Stress and integrity analysis of steam superheater tubes of a high pressure boiler

Abstract

Sources that can lead to deterioration of steam superheater tubes of a high pressure boiler were studied by a stress analysis, focused on internal pressure and temperature experienced by the material at real operating conditions. Loss of flame control, internal deposits and unexpected peak charge are factors that generate loads above the design limit of tube materials, which can be subjected to strain, buckling, cracks and finally rupture in service. To evaluate integrity and dependability of these components, the microstructure of selected samples along the superheater was studied by optical microscopy. Associated with this analysis, dimensional inspection, nondestructive testing, hardness measurement and deposit examination were made to determine the resultant material condition after twenty three years of operation

Phase Identification and Internal Stress Analysis of Steamside Oxides on Plant Exposed Superheater Tubes

“…It can be considerably different at various positions on the tube in longitudinal and circumferential direction, and it may increase gradually over several years as a consequence of oxide scale thickening. [10,11] Often, the steel temperature during service exposure is estimated only afterward based on the measured thickness of grown oxide scales, but apart from the uncertain assumptions on the kinetics of scale formation, this cannot account for already occurred spallation. Calculations of the temperature at the steel surface based on measurements of the steam temperature at the inlet and outlet of the loops are also difficult because additional information on the pressure, heat flux, and flow rate of the steam, as well as the influence of already formed oxide phases, needs to be considered [11,12] ; the corresponding phases, however, are often unknown.…”

“…[10,11] Often, the steel temperature during service exposure is estimated only afterward based on the measured thickness of grown oxide scales, but apart from the uncertain assumptions on the kinetics of scale formation, this cannot account for already occurred spallation. Calculations of the temperature at the steel surface based on measurements of the steam temperature at the inlet and outlet of the loops are also difficult because additional information on the pressure, heat flux, and flow rate of the steam, as well as the influence of already formed oxide phases, needs to be considered [11,12] ; the corresponding phases, however, are often unknown. Enormous temperature gradients were calculated for plant exposed tubes [1,13] as a consequence of huge temperature differences between the combustion gas and the steam.…”

Modeling and Simulation of Pore Formation in a Bainitic Steel During Creep

“…Intergranular failure is caused by the coalescence of cavities along the grain boundaries and characterizes the beginning of tertiary creep. [14] The proposed model and experimental results as well as previous studies [15] have identified cavities at grain boundaries to appear more frequently and grow more quickly than those elsewhere in the microstructure, therefore playing a critical role in material creep life.…”

“…Equation [13] is adapted as follows to generate Eq. [14] for the growth rate of the radius _ r: r now represents the hydrostatic stress instead of the chemical driving force (analogous to our modifications to CNT), the diffusion coefficient D 0 is replaced with that for vacancy diffusion D v , the mean site fraction u 0 is replaced by the vacancy concentration N V and the sintering stress term (2c/r) now incorporates the free surface energy c m . X is redefined from the molar volume to the atomic volume and correspondingly the Boltzmann constant k b is used in place of the gas constant R.…”

تحلیل خرابی و دینامیک سیالات محاسباتی لوله‌های سوپرهیتر پلاتن در یک نیروگاه ۳۲۰ مگاواتی برای ارائه‌ی طرح چیدمان بهترین جایگزین

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