Visual Testing

Visual inspection (VT) refers to the detection of surface imperfections using the eye. Usually being applied without any kind of additional equipment, VT can be improved by using aids such as a magnifying glass to improve its effectiveness and scope. VT is one of the primary NDT methods. Since it relies on an evaluation made using the eye, VT is generally considered to be the primary and oldest method of NDT. Due to the relative simplicity and as it does not require sophisticated apparatus, it is a very inexpensive method thus provides an advantage over other NDT methods. VT is an ongoing inspection that can be applied at various stages of construction. The primary limitation of VT is it is only capable of evaluating discontinuities, which can be seen on the surface of the material or part. On several occasions, there are some visual indications of a subsurface imperfection that may need an additional NDT method to provide verification of the subsurface discontinuity. VT is often taken to be effective when it is performed at all stages of any new fabrication and is the main method used during the inspection of pressure equipment. If applied after welding has been completed, it is possible that subsurface flaws may not be detected. Thus it can be said that VT will only be fully effective if it is applied throughout any fabrication or inspection. An effective VT that is applied at the correct time will detect most defects or discontinuities that may later be found by some other costly and time-consuming NDT method. A flaw, such as incomplete fusion at the weld root, can be repaired easily and quickly right after it is produced, saving on expense and time required repairing it after the weld has been inspected using some other NDT technique. VT provides immediate information on the condition of pressure equipment regarding such things as corrosion, bulging, distortion, correct parts, failures, etc. VT requires three basic conditions to be in place. Good vision: to be able to see what we are looking for, good lighting: the correct type of light is important & experience: to be able to recognize problems. As mentioned previously, one of the advantages of VT is that there is little or no equipment required, which improves its economy or portability. Equipment so as to improve the accuracy, repeatability, reliability, and efficiency of VT, include various devices. Magnifying glasses can also be used for a more detailed look at some visual feature. As such proper care must be taken to avoid making erroneous decisions regarding the size or extent of some discontinuity when its image is magnified.