Visual inspection is probably the most unappreciated and often abused method of welding inspection. Because of its simplicity and the absence of sophisticated equipment, the potential of this method of examination is often underestimated. However, visual inspection of welding can often be the easiest to perform and is usually the least expensive to conduct. If carried out correctly, this inspection can often be a highly effective method of maintaining acceptable welding quality and preventing welding problems. In addition, this inspection method can verify and evaluate many areas within the welding operation.
When designing an inspection plan, we must establish the most appropriate areas to apply our inspection. We must consider preventing welding-related problems rather than finding issues that may have already occurred. Non- destructive testing (NDT), typically used to inspect completed welds, is usually designed, and conducted to find welding problems after 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 usually divided into three areas. First, and frequently the least used, is pre-weld inspection. This inspection can often detect and correct unacceptable conditions before they become actual welding problems. Second, inspection during the welding operation can often prevent problems in the completed weld by verifying the welding conditions and procedural requirements. Third, post-weld visual inspection is a relatively easy method of conducting a completed weld quality evaluation. We shall consider each of these inspection stages in more detail.
Pre-Weld Inspection – This inspection is conducted before the welding operation. This type of inspection is typically associated with checking the preparation of the welding joint and verifying parameters that would be difficult or impossible to confirm during or after welding. This is the inspection area where we can best introduce controls to 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 a 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 producing a sound weld and stress concentration at its location, reducing fatigue life. Plate surface condition and cleanliness, pre-cleaning before welding, can often be critical. Improper or inadequate cleaning can result in unacceptable porosity levels in the completed weld. Other pre-weld inspections may include preheating verification, temperature and heating method, presence and location of heat treatment monitoring devices, and gas purging type and efficacy, 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.
Inspection During Welding – This is the inspection carried out during the welding operation and is mainly concerned with the welding procedure specification (WPS) requirements. This inspection includes interpass cleaning methods, interpass temperature control, welding current settings, welding travel speed, shielding gas type, gas flow rate, and welding sequence. Also, any environmental conditions may affect the weld’s quality, such as rain, wind, and extreme temperatures.
Post-Weld Inspection – This inspection is typically conducted to verify the integrity of the completed weld. Many non-destructive testing (NDT) methods are used for post-weld assessment. However, even if the weld is subjected to NDT, it is usually wise to conduct a visual inspection first. One reason for this is that surface discontinuity, 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 the visual inspection are undersized welds, undercut, overlap, surface cracking, surface porosity, underfill, incomplete root penetration, excessive root penetration, burn through, and excessive reinforcement.
Conclusion – An excellent pre-weld inspection plan may provide a perfect opportunity to prevent welding problems before they start by detecting and correcting situations that may cause welding problems or welding discontinuities.
An inspection conducted during the welding operation can often detect problems before they escalate and helps to provide confidence in the final welded product.
Post-weld inspection can often provide an economical method of determining a weld’s acceptability concerning many surface discontinuities.