Vocational Training Report I am very grateful to “Larsen & Toubro, Hazira” and “Unnat Engineering Privet Limited” for providing me an opportunity for vocational training. I place on record my sincere thanks to our Training Guide Mr. Vijayan Piellai & Mr. Chetan Patel for providing us the necessary facilities.
I feel in debt to my Project Guide Mr. Vijayan Piellai, Mr. Bhavik Rana and All Supervisors of U. E. P.
L for their valuable guidance and enduring support throughout my projects. Lastly I would like to thank all the managers and employees of “Larsen & Toubro” With whom I have interacted during my course of study.I thank them for giving their precious time to guide me and provide me their valuable comments. Thanking You to All Preface Teaching gives theoretical aspects of the technology while training gives practical knowledge of the industrial field. Therefor technical studies cannot be perfect without training hence practical training is of great value for the engineering students. The actual aim of the training is to get knowledge about the most advance technical knowledge & get acquainted with sophisticated instruments, which are generally not available anywhere else . oreover it aims to learn industrial management & discipline & to get accustomed to it helps in future. This report in general contains all the practical knowledge that I gained during my training period.
The major process carried out for fabrication is welding and this report contains various welding processes with their NDT test discussed in detail. All this has been an invaluable experience. INDEX NO| Content| Page| 1| L&T Company Profile| 5| 2| Introduction to M. M. F| 10| 3| U. E. P. L Profile| 14| 4| Welding Process| 16| 5| Types of Welding Process| 17| 6| Testing of Weld Joint| 33| 7| Welding Defects| 48| | Welding FAQs| 53| 9| Grinding Process| 56| 10| Types of Grinding Process| 57| 11| Grinding Machines| 63| 12| Grinding Wheels| 63| 13| Gas Cutting| 66| 14| Safety Aspects| 70| 15| Reference| 73| * Larsen & Toubro Company Profile: * The evolution of L&T into the country’s largest engineering and construction organization is among the most remarkable success stories in Indian industry.
* L;amp;T was founded in Bombay (Mumbai) in 1938 by two Danish engineers, Henning Holck-Larsen and Soren Kristian Toubro. Both of them were strongly committed to developing India’s engineering capabilities to meet the demands of industry.Henning Holck-Larsen Soren Kristian Toubro (4. 7. 1907 – 27.
7. 2003) (27. 02. 1906 – 4.
3. 1982) * Beginning with the import of machinery from Europe, L&T rapidly took on engineering and construction assignments of increasing sophistication. Today, the company sets global engineering benchmarks in terms of scale and complexity. * Early Days * Henning Holck-Larsen and Soren Kristian Toubro, school-mates in Denmark, would not have dreamt, as they were learning about India in history classes that they would, one day, create history in that land. In 1938, the two friends decided to forgo the comforts of working in Europe, and started their own operation in India. All they had was a dream. And the courage to dare.
* In the early years, they represented Danish manufacturers of dairy equipment for a modest retainer. But with the start of the Second World War in 1939, imports were restricted, compelling them to start a small work-shop to undertake jobs and provide service facilities. * Germany’s invasion of Denmark in 1940 stopped supplies of Danish products. This crisis forced the partners to stand on their own feet and innovate. They started manufacturing dairy equipment indigenously.These products proved to be a success, and L;amp;T came to be recognized as a reliable fabricator with high standards.
* The war-time need to repair and refit ships offered L;amp;T an opportunity, and led to the formation of a new company, Hilda Ltd. , to handle these operations. L;amp;T also started two repair and fabrication shops – the Company had begun to expand. * Again, the sudden internment of German engineers (because of the War) who were to put up a soda ash plant for the Tata’s, gave L;amp;T a chance to enter the field of installation – an area where their capability became well respected. The Journey * In 1944, ECC was incorporated. Around then, L;amp;T decided to build a portfolio of foreign collaborations. By 1945, the Company represented British manufacturers of equipment used to manufacture products such as hydrogenated oils, biscuits, soaps and glass.
* In 1945, L;amp;T signed an agreement with Caterpillar Tractor Company, USA, for marketing earthmoving equipment. At the end of the war, large numbers of war-surplus Caterpillar equipment were available at attractive prices, but the finances required were beyond the capacity of the partners.This prompted them to raise additional equity capital, and on 7th February 1946, Larsen ;amp; Toubro Private Limited was born. * Independence and the subsequent demand for technology and expertise offered L;amp;T the opportunity to consolidate and expand.
Offices were set up in Kolkata (Calcutta), Chennai (Madras) and New Delhi. In 1948, fifty-five acres of undeveloped marsh and jungle was acquired in Poway. * Today, Poway stands as a tribute to the vision of the men who transformed this uninhabitable swamp into a manufacturing landmark. * Public Limited Company In December 1950, L;amp;T became a Public Company with a paid-up capital of Rs. 2 million.
The sales turnover in that year was Rs. 10. 9 million. * Prestigious orders executed by the Company during this period included the Amul Dairy at Anand and Blast Furnaces at Rourkela Steel Plant. With the successful completion of these jobs, L;amp;T emerged as the largest erection contractor in the country. * In 1956, a major part of the company’s Bombay office moved to ICI House in Ballard Estate. A decade later this imposing grey-stone building was purchased by L&T, and renamed as L&T House – its Corporate Office.
The sixties saw a significant change at L&T – S. K. Toubro retired from active management in 1962.
* The sixties were also a decade of rapid growth for the company, and witnessed the formation of many new ventures: UTMAL (set up in 1960), Audco India Limited ( 1961), Eutectic Welding Alloys (1962) and TENGL (1963) * Expanding Horizons * By 1964, L&T had widened its capabilities to include some of the best technologies in the world. In the decade that followed, the company grew rapidly, and by 1973 had become one of the Top-25 Indian companies. In 1976, Holck-Larsen was awarded the Magsaysay Award for International Understanding in recognition of his contribution to India’s industrial development. He retired as Chairman in 1978. * In the decades that followed, the company grew into an engineering major under the guidance of leaders like N. M.
Desai, S. R. Subramaniam, U. V. Rao, S. D. Kulkarni and A. M.
