Metallurgy (Corrosion and Cracking)

Metallurgy is a science and technology of the metal structure and property.

Corrosion is a natural process of an oxidation or destruction of a component. It is the gradual destruction of materials (usually metals) by chemical reaction with their environment.

Crack is a partial split or break. A Cracking is a fracture of a material along a path that produces a linear discontinuity.

Material Selection Diagram (MSD) is an engineering drawing which shows the material selection information and specification of the piping and equipment in the process and utility facility that is a step in the process of designing any physical object of the material. The main goal of Material Selection is to minimise cost while meeting product performance requirements, and the systematic selection of the best material for a given application begins with properties and costs of candidate materials. A MSD is normally developed from simplified Process Flow Diagrams (PFDs) by the Process Engineer, Material Engineer and Metallurgist of a project. The Material Engineer uses the Material Selection Diagram to assign a line class and specification to each line on the Piping and Instrumentation Diagram (P&ID) (or Process Engineering Flow Scheme (PEFS)).

Metallurgy is a science and technology of the metal structure and property.

Ageing (or Aging) is 1) to getting older; 2) the process of exposing materials to an environment for a duration of time that generally occurs slowly at room temperature (natural aging) and more rapidly at higher temperature (artificial aging).

Alchemy is a type of chemistry that was an ancient tradition of sacred chemistry aiming to achieve the transmutation of the base metals into gold, and trying to find a medicine for any disease, etc.

Alkali Metal is a chemical element that is reactive, soft metal with low densities. The Alkali Metals are Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), and Francium (Fr). 

Alloy is a mixture of two elements that is the metal substance made by combining two or more metallic elements. Alloys often have properties that are different to the metals they contain, and more useful than the pure metals alone.

Alloy Steel is an iron based alloy containing carbon (usually less than 2.5 % by weight), manganese (usually greater than 0.25 % by weight), and a variety of elements in total amounts between 1.0 % and 50 % by weight to improve its mechanical properties. Low Alloy Steel (less than 5 %) to increase strength or hardenability, and High Alloy Steel (over 5 %) to achieve special properties, such as corrosion resistance or extreme temperature stability.

Anneal means to make ​metal or ​glass ​soft by ​heating and then ​cooling it ​slowly for reducing hardness, improving machinability of the material.

Austenitic Stainless Steel is the most common types of stainless steel that has austenite and is the alloys containing chromium and nickel, and sometimes molybdenum and nitrogen.

Austenitizing is the forming austenite by heating iron or iron-based alloys that is heating a steel above the critical temperature, holding for a period of time long enough for transformation to occur.

Base Metal is any common and inexpensive metal used for jewellery or in industry. The most common Base Metals are copper, lead, nickel, tin, aluminium, and zinc.

Bimetal is the objects consist of layers of different metals that used in a thermostat, will bend in one direction when heated, and in the other when cooled, and can be used to open or close electrical circuits.

Brittle Fracture is the fracture that is the sudden, very rapid cracking of material or equipment under stress. (Contrast to the Ductile Fracture)

Bronze is an alloy of copper, usually containing with up to one-third tin as its main addition.

Carbon Steel is the carbon and iron containing up to 2 mass percent carbon that has a higher carbon content, lower melting point and greater durability compared to stainless steel.

Carburizing is a heat treatment process that is the absorption and diffusion of carbon in iron or an iron-based alloy in contact with a suitable carbonaceous environment at elevated temperature.

Cast Iron is a type of hard iron that is made into shapes by being poured into a mould when melted containing 2 to 4 percent carbon along with varying amounts of silicon and manganese and traces of impurities such as sulphur and phosphorus by weight whereas carbon steel contains less than 0.5 percent. The Cast Iron is formed by smelting iron ore, or melting pig iron, and then poured into molds and allowed to cool and solidify.

Casting is a component or part made by hot liquid into a finished shape by the solidification of liquid material in a mold.

Ductile Iron is a type of cast iron that has been treated as the impact and fatigue resistance, and elongation while molten with an element. The Ductile Iron was invented in 1943 by Keith Millis. (Also, called as a ductile cast iron).

