Article published in Chemical Engineering World, May 2011

1. Features
Corrosion Management
Material Selection: Challenge
for Corrosion Management in
Process Plants
Proper material selection and material protection, i.e. protection against various
corrosion phenomena in chemical environments, is of prime importance in the chemical,
petrochemical, and other process industries. In the process industries, proper materials
engineering and corrosion control are key issues with respect to production economics,
safety and environmental issues.
C
orrosion is a process rapid attack can occur in the materials from pipes or vessels.
which exerts its influence presence of reactive gases, It can also result in the sudden
in all fields of endeavour, high temperatures, and in catastrophic failure of critical
and its consequences affect combination with abrasion components, particularly
every individual. It is driven by and wear. It is inevitable where corrosion-assisted
thermodynamic considerations, that corrosion can incur cracking takes place, with an
which dictate that metallic huge financial costs, not only associated threat of injury and
materials will tend to return to due to the need to replace loss of life.
their most stable state, often as manufactured components
oxides or other combined forms, and plant, which become Proper materials selection
particularly under aggressive degraded by the process, but and materials protection, i.e.
environmental conditions also due to the consequences protection against various
which accelerate the process. of corrosion for health and corrosion phenomena in
Corrosion can manifest itself in safety, the environment and chemical environments, is
many forms, both general and the quality of life of individuals. of prime importance in the
localised (including cracking Corrosion can be a major cause chemical, petrochemical, and
under conditions of tensile or of pollution where it results other process industries. In
cyclic stressing). Particularly, in the leakage of hazardous the process industries, proper
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2. Features
materials engineering and corrosion
control are key issues with respect Dixon and Poli suggest a four level approach to materials selection
to production economics, safety and
environmental issues.  Level l - Based on critical properties, determine whether the part will be made from metal,
plastic, ceramic, or composite.
 Level II - Determine whether metal parts will be produced by a deformation process (wrought)
The selection of correct materials for
or a casting process; for plastics, determine whether they will be thermoplastic or thermo­
a design is a key step in the process
setting polymers.
because it is the crucial decision
 Level III - Narrow options to a broad category of material. Metals can be subdivided
that links computer calculations into categories such as carbon steel, stainless steel, and copper alloys. Plastics can be
and lines on an engineering drawing subdivided into specific classes of thermoplastics and thermosets such as polycarbonates
with a working design. Materials and polyesters.
and manufacturing processes that  Level IV - Select a specific material according to a specific grade or specification.
convert the material into a useful
engineering design. An incorrectly
chosen material can lead not only is dictated by the unique resistant materials. In many cases,
to failure of the part, but also to environmental conditions that this approach is an economical
unnecessary cost. Selecting the pertain to a specific application at alternative to other corrosion control
best material for a part involves all stages in a component lifetime methods. Corrosion resistance is not
more than selecting a material that including procurement, fabrication, the only property to be considered
has the properties to provide the transportation, storage, installation, in making material selections, but
necessary performance in service; commissioning, operation and it is of major importance in the
it is also intimately connected with maintenance. Corrosion failures chemical process industries.
the processing of the material into have occurred because of
the finished part. A poorly chosen unexpected causes that resulted Selection Process - Is it a Material
material can add to manufacturing from a lack of information about or Process Issue?
cost and unnecessarily increase the corrosion, sometimes the direct A materials selection problem
cost of the part. Also, the properties result of poor communication and/ usually involves one of two
of the material can be changed or a lack of appreciation of the true situations: selection of the materials
by processing (beneficially or service conditions. and the processes for a new product
detrimentally), and that may affect or design and materials substitution
the service performance of the part. From a purely technical standpoint, for an existing design.
an obvious answer to corrosion
The type and extent of corrosion problems would be to use more When selecting construction
materials, it is essential to know
how the materials will behave when
exposed to the actual operating
environment. In particular, special
attention must be given to the
following factors; potential for
corrosion, operating temperatures
and pressures, unexpected
operating conditions and startup
and shut-down procedures. A large
share of equipment operation and
maintenance costs in the chemical
processing industries are the result
of materials failure due to abrasive,
corrosive or high temperature
environments. If corrosion is not an
issue, the least expensive material
with the appropriate mechanical
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3. Features
Material Selection Chart
properties is usually selected. areas that are difficult to repair or designed and fabricated, will require
in components that would cause minimum maintenance and will
Costs and Related Aspects of major shutdowns in case of failure. function reliably. Rising labour costs
Materials Selection In these situations, the original cost in most industries, together with the
The decision on materials selection of the material can be insignificant need for high reliability in capital-
ultimately will come down to a compared to the loss of production intensive plants has produced a
trade-off between performance caused by the use of a lower-cost, trend to this type of system.