Naik. * Today, L;amp;T is one of India’s biggest and best known industrial organizations with a reputation for technological excellence, high quality of products and services, and strong customer orientation.It is also taking steps to grow its international presence. * For an institution that has grown to legendary proportions, there cannot and must not be an ‘end’.
Unlike other stories, the L&T saga continues…..
* Modular Fabrication Facility: * L&T’s Modular Fabrication Facility (MFF) at Hazira, is one of the biggest of its kind in Asia built with two decades expertise in the Fabrication of Modules and Large Reactors for the oil and gas industry,. It is located in Hazira near Surat and is 295 km from Mumbai. * The facility occupies an area of 240,000m? which includes more than 85,000m? f covered work space with internal overhead cranes suitable for carrying out fabrication and assembly activities under cover. * The covered areas house the latest welding and CNC cutting machinery. The yard was designed to allow optimum production based on a clear and logical flow of material through the facility. In addition to the covered fabrication areas it has extensive open fabrication areas that are equipped with gantry and mobile crawler cranes. These open areas are used to assemble the final structures. * Hazira yard maintains a core yard labor force of more than thousand skilled tradesmen.
This can be supplemented with subcontracted manpower to meet the requirement. * Location: * L & T’s Hazira Modular Fabrication Facility is located in Gujarat, 295 km north of Mumbai and 21 km from Surat on the banks of river Tapti, has unimpeded passage to Arabian Sea 8 km away. * MFF is certified to various international standard such as ISO 9001, ISO 14001, ISO 29001 and OHSAS 18001 and has certificate of authority to use API monogram for products manufactured as per specification API 5L and API 2B. The facility is also authorized to use ASME U & S stamps and NBBI’s R stamp. Infrastructure: Modular fabrication area: 475000 Sq. meter Piping spool shop : 8000 Sq. meter Pre fabrication shop : 6000 Sq.
meter Covered warehouse: 5000 Sq. meter Open warehouse : 20000 Sq. meter Vessels and skid shops : 4500 Sq. meter Blast & paint shops : 8000 Sq. meter Brace shops : 600 Sq.
meter Office space : 3000 Sq. meter Client offices : 1000 Sq. meter * JETTY/WHARF: Main jetty: 200m ? 18m Heavy Load out facility: 80m ? 42m Roll on roll of jetty: 100m ? 40m * RANGE: Offshore platforms & modules * Process modules and skid mounted equipment * Fired heaters * Modular process plants * Heat recovery steam generators * Desalination plant and equipment * Refinery & gas processing modules * Modular furnace & reformer package * TEMPERATURE: * Average daily: 33. 6°C Max. & 21. 9°C Min. * RAINFALL: * Mean annual 1203 mm (June-September) * RAIL: * Broad gauge railway siding 5 km away * ROAD: * Located on state highway, National highway 26 km away * AIR: * Surat airport 12 km away * U.
E. P. L Company Profile: * UNNAT Engineering Pvt.
Ltd. UEPL) is one of the largest client-centered Engineering and Construction companies with additional expertise in Civil and Mechanical fields. * With the Head Office situated in Surat (Gujarat), UEPL operates in India with the highest ethical and professional standards. UEPL’s vision encompasses the tradition of quality construction practices. * U. E. P. L is a client-centered and quality-conscious organization offering a complete portfolio of product development, game development and independent testing services.
* U. E. P. L major values: 1. Dedication to every client’s success. 2. Innovation that matters – for our company and for the world. | 3.
Trust and personal responsibility in all relationships. * Till April, 2005 it was in the name of “Udyog Engineering Works”, now it has become a “Private Limited” organization under the name of “Unnat Engineering Private Limited”. * Over the years U. E. P. L maintain a tradition of excellence and has become one of our TOP PRIORITY. Therefore, it continually developing technology, operational performance and willingness to innovate mean it can offer their clients a service of the highest quality.
Now it is an ISO 9001 – 2008 company. * UEPL is committed in developing a diverse workforce and good work culture wherein every employee would be treated fairly, with respect and has the opportunity to contribute to business success while always being given the opportunities to realize their full potential as individuals. * UEPL considers health and safety an integral part of business and aims to have a record of safety performance and standards far better than the industry average. It will continuously endeavor to ensure and comply with all statutory obligations and contractual requirements of occupational health and safety, which are among the prime responsibilities of our management.
We undertake that our employees’ health and safety requirements will be taken into account in decisions concerning quality, finance and productivity. * Clients: Company Name| Place| City| | LARSEN ;amp; TOUBRO LTD. | Hazira| Surat| L;amp;T MHI BOILERS PRIVATE LTD. | Hazira| Surat| ESSAR HEAVY ENGINEERING WORKS| Hazira| Surat| GUJARAT GAS CO. LTD| Hazira| Surat|HPCL| Hazira| Surat| IOCL| Hazira| Surat| GAIL| Hazira| Surat| KRIBHCO| Hazira| Surat| NTPC| Hazira| Surat| GDC| Hazira| Surat| VESUVIUS INDIA LTD. | -| Kolkata| RIL| Motikhavdi| Jamnagar| | * Welding Process: * Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence.
* This is often done by melting the work pieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. * While often an industrial process, welding may be performed in many different environments, including open air, under water and in outer space. * Welding is a potentially hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation.
Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join iron and steel by heating and hammering. * Today, the science continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality. * Types of Welding Process: * There are following types of welding process generally used in industries: 1) Arc Welding: These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. * They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes.
The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well. * There are also different types of Arc Welding which are mostly applicable in almost all industries: 1. Shielded Metal Arc Welding. 2. Gas Metal Arc Welding. 3. Flux-Cored Arc Welding.
. Gas Tungsten Arc Welding. 5. Submerged Arc Welding.
I. Shielded Metal Arc Welding (SMAW): * One of the most common types of arc welding is shielded metal arc welding (SMAW); it is also known as manual metal arc welding (MMA) or stick welding. * Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of steel and is covered with a flux that protects the weld area from oxidation and contamination by producing carbon dioxide (CO2) gas during the welding process. * The electrode core itself acts as filler material, making separate filler unnecessary. The process is versatile and can be performed with relatively inexpensive equipment, making it well suited to shop jobs and field work. * WELDING ELECTRODE CLASSIFICATIONS: 1. MILD STEEL COATED ELECTRODES: E7018-X E Indicates that this is an Electrode 70 Indicates Strength of this electrode is when welded. Measured in thousands of pounds per square inch.