Duplex Stainless Steel is a family of stainless steels whose microstructure at room temperature consists primarily of a mixture of austenite and ferrite.

Fatigue is a process of progressive localized permanent structural change that is weakness in something, such as a ​metal ​part or ​structure, often ​caused by ​repeated ​bending.

Ferrite is the typically metallic materials that is a metal oxide ceramic made of a mixture of Fe2O3 and either manganese zinc or nickel zinc oxides pressed or extruded into a range of core shapes. The Ferrite is the body-centred cubic crystalline phase of iron or iron-based alloys with magnetic properties that are useful in many types of electronic devices. Ferrites are hard, brittle, iron-containing, and generally gray or black and are polycrystalline.

Ferritic Stainless Steel is stainless steel whose microstructure at room temperature consists predominantly of ferrite containing a minimum of 10.5% chromium that can resist oxidation and corrosion, specifically stress cracking corrosion (SCC).

Heat Treatment is a process of heating and/or cooling to improve the metal properties.

Ingot is a casting of material relatively pure material. (e.g., crystalline silicon, from which slices or wafers can be cut for use in a solar cell)

Low Alloy Steel is the alloy steel that is improved strength or hardenability with a total alloying element content of less than approximately 5 percent. 

Low Carbon Steel is a steel having composition of 0.05%~0.25% carbon and up to 0.4% manganese. The Low Carbon Steel is easy to shape so can be made into thin sheets.

Martensitic Steel is a specific type of stainless steel alloy in which a microstructure of martensite can be attained by quenching at a cooling.

Noble Metal is a metal or alloy that formed with a small negative or a positive free-energy change to resist the corrosion and oxidation in moist air. (e.g., ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold)

Post Weld Heat Treatment (PWHT) is any heat treatment after welding that is to improve the properties of a weldment.

Quenched and Tempered is the quench hardened and then tempered that consists of a two-stage heat-treatment process. Stage one includes hardening, in which the steel is austenitised to approximately 900°C and then quickly cooled with water or oil. Stage two consists of tempering the material to obtain the desired material properties. One of the main advantages of tempering over quenching is that it helps to improve the toughness of the material without making it too hard. One of the main advantages of quenching over tempering is that it helps to harden the material, making it more resistant to wear and tear.

Quenching is 1) the rapid cooling from an elevated temperature to adjust the mechanical properties of its original state in a short time that is the soaking in oil or water of a metal at a high temperature followed by a rapid cooling process to obtain certain desirable material properties. The Quenching technique is commonly applied to steel objects, to which it imparts hardness; 2) severe cooling of the reaction system in a short time, almost instantaneously freezing for the status of a reaction and prevents further decomposition or reaction. (Refer to the Tempering)

Sensitising Heat Treatment is a heat treatment that is the precipitation of carbides at grain boundaries in a stainless steel or alloy to become susceptible to intergranular corrosion or intergranular stress corrosion cracking.

Shot Peening is a cold working process that is the inducing compressive residual stress layer and modify mechanical properties and composites in the surface layer of a material by bombarding it with a steel shot.

Solution Heat Treatment is a metal heat treatment process in a suitable temperature and holding at that temperature long enough to allow a desired constituent to enter into the solid solution, followed by rapid cooling.

Stainless Steel is a type of metal product that is more resistant to rust, staining and corrosion than regular steel that contains 10.5 mass percent or more Chromium, the amount of Chromium gives an increased resistance to corrosion, possibly with other elements added to secure special properties. Stainless Steel also contains varying amounts of Carbon, Silicon and Manganese. Other elements such as Nickel and Molybdenum may be added to impart other useful properties such as enhanced formability and increased corrosion resistance.

Stress Relieving (Thermal) is accompanied by the restoration of several physical properties in the deformed metal that is a heating a metal to a suitable temperature, holding at that temperature long enough to reduce residual stresses, and then cooling slowly enough to minimize the development of new residual stresses. Cold working, hot rolling, grinding, quenching treatments, welding, and thermal cutting all can induce residual stress into metal that can cause loss of tolerance, cracking and distortion, and contribute to in-service failures. (Refer to the Post Weld Heat Treatment (PWHT))

Tempering is a process of improving the characteristics of a metal by the heat treatment that is used to increase the toughness of iron-based alloys and to make it more resistant to stress.

