NDTnet 1998 Aug, Vol.3 No.8

Abstract

The available data have been reviewed of in-service creep damage, as it appears in replica inspection results from Nordic and European high temperature (> 500°C) steam systems in ageing power plants. The present practice used for evaluating replica inspection results, such as that in the Nordtest methods, are stiff and conservative, and do not differentiate much between materials or components (1). Analysis of the inspection results showed that there are considerable differences between the common pipe steels 14 MoV 6 3, 13 CrMo 4 4, 10 CrMo 9 10 and X20 CrMoV 12 1 in long term service, especially when welded. Recommendations have been produced for performing and evaluating replica inspection results (2). For example, the time to start the first in-service replica inspections are given as material dependent (Table 1), as well as the proposed maximum time to next inspection. These recommendations apply in particular to the common case where no earlier inspection data are available from exactly the same location, and where only the parallel experience can be used as a guideline. As there are different approaches in Europe in this context, different options have been considered for obtaining the recommended reinspection times as a function of the observed creep damage.

Table 1. Recommended maximum time in service before starting the first in-service replica inspections, obtained from material specific statistical assessment of results from European replica inspections (1).

Material type	Recommended maximum time in service (h) to initiate in-service replica inspections Welds and bends, service temperature at least 500°C
14 MoV 6.3	50 000 h
13 CrMo44	1000 000 h
10 CrMo9 10	1000 000 h
X20 CrMoV 12 1	120 000 h

The replica inspection data necessarily reflects the large variability of service conditions and material response of the structures inspected. The present work demonstrates the potential of extending and extracting rules from replica inspection results with conclusions on scheduling of the subsequent action in plant.

1. Nordlest Method NTNDT 010, 1991. High temperature components in power plants: Reminant lifetime assessment, replica inspection. Nordtest, Espoo, Finland. 6 p.
2. Auerkari, P., Holmstrom, S., Salonen, K, Borggreen, K, Storesund, J., Mu, R., 1997. _ Evaluation of creep damage from replica inspection results. VTT Manufacturing Technology, Espoo, Finland. Report VALB-211. 20 p.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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