All of the equipment and lines in a petrochemical or refinery plant are made of specific materials. It is so important to choose the proper type of materials for each application. In fact, selecting the suitable materials in oil and gas industry has been always challenging. Therefore, It shall be done by material experts. To choose the right material, it is necessary to consider all the possible aspects including finished price, maximum temperature tolerance, maximum working pressure, working fluid specifications and corrosion consideration. Making even a simple mistake may lead to a catastrophic result like equipment failure or explosion.

ASTM (American Society for Testing & Materials) is one of the most important standard which provides almost all of the available materials specifications. ASME (American Society of Mechanical Engineers) is another valuable standard which gives some guidance on material selection for different situation.

Consequently, it is crucial for any oil & gas engineer to have a general knowledge about the mostly used materials and their terms and specifications. In the following section, we will review some of the basics of frequently used materials in oil and gas industry.

Important terminologies of materials in oil and gas industry

Stiffness: Metal’s deflection resistance (elasticity)

Toughness: Metal’s tendency to dump the cracks (plasticity)

Elongation: Stretching limit before cracking.

Ductility: Ability to change to wire. Lower stiffness and higher toughness may increase ductility.

Tensile strength: Metal’s pressure tolerance limit before rupture.

Yield strength: Maximum pressure a metal can withstand without permanent deformation.

Post weld heat treatment (PWHT): The practice of slowly reheating a welded metal, increasing its temperature, hold it for a specific amount of time then cool it down in a controlled way in order to let the regular crystal structures form. This treatment is usually done to cast iron to recover its ductility.

Tempering: A heat treatment to improve toughness and elongation.

Iron (Fe) is the primary element in all conventional steels. Carbon content of steels ranges from 0.03 up to 2%. Carbon content of stainless steel is less than 1% whereas for cast iron it’s more than 2%. Generally low carbon content increases the ease of forming and welding. Maximum operating temperature for carbon steel is about 370 °C. Examples of most common carbon steel grades are ASTM A 53, A 105, A 106.

Alloy steels are designed for severe conidiations like high temperature (around 700 °C). Alloy contents (Ni, Cr, …) ranges from 3 to more than 10%.