Table Of ContentEuropean Federation of Corrosion
Publications
NUMBER 14
A Working Party Report on
Guidelines for Methods of
Testing and Research in
High Temperature Corrosion
Edited by
H. J. GRABKE D. B. MEADOWCROFT
AND
Published for the European Federation of Corrosion
by The Institute of Materials
THE INSTITUTE OF MATERIALS
1995
Book Number 604
Published in 1995 by The Institute of Materials
1 Carlton House Terrace, London SWlY 5DB
0 1995 The Institute of Materials
All rights reserved
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Available on application
ISBN 0-901716-78-2
Neither the EFC nor The Institute of Materials
is responsible for any views expressed
which are the sole responsibility of the authors
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Made and printed in Great Britain
Contents
Series Introduction ........................................................................................................... vii
Introduction ....................................................................................................................... ix
List of Abbreviations ......................................................................................................... xi
1 Guidelines for Plant Measurements of High Temperature .............................. 1
Corrosion
D. B. MEADOWCROAFNTD J. E. OAKEY
2 Discontinuous Measurements of High Temperature Corrosion.. ................1. 1
J. R. NICHOLLS
3 In Situ Measurement Techniques ....................................................................... 37
M. I. BENNETT
4 Thermogravimetry ............................................................................................... 52
H. 1. GRABKE
5 Definition and Preparation of Gas Atmospheres ............................................ 62
H. J. GRABKE
6 Corrosion in the Presence of Melts and Solids ................................................. 85
S. R. J. SAUNDERS
7 Simultaneous Corrosion and Mechanical or Thermal Stresses ...................1 04
M. SCHUTZE,V . GUTTMANMN,. F. STROOSNIJDER
8 Corrosion and Wear or Erosion ....................................................................... 121
F. H. STOTT
9 Oxidation/Corrosion of Advanced Ceramics: A Review of the .................1 36
Progress Towards Test Method Standardisation
D. J. BAXTER
10 Metallography, Electron Microprobe and X-Ray Structure ......................... 147
Analysis
A. RAHMEALN D V.K OLARK
vi Contents
11 Surface Microsurgery Preparation Procedures for High .............................. 158
Temperature Corrosion Characterisation
M. 1. BENNETT
12 The Application of Transmission Electron Microscopy in the .................... 177
Analysis of High Temperature Corrosion
M. RUHLE AND E. SCHUMANN
13 The Application of Surface Analysis Techniques in High ........................... 189
Temperature Corrosion Research
W.J. QUADAKKEANRDS H . VIEFHAUS
lndex ................................................................................................................................. 218
Introduction
High temperature oxidation and corrosion cause great problems in power plants,
petrochemical and chemical industries and in engines. In recent years new problems
have arisen in energy recovery from chemical processes and waste incineration and
also in special technologies, e.g. high temperature fuel cells, space craft components,
aircraft engines, etc. Thus, there is a great need for materials testing for such
applications. New materials are mostly developed to exhibit mechanical strength and
reliability at high temperatures and the corrosion resistance is often only a secondary
consideration. However, new materials should also be tested in the environments of
their applications from the beginning of their development.
The great need for testing is obvious, both in the research and development
laboratories as well as in industrial and application environments. But it must be
admitted that, at present, there are no standards or even guidelines for material
testing for high temperature corrosion, in contrast, for example, to the situation in wet
corrosion and mechanical testing. As yet, the laboratories of material producers and
users and research institutions have conducted testing and research according to their
own methods and ideas. This certainly leads to mistakes in the performance and
errors in the evaluation, as are reflected in the wide range of results on oxidation
constants and corrosion resistance.
The working party ‘Corrosion by Hot Gases and Combustion Products’ of the EFC
decided to tackle the task to develop guidelines and standards for high temperature
corrosion research and testing. One milestone in this approach was a workshop in
January 1994 in Frankfurt, at which eleven presentations provided information on
methods of corrosion measurement and testing and on the investigation of corroded
specimens and corrosion products. In most cases the presentations were the outcome
of joint efforts of many colleagues from numerous laboratories concerned with high
temperature corrosion. Most work was done by the coordinators of each topic, who
had corresponded and discussed with the other experts, put together the most
important points to be considered and presented the outcome in oral presentations
at the workshop. These contributions form the basis of the guidelines published in
this book, and take into account the discussions and comments at the workshop.