White Metal is any of various whitish alloys as well as any of several lead-based or tin-based alloys used for the wide range of applications including the creation of ornaments, decorative pieces, and different types of novelty items.

Wrought is metal in the solid condition that is made or done in a careful or decorative way at an elevated temperature.

Zirconium (Zr) Alloy is the solid solutions of zirconium or other metals used to contain uranium fuel pellets, which in turn form part of a reactor fuel bundle.

Corrosion is a natural process of an oxidation or destruction of a component. It is the gradual destruction of materials (usually metals) by chemical reaction with their environment.

Anion is the ionic species having a negative charge atom that has gained electrons. Anions are one of the two types of ions, the other type is called a cation.

Anode is an electrode of the electrochemical cell at which oxidation occurs. The Anode is a positively charged electrode, as of an electrolytic cell, storage battery, or electron tube, and a negatively charged terminal of a primary cell or of a storage battery that is supplying current.

Anode Cap is a device that is an electrical insulating material placed over the end of the anode at the lead wire connection.

Anodic Inhibitor is a chemical substance that decreases or prevents the rate of the anodic or oxidation reaction. (Also, called as the Passivator)

Anode Corrosion Efficiency is the ratio of actual corrosion to theoretical rates calculated from the quantity of electricity that has passed between the anode and cathode using Faraday's law.

Anodic Protection is the method to reduce the corrosion rate of a metal surface with a low voltage direct current by connecting it as an anode with respect to an inert cathode in the cell formed due to an electrochemical reaction in the corrosive environment, and ensuring that the electrode potential is controlled to keep the metal in a passive state. The Anodic Protection is more suitable than cathodic protection for stainless steels specially in extremely corrosive environments, as in the handling and storage of concentrated sulphuric acid.

Anodising (Anodizing)

Crack is a partial split or break. A Cracking is a fracture of a material along a path that produces a linear discontinuity.

Caustic Cracking is a cracking that is most frequently encountered in carbon steels or iron-chromium-nickel alloys under the combined action of tensile stress and corrosion in the presence of a strongly basic solution.

Caustic Embrittlement is the phenomenon that becomes brittle due to the accumulation of caustic substances. (Refer to the Caustic Cracking)

Chloride Stress Corrosion Cracking (CLSCC) is a type of Stress Corrosion Cracking (SCC) which is one of the most well known forms of SCC in the refining and chemical processing industries. The CLSCC is one common reason why austenitic stainless steel pipework and vessels deteriorate in the chemical processing and petrochemical industries. It can lead to failures of plant that can be prevented by an awareness of the onset and evolution of CLSCC, and by periodic inspection to monitor the extent of cracking.

Cold Cracking is a welding discontinuity or welding defect that occurs at temperatures blow 200°C after solidification that is complete in welding or after cooling to ambient temperature, sometimes after a considerable time delay. The Cold Cracking is likely to occur in all ferritic and martensitic steels such as carbon steel, low alloy steel and high alloy steel unless adequate precautions, mainly preheating, are employed. (Also called as the HIC (Hydrogen Induced Cracking))

Delayed Cracking is a cracking under high strength steel, high stress level, and a source of hydrogen in a metal occurring after plating or pickling, sometimes after a considerable time delay. (Refer to the Hydrogen Induced Cracking (HIC); Cold Cracking)

Embrittlement is Embrittlement is a process of reduction of ductility, toughness, or both of the material by exposure to certain environments or heat treatments.

High-Temperature Hydrogen Attack

NACE (formerly known as the National Association of Corrosion Engineers) Institute will improve public safety and environmental protection by advocating corrosion awareness and action, and provide unparalleled qualification programs that drive corrosion industry performance. The NACE International, The Worldwide Corrosion Authority, serves nearly 36,000+ members in 130 countries and is recognized globally as the premier authority for corrosion control solutions. The organization offers technical training and certification programs, conferences, industry standards, reports, publications, technical journals, government relations activities and more. (Source: NACE)