Glossary of Welding and Mechanical Carpentry – Solmaz
Steel
It is the name given to an alloy composed mainly of iron and carbon, the latter in a percentage not exceeding 2.06 percent. In the world over a billion tons of steel are produced every year, obtained both from the integral cycle with the refining of the blast furnace cast iron and from the smelting of ferrous scrap and, subsequently, processed through various industrial production processes, such as for example rolling, forging, heat treatment and stamping.
Iron
The word iron is used in common parlance to indicate low strength iron alloys called mild steels. This element is always found linked to others such as: carbon, silicon, manganese, chromium, nickel, etc. With carbon, iron forms its two best known alloys: steel and cast iron. At an industrial level it is possible to obtain iron with a purity that is close to one hundred percent: this product is then used to be linked to other chemical elements to obtain alloys with the most diverse characteristics. Extremely important in technology for its mechanical characteristics and its workability, in the past it was so important that it gave its name to an entire historical period, the Iron Age.
Cast iron
The production of cast iron generally takes place by reducing iron oxides by burning coal in contact with them, in equipment called blast furnaces. The ore is arranged in alternating layers with low-sulfur coal; the iron contained in the mineral, when it reaches the molten state, drips downwards and collects in special containers. The main use of cast iron is the intermediate one in the production of steel, which is obtained by decarburizing the cast iron in equipment called converters into which oxygen or air is blown: this, when combined with carbon, reduces its rate in the molten metal and is evacuated as carbon dioxide.
Piping
Piping system (“piping”) used for the handling of hydrocarbons. A piping system (in English, piping), in engineering, indicates the more or less complex piping systems that connect the various equipment of a plant (for example hydraulic, chemical or petrochemical). The piping system allows the transport, accumulation and interception of fluids destined for the various users.
Corrosion Protection
The corrosion protection of all the most important areas of the plant is now carried out on all plants subject to particularly variable atmospheric conditions. In addition to galvanizing, high-quality primer layers are made. Corrosion protection ensures the structural soundness of the plant over the entire life cycle and saves resources by extending the life of the components.
Electrode welding
The coated electrode process derives from the first arc processes developed between the end of the 19th century and the beginning of the 20th century. In these processes, initially the electrode, of the same type of material as the one to be welded, was not protected, therefore it oxidized very quickly and, much more seriously, introduced oxides and other impurities into the weld pool. It was soon seen that adding fluxes to the electrode material gave better results, initially these fluxes were inside the electrode, but subsequent developments showed the usefulness of having a coating on the outside of the metal material of which the inside is composed.
TIG welding
TIG welding, Tungsten Inert Gas, is an arc welding process with an infusible tungsten electrode, under protection of inert gas, which can be performed with or without filler metal. TIG welding is one of the most popular methods, it provides high quality joints, but requires highly specialized operators. This welding technology was first developed for the aircraft industry during World War II to replace rivets with welds on aircraft.
Steel industry
The term steel industry indicates a specific sector of metallurgy, which concerns the technique relating to the treatment of minerals with a high iron content in order to obtain iron or different types of alloys containing iron, including steel, cast iron and steels related. The process of transforming iron ore begins immediately after its extraction in the mine. Iron is a particularly reactive chemical element, so in nature it is generally found in the form of oxides, hematite and magnetite, hydroxides, limonite, carbonates, siderite, silicates and sulphides. Ferrous minerals, in addition to the above compounds, contain impurities of various types, which are called by the name of ganga. Part of the gangue can be separated before the iron ore is sent to the actual steelmaking process, either by separation by density difference, or by magnetization.
Skid
Base for housing technical modules used in oil, gas, food, water systems … and can be cabinets in relation to the protection needs of the equipment and functions of use.
Plasma cutting
It comes from an already existing technology, that of plasma jet welding. It was made through a system whereby it was possible to create a plasma jet with a high energy content able to work the surface of the piece, both to carry out surface treatments and to obtain a real welding. The inventive step leading to Plasma Cutting is found in Robert Gage’s 1955 patent for Union Carbide. As a result of his research, Gage introduces a nozzle, or a wall which, placed along the path of the hot plasma, forces it into a well-defined shape. The result of the presence of this component is a much thinner, stiffer and more stable jet, such as to have a specific power so high as to be able to cut metals.