1 Indicates in what Welding Positions it can be used. 8 Indicates the Coating, Penetration, and Current type used. X Indicates that there are More Requirements. 2. Electrode Strength ( E “XX” _ _ _ ) Class Min. Tensile Strength Min.
Yield Strength 60 62,000 psi 50,000 psi 70 70,000 psi 57,000 psi 80 80,000 psi 67,000 psi 90 90,000 psi 77,000 psi 100 100,000 psi 87,000 psi 110 110,000 psi 95,000 psi 120 120,000 psi 107,000 psi . WELDING POSITIONS: 1 for Flat, Horizontal, Vertical (up), Overhead 2 for Flat, Vertical 4 for Flat, Horizontal, Overhead, Vertical (down) Flat Position- Usually groove welds (like “V” shape) Horizontal – Fillet welds, welds on walls (travel is from side to side). Vertical – Welds on walls (travel is either up or down). Overhead – Weld that needs to be done upside down. 4. Type of Electrode Coating (E _ _ _ “N” _ ): “0” having coating of “Cellulose, Sodium” “1” having coating of “Cellulose, Potassium” “2” having coating of “Rutile, Sodium” “3” having coating of “Rutile, Potassium” 4” having coating of “Rutile, Iron Powder” “5” having coating of “Low Hydrogen, Sodium” “6” having coating of “Low Hydrogen, Potassium” “7” having coating of “Iron Powder, Iron Oxide” “8” having coating of “Low Hydrogen, Iron Powder” “9” having coating of “Iron Oxide, Rutile, Potassium” 5.
Additional Requirements: Suffix| Additional Requirements| -1| Increased toughness (impact strength) for E7018 electrodes. Also increased ductility in E7024 electrodes. | -M| Meets most military requirements – greater toughness, lower moisture content as received after exposure, diffusible hydrogen limits for weld metal.
-H4-H8-H16| Indicates the maximum diffusible hydrogen limit measured in millimeters per 100 grams (mL/100g). The 4, 8, and 16 indicates what the limit is. Example: -H4 = 4mL per 100 grams| II. Gas Metal Arc Welding: * Gas Metal Arc Welding (GMAW), also known as metal inert gas or MIG welding, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and an inert or semi-inert gas mixture to protect the weld from contamination. * Since the electrode is continuous, welding speeds are greater for GMAW than for SMAW. Gas Metal Arc Welding III.
Flux-Cored Arc Welding: * A related process, Flux-Cored Arc Welding (FCAW), uses similar equipment but uses wire consisting of a steel electrode surrounding a powder fill material. * This cored wire is more expensive than the standard solid wire and can generate fumes and/or slag, but it permits even higher welding speed and greater metal penetration. IV. Gas Tungsten Arc Welding: * Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding, is a manual welding process that uses a non-consumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler material.
9] Especially useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds. * GTAW can be used on nearly all weld-able metals, though it is most often applied to stainless steel and light metals. * It is often used when quality welds are extremely important, such as in bicycle, aircraft and naval applications. GTAW * A related process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc.The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process. Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process and it is much faster. * It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is one important application of the process. A variation of the process is plasma cutting, an efficient steel cutting process.
V. Submerged Arc Welding: Submerged arc welding (SAW) is a high-productivity welding method in which the arc is struck beneath a covering layer of flux. * This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself, and combined with the use of a continuous wire feed, the weld deposition rate is high. * Working conditions are much improved over other arc welding processes, since the flux hides the arc and almost no smoke is produced.
* The process is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels. Other arc welding processes include atomic hydrogen welding, electro slag welding, electro gas, and stud arc welding. 2) Gas Welding: * The most common gas welding process is oxyfuel welding, also known as oxyacetylene welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. It is still widely used for welding pipes and tubes, as well as repair work. * The equipment is relatively inexpensive and simple, generally employing the combustion of acetylene in oxygen to produce a welding flame temperature of about 3100 °C.
The flame, since it is less concentrated than an electric arc, causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals 3) Resistance Welding: * Resistance welding involves the generation of heat by passing current through the resistance caused by the contact between two or more metal surfaces. * Small pools of molten metal are formed at the weld area as high current (1000–100,000 A) is passed through the metal. 14] In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the equipment cost can be high. Resistance Welding * Spot welding is a popular resistance welding method used to join overlapping metal sheets of up to 3 mm thick.
Two electrodes are simultaneously used to clamp the metal sheets together and to pass current through the sheets. * The advantages of the method include efficient energy use, limited work piece deformation, high production rates, easy automation, and no required filler materials. Weld strength is significantly lower than with other welding methods, making the process suitable for only certain applications. * It is used extensively in the automotive industry—ordinary cars can have several thousand spot welds made by industrial robots. A specialized process, called shot welding, can be used to spot weld stainless steel.
* Like spot welding, seam welding relies on two electrodes to apply pressure and current to join metal sheets. However, instead of pointed electrodes, wheel-shaped electrodes roll along and often feed the work piece, making it possible to make long continuous welds.In the past, this process was used in the manufacture of beverage cans, but now its uses are more limited. * Other resistance welding methods include Butt Welding, Flash Welding, Projection Welding, and Upset Welding. 4) Energy Beam Welding: * Energy beam welding methods, namely laser beam welding and electron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are quite similar, differing most notably in their source of power. * Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses an electron beam.Energy Beam Welding * Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area.
Both processes are extremely fast, and are easily automated, making them highly productive. * The primary disadvantages are their very high equipment costs (though these are decreasing) and a susceptibility to thermal cracking. * Developments in this area include laser-hybrid welding, which uses principles from both laser beam welding and arc welding for even better weld properties, laser cladding and X-ray welding. 5) Solid-state Welding: Like the first welding process, forge welding, some modern welding methods do not involve the melting of the materials being joined. * One of the most popular, ultrasonic welding, is used to connect thin sheets or wires made of metal or thermoplastic by vibrating them at high frequency and under high pressure. * The equipment and methods involved are similar to that of resistance welding, but instead of electric current, vibration provides energy input. * Welding metals with this process does not involve melting the materials; instead, the weld is formed by introducing mechanical vibrations horizontally under pressure. When welding plastics, the materials should have similar melting temperatures, and the vibrations are introduced vertically.
