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

Auerkari, Pertti; Holmström, Stefan; Veivo, Juha; Salonen, Jorma

doi:10.1016/j.ijpvp.2006.09.011

Cited by 25 publications

(13 citation statements)

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“…Being considered a vintage alloy in the 9%–12% Cr steel group, X20 has been in service as main steam piping in coal-fired power plants for over 60 years [1]. However, there is continued interest in this steel, as it is currently in use in about half of the power stations in South Africa and, in some cases, has outperformed its replacement P91 (X10CrMoVNb9-1) in terms of damage accumulation [2].…”

Section: Introductionmentioning

confidence: 99%

“…However, this technique suffers from several limitations [4]: it is only restricted to the surface of the pipe; void formation from the replica preparation results in spurious measurements; an incorrect judgment of damage can result from an apparent reduction in void density due to coalescence nearing the end of component life; and, other forms of microstructural degradation can mask the effects of cavity growth [6]. In some cases [2], X20 piping has not manifested damage in terms of creep cavitation up to 200,000 hours of service exposure, which requires an alternative means of microstructural damage assessment.…”

Section: Introductionmentioning

confidence: 99%

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Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

et al. 2019

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The lifetime of steam pipelines in long-term operation in coal-fired power plants are limited due to material damage that resulted from creep exposure. In the present study, the authors comparatively assess the damage of ex-service 12% Cr piping steel with varying degrees of exposure while using accelerated creep tests that employ digital image correlation (DIC) as well as microstructural investigation that is based on electron microscopy. The DIC technique, which allows multiple creep curves to be measured at temperatures ranging from 550–600 °C from a single specimen, revealed higher Zener–Hollomon parameters for a high damage material with a high void density when compared to a material with lower damage and lower void density. Both of the material states showed similar hardness values, subgrain sizes, and boundary character, despite the difference in void densities. Slightly higher inter-particle spacing of MX precipitates results in a lower threshold stress of 79 MPa for the high damage steel when compared to 97 MPa for the low damage material. Besides large Laves phase particles (>0.2 µm) that are found in the higher damaged materials that result in solid solution depletion, the most prominent microstructural damage indicator was a lower density of M23C6 precipitates. Therefore, the observations indicate that the Zener–Hollomon parameter and M23C6 particles are good damage assessment indicators between the most extreme damage states and they predict a lower damage level for a medium void density material.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

et al. 2019

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“…Thus, reviews of performance have been published showing that remarkable few components have been found with creep voids detectable by optical microscopy. 10 In contrast, some experience has shown that creep cracking in components has occurred and replacement of components has been required. While these observations have all been made for steels operating beyond 100,000 hours, it could be that the variation in observations is linked to the temperature of operation.…”

Section: Damage In 12%cr (X20) Steelmentioning

confidence: 99%

Creep fracture in tempered martensitic steels

Parker¹,

Siefert²

2018

IPCSE

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As long term laboratory creep data became available the original estimates of the allowable design stresses for creep strength enhanced ferritic steels (CSEF) were reduced. Thus, even in properly processed steel, the long term performance and creep rupture strength reported is below that originally predicted from a simple extrapolation of short term data. In addition, the typical alloy compositions for these steels specified by Codes provide reasonable strength but can steels can exhibit brittle creep behavior. This inherent brittle behavior results in notch weakening and the need to invoke weld strength reduction factors. Moreover, creep brittle behavior, and the associated micro void development, promotes burst rather than leak type fracture in components. The existence of significant densities of voids further complicates in-service assessment of condition and weld repair of these steels. It is now clear that the levels of ductility required in engineering applications necessitate proper control of composition (including trace elements), steel making and processing and all heat treatments. This paper examines background on the development of creep voids in martensitic steels and discusses metallurgical and stress state factors which promote brittle behavior.

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“…There are reports of failures of these steel weldments after only a few years in service. [4][5][6][7][8][9] These failures have been credited to the non-equilibrium microstructures in FGHAZ regions, described elsewhere. [7][8][9] The premature failures at the FGHAZ are called ''Type-IV cracking.''…”

Section: Introductionmentioning

confidence: 99%

Toward Improving the Type IV Cracking Resistance in Cr-Mo Steel Weld Through Thermo-Mechanical Processing

Shassere

Yamamoto

Babu

2016

Metall Mater Trans A

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Detailed microstructure characterization of Grade 91 (Modified 9Cr-1Mo, ASTM A387) steel subjected to a thermo-mechanical treatment process was performed to rationalize the cross-weld creep properties. A series of thermo-mechanical processing in the austenite phase region, followed by isothermal aging at temperatures at 973 K to 1173 K (700°C to 900°C), was applied to the Grade 91 steel to promote precipitation kinetics of MX (M: Nb and V, X: C and N) in the austenite matrix. Detailed characterization of the base metals after standard tempering confirmed the presence of fine MX dispersion within the tempered martensitic microstructure in steels processed at/and above 1073 K (800°C). Relatively low volume fraction of M 23 C 6 precipitates was observed after processing at 1073 K (800°C). The cross-weld creep strength after processing was increased with respect to the increase of MX dispersion, indicating that these MX precipitates maintained during weld thermal cycles in the fine-grained heat-affected zone region and thereby contribute to improved creep resistant of welds in comparison to the welds made with the standard ''normalization and tempering'' processes. The steels processed in this specific processing condition showed improved cross-weld creep resistance and sufficient room temperature toughness. The above data are also analyzed based on existing theories of creep deformation based on dislocation climb mechanism.

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

Cited by 25 publications

References 0 publications

Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

Creep fracture in tempered martensitic steels

Toward Improving the Type IV Cracking Resistance in Cr-Mo Steel Weld Through Thermo-Mechanical Processing

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