There are many ways to join the parts together. Usually this can be done by fasten them with rivets or bolts, solder or weld them together. If you need to do the continuous joint on long parts of joining surfaces you need welding. This is the main advantage of welding, especially for enclosed containers such as boilers, etc. The original fusion technique is known from the earliest uses of iron. People heated small pieces of iron to welding temperature and then hammered or pressed them to create larger useful pieces. The most common today’s welding techniques are arc welding, oxyacetylene welding, resistance, electron-beam, friction, laser welding and other. The shielded metal-arc welding is the most used technique. In this process, an electric arc is used to melt the electrode’s metal and transfer it to the joint. Another technique is gas (usually oxyacetylene) welding. For fusion process heat is supplied by burned acetylene in oxygen. The resistance welding is a process when the required heat is generated from electrical resistance of the joint. Such welds are made using low-voltage and high current power source with pressure applied (see also best welding caps). Electron-beam welding is based on a dense stream of high-velocity electrons bombarding the joint. The friction welding is based on heating joining parts by friction. Laser welding is accomplished when materials are fused together by heat generated from a laser source. The process of creating welding joint is caused by fusion on joining materials, thus leading to melting of the base metal or other material. In addition, filler materials are typically added to the joint. The joint is created in the process of cooling the pool of those molten materials. Joint is usually stronger than a base material. The pressure also can be applied during the welding process. Welding parts can be geometrically prepared in different ways. The basic types of weld joints are the butt joint, V-butt joint, lap joint and T-joint. Other variations exist as well. Many welding processes require the particular joint design. For example, laser, resistance, and electron-beam welding are performed on the lap joints. The most widely used materials in welded constructions are carbon and low-alloy steels. The weldability of steels varies depending on a carbon content and total alloying content. Aluminium alloys are also generally weldable. Despite the high thermal conductivity that makes its welding difficult, copper and its alloys are also well weldable. Glass and plastic are usually well weldable. They usually welded by heating to melting range and by simply pressing surfaces together. The quality of weld depends on the base material, filler and flux material, energy and design. The strength of material and weld depends on the welding method and concentration of energy input, type of the flux and filler, and weldability of the base material. The weld quality also much depends on the heat-affected zone. Usually, one of the destructive or nondestructive methods is used to test the quality of the weld. Possible defects of welds are cracks, gas, and non-metallic inclusions, distortions, incomplete penetration, lack of fusion and lamellar tearing.