Materials of Construction in Chemical Engineering

Importance of Material Selection in Chemical Engineering

• The selection of materials of construction is crucial in chemical engineering to ensure safe, economical, and high-quality production of chemicals.
• The choice of materials affects the production, handling, transportation, and storage of chemical products.

Primary Considerations for Material Selection

• Fabricability, machinability, strength, thermal conductivity, formability, hardenability, availability, and corrosion resistance are key properties to consider when selecting a material.

Purpose of Studying Materials of Construction (MOC)

• The purpose of studying MOC is to introduce chemical engineers to the materials needed to operate process facilities safely and economically.
• Corrosion and materials engineers should be engaged to choose the appropriate materials of construction.

Deciding on a Material of Construction

• The first step in determining the materials of construction is to evaluate the environments present to determine if they are corrosive to common materials.
• Carbon steel is often the material of choice if corrosion is not a concern and the maximum temperature does not exceed 425°C (800°F).
• Organic chemicals and gases are not typically corrosive to steel, but acids, molten salts, and aqueous liquids require resistant materials.

Cast Irons

• Cast irons are ferrous alloys with a high carbon content (2-4%), making them affordable but brittle and prone to unpredictable failure.
• Cast irons offer advantages, including a low melting point, making them ideal for casting complex shapes, and excellent heat retention.

Types of Cast Iron

• Gray cast iron: the most common type, with a grayish fracture surface due to graphite flakes.
• Ductile cast iron: known for its superior strength and ductility, making it popular in the chemical industry.
• Malleable cast iron: achieves ductility through heat treatment.
• White cast iron: very hard and brittle due to the absence of flake-like graphite.

Balancing Cost and Performance

• Unalloyed cast iron is the most economical option, but alloying elements can be added to enhance corrosion resistance.
• High-silicon cast irons, for example, demonstrate excellent resistance to erosive corrosion.

Corrosion Resistance of Cast Iron

• Cast irons generally behave similarly to carbon steel in terms of corrosion resistance.