Non Destructive Testing of Steels Jan19

Non Destructive Testing of Steels...

Non Destructive Testing of Steels Non destructive testing (NDT) of steels is a group of analysis techniques used for evaluating the properties of steel materials, components, or welds without causing any damage to them. NDT techniques are used to detect and evaluate internal and surface defects (such as imperfections, discontinuities, and flaws etc.) that may cause failure under the designed operating conditions. These internal and surface defects may be the areas of lower integrity in comparison to other portion of the steel material or may consists of the presence of cracks, voids and other imperfections. NDT gives indirect yet valid results and, by definition, leave the test object fit for its intended use. The terms non destructive examination (NDE), non destructive inspection (NDI), and non destructive evaluation (NDE) are also used for these testing techniques. Since there is no permanent alteration  in the steel material being tested  by NDT techniques, the NDT techniques are considered very important for material inspection. NDT saves both money and time in product evaluation, troubleshooting, and research. NDT techniques constitute very specialized type of work that plays a critical function. These techniques need the service of highly specialized and qualified technicians who use sophisticated equipment and methods to evaluate areas of the steel component that are difficult or impossible to examine using the naked eye. The NDT techniques are used for detecting defects during manufacture and  fabrication as well as the defects developed during service of the steel components. However, it is not possible to detect all the possible defects by examining a component by NDT. Further in NDT, it is not the defect that is detected but the resulting effect on the material such as the modification of physical properties (attenuation to ultra sound or the electrical conductivity etc.). NDT techniques do not provide direct information...

Oxygen and Steels

Oxygen and Steels  Oxygen (O) (atomic number 8 and atomic weight 15.999) has density of 1.429 gm/litre at standard temperature and pressure. Melting point of oxygen is -218.79 deg C and boiling point is – 182.96 deg C. It is a colourless gas but the colour of liquid oxygen is pale blue. The phase diagram of the Fe-O binary system is at Fig 1. Fig 1 Fe- O binary phase diagram  There is a very strong relationship between oxygen  and steel. Oxygen is first used in the steel making process which is a controlled oxidation process. Excess oxygen going to steel during steel  making process,  if not properly taken care of, is source of many steel defects like porosity, inclusions etc. Oxygen is used in the processes of cutting, lancing, scarfing and welding of steels. Oxygen is also the cause of steel destruction by the processes of rusting, scaling and corrosion. Further transport of oxygen takes place in cylinders, tanks and pipelines made of steel. Oxygen is also used (oxy-fuel process) for heating of the steel. During steel making process, the main sources of oxygen in steel are as follows. Oxygen used for blowing in the steel making process Use of oxidizing slags and oxidizing materials ( ores, sinter etc.) during steel making processes Atmospheric oxygen dissolves in the liquid steel during steel tapping and casting operations Oxidizing refractories used in various vessels for holding liquid steel in the process of steel making Rusted and wet scrap Solubility of oxygen in liquid steel is 0.23 % at the steel making temperatures ( 1600 – 1700 deg C). However it decreases during cooling down and then drops sharply during solidification of steel reaching a level of 0.003 % in solid steel. Solubility of oxygen in steel...

Sustaining High Performance for Excellence...

Sustaining High Performance for Excellence The high performance of an organization is determined by how well it is meeting the expectations of its key stakeholders (customers, investors, employees, suppliers, regulatory authorities and the public). In the turbulent  environment which the organization has to undergo in its life span, creation and sustenance of high performance is always a challenge for the organization. There are many cases where  highly successful organizations of the past have failed to exist today or just have become an average performing organization. The environment under which an organization operates undergoes a constant change and hence it calls for new approaches and processes by which change is to be addressed in the organization. The organization can succeed in the new environment only if it plays its role with competence and it focuses on using knowledge to guide its actions. The organization culture must be built to thrive in the performance in an environment of continuous change. It must have processes which are not only continuous evolutionary or incremental, but also continuous and transformational. Though for sustaining high performance, the strategy, operational discipline, talented people are normally considered as essential requirements, but the key for the sustenance of high performance is the developmental culture of the organization which is not replicable outside the organization. The high performance culture of the organization must have a unique personality and soul which cannot be invented and imposed. The organizational character is to be discovered from within the organization based on shared value and heritage. The unique personality and soul of the organization must have high performance values and behaviors (Fig 1) such as high aspirations and a desire to win, external focus, think like owners, bias to actions, individuals who team, and passion and energy etc....

Oxy- Fuel Combustion and its Application in Reheating Furnace Jan13

Oxy- Fuel Combustion and its Application in Reheating Furnace...

Oxy- Fuel Combustion and its Application in Reheating Furnace Steel reheating is an energy intensive process requiring uniform temperature distribution within reheating furnaces. Historically, recuperators have been used to preheat combustion air, thereby conserving energy. More recent innovations include oxygen (O2) enrichment and the use of regenerative burners, which provide higher preheat air temperatures than recuperators. These processes have limitations such as equipment deterioration, decreasing energy efficiency over time, high maintenance costs, and increased NOx emissions with increased air preheat temperature, unless special equipment is used. Three things are necessary for the starting and sustenance of combustion. These are fuel, oxygen and sufficient energy for ignition. The efficiency of the combustion process is highest if fuel and oxygen can meet and react without any restrictions. But during heating practice, besides efficient combustion, transfer of heat is also of practical considerations. Normal air used for combustion contains nitrogen (N2) and argon (Ar) besides oxygen. In an air – fuel burner the burner flame contains nitrogen from the combustion air. A significant amount of the fuel energy is used to heat up this nitrogen. The hot nitrogen leaves through the stack, creating energy losses. Hence air does not provide optimum conditions for combustion as well as heat transfer. Heat absorbed by nitrogen either gets wasted or is to be recovered for the purpose of energy conservation. Present day best air- fuel heating system in the reheating furnace need at least 310 M Cal for a ton of steel for achieving the right temperature of the steel product for rolling. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame. Introduction of an innovative oxy...

Non Metal Inclusions in Steels...

Non Metal Inclusions in Steels Non metallic inclusions are naturally occurring and typically undesired products that are formed into various types depending on their favourable thermodynamic conditions during the production of steel and in all manufacturing and treatment processes involving liquid steels. They are constituted by glass-ceramic phases embedded in steel metal matrix.All steels contain non metallic inclusions to a greater or lesser extent. The type and appearance of these non metallic inclusions depends on factors such as grade of steel, steel making process, secondary metallurgy treatments and casting of steel etc. Because of this, it is of particular significance to determine how pure the steel is. The term steel cleanness is relative one, since even steel with only 1 ppm each of oxygen and sulphide will still contains billion to trillion non metallic inclusions per ton. Various factors which influence the non metallic inclusions in steel are shown in Fig 1. Fig 1 Factors influencing the non metallic inclusions in steel  Non metallic inclusions are chemical compounds of metals (e.g. iron, manganese, aluminum, silicon, and calcium) with non metals (e.g. oxygen, sulphur, carbon, hydrogen, and nitrogen). Non metallic inclusions form separate phases. The non metallic phases containing more than one compound (e.g. different oxides, oxide + sulphide) are called complex non metallic inclusions (spinels, silicates, oxy-sulphides, carbonitrides). Despite the presence of non metallic inclusions in steels in small percentage (0.01 % to 0.02 %), they have a significant effect on the properties of steels. They are the cause for dangerous and serious material defects such as brittleness and a wide variety of crack formations. However, some of these inclusions can also have a beneficial effect on steels properties by nucleating acicular ferrite during the austenite to ferrite phase transformation especially in low carbon steels.  The...