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Metals 2016, 6(3), 62; doi:10.3390/met6030062

The Early Morphological Development of the Near Surface Region of Pickled Grade 91 Tubing Exposed to Steam and Its Long Term Implications

National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK
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Author to whom correspondence should be addressed.
Academic Editor: Hugo F. Lopez
Received: 29 January 2016 / Revised: 26 February 2016 / Accepted: 8 March 2016 / Published: 14 March 2016
(This article belongs to the Special Issue Oxidation of Metals)
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Abstract

To improve intra-laboratory consistency and experimental repeatability during high temperature oxidation testing, metallic coupons undergo a standardised surface preparation. It is stipulated in international testing standards that grinding of a coupons surface acceptably replicates surface conditions encountered in industrial settings whilst ensuring that each coupons surface is chemically and topographically homogenised [1,2]. Grade 91 steel tubing exposed in the laboratory to flowing steam at 650 °C and 1 bar for up to 3000 h has been compared with Grade 91 tubing exposed in a commercially operated boiler system at elevated pressures at temperatures in the range of 500 to 650 °C for 91 kh. It has been found that a pre-existing surface structure dissimilar from that of the bulk alloy and that of a ground surface, is present on the inside surface of the tubing. The presence of pre-existing surface features in commercially exposed material has implications on the long term morphological development of the oxidation region and may account for some of the discrepancies between observations made in laboratory and service exposures. View Full-Text
Keywords: silicon oxide; pickling; steam; T91 tubing; long term exposure silicon oxide; pickling; steam; T91 tubing; long term exposure
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Gorman, D.M.; Fry, A.T. The Early Morphological Development of the Near Surface Region of Pickled Grade 91 Tubing Exposed to Steam and Its Long Term Implications. Metals 2016, 6, 62.

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