Abstract
Recent developments in the engineering industry require joining of like and unlike materials with different properties such as melting point, coefficient of thermal conductivity, solubility, difference in electrochemistry, etc. as part of machines, tools, and more specific applications. Materials including those similar and dissimilar in nature are successfully joined by fusion and solid-state welding processes. In accordance with ASME Sec IX and AWS D1.1 codes and API 1104 standard, welding procedures specifications (WPS) through procedure qualifications (PQR) are required prior to commencing any fabrication work pertaining to pressure vessels, piping and pipeline, storage tanks, offshore platform structural parts, and so on. A specific welding process must be chosen based on the design of the component, the material, thickness, production, availability of equipment, people, and other factors. Weldment testing, including destructive and non-destructive examinations, are crucial during procedure qualification, welder qualification, and the production welding process.
TopIntroduction
Welding is a joining process which involves heating materials to the welding temperature, either with or without the application of pressure, and with or without the use of filler metal. In industry, there are various welding methods available; however, arc welding is particularly prevalent and widely employed in the oil, gas, chemical, and power industries. A master chart of welding and related processes utilized in current metal fabrication and maintenance services is shown in Figure 1 (Jeffus, 2020).
Figure 1. Master chart of welding and allied processes
TopOverview Of Welding Process
Gas Welding
A gas flame is used as a source of heat in one of the most prevalent welding procedures. Heat is generated by burning a combustible gas, such as MAPP (methylacetylene-propadiene) or acetylene, combined with oxygen in the oxyfuel gas welding process (Abdulateef et al 2010). Because oxygen and fuel cylinders are easy to transport, gas welding is commonly employed in maintenance and repair operations.
Arc Welding
This is a method of joining metals using an electric arc. The concentration of heat is a notable benefit of arc welding over gas welding. The flame in gas welding spreads out across a vast area, which can cause thermal distortion. Arc welding's heat concentration is advantageous because reduced heat diffusion lowers buckling and warping (Kumar et al. 2009). This heat concentration also increases penetration depth and speeds up the welding process; as a result, arc welding is typically more practical and cost-effective than gas welding. There are three things that all arc welding procedures have in common: a heat source, filler metal, and shielding. Arc welding generates heat by arcing an electrical current between two conductors.
By striking an arc between a coated-metal electrode and the base metal, shielded metal arc welding is done. Once the arc is produced, the molten metal from the electrode's tip joins the molten metal from the base metal's edges to form a sound junction. Stick electrode welding, coated electrode welding, and manual metal arc welding are all terms used to describe this procedure. Because the electrode coating produces a protective covering over the weld deposit, sheltering it from contamination, the method is known as shielded metal arc welding. The main benefits of shielded metal arc welding are that it produces high-quality welds quickly and at a reasonable cost. The method is very versatile, and it can be used for any position and any metal, including low carbon steel, low alloy steels, quenched and tempered steels, high alloy steels, corrosion resistant steels, and so on. It has a limited application in aluminium welding (Matusiak & Pfeifer (2013)).
Gas Shielded Arc Welding
The type of shielding employed distinguishes shielded metal arc welding from gas shielded arc welding. Both the arc and the molten puddle are shielded by an inert gas in gas shielded arc welding. The inert gas barrier protects the weld from contamination by the atmosphere, resulting in a superior weld. Helium, argon, or carbon dioxide are the main gases employed in this process (Kah & Martikainen, (2013)). A blend of these gases is sometimes utilised. Gas tungsten arc welding (GTAW), gas metal arc welding and plasma welding method are three types of gas shielded arc welding technologies.
Key Terms in this Chapter
Non-Destructive Examination: Testing without destroying the component.
Magnetization: Induce magnetic field in longitudinal & transverse direction.
Defects: A size of discontinuity which is not accepted by code/standard.
Solidification: The process of transformation of a liquid to a solid.
Code: A set of rules and specifications for the correct methods and materials.
Heat Affected Zone: Portion of metal structure affected by heating.
Standard: A set of procedure or system to perform the work.
Discontinuity: Deviation in the geometry/size.
Coalescence: Joining of two pieces of metal together by heating process.
Destructive Testing: Testing with destroying the component specimen.
Weldments: A component fabricated and assembled after welding operation.
Piping: System of pipes used to carry fluids from one place to another including flange, valve, instrument, supports, etc.