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.

Oil and Gas sector in India

The oil and gas sector is pretty well developed in India, and contributes a large share to India’s energy basket and will be doing the same for the next 15–20 years. Oil and gas is a major part of the energy sector, which is essential for the growth of the manufacturing, utilities, infrastructure and commercial services industries. An estimated 7 per cent growth in the Indian economy is expected to approximately double India’s per capita energy consumption over the next 20 years. Since there is a link between energy demand and economic growth, the Indian oil and gas sector, which provides the country with a significant portion of its energy requirements, is a key metric that will drive future GDP growth. The future opportunities for the sector include assessing the feasibility of using non-conventional fuels such as coal bed methane, hydrogen and biodiesel. The sector must lay greater focus on developing midstream infrastructure, with specific attention on city gas distribution networks, and the construction of strategic storage facilities as a safeguard against short term disruptions in fuel supply. The government is constructing a total capacity of 15 million metric tons(MMT) in the form of strategic storage facilities for crude oil and petroleum products. As such this can be used as an emergency mechanism in the case of short term disruptions in fuel supply. In the first phase, the construction of the 5 MMT storage space has been started simultaneously at Vishakapatnam (1.3 MMT), Mangalore (1.5MMT) and Padur (2.5 MMT).

The proposed storage structure is expected to become underground. Effectively capitalising upon potential opportunities, clubbed with the increasing demand for natural gas, favourable government policies, large scale investments and the recent discovery offshore gas reserves are expected to fuel strong growth in the Indian oil and gas sector. State-run oil and gas companies in India must form partnerships or joint ventures with foreign players so as to effectively use the technology and monetary resources for ultradeep water exploration, which can yield significant results. Currently, Indian companies are only equipped with the technology that helps in exploring on land, or in shallow basins. The Indian oil and gas industry has been providing significant opportunities in the development of midstream infrastructure, with expected capacity addition of 6,000–8,000 km pipeline to the National gas grid in different parts of the country. Apart from this, the gas distribution network is not developed in most parts of the country except in cities such as Delhi and Mumbai. This particularly offers alternative fuel in the vehicular segment, which offers a 20 per cent cost benefit over diesel.

Liquid Penetrant Test

Non-destructive Examination (NDE) refers to those inspection methods, that allow materials to be examined without changing or destroying their usefulness. NDE is a very important part of the quality assurance program. Different NDE methods are employed to ensure that the weld meets design specifications and does not contain defects. The liquid Penetrant test is capable of detecting surface - connecting discontinuities in ferrous and nonferrous alloys. Liquid penetrant tests are used to examine the weld joint surfaces, intermediate checks of individual weld passes and completed welds. PT is commonly employed on stainless steels where magnetic particle examination is not possible. The examiner should recognize that many specifications limit contaminants in the penetrant materials which could adversely affect the weld or parent materials. Most penetrant manufacturers will provide material certifications on the amounts of contaminants such as chlorine, sulfur, and halogens. A limitation of PT is that standard penetrant systems are limited to a maximum of 125°F (52°C) so the weld must be cool which significantly slows down the welding operation. High-temperature penetrant systems can be qualified to extend the temperature envelope. During PT, the test surface is cleaned and coated with a penetrating liquid that seeks surface-connected discontinuities. After the excess surface liquid penetrant is removed, a solvent-based powder suspension (developer) is normally applied by spraying. The liquid in any

discontinuity bleeds out to stain the powder coating. An indication of depth is possible if the Inspector observes and compares the indication bleed out to the opening size visible at the surface. The two general penetrant techniques approved for use include the colour contrast penetrant technique (normally red in colour to contrast with a white background) and the fluorescent penetrant technique, which uses a dye that is visible to ultraviolet light. For sensitivity, fluorescent penetrant techniques may be used to detect fine linear type indications. The examination is performed in a darkened area using a filtered blacklight. Three different penetrant systems are available for use with both of the techniques, they include a. Solvent removable. b. Water washable. c. Post emulsifiable. Compatibility with base metals, welds, and process material should be considered before penetrants are used since they can be difficult to remove completely. Some requirements listed in article6 0f ASME include:

a. Inspection is to be performed in accordance with a procedure (as specified by the referencing code section).

b. Type of penetrant materials to be used.

c. Details for pre-examination cleaning which includes minimum drying time.

d. Dwell time for the penetrant.

e. Details for removing excess penetrant, applying the developer, and time before interpretation.

f. Evaluation of indications in terms of the accepted standards of the referencing code.

g. Post examination cleaning requirements.

h. Minimum surface illumination (visible or blacklight) of the part under examination.

