The 5 Most Common Mistakes Found by Welding Inspectors
Welding inspectors have a responsibility to the company they work for and the general public to ensure that weld quality is satisfactory. Failure to fulfill their duties can result in property damage, injury, and death. Most welding inspectors, therefore, take their job very seriously. Welding inspectors spend years honing their ability to detect and size welding discontinuities and defects. While they must be proficient at identifying all discontinuities and defects, some of these weld irregularities are more readily detectable than others.
1. Surface Porosity
Porosity is gas that has been trapped in the weld; this results in cavity formation within the weld. Porosity can cause reduced weld strength. Welding inspectors who are not trained in other forms of nondestructive testing are limited to viewing the surfaces of welds. So while not all forms of porosity can be detected by a welding inspector, porosity that extends to the surface of the weld can.
Surface porosity can be caused by a variety of reasons. Filler metals and electrodes that have not been properly handled can cause surface porosity. Welding processes that use shielding gas can create welds with surface porosity if the shielding gas is contaminated or if its flow is restricted. Surface porosity can also be created by welders who are not using proper welding technique. Surface porosity is also referred to by the non-standard term “pinhole”.
Weld undercut is a surface discontinuity that occurs at the toe of the weld. Undercut is defined as an erosion of base material at the weld interface caused by the energy created during welding that filler metal has not been deposited on. Undercut is geometrically sharp. This sharpness causes it to be a stress concentrator when left unaltered. Stress concentrators can cause premature failure of a part or structure.
“Stress concentrators can cause premature failure of a part or structure.”
Welding inspectors can used a variety of means to detect undercut. One of the quickest and simplest ways to check for undercut is the fingernail check. All that the fingernail check entails is scratching a fingernail transversely across the weld. If the fingernail catches at the toe of the weld, there could be undercut. Once undercut is detected, it must be measured to determine whether or not the amount of undercut present is acceptable. This can be done by an optical comparator, a laser gauge, or other types specialized welding gauges.
3. Incomplete Joint Penetration
Incomplete joint penetration is a weld discontinuity that occurs when the weld does not extend through the entirety of the joint that was welded. Incomplete joint penetration can be detrimental to a weld for a number of reasons. One is that the interface between the weld and the unfused base material can have a sharp geometry. This will make it act as a stress concentrator.
“Incomplete Joint Penetration can not be detected visually if there is no access to the root side of the joint”
This geometry also acts as a gathering place for organisms and foreign materials that can cause rapid corrosion. Incomplete joint penetration also negatively impacts the strength of the weld joint because the total thickness of the base material has not been joined together. Incomplete joint penetration can be visually detected when welding only occurs on one side of the weld joint and there is visual access to the root side of the weld joint. It can not be detected visually if there is no access to the root side of the joint or if welding occurs from both sides and the incomplete joint penetration is actually in the middle of the joint, as opposed to the root side of the joint. Tools that welding inspectors use to determine if there is incomplete joint penetration include borescopes, mirrors, and magnifiers. