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Lack of fusion is the poor adhesion of the weld bead to the base metal. Incomplete penetration is a weld bead that does not start at the root of the weld groove, leaving channels and crevices in the root of the weld. This causes serious issues in pipes because corrosive substances can settle in these areas.
Examples include joint mismatch, cracks, porosity, voids, inclusions, lack of penetration and lack of fusion (cold joints). However, the lack of defects does not necessarily mean the weld is adequate and thus NDE does not provide a good indication of weld strength, long term performance, or its ability to handle cyclic loading. [1]
Other weld defects, such as inclusions and lack of penetration, should also be avoided due to these defects being the source of where cracks can initiate. [5] Detailed review of the welded joint during the design is another way to reduce failures. Ensuring that the design is able to handle the cyclic loading profile will prevent premature ...
Engineering Critical Assessment (ECA) is a procedure by which the safety of a welded structure with defects or flaws can be determined. ECAs utilize the material properties and expected stress history to determine a flaw acceptance criteria which will ensure that welds will not fail during the construction or service life of the welded structure. [1]
Weld mapping is the process of assigning information to a weld repair or joint to enable easy identification of weld processes, production (welders, their qualifications, date welded), quality (visual inspection, NDT, standards and specifications) and traceability (tracking weld joints and welded castings, the origin of weld materials).
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. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area.
Amongst these, tunneling defect is the most common defect in DFSW resulting from improper material flows throughout welding. It is mainly attributed to inappropriate selection of welding parameters particularly welding speed, rotational speed, tool design and tool penetration leading to either abnormal stirring or insufficient heat input. [18]
Cold welds - This is caused by incomplete or partial intermolecular diffusion which results in a brittle failure. Induced by cold temperatures or if there is a large gap between the pipe and fitting. Under penetration - This type of defect is caused by clamps not being properly secured during the welding process.