The most extensively used nondestructive examination of weldments. It is a primary method of determining important information about conformity to specifications. Visual inspection does not normally require special equipment; however, the requirements are that the inspector is knowledgeable and has good vision.
Advantages- Visual inspection should be the primary evaluation method of any quality control program. It can, in addition to flaw detection, discover signs of possible fabrication problems in subsequent operations, and can be incorporated in process control programs. Prompt detection and correction of flaws can result in significant cost savings. Conscientious visual inspection before, during, and after welding can detect many of the discontinuities that would be found later by more expensive nondestructive examination methods.
Equipment- Auxiliary lighting equipment may be needed to assure good visibility. If the area to be inspected is not readily visible, the inspector may use mirrors, borescopes, flashlights or other aids.
Inspection of welds usually includes quantitative as well as qualitative assessment of the joint. Numerous standard measuring tools are available to make various measurements, such as joint geometry and fit-up, weld size, weld reinforcement height, misalignment, and depth of undercut. Contact pyrometers and crayons should be used to verify that the preheat and interpass temperatures called for in the welding procedure are being used.
Prior to Welding- Before welding, the base metal should be examined for conditions that tend to cause weld defects. Scabs, seams, scale, or other harmful surface conditions may be found by visual examination. Plate laminations may be observed on cut edges.
Dimensions should be confirmed by measurement. Base metal should be identified by type and grade. Corrections should be made before work proceeds.
After the parts are assembled for welding, the inspector should check the weld joint for root opening, edge preparation and other features that might affect the quality of the weld. The inspector should check the following conditions for conformance to the applicable specifications:
(1) Joint preparation, dimensions, and cleanliness
(2) Clearance dimensions of backing strips, rings, or consumable inserts
(3) Alignment and fit-up of the pieces being welded
(4) Welding process and consumables
(5)Welding procedures and machine settings
(6) Specified preheat temperature
Inspection During Welding- Visual inspection is the primary method for controlling quality during welding. Some of the aspects of fabrication that can be checked include the following:
(1) Treatment of tack welds
(2) Quality of the root pass and the succeeding weld layers
(3) Proper preheat and interpass temperatures
(4) Sequence of weld passes
(5) Interpass cleaning
(6) Root condition prior to welding a second side
(7) Distortion
(8) Conformance with the applicable procedure
The most critical part of any weld is the root pass because many weld discontinuities are associated with the root area. Competent visual inspection of the root
pass may detect a condition that would result in a discontinuity in the completed weld. Another critical root condition exists when second-side treatment is required of a double welded joint. This includes removal of slag and other irregularities by chipping, arc gouging, or grinding down to sound metal.
The root opening should be monitored as welding of the root pass progresses. Special emphasis should be placed on the adequacy of tack welds, clamps, or braces designed to maintain the specified root opening to assure proper joint penetration and alignment.
Inspection of successive layers of weld metal usually concentrates on bead shape and interpass cleaning, sometimes with the assistance of workmanship standards. Standards show examples of joints similar to those in manufacture in which portions of successive weld layers are shown. Each layer of the production weld may be compared with the corresponding layer of the workmanship standard. Each weld layer should be visually checked by the welder for surface irregularities and adequate interpass cleaning to avoid subsequent slag inclusions or porosity.
After Welding- The following are among the items that can be checked by visual inspection:
(1) Final weld appearance
(2) Final weld size
(3) Extent of welding
(4) Dimensional accuracy
(5) Amount of distortion
Most codes and specifications describe the type and size of discontinuities which can be accepted. Many of the following discontinuities on the surface of a completed weld can be found by visual inspection:
(1) Cracks
(2) Undercut
(3) Overlap
(4) Exposed porosity and slag inclusions
(5) Unacceptable weld profile.
The weld surface should be thoroughly cleaned of oxide and slag in order to accurately detect and evaluate discontinuities.
When a postweld heat treatment is specified, the operation should be monitored and documented by an inspector. Items of importance in heat treatment may include the following:
(1) Area to be heated
(2) Heating and cooling rates
(3) Holding temperature and time
(4) Temperature measurement and distribution
(5) Equipment calibration.
Discretion should be used when judging the quality of a weld from the visible appearance alone. Acceptable surface appearance does not prove careful workmanship or subsurface weld integrity; however, proper visual inspection procedures before and during fabrication can increase product reliability over that based only on final inspection.