* Ultrasonic welding is commonly used for making electrical connections out of aluminum or copper, and it is also a very common polymer welding process. * Another common process, explosion welding, involves the joining of materials by pushing them together under extremely high pressure. * The energy from the impact plasticizes the materials, forming a weld, even though only a limited amount of heat is generated.The process is commonly used for welding dissimilar materials, such as the welding of aluminum with steel in ship hulls or compound plates. * Other solid-state welding processes include friction welding (including friction stir welding), electromagnetic pulse welding, co-extrusion welding, cold welding, diffusion welding, exothermic welding, high frequency welding, hot pressure welding, induction welding, and roll welding.
* Non Destructive Test (NDT) for Welding: * NDT may be used to reveal defects that would be difficult or impossible to detect by visual examination.The techniques are used during manufacture as a quality control tool to determine the quality of the work. * The extent of NDT depends upon the application and the criticality of the joint and is generally specified in the relevant application standards or contract specification. * It is important for NDT to be included in the planning of the fabrication process as it can require substantial time and resources. * Full account of this must be taken if disruption of production and delays to the programmed are to be avoided. The requirement to perform NDE must also be taken into account during the design phase.
As with welding, access for NDT must be planned into the component. The implication of this is that both welding engineers and designers must be conversant with the techniques and their limitations if the processes are to be used effectively. * There are following NDT process: 1. Penetrant Examination 2. Eddy Current Examination 3. Ultrasonic Examination 4.
Radiographic Examination 1 Penetrant examination * This is a technique that is capable of detecting surface breaking defects only. It relies upon a colored or fluorescent dye, sprayed upon the surface, penetrating these defects. After cleaning the excess from the surface, the dye within the defect is drawn to the surface by spraying on a developer in the case of the color contrast dye or by exposing the surface to ultra-violet light. * The defect is revealed by the dye staining the developer or by fluorescing. * The fluorescent dye gives greater sensitivity than the color contrast dye and does not require the use of a color contrast developer but does require the use of an ultraviolet light and preferably a darkened room. The cleaners, penetrant dyes and developers can all be obtained in aerosol cans, making the process extremely portable and ideal for site use. The dye used as a penetrant must be capable of penetrating narrow cracks but must not be removed from more open defects during the cleaning operation carried out before the application of the developer. * The dye must have a high contrast with the developer.
It is important that the test piece is thoroughly pre-cleaned – any dirt, oil or water in the crack may prevent the penetrant from entering. * Degreasing should be carried out by swabbing or immersing the item in one of the proprietary cleaners, acetone or methanol.Immersion in an ultrasonic cleaning bath is probably the best method. Penetrant Examination * Wire brushing or grinding should not be used unless it can be followed by an acid etch as mechanical methods of cleaning can smear over defects and prevent the dye from penetrating. Inspection in other than the flat position is difficult but penetrants have been developed with a jelly-like consistency that can be used to carry out inspections in the vertical and overhead positions. * Automated methods may be used, with the components loaded into baskets and processed on a conveyor line.The fluorescent dyes are better in this application than color contrast dyes because of their greater sensitivity. Sensitivity of the process can be checked using standard test blocks.
* For the examination of aluminum components, these are available in 2024 alloy heat treated to give real cracks of a standard size. These blocks should be scrupulously cleaned after each check to ensure that the cracks do not become clogged with debris. * Advantages: • It can be used on both ferrous and non-ferrous metals. • It is very portable. • Large areas can be examined very quickly. It can be used on small parts with complex geometry.
• It is simple, cheap and easy to use and interpret. * Disadvantages: • It will only detect defects open to the surface. • Careful surface preparation and cleanliness are required. • It is not possible to retest a component indefinitely.
•There may be health and safety problems with some of the chemicals. 2 Eddy Current Examination: * Eddy current examination is a process that may be used on any material that will pass an electric current. A coil carrying an alternating current is placed close to the item to be examined, inducing an eddy current in the specimen. Defects in the specimen will interrupt this eddy current flow and these perturbations can be detected by a second, search coil.
* The coils can Weld defects and quality control 207 be placed either side of a thin plate-like sample or can be wound to give side-by-side coils in a single probe. These may be shaped to fit in the bore or around the outside of pipes and tubes and in these applications the process lends itself to automation. * The equipment is calibrated using a defect-free specimen. The accuracy can be affected by metallurgical condition, stand-off and coil dimensions. For these reasons eddy current testing is used only rarely on welded components, although it is excellent in examining continuously welded tube from pipe mills. The process has been developed over recent years to make it more portable and simpler to use. * Microprocessor-based control and recording units, improved and more tolerant probes and light-weight electronics have enabled the technique to be used on-site for the examination of structures in service, where it is an effective tool for the detection of cracking and corrosion problems.
3 Ultrasonic Examination: The ultrasonic examination of welds uses the same principles as when sonar is used for the detection of submarines. * A ‘sound’ wave emitted from a transmitter is bounced off an object and this reflection captured by a receiver. The direction and distance of the object can be determined by measuring the elapsed time between transmission and detection of the ‘echo’.
* In welded components this is usually done by moving a small probe, containing both transmitter and receiver, over the item to be examined and displaying the echo on an oscilloscope screen. The probe transmits a beam of ultrasound that passes through the metal and is reflected back from any defects, much like shining a torch at a mirror, in principle with the same rules applying to the reflection of the beam. * Deeply buried defects such as lack of fusion, lack of penetration and cracks in addition to volumetric defects such as slag entrapment and porosity are all easily detected. * The success of the technique depends upon the use of trained, experienced operators who know precisely the characteristics of the metal being examined, the beam direction, its amplitude and frequency and the weld geometry.It is recommended that operators should be approved to one of the certification schemes such as those operated by the BINDT or the ASNT. * The frequency of the ultrasonic waves is generally in the range of 2 to 5 MHz, the lower frequencies being used for the examination of coarse-grained material and on rough surfaces. Ultrasonic Test * The higher frequency probes are used for the detection of fine defects such as cracks, non-metallic inclusions, lack of fusion and voids.
* The beams are transmitted as either compression waves or shear waves and, ideally, a defect should be oriented normal to the wave to give the maximum reflection. Projecting the beam at a glancing angle at a planar defect can result in the beam being reflected away from the receiver and lost – remember the analogy of the torch and the mirror. * The probe angle should be selected to optimize the reflection of the sound beam. Probes that project the beam into the test piece at an angle normal to the plate surface are ideally suited to the detection of laminar defects, i. e. those lying parallel to the plate surface and for determining the plate thickness.
Probes can be obtained that project the beam into the test piece at an angle, the most common being 45°, 60° and 70°. * The angled probes are best suited for the detection of defects at an angle to the plate surface such as lack of sidewall fusion. * Here the defect is at the angle of the original weld preparation and is easiest to detect by a probe of an appropriate angle. * Note that the beam may be ‘skipped’ along the interior of a plate, enabling defects a long distance from the probe to be found. * Before commencing the examination some preparation work is necessary.Data on material and heat treatment, welding process and procedure and weld preparation design are necessary if accurate determinations of defect types, orientations and sizes are to be made. * The normal inspection method is to scan the probe on the surface of the parent metal adjacent to the weld.
To do this the surface must be free of scale, spatter and roughness and the parent metal should ideally be free of laminations and excessive inclusions. * A couplant, generally water, oil, grease or glycerin, i s applied to form a film on the surface of the test piece. This aids the transmission of the beam into the sample. To ensure that all of the defects in both the weld and the HAZ are detected the probe must be scanned over the full cross-section and the full length of the weld. * Accurate sizing and positioning of any defects relies upon accurate marking out of the weld. Flaws that lie parallel to the beam may be missed and to ensure that this does not occur it is necessary to scan in two directions at 90° to each other. * Interpretation of the reflections from regions such as root penetration beads, backing straps and fillet weld roots can be very difficult, leading to incorrect defect sizing and sentencing.For this reason the root area is frequently excluded from the area to be ultrasonically examined.
* Advantages: • It is very good for the detection of planar defects and cracks. • It can easily determine defect depth. • It is readily portable. • Access is required to one side only. • There are none of the health and safety problems associated wi th the radiographic technique.
* Disadvantages: • Very skilled operators are required. • Surface breaking defects are difficult to detect. • Accurate sizing of small ( ;lt;3 mm) defects is difficult or impossible.
The geometry of the joint can restrict the scanning pattern and prevent accurate interpretation. • No permanent objective record is available. • The process can be slow and laborious. 4 Radiographic Examination: * Electromagnetic radiation has properties that are useful for industrial radiography purposes. * The rays travel in straight lines and cannot be deflected or reflected by mirrors or lenses; they have wavelengths that enable the radiation to penetrate many materials, including most metals. * They will, however, damage living tissue and therefore present some health and safety problems. The radiation, either X-rays from a suitable source or gamma rays from a radioactive isotope, is absorbed as it passes through the material.
* This absorption increases as the density of the material increases so that if a photographic film is placed on the side opposite the radiation source, any less dense areas will appear as darker areas on the film to give a shadow picture of the internal features of the test sample once the film has been processed. * Thus voids, porosity, slag, cracks and defects of geometry can all be identified, although planar defects normal to the beam may not be detected.Principles of Radiographic Examination of a weld * To radiograph a welded joint a suitable source of radiation, a film in a light-proof cassette and some method of processing the film are required. * This latter generally requires a dark room where the film can be developed, fixed, washed, dried and viewed. * The radiation can be produced from an X-ray tube, the energy generally being described by the voltage and current at which the tube is operated.
Longitudinal crack at the weld start in close square TIG butt weld Gross porosity in TIG butt weld These may vary from 20 kV to 30 MV and 10 to 30 mA, although the normal limit for the commonly available industrial units is around 400 kV. * A 400 kV unit is capable of penetrating up to 100 mm of steel and 200 mm of aluminum. * Gamma radiation is produced by the decay of a naturally occurring or manufactured radioactive isotope. * As a gamma ray source cannot be switched off the isotope is stored in a special container equipped with either a port that can be opened remotely to expo se the source or from which it can be wound out when required. (As shown in figure)Radioactive isotope projection system * Neutron and electron guns are also used to produce high-energy beams. * These can be used for interrogating materials in the same way as X- and gamma radiation.
This equipment is not as readily available but has its uses in industry, particularly for very thick components where long e exposure times would be required using conventional lower energy sources. * Radiographic interpretation should be entrusted to well-trained experienced radiographers and should be performed in a darkened viewing room on a viewer designed for the task. Advantages: • A permanent record is available.
• Both buried and surface defects can be detected and the technique is particularly good for finding volumetric defects such as slag and porosity. • The equipment is portable, particularly the gamma ray sources. • All materials can be examined. * Disadvantages: • The capital cost of equipment, which will need to include the processing and viewing facilities. •Radiographers must also be monitored for exposure to radiation. • Access is required to both sides of the component, the source on one side, the film on the other. There are problems in detecting planar defects and fine cracks if these are normal to the beam.
• There is a limitation on the thickness that can be radiographed and defects easily detected. • Skilled and experienced radiographers are required. • The depth and through thickness dimension of a defect is very difficult to determine. * Welding Defects: * Welding defects can greatly affect weld performance and longevity.
Having an understanding of the various defects, their causes and remedies can help to ensure higher-quality and longer lasting welds. This article details some of the more common welding defects, their causes and possible preventative and corrective measures. a) Misalignment a) This type of geometric defect is generally caused by a setup/fit up problem, or trying to join plates of different thickness. Misalignment b) Overlap * The protrusion of weld metal beyond the weld toe or weld root.
It is caused by poor welding techniques and can generally be overcome by an improved weld procedure. The overlap can be repaired by grinding off excess weld metal and surface grinding smoothly to the base metal. b) Undercutting Undercutting is one of the more severe welding defects.
It is essentially an unfilled groove along the edge of the weld * The causes are usually associated with incorrect electrode angles, incorrect weaving technique, excessive current and travel speed. Undercutting can be avoided with careful attention to detail during preparation of the weld and by improving the welding process. It can be repaired in most cases by welding up the resultant groove with a smaller electrode. c) Concave ;amp; Convex Weld * Misshaped welds are caused by a combination of incorrect electrode current and speed. Excessive concavity (lack of reinforcement) results in insufficient throat thickness in relation to the nominated weld size. d) Tearing * Lamellar tearing is a type of defect that is most likely to occur below a welded joint at points of high stress concentration.
* It is created by non-metallic inclusions being rolled into the hot plate metal during fabrication. * These tears occur when weld metal is deposited on the surface of a joint where there is high restraint. e) Inclusions * Inclusions are generated by extraneous material such as slag, tungsten, sulfide and oxide inclusions becoming part of the weld. These defects are often associated with undercut, incomplete penetration and lack of fusion in welds.
Insufficient cleaning between multi-pass welds and incorrect current and electrode manipulation can leave slag and unfused sections along the weld joint. f) Porosity * Porosity is a collective name describing cavities or pores caused by gas and non-metallic material entrapment in molten metal during solidification. * There are many causes which include contamination, inadequate shielding, and unstable arc, arc gap too short and poor welding technique in general. Porosity ) Incomplete Fusion/Penetration * Incomplete fusion or penetration is an internal planar discontinuity that is difficult to detect and evaluate, and very dangerous. * It occurs when the weld metal does not form a cohesive bond with the base metal or when the weld metal does not extend into the base metal to the required depth, resulting in insufficient throat thickness. h) Spatter * Metal drops expelled from the weld that stick to surrounding surfaces. * Spatter can be minimized by correcting the welding conditions and should be eliminated by grinding when present. Spatter * Welding FAQs: .
What is welding? * Welding is the art of heating metal to the melting point and then allowing parts of the metal and filler metal to flow together. * Welding is a diverse technology, and there are 94 different welding and allied processes. 2. How do you finish the welds? * Every welding job’s requirements are different, but Advantage Fabricated Metals’ welders often grind the welds, polish the welds, descale the welds, prepare the welded surfaces for painting, and prime the prepared surface after the welding process is completed all based on individual customer requirements. .
What is robotic welding? * Robotic welding is the use of mechanized programmable robots which completely automates a welding process by both performing the weld and handling of the component. * Robotic welding is commonly used for resistance spot welding and arc welding in high production applications, such as the automotive industry and high volume manufacturing. 4. Does Advantage Fabricated Metals offer robotic welding? * Yes, Advantage Fabricated Metals provides robotic MIG welding using a machine with a 55-inch reach.Our management and welding staff understand the special requirements of robot cells in welding environments such as parts design, part and gap tolerances, fixture design, weld process expertise, and the quality of the operating programs.
* Cell is equipped to execute most MIG, TIG, Cold Wire TIG, and Flux core welding applications and has an integrated rotary positioning station. 5. What is hard facing? * Hard facing, which is also known as hard surfacing, is the application of buildup, or wear-resistant, weld metals to a part’s or component’s surface by means of welding or joining.Hard facing provides a continuous nonporous wear and or impact resistant surface. 6. How do you inspect your welds? * We visually inspect all of our welded components for size and quality of the weld deposit.
When required, we can additionally provide Dye Penetrant, Magnaflux, and Radiograph inspection to meet a customer’s requirements. 7. What other welding-related services do you provide? * Advantage Fabricated Metals offers a number of welding-related services including: * Tool and die repair * Hard facing * Cobalt overlays * Brazing * Silver soldering * Soft soldering. . What is the maximum size work piece you can work on? * It depends on what exactly needs to be done to the piece and if the piece needs to be preheated. However, 20-ton overhead cranes to move pieces around our facility.
9. How thick a work piece can you weld? * That really depends on a number of factors. The thickness we can weld is dependent on the type of joint, the configuration of the base material and the actual welding process we need to use. * Grinding Process: * Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.
A wide variety of machines are used for grinding: * Hand-cranked knife-sharpening stones (grindstones) * Handheld power tools such as angle grinders and die grinders * Various kinds of expensive industrial machine tools called grinding machines * Bench grinders often found in residential garages and basements * Grinding practice is a large and diverse area of manufacturing and tool making. It can produce very fine finishes and very accurate dimensions; yet in mass production contexts it can also rough out large volumes of metal quite rapidly. It is usually better suited to the machining of very hard materials than is “regular” machining (that is, cutting larger chips with cutting tools such as tool bits or milling cutters), and until recent decades it was the only practical way to machine such materials as hardened steels. * Compared to “regular” machining, it is usually better suited to taking very shallow cuts, such as reducing a shaft’s diameter by half a thousandth of an inch (thou) or 12. 7 um.
* Grinding is a subset of cutting, as grinding is a true metal-cutting process. Each grain of abrasive functions as a microscopic single-point utting edge (although of high negative rake angle), and shears a tiny chip that is analogous to what would conventionally be called a “cut” chip. * Types of Grinding Processes: * There are following types of grinding processes: 1) Surface grinding: * Surface grinding uses a rotating abrasive wheel to smooth the flat surface of metallic or nonmetallic materials to give them a more refined look or to attain a desired surface for a functional purpose. * The tolerances that are normally achieved with grinding are ± 2 ? 10? 4 inches for a grinding a flat material, and ± 3 ? 0? 4 inches for a parallel surface * The surface grinder is composed of an abrasive wheel, a work holding device known as a chuck, either electromagnetic or vacuum, and a reciprocating table. * Typical work piece materials include cast iron and minor steel. These two materials do not tend to clog the grinding wheel while being processed. Other materials are aluminum, stainless steel, brass and some plastics. 2) Cylindrical Grinding: * Cylindrical grinding (center-type grinding) is used in the removing the cylindrical surfaces and shoulders of the work piece.
The work piece is mounted and rotated by a work piece holder, also known as a grinding dog or center driver. * Both the tool and the work piece are rotated by separate motors and at different speeds. The axes of rotation tool can be adjusted to produce a variety of shapes. * The five types of cylindrical grinding are: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and center less grinding.
* A cylindrical grinder has a grinding (abrasive) wheel, two centers that hold the work piece, and a chuck, grinding dog, or other mechanism to drive the machine. Most cylindrical grinding machines include a swivel to allow for the forming of tapered pieces. The wheel and work piece move parallel to one another in both the radial and longitudinal directions. The abrasive wheel can have many shapes. * Standard disk shaped wheels can be used to create a tapered or straight work piece geometry while formed wheels are used to create a shaped work piece. The process using a formed wheel creates less vibration than using a regular disk shaped wheel. * Tolerances for cylindrical grinding are held within five ten-thousandths of an inch (+/- 0.
005) (metric: +/- 13 um) for diameter and one ten-thousandth of an inch (+/- 0. 0001) (metric: 2. 5 um) for roundness. Precision work can reach tolerances as high as fifty millionths of an inch (+/- 0. 00005) (metric: 1. 3 um) for diameter and ten millionths (+/- 0.
00001) (metric: 0. 25 um) for roundness. Surface finishes can range from 2 to 125 micro inches (metric: 50 nm to 3 um), with typical finishes ranging from 8-32 micro inches.
(metric: 0. 2 um to 0. 8 um). 3) Creep-Feed Grinding: * Creep-feed grinding (CFG) was invented in Germany in the late 1950s by Edmund and Gerhard Lang.Unlike normal grinding, which is used primarily to finish surfaces, CFG is used for high rates of material removal, competing with milling and turning as a manufacturing process choice. * Depths of cut of up to 6 mm (0. 25 inches) are used along with low work piece speed.
Surfaces with a softer-grade resin bond are used to keep work piece temperature low and an improved surface finish up to 1. 6 micrometers Rmax. * With CFG it takes 117 sec to remove 1 in.
3 of material, whereas precision grinding would take more than 200 sec to do the same.CFG has the disadvantage of a wheel that is constantly degrading, and requires high spindle power, 51 hp (38 kW), and is limited in the length of part it can machine. * To address the problem of wheel sharpness, continuous-dress creep-feed grinding (CDCF) was developed in the 1970s. It dresses the wheel constantly during machining, keeping it in a state of specified sharpness. * It takes only 17 sec. to remove 1 in3 of material, a huge gain in productivity. 38 hp (28 kW) spindle power is required, and runs at low to conventional spindle speeds.The limit on part length was erased.
* High-efficiency deep grinding (HEDG) uses plated super abrasive wheels, which never need dressing and last longer than other wheels. This reduces capital equipment investment costs. * HEDG can be used on long part lengths, and removes material at a rate of 1 in3 in 83 sec. It requires high spindle power and high spindle speeds. * Peel grinding, patented under the name of Quick point in 1985 by Erwin Junker Maschinenfabrik, GmbH in Nordrach, Germany, uses a tool with a with super abrasive nose and can machine cylindrical parts.
VIPER (Very Impressive Performance Extreme Removal), 1999, is a process patented by Rolls-Royce and is used in aerospace manufacturing to produce turbine blades. It uses a continuously dressed aluminum oxide grinding wheel running at high speed. * CNC-controlled nozzles apply refrigerated grinding fluid during the cut. VIPER is performed on equipment similar to a CNC machining center, and uses special wheels.
* Ultra-high speed grinding (UHSG) can run at speeds higher than 40,000 fpm (200 m/s), taking 41 sec to remove 1 in. 3 of material, but is still in the R&D stage. It also requires high spindle power and high spindle speeds. ) Other Grinding: * Form grinding is a specialized type of cylindrical grinding where the grinding wheel has the exact shape of the final product. The grinding wheel does not traverse the work piece. * Internal grinding is used to grind the internal diameter of the work piece. Tapered holes can be ground with the use of internal grinders that can swivel on the horizontal.
* Center less grinding is when the work piece is supported by a blade instead of by centers or chucks. Two wheels are used. The larger one is used to grind the surface of the work piece and the smaller wheel is used to regulate the axial movement of the work piece. Types of center less grinding include through-feed grinding, in-feed/plunge grinding, and internal center less grinding.
* Pre-grinding when a new tool has been built and has been heat-treated, it is pre-ground before welding or hard facing commences. This usually involves grinding thread slightly higher than the finish grind OD to ensure the correct finish size. * Electrochemical grinding is a type of grinding in which a positively charged work piece in a conductive fluid is eroded by a negatively charged grinding wheel. The pieces from the work piece are dissolved into the conductive fluid. Electrolytic in-process dressing (ELID) grinding is one of the most accurate grinding methods.
In this ultra-precision grinding technology the grinding wheel is dressed electrochemically and in-process to maintain the accuracy of the grinding. * An ELID cell consists of a metal bonded grinding wheel, a cathode electrode, a pulsed DC power supply and electrolyte. The wheel is connected to the positive terminal of the DC power supply through a carbon brush whereas the electrode is connected to the negative pole of the power supply. * Usually alkaline liquids are used as both electrolytes and coolant for grinding.A nozzle is used to inject the electrolyte into the gap between wheel and electrode. * The gap is usually maintained to be approximately 0. 1mm to 0.
3 mm. During the grinding operation one side of the wheel takes part in the grinding operation whereas the other side of the wheel is being dressed by electrochemical reaction. * The dissolution of the metallic bond material is caused by the dressing which in turns results continuous protrusion of new sharp grits. * Grinding Machines: * Grinding Wheels are designed for use on a wide variety of machines.The relevant machine types are easily identified by the following pictograms that are contained both in the catalogue tables and on the product itself. * Grinding Wheels: * A grinding wheel is an expendable wheel used for various grinding and abrasive machining operations. * It is generally made from a matrix of coarse abrasive particles pressed and bonded together to form a solid, circular shape, various profiles and cross sections are available depending on the intended usage for the wheel.
* Grinding wheels may also be made from a solid steel or aluminum disc with particles bonded to the surface. For grinding of the “Beam” or beam section generally Carbon Steel Grinding wheels are used for both grinding as well as cutting purpose. * Where as in grinding and cutting of Cu-Ni material Standard Steel Grinding wheels are used for grinding as well as cutting purpose. * Angle Grinders are mostly used because it’s mobile machine with light weight and there is no difficulty in changing the grinding wheel.
* Gas Cutting: * The equipment and accessories for oxy-gas cutting are the same as for oxy-gas welding except that you use a cutting torch or a cutting attachment instead of a welding torch. The main difference between the cutting torch and the welding torch is that the cutting torch has an additional tube for high -pressure oxygen, along with a cutting tip or nozzle. * The tip is provided with a center hole through which a jet of pure oxygen passes. Mixed oxygen and acetylene pass through holes surrounding the center holes for the preheating flames.
* The number of orifices for oxyacetylene flames ranges from 2 to 6, depending on the purpose for which the tip is used. The cutting torch is controlled by a trigger or lever operated valve.The cutting torch is furnished with interchangeable tips for cutting steel from less than ? ” to more than 12. 0” in thickness.
1. Cutting Thick Steel: * Steel, that is greater than 1/8 inch thick, can be cut by holding the torch so the tip is almost vertical to the surface of the metal. If you are right -handed, one method to cut steel is to start at the edge of the plate and move from right to left. * Left-handed people tend to cut left to right. Both directions are correct and you may cut in the direction that is most comfortable for you. Figure below shows the progress of a cut in thick steel. After heating the edge of the steel to a dull cherry red, open the oxygen jet all the way by pressing on the cutting lever.
* As soon as the cutting action starts, move the torch tip at an even rate. Avoid unsteady movement of the torch to prevent irregular cuts and premature stopping of the cutting action. * To start a cut quicker in thick plate, you should start at the edge of the metal with the torch angled in the opposite direct ion of travel.
* When the edge starts to cut, bring the torch to a vertical posit ion to complete the cut through the total thickness of the metal. As soon as the cut is through the metal, start moving the torch in the direction of travel, two other methods for starting cuts are used. * In the first method, you nick the edge of the metal with a cold chisel at the point where the cut is to start. * The sharp edges of the metal upset by the chisel will preheat and oxidize rapidly under the cutting torch, allowing you to start the cut without preheating the entire edge of the plate. * In the second method, you place an iron filler rod at the edge of a thick plat e.As you apply the preheat flames to the edge of the plate, the filler rod rap idly reaches the cherry red temperature. At this point, turn the cutting oxygen on and the rod will oxidize and cause the thicker p l ate to start oxidizing. 2. Cutting Thin Steel: * Though the gas cutting is more useful with thick plates, thin sheets (1/8 inch or less) can also be cut by this process taking special precautions. * Tip size chosen should be as small as possible. If small tips are not available, then the tip is inclined at an angle of 15 to 20 degree s and point the tip in the direction the torch is traveling. By tilting the tip, you give the preheating flames a chance to heat the metal ahead of the oxygen jet. If you hold the tip perpendicular to the surface, you decrease the amount of preheated metal and the adjacent metal could cool the cut enough to prevent smooth cutting action. * Common gauge settings for cutting • 1/4” material – Oxygen: 30 -35psi; Acetylene: 3-9 psi • 1/2” material – Oxygen: 55 -85psi; Acetylene: 6-12 psi • 1” material – Oxygen: 110-160psi; Acetylene: 7-15 psi * General Cutting Info * There is a wide variety of cutting tip styles and sizes available to suit various types of work. The thickness of the material to be cut generally governs the selection of the tip. * The cutting oxygen pressure, cutting speed, and preheating intensity should be controlled to produce narrow, parallel sided kerfs. * Cuts that are improperly made will produce ragged, irregular edges with adhering slag at the bottom of the plates. * Safety Aspects: * You must wear: * Face-shield * Gloves * Safety shoes * Apron * Long pants * Eye protection (Must wear face-shield with eye protection) * When required use a dust mask or approved respiratory protection appropriate for materials being abraded or ground. Hearing protection (required when the operators are exposed to noise levels exceeding the established threshold levels). * Acetylene is unstable at pressures above 15 PSI; * NEVER release acetylene, or any other fuel gas in confined spaces, where it might cause a fire or explosion; * DO NOT open an acetylene cylinder valve more than one turn. This permits adequate flow of acetylene from the cylinder and allows for quick closing of the valve in an emergency situation; * To open and close acetylene cylinder valves not provided with hand-wheels, always use the special wrench or key provided by the supplier.Leave the wrench or key in position, ready for immediate use should it be necessary to close the valve promptly. (When several cylinders are manifold together, a wrench on every cylinder is not required. ) * More than 1/10 the capacity of the cylinder should not be used per hour. This causes the acetylene to rapidly come out of solution, like carbon dioxide bubbles violently fizzing from a fizzy soft drink that has just been shaken; * Oxygen cylinder contains pressures over 2000 PSI and must be handled carefully; * Pure oxygen will accelerate combustion to the point that it can cause an explosion; Do not use oxygen to dust off clothing or the work area; Use the correct size wrench when tightening or loosening fittings. They are made of brass and can be damaged easily; * When not in use, cylinder must have a protective cap installed; * NEVER use a cylinder that is leaking. If leakage around the cylinder valve stem is detected after the valve has been opened (one and one-half turns for an acetylene cylinder, as far as possible for an oxygen cylinder) close the valve tight and return it to your supplier after tagging the cylinder to tell him that the valve is unserviceable; Stand to the side of the equipment when opening the cylinder valves, and open them slowly. This will limit the risk of injury due to exploding regulators; * Only use a friction lighter to light your torch; * Hot metal left out should be marked “HOT” so the others will not be burned by it; * Use pliers or tongs to grab hot metal; * Do not weld or cut on a closed container; * Inspect the hoses frequently and when necessary replace them; * ALWAYS keep oxygen and acetylene cylinders vertical upright at all times.Do not store them in the horizontal position; if an acetylene cylinder is used in the horizontal position, solvent may be lost and flame quality may be affected; * Store oxygen cylinders separately from fuel gas cylinders. Unless a fire-resistant noncombustible partition, at least 5 feet high, is used to separate the two types of cylinders or a minimum 20-foot separation should be maintained; * Oil, grease, coal dust, and similar organic materials are easily ignited and burn violently in the presence of high oxygen concentrations.Never allow such materials to come in contact with oxygen or oxy-acetylene equipment, including hose. Oxy-acetylene apparatus does not require lubrication; * DO NOT use pipe-fitting compounds or thread lubricants for making connections. Connections for oxy- acetylene and oxygen-fuel gas equipment are designed so that they can be made up tight without the need for lubricants or sealants. Of special importance is the need to keep all materials containing oil and grease away from equipment that uses oxygen. * Reference : * www. google. co. in * www. wikipidia. com * www. uepl-india. com