Great efforts were made by the authors to compile their papers which provide
much information and advice. The editors are extremely grateful to the coordinators
of the workshop and authors of the chapters. Furthermore, all scientists and engineers
concerned with the problems of high temperature corrosion should be very grateful
for the efforts made by the authors.
Following the organisation of the workshop, this book may now be considered as
a second milestone on the way to codes of practice and standards in high temperature
corrosion research and testing. Further effort is necessary for progress in
standardisation and in fact projects are under way for developing the codes of
practice for discontinuous exposures and the definitions of gas atmospheres. But
Introduction
X
these developments will take some years and just now the present guidelines will, it
is hoped, be useful to many colleagues already active or just starting in high
temperature corrosion testing and research, and should help them to avoid mistakes
and to obtain reliable relevant data.
H. J. Grabke
Chairman of EFC Working Party on
Corrosion by Hot Gases and Combustion Products
European Federation of Corrosion Publications
Series Introduction
The EFC, incorporated in Belgium, was founded in 1955 with the purpose of
promoting European co-operation in the fields of research into corrosion and corro-
sion prevention.
Membership is based upon participation by corrosion societies and commit-
tees in technical Working Parties. Member societies appoint delegates to Working
Parties, whose membership is expanded by personal corresponding membership.
The activities of the Working Parties cover corrosion topics associated with
inhibition, education, reinforcement in concrete, microbial effects, hot gases and
combustion products, environment sensitive fracture, marine environments, surface
science, physico-chemical methods of measurement, the nuclear industry, computer
based information systems, corrosion in the oil and gas industry, and coatings.
Working Parties on other topics are established as required.
The Working Parties function in various ways, e.g. by preparing reports,
organising symposia, conducting intensive courses and producing instructional
material, including films. The activities of the Working Parties are co-ordinated,
through a Science and Technology Advisory Committee, by the Scientific Secretary.
The administration of the EFC is handled by three Secretariats: DECHEMA
e. V. in Germany, the Societe de Chimie Industrielle in France, and The Institute of
Materials in the United Kingdom. These three Secretariats meet at the Board of
Administrators of the EFC. There is an annual General Assembly at which delegates
from all member societies meet to determine and approve EFC policy. News of EFC
activities, forthcoming conferences, courses etc. is published in a range of accredited
corrosion and certain other journals throughout Europe. More detailed descriptions
of activities are given in a Newsletter prepared by the Scientific Secretary.
The output of the EFC takes various forms. Papers on particular topics, for
example, reviews or results of experimental work, may be published in scientific and
technical journals in one or more countries in Europe. Conference proceedings are
often published by the organisation responsible for the conference.
In 1987 the, then, Institute of Metals was appointed as the official EFC
publisher. Although the arrangement is non-exclusive and other routes for publica-
tion are still available, it is expected that the Working Parties of the EFC will use The
Institute of Materials for publication of reports, proceedings etc. wherever possible.
The name of The Institute of Metals was changed to The Institute of Materials
with effect from 1 January 1992.
A. D. Mercer
EFC Scientific Secretary,
The Institute of Materials, London, UK
...
Vlll Series Introduction
EFC Secretariats are located at:
Dr J A Catterall
European Federation of Corrosion, The Institute of Materials, 1 Carlton House
Terrace, London, SWlY 5DB, UK
Mr R Mas
Federation Europeene de la Corrosion, Societe de Chimie Industrielle, 28 rue Saint-
Dominique, F-75007 Paris, FRANCE
Professor Dr G Kreysa
Europaische Foderation Korrosion, DECHEMA e. V., Theodor-Heuss-Allee 25,
D-60486, Frankfurt, GERMANY
1
Guidelines for Plant Measurements of High
Temperature Corrosion
D. B. MEADOWCROFT and J. E. OAKEY*
ERA Technology, Ltd, Cleeve Road, Leatherhead, KT22 7SA, UK
*British Coal, Coal Technology Development Division, PO Box 199, Stoke Orchard, GL52 4ZG, UK
ABSTRACT
This paper gives broad guidelines for the procedures to be followed when carrying out
plant measurements of high temperature corrosion. It covers the selection of exposure
conditions, the design of metal loss probes and component inserts, the measurements
of metal loss and other post-exposure analyses,e xperimental design, and other methods
of predicting metal loss including high temperature corrosion monitors.
