of 61 MPa and at a temperature of 1000°C for samples Sample 1 (original), Sample 2, Sampl...
International Materials Reviews, 2017
The safe operation of components operating at high temperature and pressure faces numerous challenges associated with ageing materials and maintaining commercial viability whilst economies transition to a lower carbon future as part of their climate change commitments. Due to these challenges the plant operator faces increasing pressure to ensure that any capital or operational expenditures are optimised and must ensure that they duly recognise plant age, condition, operating regime and ultimately the planned closure date. This review, for the first time, describes how small specimen creep testing can be applied within a practical and deployable life assessment framework and in conjunction with other assessment techniques. The current state of the art for small specimen creep testing is critically reviewed; this also includes a review of traditional techniques used on site for the metallurgical assessment of material condition, with examples from site investigations and assessment campaigns in both conventional and nuclear plant applications. Nomenclature A, B, C, …, I Coefficient in parametric equation A' Material constant a' Elliptical ring half-axis ap Receiving hole radius in small punch creep test b Length of impression creep test specimen b' Elliptical ring half-axis bT Two-bar specimen width d Width of impression creep test indenter d' Thickness of the ring in the axis direction d0 Thickness of the ring in the radial direction dT Two-bar specimen thickness DT Diameter of the loading pins h High of impression creep test specimen h' Cut depth k Length of the loading pins supporting end KSP Correction factor LT Initial bar length n Material constant ̅ Mean indenter pressure P Applied load R Radius of the circular ring Rs Punch radius t, tf Current and fracture thickness of small punch specimen wt Wall thickness t0 Initial thickness of small punch creep test specimen w Width of impression creep test specimen α Stress multiplier β Conversion factor Δ, Δf Creep displacement and creep displacement at fracture ∆̇ Creep displacement rate ε Strain at the contact boundary Creep strain in the steady-state ̇ Minimum creep strain rate η Conversion factor σm Membrane stress σMDH Mean diameter hoop stress σR Rupture stress Equivalent uniaxial stress ϕ Outer diameter
Creep failures in steam lines operating below limit temperatures for creep design
A couple of unexpected and serious creep failures in live steam pipe components occurred in Sweden some years ago. The service temperature was 450°C which is 30°C below the limit temperature for creep design for the used steel grade in the cases of point, 13 CrMo 4 4 (1Cr0,5Mo). This steel is also the most commonly used material in Sweden for steam lines operating at 420 -480°C.
Performance Evaluation of a Low Cost Creep Testing Machine
American journal of mechanical engineering, 2019
Mechanical systems and components like steam generators or boilers, nuclear reactors, turbine rotors are operated at very high temperature under significant stress. For this reason, the components and structures need to be designed so that excessive creep distortion must not occur within the expected operating life of the system. Creep is defined as a time-dependent deformation that happens when metals are subjected to constant load at high temperature over a period of time. Knowledge of the creep behavior of metals is therefore important and for this reason Creep testing machines are predominantly used to measure how a given material will perform under constant load, at elevated temperature. This paper aims to study creep properties of various materials being used in high temperature applications through locally made creep testing machine. The basic design of a creep testing machine is the support structure, the loading device, the fixture device (grips and pull rods), and the furn...
SP creep properties of Gr.91 boiler pipings service-exposed in different USC power plants
Ubiquity Proceedings, 2018
The small punch (SP) testing technique was applied to five heats of Gr.91 steel, which had been actually used for boiler pipings in different USC power plants for long periods of time to investigate the applicability of this technique to the assessment of heat-to-heat variation of creep property. The experimental results revealed that the SP creep rupture strength and deformation behavior were quite different depending on the heat. Those differences in SP creep property, which could not be evaluated by hardness measurement, were qualitatively similar to those in standard uniaxial creep one. It was expected that the SP creep testing technique was applicable to the assessment of heat-to-heat variation for in-service boiler pipings.
Metallurgical evaluation of creep-failed superheater tubes
Engineering Failure Analysis, 2009
The present study is focused on the metallurgical factors induced during high-temperature operation of a pipeline that resulted in its short-time failure. The pipeline is used as superheater in a lignite power-plant unit and is constructed by an array of steel tubes jointed together by circumferential weldments. Systematic recording of data over one year of service indicated that local material's failures were occurring, on an average, every 15 days and localised either at curved areas of the tubes, or in the neighbourhood of circumferential weldments. Visual inspection, macrographic examination and microscopic observations of representative failed parts revealed microstructural features indicative of creep rupture. In both cases, the material failed due to the rapid growth and coalescence of creep voids, initiated at a service temperature equal to 43% of the steel melting point.