and cost. There is a spectrum of but less-effective, material. The
applications varying from - those following two extreme alternatives In practice, many systems are a
where performance is paramount describe the consideration given mixture of these extreme options,
(defense-related aerospace) to those to economic factors when selecting resulting in the high initial costs
where cost clearly predominates materials for specific service. One of one and the high maintenance
(household appliances). The total is a low initial cost system largely costs of the other. For example,
cost of a part includes the cost of the based on carbon steel and cast a plant that has experienced
material, the cost of tooling (dyes, iron that will require considerable costly replacement to galvanised
fixtures), and the processing cost. maintenance over the life of the steel piping may replace it with
plant. copper alloy piping, leaving valve
The important criterion should not fittings and other equipment in
be the initial cost of a material, but its Such a system is a reasonable choice carbon steel and cast iron. The
life-cycle cost or cost effectiveness. It in areas where labour costs are low resulting galvanic corrosion effects
usually is much more cost-effective and material is readily available. The result in reduced life for these
to specify a material that will provide second one is a system based mainly parts. Thus, avoidance of higher
an extended life, particularly in on alloy materials that, if correctly initial costs will result in reduced
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4. Features
reliability and high maintenance specifications, research reports, as it is large, with a number of major
costs. Unfortunately, competitive technical publications, market sectors including manufacturing
bidding and corporate bottom survey reports, materials databases, industries, agriculture, textiles,
lines frequently create barriers expert systems, and process specific handicrafts and services. The
that inhibit realisation of long research studies. Indian chemical industries
equipment life. The enlightened comprise small, medium and large-
company will recognise the value Internet-based systems play a scale units. Development of process
of the life-cycle cost approach on crucial role in assisting the designers specific research studies, material
long-term financial health and not and material selection personnel testing programmes, material
embrace only the low initial cost to fetch the proven experience of databases and corrosion-related
option. materials considered for similar standards for our Indian conditions
process situations elsewhere in the is always a grand challenge for our
In order to prevent corrosion related world. The modern day social and industries. In spite of tremendous
failure modes from occurring they technology networking systems progress in recent times, India
should be considered during the facilitate the researchers, material continues to face challenges
design and material selection stages suppliers, designers, consultants that could derail its ‘science and
of system development. Accounting and industries personnel to technology’ aspirations. There is
for many of the issues that are exchange their views on selection a large gap between the installed
correlated with corrosion, including and find appropriateness of capacity and projected needs in
test, design, and metallurgical selected materials. “We can control basic infrastructure, including
factors facilitates the development corrosion in India” is an example of power, roads, telecommunications,
of an inherently corrosion such a networking group. seaports and airports.
resistant design. For many forms of
corrosion, there are no quantitative This group establishes global level Source
1. ISO TC156 – Corrosion of Metals and Alloys.
measurement techniques, and thus multi-dimensional communication
2. Materials Engineering for the Chemical
materials are only rated based upon pathways (Technology Providers- Process Industries, MTI, 2006.
their relative susceptibilities. Technology Users-Academic and 3. Overview of the Materials Selection Process
Research Institutions-Professional by George E. Dieter, University of Maryland.
4. ASM Handbook Volume 13A, Corrosion:
Information Management for Associations-Legislation Support) Fundamentals, Testing, and Protection, 2003.
Material Selection: Influence and guides professionals from 5. Handbook of Corrosion Engineering by Roberge
of Social and Technology various disciplines and other Pierre.
6. E n g i n e e r i n g D e s i g n a n d D e s i g n f o r
Networking Systems technology groups to network
Manufacturing, Field Stone Publishers, 1995.
A new material cannot be employed with the best material selection 7. Overview of the Materials Selection Process
in a design unless the engineer knowledge source for corrosion by George E Dieter, University of Maryland.
has access to reliable material management. 8. Handbook of Corrosion Engineering by Roberge
Pierre.
properties and, hopefully, costs.
9. NiDI Technical Series 10071, Nickel
This illustrates one reason why the Our Indian Scenario Development Institute, 1992.
tried and trusted materials are used The cost of developing and 10. Corrosion Conscious Design, The AMPTIAC
repeatedly for designs even though incorporating advanced materials is Quarterly, Volume 9, Number 3, 2005.
11. Corrosionmanagementsurvey.in.
better designs could be achieved high. The reliability of new materials 12. Technology Roadmap for Materials of
with newer materials. At the start is unproven in most practical Construction, Materials Technology Institute,
of the design process, low-precision applications, and exploring their USA, 1998.
but all inclusive data are needed. At use in a process environment is risky. 13. S & T Strategies of Six Countries, National
Academy of Sciences, USA, 2010)
the end of the design process, data Significant R&D, from bench scale
are needed for only a single material, experiments to the construction
but they must be accurate and very and testing of prototypes, is usually Author Details
detailed. necessary before a new material M Vallippan
can be implemented in chemical Corrosion Mgmt. Consultant,
Information comes through various processing equipment. Kuwait Oil Company &
channels; handbooks, international/ Corrosion Mgmt. Services
national/company standards and The economy of India is as diverse E-mail: corrosion.management@gmail.com
www.cewindia.com Chemical Engineering World | 74 | MAY 2011
Feature-Challenge for Corrosion 74 74 5/31/2011 7:50:03 PM