The
significance of material selection for small and complicated materials
discovered in equipment crucial to the chemical process industries cannot be
underrated. For tiny metallic parts for example threaded fasteners, the product
engineers take steps to choose a material for linear selection. The performance
and application media for the materials and choice of material is decided by an
engineer.
Natural
factors considered are corrosion resistance, interaction of severe chemicals
and high temperatures. Subsequent to analyzing the material on the base of these factors, the engineers usually make the final choice on the material for
the certain part. Although the required material may have specific characteristics
that can meet the challenges in operation and machining and the designer may
not be familiar about the future problems that may arise during use.
There
is a significant connection among material choice and correctness, machining
and final finish that is usually ignored. These factors have important effect
on the quality and cost of the component. The unsuitable machining method for
tiny parts can result into problems in several materials, particularly if they
are hardly machinable. These problems are service conditions, premature
component damage and oxidation and the outcome of inappropriate machining and
material selection.
Selection Factors
Basically
in service condition is normally a high priority for material choice of parts,
particularly when it comes to the long and short term protection and reliability
of the system. The following factors are
essential to consider for material choice for major and minor applications:
Corrosion:
Corrosion
is a critical problem that states the material choice in various service media
such as chloride stress corrosion cracking in stainless steels. Titanium is a
preferred material for its chloride resistant characteristics. Considering the corrosion
resistance capacity of a material is essential because corrosion may deform the
component severely resulting into explosions, fire, mechanical failure and
economy loss.
Oxidation
usually occurs in stainless steel alloys. These metals naturally produce oxide
layers for resistance from corrosion that can result into rough surfaces. This
needs passivation treatment to decrease the negative effects of the oxide
layers and to maintain the surface smoothness and keep it free from imperfections
that can result into equipment damage.
Chemical Exposure
Materials
can result into adverse reactions to chemicals in the different media. Chemical
interaction of materials in an environment can involve high acidity and availability
of oxygen or aqueous solutions or hard cleaning or sanitizing agents. However
the production environment can be non-attacking, the availability of these
chemicals can result into material reaction therefore a designer should
consider these factors while choosing the materials.
Temperature
The
mechanical limits of materials can be severely affected by elevated temperatures,
resulting into heat failure or deformation. These materials are also chosen on
the base of temperature resistance as the effect of extreme temperature on
materials can result into increased corrosion. The materials fit for use at the
high temperatures are nickel based alloys, iron alloys and cobalt base alloys.
Price
Price
of a material is a crucial factor that has major role in choosing a material
for a specific set of materials. Cost influences the balance between materials
and machining in the case of material grades. An engineer selects Inconel as
the material for the product, the grade affects the machining cost. As machining of Inconel alloy 600 is easier than Inconel 718, the time and price of
machining can vary significantly on the base of type of material selected. Although
the cost is often secondary to other factors that are essential for choosing a
consistent and reliable material for an operation.
Selective set of applications: In many CPI applications, the choice
of a suitable material can often eliminate the negative effects related with
the service media; however few applications are more limited. Due to the tight
application – media levels, production parts for specific applications for
example nuclear processing can be limiting while choosing a material.
Metals
and alloys that are strong, resistant to cracking and fatigue and are easily
machinable, are preferred. They play a major role in the performance and
longevity of chemical processing units.
Machining
Exotic
and hardly machinable materials for example stainless steels, titanium and
nickel based alloys are preferred for industrial applications for their
physical characteristics. But these materials also possess some undesirable characteristics
that can be challenging which can be overcome by choosing a suitable machining
method.
Easy machining: Ductility is a significant property that describes the
machinability of a material. Steels and nonferrous metals are less ductile due
to which they can easily break. But it is tough to deform them and they need
large amount of pressure to develop threads, they usually roll effectively.
Smooth Surface: After cutting a material, the microscopic particles that are
left behind, results into thread galling. Galling is a kind of wear resulted by
sliding and friction among two metal surfaces. When a metal surface galls,
microscopic particles crack and foul the application media.
Security against oxidation: Oxide layers
develop in various kinds of metals like stainless steel, titanium, for good
corrosion resistance. Although, this results into significant issues for
threads and mated components.
The
surface finishes are utilized as a different measure; however in several
chemical processing applications for example food or pharmaceutical processing,
the chosen finish should meet the regulations.
Production Costs- The machining method can result into impact costs. The thread
rolling process is better than cutting and in few cases, it can decrease the
production time by 90%. Die lifetime is an essential factor in choosing the
machining costs. Although, if an application doesn’t need full thread crest,
the costs will be decreased however the die life is reduced when the crest is
not full.
An
understanding of the required service and operating condition is crucial in
choosing a material for a specific set of applications.