Oil and Natural Gas

Oil and natural gas are strings of carbon and hydrogen formed from the organic material that has been compressed over millions of years. Oil and natural gas are generally referred to as petroleum. They are often found together. If a reservoir i.e an area underground has only gas and no oil, it is called non-associated gas. A reservoir containing both oil and gas is referred to as associated gas. The oil and gas found underground come in different grades or qualities. In an ordinary sense, the quality of oil is described in terms of its sweetness and heaviness. An increase in the amount of sulfur in the oil leads to the sweetness of oil. Oil with less sulfur is sweeter and requires less processing before use, and is, therefore, more valuable. The heaviness of oil refers to its density. The lighter crude oil can be refined and converted into higher value products, such as the gasoline (or petrol) used by car owners. Heavier crude tends to flow slowly and has more unwanted chemicals that must be refined out. A degree-based gravity scale created by API help compares the relative density of various crudes. Light crude is measured above 31.1API while heavy crude measures below 22.3API. Natural gas is a mixture of methane and some other contaminants. On the amount of hydrogen sulfide in the reservoir, it can be described as either sweet or sour. Refined gas, leaving mostly methane, it is called dry gas. Often natural gas is condensed into natural gas liquids, such as propane and butane. The British thermal unit (BTU) is used to measure the energy output of gas. As gas burns cleaner and has a less destructive environmental impact upon use than oil or coal, the challenges associated with storage and transport makes it more expensive. The oil reserves are usually measured in tons or barrels of oil. Production quantities are abbreviated using “bbl” (or barrels of oil per day, bbl/d or bpd). One tonne is somewhere between six and eight barrels of oil.

Reserves and production quantities of gas are measured in cubic meters (m3) or standard cubic feet (scf) The process of getting oil and gas out of the ground begins with exploration and appraisal. The Oil and gas found underground in reservoirs are sealed but connected to other chambers of oil and gas underground. On identifying a reserve of oil is, the company's often produce a description of the quality of the oil and the estimated amount is measured either by volume (barrels) or by weight (tons) Price fluctuations in oil and gas can impact the direction of the industry because costs are different at different extraction points. Even though the prices are fluctuating, the demand for energy, including oil and gas, is increasing globally. Even though the alternative forms of energy are becoming more popular, there are still strong indications that the use and production of oil and gas will continue. With the increasing industrial energy efficiency, the demand for transportation and increasing population means there is an overall increasing need for energy.

What is meant by Lack of Fusion in welding?

Lack of fusion is the discontinuity in the weld where fusion has not occurred between weld metal and

parent metal or between adjoining weld beads so that we may have lack of side fusion, lack of inter-bead fusion or lack of fusion at the weld root. Incomplete fusion is produced during welding, most often unnoticed by a welder or an operator. After welding, it is most difficult, if not impossible, to detect it by the visual inspection or other non-destructive testing methods. It is most often detected in bend testing of the welded joint when the fracture occurs at the location of lack of fusion in spite of a relatively low load applied. The defect will usually run along the weld interface or individual beads, and thus indicate that there really is lack of fusion.

The main reason for the occurrence of lack of fusion is insufficient energy input at the weld area. Consequently, the parent metal in the weld groove or the previously made beads is not heated up to the melting temperature that is required for the parent metal to mix with the material and make a uniform weld. The lack of fusion is not due to the filler material used but exclusively to improper weld preparation, an unsuitable welding technology, including welding parameters, and weak performance of the qualified procedure. In practice, it has turned out that welders themselves are most often producers of the incomplete fusion. A well- qualified welder will melt the parent metal with an arc, mix it with the filler material, and thus make a weld.