Solmaz, description of the main welding procedures
The table shows the main welding processes, with the Italian name, that of the AWS (American Welding Society) and the abbreviation used by the AWS. For the details of the single procedure, refer to the relative item.
| IT denomination | AWS naming | Theme song |
| Oxyacetylene | Oxyfuel Gas Welding | OFW |
| Coated electrode | Shielded Metal Arc Welding | SMAW |
| Submerged arc | Submerged Arc Welding | SAW |
| MIG / MAG | Gas Metal Arc Welding | GMAW |
| TIG | Tungsten Arc Welding Gas | GTAW |
| Plasma welding | Plasma Arc Welding | PAW |
| Electroscoria | Electroslag Welding | ESW |
| Electrogas | Electrogas Welding | EGW |
| Laser welding | Laser Beam Welding | LBW |
| Electron beam welding | Electron Beam Welding | EBW |
| Resistance welding | Resistance Welding | RW |
| Friction welding | Friction Stir Welding | FSW |
Heterogeneous welding or brazing
Heterogeneous welding is commonly called brazing and allows the parts to be joined by melting only the filler alloy and keeping the edges of the joint intact. In the field of brazing, the following are distinguished:
- strong brazing: temperatures over 450 ° C but below the melting point of the materials to be welded; the joint must be prepared in such a way as to favor the penetration of the filler material by capillarity
- soft brazing: it is carried out with temperatures below 450 ° C and below the melting point of the materials to be welded; the joint must be prepared in such a way as to favor the penetration of the filler material by capillarity
- brazing: filler alloys are flux alloys at even higher temperatures than those used in hard brazing but always lower than the melting point of the materials to be welded; the joint is prepared similarly to the preparation for an autogenous welding.
Spot welding
Also called spot welding (English spot welding) or welding nails, often carried out by induction welding machines, is a type of resistance welding and consists in making the parts of material to be welded match and in compressing the two pieces by means of a machine. Subsequently, the passage of electricity heats the bodies to be welded until they reach the melting point in less than 15 seconds, thus joining the two materials by a particularly resistant internal nail that lasts over time. This kind of welding is used in many preshaping centers to make double brackets produced in a single pass more rigid and therefore manageable.
Spot welding
Tack welding, except when the term is not used improperly to indicate the above-mentioned point welding, does not refer to a particular welding process, but rather to a particular application of the welding processes already mentioned. It involves generating welding points on the perimeter of the pieces to be joined, that is, without creating a weld bead or a continuous welding without interruptions, but by creating multiple points at more or less regular distances between them. This procedure is often used to join parts subjected to low mechanical stress, or in any case between which the welding must not create a hermetic joint. It is typically used in non-automated welding processes as basting useful for holding parts together in view of a subsequent continuous weld.
Ultrasonic welding
In ultrasonic, high frequency welding (15kHz to 40kHz) the low amplitude vibration is used to create heat by means of friction between the materials to be welded. The interface of the two parts is specially designed to concentrate energy for maximum welding resistance. Ultrasonic welding can be used on almost all plastics. It is the fastest heat sealing technology available.
Control of welds
The safety implications associated with the use of welding, especially in the field of pressure vessels and civil engineering, have imposed criteria on guaranteeing the reliability of welds. This control takes place in two distinct phases:
- Control of personnel and procedures (preventive control)
- Control of the welded joint (production control)
- Control and qualification of welding procedures
Welding must only be carried out by qualified personnel and using qualified procedures, the qualification standards of the procedures vary according to the field of application and according to the material to be welded (essential variables). In particular in the European context, UNI EN ISO EN 15614-1 is followed for the qualification of voltaic arc procedures of steels and nickel alloys and UNI EN 287/1, UNI EN ISO 9606/1: 2013 and UNI EN 1418 for the qualification of welders, while in the United States the rules apply. ASME Sect. IX
In general, in order to qualify a procedure, bead beads must be performed, which are checked with non-destructive methods and from which specimens for destructive tests are obtained (traction, straight bends, reverse bends, resilience, hardness etc.)
Control of welded joints after production
The welded joints, after execution, are subjected to non-destructive tests (radiography, ultrasound, penetrating liquids, etc.) more or less extensive, depending on the reliability required of the joint. Furthermore, for a predetermined number of meters of welding or joints (depending on the field of application), other beads are produced which will be subjected to destructive tests (generally the most significant ones among those already undergone during the qualification of the procedure).