1. Introduction
The aim of this document is to bring together best practices for the effective determi-
nation of the high temperature corrosion behaviour of operational plant. The pur-
poses of such measurements are therefore always ultimately directed towards
optimising the operation of the plant, either by improved lifetime prediction for the
materials of construction, or towards recommending a replacement material. Re-
quired lifetime predictions are generally measured in tens of thousands of hours if
not years. Mechanistic arguments can, and should, be used to aid these predictions,
but are never the purpose of the work. For instance, it is necessary to establish whether
the observed corrosion kinetics are a long term value or are an incubation rate prior
to an accelerated propagation rate. Even if the corrosion kinetics are established,
extrapolation of measurements by even one order of magnitude must be made with
caution, and should be based on a series of measurements made over different time
intervals (e.g. data at a range of times up to 10 000 h for 100 000 h lifetime predic-
tions). It must also be emphasised that, even more so than in mechanistic laboratory
experiments, the basic requirement is rate of metal loss, not 'mass gain', and due
allowance must be made for sub-surface penetrations such as internal oxidation or
carburisation. Other points of general concern in plant measurements are that it is
usually the maximum corrosion rate which defines the component lifetime, and that
frequently the components of interest are cooled relative to the hot gas.
The entire subject should include specifications for measurements made directly
on standard plant components as well as on component inserts, probes or corrosion
monitors exposed in the plant specifically for lifetime prediction purposes. There
2 High Temperature Corrosion Research and Testing
are, remarkably, few published standards even for measurements on standard tubes
(for instance, in the UK the CEGB published general guidelines many years ago -
’The Control of Fireside Corrosion’ [l]b ased on repeated ultrasonic tube wall meas-
urements). However, it is not the intention to pursue measurements of standard
components in this paper, although the issues discussed and methods described in
this paper are often applicable. This present paper addresses those cases where com-
ponent inserts, probes or corrosion monitors are used as sensors to assess lifetimes.
The difference between probes and monitors is that probes are samples of materials
exposed, cooled if appropriate, in the process gas stream, and subsequently ana-
lysed by changes in mass, dimensions, and metallography, whilst monitors are able
to give an on-line indication of metal wastage, again as a function of temperature if
required.
The primary purpose of the document is therefore to cover pre- and post-expo-
sure mensuration techniques, and the associated metallurgical examinations from
which extrapolations about future rates of material loss can be made. The selection
of appropriate designs of inserts and probes is an integral part of such studies, as is
characterisation of the environment. In addition, the development in the past few
years of novel high temperature corrosion probes, specifically electrochemical and
resistance probes, will widen the scope of plant measurements as these techniques
become established. It is proposed that independent assessment of these techniques
is required.
The document therefore, in turn, considers the factors related to the selection of
exposure conditions, the design of metal loss probes and component inserts, the
measurements of metal loss and other post-exposure analyses, experimental design,
and other methods of predicting metal loss including high temperature corrosion
monitors. Most of the considerations relate equally to other forms of surface wast-
age such as erosion and wear, but for clarity only corrosion processes will be consid-
ered explicitly.
2. Selection of Exposure Conditions
2.1. Physical Location of Measurement Positions
The criteria to consider include:
(a) That the positions should be near where the maximum corrosion rate is, or is
expected to be experienced. Unless attack in very localised areas is under
investigation, e.g. near burners, unique or atypical positions should be
avoided. Preferably the measurements should be made where the environ-
ment is known or can readily be measured.
(b) A probe should not significantly affect the gas flows normally present. How-
ever, in complex gas atmospheres, free flowing gas or stagnant conditions
can give the most aggressive conditions in different cases, and both extremes
must be considered.