The Operators must use a proper procedure in automatic and robotic welding. An unskilled or, often, the careless welder is bound, for various reasons indicated below, to produce the incomplete fusion in the weld. The lack of fusion can also be called a planar discontinuity of various sizes and shapes. If often happens that only one dimension, i.e. the one in the direction of weld progression, is particularly remarkable There seem to be two causes of lack of fusion, the first being an improper positions of the burner and the second an arc voltage too high, i.e., an arc too long. It can be said that the long arcs in welding with the two wires are the reason for the occurrence of lack of fusion. This statement can be substantiated by the high arc voltage and a very wide weld face. This indicates that the arc energy of the two arcs is distributed over a large area, the energy density is small, and the energy supplied is not sufficient to melt the parent metal. To improve the weld quality the arc length and, consequently, the arc voltage should be reduced and welding parameters should be recorded and stored.

The composition of produced petroleum?

The molecular and atom composition of the  fossil fuel is set by complicated chemical, physical, and biological processes.Generation and expulsion from the supply rocks, is a part of the process because the fossil fuel moves from supply to reservoir, reservoir fill history, and secondary alteration processes  and all influence oil and gas compositions. Every supply facies generates oil with distinct chemical composition that reflects organic phenomenon input, depositional setting, and thermal history . For example, a body of water and coal supply rocks generate waxy, low-sulfur crudes, whereas carbonate and deposit supply rocks generate mineral, high-sulfur crudes. These integrative variations are most apparent throughout the initial stages of oil expulsion and quieten down distinct because the supply issue through catagenes is wherever secondary cracking reactions become prevailing.
Although fossil fuel comes from biological organic matter, most of the individual compounds can't be allotted to a selected organic chemistry precursor. Some fossil fuel hydrocarbons, termed bio-markers, retain enough of their original carbon structure that a possible organic chemistry precursor will be allotted.The abundance and distribution of bio-markers permit geo-chemists to understand  the origin and thermal history of oils. Once generated and expelled from the supply rock, fossil fuel composition will be any changed throughout migration and defense at intervals the reservoir. In most fossil fuel systems, the supply formation is at larger temperature and pressure than the reservoir and migrating fossil fuel fluid might separate into gas and liquid phases that may then migrate severally.Petroleum conjointly interacts with water and also the a lot of soluble hydrocarbons might by selection partition into the binary compound part.Once within the reservoir, secondary processes will alter oil composition. The consumption of hydrocarbons by microorganisms,usually  takes place in the  shallow, cool reservoirs (<80°C).This method by selection removes saturated hydrocarbons, enriching the residual rock oil in polar and mineral material. Bio degradation forms acids and biogenic CH4, CO2, and H2S. microbic alteration of crude oils could be a comparatively quick method and will occur naturally or result from poor production practices. Thermochemical sulphate reduction (TSR) is another reservoir alteration process that may have an effect on oil quality and amount. it's a chemical reaction method that happens at comparatively high temperatures (>120°C), wherever hydrocarbons are  modified to carbonic acid gas and sulphate is reduced to H2S.The petroleum is depleted in saturated hydrocarbons and enriched in sulfur-aromatic species. Reservoir charging and fill history can also alter oil composition.The composition of rock oil that arrives at a works isn't similar to reservoir fluids. Gas and water is separated at the well head and emulsions are broken. Consequently, oil loses some light-weight hydrocarbons (throughout production and transport). Pipeline and tanker oils are a  blend of oils from multiple fields and reservoirs, that on an individual basis could also be of variable composition and quality. Thus  testing of subterraneous fluids from individual reservoirs is important to see field economic science and style reservoir management practices.

The accumulation of economic quantities of fossil fuel (oil and gas) invloves a series of processes  that occur at intervals  at substance basins. Organic-rich sediments are deposited solely beneath specific conditions that promote the assemblage and/or transport of biogenic organic compounds and also the selective preservation of this material. The substance organic matter converts to kerogen, associate degree insoluble molecule with a composition that reflects the organic phenomenon input and chemical alterations (sulfurization, condensation, de functionalization, and aromatization) that occur throughout diagenesis. Once lithofied, these organic-rich strata have the potential to come up with oil and gas once buried and heated to push thermal cracking. Expelled fossil fuel migrates from the supply through fractures and porous strata. Economic reserves occur once earth science conditions yield the buildup, retention, and preservation of great volumes of migrated fossil fuel.