摘要:

A creep damage investigation was made on a service-exposed header of 2.25Cr 1Mo steel with a service time of 200 000 h. Weldments and the flanged parts at both outer and inner surfaces were studied as well as the damage in the through-thickness direction. Extensive cavitation was observed not only at the outer surface, but also well inside the component in the weldments. A model for the prediction of rupture position is introduced to explain the appearance of the observed creep damage.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689413

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Creep testing has been made on a service-exposed header of 2.25Cr1Mo steel. Four series including parent metal, weld metal and cross-weld combinations were studied. A metallographic investigation of cavitation development on ruptured samples has also been performed. A model for the stress state in a thick-wailed welded pipe has been derived. Results obtained from creep testing and metallographic investigation have been analysed and compared with the model.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689414

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Normalized 2¼Cr-1Mo steel was isothermally oxidized at 973 K in air to develop an oxide scale of about 40μm thickness. The pre-oxidized specimens were then subjected to thermal cycling between 973 and 373 K in air for a maximum of 15 cycles by thermogravimetry (TG). The kinetics of oxidation were continuously followed to monitor the spalling behaviour of the scale during each cycle, and its influence on the subsequent oxidation. Cracking and spalling behaviour of the scale during thermal cycling was also assessed by monitoring the acoustic emission (AE) signals. Both TG and AE tests suggested that spallation occurred during each cooling cycle, but after a few cycles of thermal cycling spallations were substantial. Electron-optical examinations of the surfaces and the cross sections of the oxidized specimens suggested the formation of two types of oxide scales, morphologically different from each other and dissimilar in their cracking and spalling pattern.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689415

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Since Al2O3−forming nickel-and iron-nickel-base alloys are known to be more effective than Cr2O3−forming alloys in sulphur-containing gases, several commercial Cr2O3−forming alloys have been pack aluminized to establish aluminide coatings for use in mixed-gas environments of high sulphur and low oxygen activity. Results are given for long-term exposures (up to 2500 h) to H2/1.6%H2O/1.1%H2S at 1000°C under thermal-cycling conditions. Uncoated specimens of such alloys are sulphidized completely in very short periods in this environment. Early work indicated that an aluminized molybdenum-containing nickel-base alloy is the most resistant system, so a series of alloys based on nickel and nickel-iron and incorporating various amounts of molybdenum was included in the tests. Most of the aluminized systems showed reasonable resistance for periods of 500 h or more. Subsequently, the protective Al2O3scale broke down following back-diffusion of aluminium into the alloy substrate and depletion of the surface in this element, thereby enabling base metal sulphides to develop rather than the protective oxide to be maintained. The aluminized Inconel 625 system was the most effective, with failure not occurring until after 2000 h, while the corresponding Incoloy 825, Alloy 904L and PK33 systems showed good resistance for 1500 h. These alloys contain 3 to 9 wt% molybdenum and were more resistant than similar alloys containing none of this element. However, aluminized alloys incorporating higher molybdenum concentrations (such as Hastelloy S, Hastelloy B2 and Hastelloy C4) were not as resistant and failed in less than 1000 h. The structures of the various aluminized systems are presented and their performances in the mixed-gas environment are considered in relation to the structures and compositions of the base alloys.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689416

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

During hot corrosion in fossil-fuel-fired power plants a molten salt layer, around 1 mm thick, forms on leading superheater and reheater tubes, under fly ash, and dissolves some of the metal surface. Previous studies have not been made with molten layers this thin. A crucible was designed to take metal coupons and maintain, for up to 2000 h, molten sulphate at 650°C around the coupons to a depth of around 1 mm. The crucibles were fabricated from a machinable glass ceramic impervious to molten sulphates. The experimental set-up is described and includes, for the first time, the continuous monitoring of both SO2and SO3in the synthetic flue gas. An account of the commissioning trials is also given. Crucibles were removed at 200 h intervals and sectioned for subsequent analysis by electron microprobe analysis (EMPA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and spectroscopic studies of the corrosion products within the 1 mm salt layer. Preliminary results from a 2000 h experimental run are given for the concentrations of the elements iron, chromium and nickel entering the thin molten sulphate layer from both oxidized and carburized samples of 304 and 310 stainless steel samples. It is concluded that the tests and evaluation were successful, and that this new crucible enables laboratory experiments to be made, which replicate closely the hot corrosion occurring on superheater and reheater tubes, and that the results accruing will reveal valid information on thin-film hot corrosion occurring in industrial power plants.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689417

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

This paper describes a study of the high-temperature performance of nickel-chromium-silicon/nickel-silicon-magnesium (Nicrosil/Nisil or Type N) thermocouples, sheathed in alloys similar in composition to Nicrosil. Thermocouples from two sources were tested for stability under continuous exposure to progressively higher temperatures within the range 1000 to 1300°C, and for stability under temperature cycling within this range. Inconel-sheathed Type K thermocouples were included for comparison purposes, and immersion tests were also made.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689418

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

A new procedure is presented for determining the Tanaka formulation of the constitutive equation representing the dependence of peak stressσpon temperatureTand strain rateεderived from torsion tests on 316 stainless steel:whereα, nandT’are constants. The peak strainεpis shown to be linearly dependent onσp. The flow curves up to the peak can be calculated by the equationwhere c is a constant evaluated as 0.193 and is associated with average errors of less than 2%. The constitutive constants are compared with those in the literature for similar stainless steels.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689419

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The 0.045% V HSLA and the C steel were deformed in torsion over the range 850–1150°C and 0.1–30 s−1. Flow stress, temperature and strain rate were related by the combination of the Arrhenius function with either the exponential or sinh functions. Based on peak stress from the sinh equation and a linear peak strain dependence, an equation is proposed for calculating flow curves. The constants in the exponential law were evaluated at strain intervals of 0.05 up toε= 0.5, so that flow curves and mean pass stresses could be estimated for any rolling condition. Calculated and measured roll separating forces were compared for a nine-pass schedule. Ferrite grain size increased linearly with risingTat constantεandε. In multistage, isothermal tests after pass strains of 0.3, the fractional softening for delay times of 1, 10 and 30 s were determined. In mill simulations of nine passes withTdeclining from 1270 to 750°C, the pass flow curves and the finishing grain sizes were determined. The behaviours of the steels are contrasted and also compared with those of other HSLA steels.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689420

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

In the cooling stage of solution treatment, fine plate-like M3B2precipitated at grain boundaries, the quantity increasing with increasing boron content in the alloy. When boron content reached 310 ppm, the precipitation of M3B2during cooling mainly concentrated on the surfaces of lump-like M3B2at grain boundaries. In the process of standard heat treatment, the quantity of granular M3B2increased with increasing boron content. Boron could suppress the segregation of plate-like MC at grain boundaries. Granular M3B2precipitated homogeneously in a disperse form. It was discovered that it could precipitate on the surfaces of blocky-like M3B2and plate-like MC when the boron content reached 310 ppm. Blocky-like and granular M3B2in the alloy were composed of tungsten, titanium, chromium, iron, etc. with a general formula MxM'3-xB2; here, in addition to some granular M3B2with x = 2, x was normally larger than 2.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689421

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689422

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor