Refining of Crude Oil

The main aim of refining is to convert crude oils of several origins and different compositions into valuable products and fuels having the qualities and quantities demanded by the market. The different types of refining processes, such as separation, conversion, finishing, and environmental protection, are done and briefly discussed. The everchanging demand and quality of fuels, as well as environmental concerns and the hurdles facing the refining industry, are also highlighted. Environmental laws have played a vital role in the advancement of the refining industry and may even change the competition between petroleum and other alternative energy sources. Refining is regarded as the processing of crude oil into a number of valuable hydrocarbon products. Processing utilizes chemicals, catalysts, heat, and pressure to separate and combine the different types of hydrocarbon molecules commonly found in crude oil into groups of like molecules. The refining process also rearranges their structures and bonding models into different hydrocarbon molecules and compounds. Therefore, it can be said that it is the type of hydrocarbon (paraffinic, naphthenic, or aromatic) and its demand that affects the refining industry. Petroleum refining has evolved continuously in response to changing demands for better and different products. The change in the demand has also been conducted by continuous advancement in product quality, such as octane number for gasoline and cetane number for diesel. The initial requirement was to generate kerosene for household use, followed by the development of the internal combustion engine and the production of transportation fuels (gasoline, diesel, and fuels). Refineries produce a variety of products including those used as feedstocks for the petrochemical industry. In the initial stages, refining consisted of mere fractionation of crude oil followed by the progress in the 1920's of the thermal cracking methods, such as visbreaking and coking. The processes crack heavy fuels into more useful and desirable products by applying pressure and heat Modern refineries incorporate fractionation, conversion, treatment, and blending operations and may also include petrochemical processing. Most light distillates are more turned into more useful outcomes by adjusting the size and arrangement of the hydrocarbon molecules through cracking, reforming, and other conversion processes. In general, the refining industry has always been considered as a high-volume, low-profit-margin industry. World refining stays to be challenged by the ambiguity of supply, challenging market circumstances, government regulation, availability of capital, and slow growth. Although shipping of refined products has been rising over the years, a close bond remains between domestic markets and domestic production. This explains the large differences in refinery schemes from one country to another and from one region to another.

What are the defects in welding?

The lack of training to the operator or careless application of welding technologies causes discontinuities in welding. Infusion welding, defects such as porosity, slag inclusion, solidification cracks etc., deteriorates the weld quality and joint properties. Common weld defects found in welded joints:

These mistakes may result in sudden crashes which are unexpected as they give rise to stress intensities. The common weld defects include:-

i. Porosity 

ii. Lack of fusion 

iii. Inclusions 

iv. Cracking 

v. Undercut 

vi.Lamellar tearing 

i. Porosity

Porosity takes place when the solidifying weld metal has gases trapped in it. The presence of porosity in most off the welded joints is due to dirt on the surface of the metal to be welded or damp consumables.

ii. Lack of Fusion

Due to very little input or slow traverse of the welding torch, lack of fusion arises. A better weld can be obtained by increasing the temperature, by properly cleaning the weld surface before welding and by choosing the proper joint design and electrodes, a better. On extending the fusion zone to the thickness of the joints fully, a great quality joint can be achieved.

iii. Inclusions

Due to the trapping of the oxides, fluxes and electrode coating materials in the weld zone, the inclusions have occurred. Inclusions are caused while joining the thick plates in several runs using flux cored or flux coated rods and the slag covering a run is not completely removed after each run and before the next run starts. By maintaining a clean surface before the run is started, providing sufficient space for the molten weld metal between the pieces to be joined, the inclusions can be prevented.

iv. Cracking

Due to the strain at the time of phase change, cracks may occur in various directions and in various locations in the weld area. Due to poor design and improper procedure of joining high residual stresses, cracking is seen. A stage-wise pre-heating process and stage-wise slow cooling will prevent such type of cracks.

v. The undercut

The undercut is caused due to incorrect settings or using improper procedure. Undercutting can be detected by a naked eye and the excess penetration can be visually detected.

vi. Lamellar Tearing

Due to non-metallic inclusions, the lamellar tearing occurs through the thickness direction. This is more evidently found in rolled plates. As the fusion boundary is parallel to the rolling plane in T and corner joints, the lamellar tearing occurs. By redesigning the joint and by covering the weld area with ductile material, the lamellar tearing can be minimized.

Visual Inspection

The structure of the visual inspection process is one of the most important features that influence its

effectiveness. From the work process perspective visual inspection consists of several stages:

• visual “screening”/search for potential defects

• finding a defect (“detection”)

• defect classification

• a decision

that classifies a component, product or service. Each of the stages has an impact on the effectiveness of inspection. The first stage, when an object is visually examined by a man, requires vigilance, heightened the sense of sight to detect potential errors. In the first and second stage of inspection, when the level of inspector’s perception is of particular significance, appropriate working conditions and inspector’s knowledge about potential defects are absolutely required. In the third stage, based on his knowledge about the defects and classification criteria, the inspector makes the decision on the type of defect detected in the product. In the final part of the inspection process, the inspector decides if the product may be forwarded to further steps of the process, or if it should be separated from good quality products. Two of the four stages mentioned above (searching for defects and decision-making) seem to be of particular importance from the point of view of visual control. It turns out that they are most exposed to decision variability of the operators. In the inspection process, they may make two types of errors classify a good quality product as defective (FALS) and classify a defective product as good The likelihood of committing these two types of errors and the fraction of products that do not conform with requirements after the inspection process are the key indicators of inspection efficiency. There are many factors that affect the efficiency of visual inspection. Making the decision concerning the quality of inspected products requires not only specific knowledge of the industry but often also an individual approach to every inspected product and high sensitivity to defects. Relevant research shows that the efficiency of visual inspection is affected by independent factors and factors related to and dependent on man. These two main groups of factors can be divided into five categories, Technical factors are associated with the physical execution of visual inspection in the production process. They include, for example, factors related to the actual quality level, product features subject to inspection (their accessibility for visual inspection), to the standards, based on which the product is controlled, the availability of tools used during the inspection, etc. Psychophysical factors are associated with mental and physical conditions of inspectors. These include age, sex, intelligence, temperament, health condition etc. Research in this area aims at identifying the characteristics comprising the profile of the ideal inspector. The next group of factors affecting the effectiveness of visual inspection are organizational factors. These include support in decision-making during the inspection, acquiring inspector skills, number and type of inspections, information on efficiency and accuracy of conducted inspections, as well as stress factors influencing the inspector, such as time, consequences of incorrect assessment (no bonus, loss of company image, etc.). Workplace environment conditions are associated with the workplace, where the inspection takes place. Light, noise, temperature, as well as the organization of the workstation itself,  come under this The last group is related to the social environment, where inspectors work. The work often involves pressure from people, whose interest is contrary to the inspector’s work. For example, production staff (often colleagues) exert pressure expecting approval of their work (which is related to the payment of salaries, bonuses). In turn, employees of the management board may exert pressure to minimize reinspections of products with an unambiguous assessment.