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Visual inspection is probably the most underrated, and often misused, method of welding inspection. Because of its simplicity, and the absence of sophisticated equipment, the potential of this method of inspection is quite often underestimated. Visual inspection of welding can often be the easiest to perform and is usually the least expensive to conduct. If carried out correctly, this type of inspection can often be an extremely effective method of maintaining acceptable welding quality and preventing welding problems. There are many areas within the welding operation that can be verified and evaluated by this method of inspection.
When designing an inspection plan, we need to establish the most appropriate areas to apply our inspection. We need to consider the possibility of preventing welding related problems, rather than finding problems which may have already occurred. Non- destructive testing (NDT), which is typically used for the inspection of completed welds, is usually designed and conducted to find welding problems after the fact, when the weld is completed. Visual inspection can often be utilized to prevent welding problems from happening in the first place. The welding inspection function is often divided into three areas. First, and often the least utilized, is pre-weld inspection. This type of inspection can often provide us the opportunity to detect and correct unacceptable conditions before they develop into actual welding problems. Second, inspection during the welding operation can often prevent problems in the completed weld through verification of the welding conditions and procedural requirements. Third, post-weld visual inspection is a relatively easy method of conducting completed weld quality evaluation. We shall consider each of these inspection stages in more detail.
Pre-Weld Inspection – This inspection is conducted prior to the start of the welding operation. This type of inspection is typically associated with checking the preparation of the welding joint and verification of parameters that would be difficult or impossible to confirm during or after welding. This is the area of inspection where we can best introduce controls that may prevent defective welding. Some areas of pre-weld inspection are joint preparation inspection/pre-weld setup. This may involve the dimensional inspection of root openings. Root openings that are too tight can cause inadequate root penetration. Root openings that are too large can cause over- penetration. Groove weld bevel angles, if too small, may cause lack of fusion, and if too large, can result in distortion of the weld joint from overheating and excessive shrinkage stress. Joint alignment (misalignment of the weld joint) can result in difficulty in producing a sound weld and stress concentration at its location, resulting in a reduction of fatigue life. Plate surface condition and cleanliness, pre-cleaning prior to welding, can often be of extreme importance. Improper or inadequate cleaning can result in unacceptable levels of porosity in the completed weld. Other pre-weld inspections may include preheat verification, temperature and heating method, presence and location of heat treatment monitoring devices, and type and efficacy of gas purging, if applicable.
Pre-weld inspection may also include evaluation and verification of documentation, material certification, filler alloy certification, welder performance qualification, welding procedure qualification, and welder and weld identification, for traceability, if applicable.
Inspection During Welding –
This is the inspection that is carried out during the welding operation and is concerned mainly with the requirements of the welding procedure specification (WPS). This inspection includes such items as interpass cleaning methods, interpass temperature control, welding current settings, welding travel speed, shielding gas type, gas flow rate, and welding sequence, if applicable. Also, any environmental conditions that may affect the quality of the weld such as, rain, wind, and extreme temperatures.
Post-Weld Inspection – This inspection typically conducted to verify the integrity of the completed weld. Many non-destructive testing (NDT) methods are used for post-weld inspection. However, even if the weld is to be subjected to NDT, it is normally wise to conduct visual inspection first. One reason for this is that surface discontinuities, which may be detected by visual inspection, can sometimes cause misinterpretation of NDT results or disguise other discontinuities within the body of the weld. The most common welding discontinuities found during visual inspection are conditions such as undersized welds, undercut, overlap, surface cracking, surface porosity, under fill, incomplete root penetration, excessive root penetration, burn through, and excessive reinforcement.
Conclusion - A good pre-weld inspection plan may provide us with an excellent opportunity to prevent welding problems before they start, through the detection and correction of situations that may cause welding problems or welding discontinuities.
Inspection conducted during the welding operation can often detect problems before they escalate and also helps to provide confidence in the final welded product.Post-weld inspection can often provide an economical method of determining a weld’s acceptability with regard to many surface discontinuities.