90; Degrau
Tg | 4 after long term service a term Se.
70; = after regenerative heat treatment] br nn nn
re __ after service ~ 75°C __ ARE
E 5 sp ET Ns
2 nl — J ve od” Te sl
5 40} - 7
3 ak |
8 10} — ireatment 45°C ad vrs
70) mmm oe Majonity
-20 0 2) . 60 . 80 100 anerated
aol a I no
Test temperature [°C] no
Fig. 8: Influence of material state on transition temperature FATT sp, vr
5. Summary
Occurrence of structure degradation processes was found in the drum material after long-term
service. 18CuNMT steel is characterized by a ferrite-bainite-pearlitic structure. After long-term Lol
service occurrences of the following phenomena were found: bainite/pearlite regions degradation :
processes; copper particles in ferrite and postbainite grain; M;C and M,C; carbides at grain and Streß
boundaries; ductility decrease expressed by impact strength values; fracture toughness decrease. The phan
The application of restorative heat treatment considerably improves the properties of the tested boller af
material. What occurs is a decrease of the amount of carbides and their coagulation as well as a HE
decrease of the density of dislocations . Also, recovery takes place. A very big influence of the RE
applied treatment on the shift of temperature FATT to lower temperatures was shown. This is very a
advantageous, due to the temperature of the hydrostatic test carried out. The experiments have Ig
shown that the majority of failures that occurred during the hydrostatic test were in the cases when designed
the temperature FATTso of the drum material corresponded to a temperature equal or higher than the Operate 4
hydrostatic test temperature. EE
In the case of their proper operation, drums can be used for much longer than 150 thousand I.
hours, whereas in the case of improper operation, having found degradation of the material, a
there is a possibility of the drum regeneration and prolongation of its operation by the time of in N
minimum 30 000 hours. oh
The results of the research carried out and the analysis of the conditions of crack initiation and to
propagation show that the tested drum, withdrawn from operation, could be still used. © &
REET
References . Zn
(1)Kielbus A.: Material basis of life prognosis of the boiler drum after long term service.” Doctor’s a
thesis, Katowice, 1999. oo
(2)Hernas A., Mirecki L.: ,Life assessment methods for low alloy steels after long-term service”,
Cape Town 1997.
(3)Ciesla M., Kielbus A., Okrajni J.,Plaza M. JRenowicz D.: ,, The investigations of energetically
boiler life.”, 111 Konferencja ,,Problemy Badawcze Energetyki Cieplnej, Warszawa, 1997
(4)Hernas A., Kietbus A.: ,Structure degradation of drum material after long term service.”, a
Krajowa Konferencja pt.: Dobor i eksploatacja materialow inzynierskich Jurata, 1997. ow
(5)Kielbus A., Hernas A.: ,,Crack resistance — the criterion of the residual life.” , XXV SIM, Rabka, - ns
1997.
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