Home Archive News Contact
PDF download
Cite article
Share options
Informations, rights and permissions
Issue image
Vol 14, Issue 1, 2023
Pages: 116 - 124
Research article
Metallic materials
See full issue

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 

Metrics and citations
Abstract views: 33
PDF Downloads: 24
Google scholar: See link
Article content
  1. Abstract
  2. Disclaimer
Published: 01.05.2023. Research article Metallic materials

MICROSTRUCTURAL DEGRADATION OF BOILER HEADERS STEELS UNDER LONG TERM EXPOSURE TO HIGH TEMPERATURE

By
Armin Husika ,
Armin Husika

Termoelektrana „Kakanj“ , Kakanj , Bosnia and Herzegovina

Belma Fakić ,
Belma Fakić
Contact Belma Fakić

Institute "Kemal Kapetanović" Zenica, University of Zenica , Zenica , Bosnia and Herzegovina

Milenko Rimac
Milenko Rimac

Maneco Kakanj , Kakanj , Bosnia and Herzegovina

Abstract

This paper describes the process of degradation of the structure of the inlet header of the 
intermediate reheater (MPr) 2 input header at the boiler of Unit 7 of the Thermal Power Plant 
Kakanj, determined on the basis of tests of replicas and hardness at characteristic places of the 
header. Headers, with minor delays, have been in continuous operation since 1988. Hardness was 
tested at replica pickup sites, on the basis of which the correlation between structure degradation 
and hardness drop resulting from exploitation during the long-term high-temperature operation 
was estimated. 
The change in hardness is certainly one of the most reliable indicators of the structure degradation 
degree, which is directly related to the service life of the installed components. The subject of the 
test was the inlet header of the intermediate heater made of low alloy steel 15Mo3, consisting of 
ferrite-pearlite microstructure, and having calculated values for the allowed hardness in the range 
from 133 to 176 HB. The structure degradation assessment was performed according to VGB-S-
517 by comparing the microstructure of the replicates with the corresponding standards, and the 
hardness was tested according to ASTM A 956/1996-method A. 
The examination has shown that in the exploitation life achieved so far, there has been a partial or 
complete degradation of the structure, which is reflected in the initial and delayed coagulation of 
the perlite lamellae (Grades 2a and 3a). The hardness at the test sites is at or below the lower than 
the prescribed 133HB. The tests confirmed that there is a good correlation between the degree of 
degradation of the structure and the hardness, which can be used in assessing the condition and 
planning the extent of testing on critical components. 
1. INTRODUCTION 
As part of the regular tests of critical components of the 

References

1.
Milenko Rimac TTDUMK, Koro A. Energoinvest Institut za materijale i kvalitet IMQ Sarajevo, Belma Fakić Institut „Kemal Kapetanović“ Zenica, Elaborat 02-19 – Utvrđivanje stanja kritičnih komponenti kotla bloka 7 u Termoelektrani. 2019.
2.
Standard DIN. 50150 - Testing of metallic materials - conversion of hardness values. 2000;
3.
Standard ASTM A 956 - method A - Standard Test Method for Leeb Hardness Testing of Steel Products. 1996;
4.
Standard DIN. 17175 – Seamless Tubes of Heat – resistant Steels. Technical Conditions of Delivery. 1979;
5.
VTT Publications 280 – Microstructural degradation of boiler tube steels under long-term exposure to high temperature, Jorma Salonen&Pertti Auerkari, Technical research center of. 1996;
6.
VGB-S-517- S. - Guidelines for rating the microstructural composition and creep rupture damage of creep-resistance steel for high-pressure pipelines and boiler components and their weld connections. 2014;
7.
E SASTM. 407-07 - Standard Practice for Microetching Metals and Alloys. 2007;
8.
Standard BAS ISO 3057 - Non-destructive testing - Metallographic replica techniques of surface examination. 1998;

The statements, opinions and data contained in the journal are solely those of the individual authors and contributors and not of the publisher and the editor(s). We stay neutral with regard to jurisdictional claims in published maps and institutional affiliations.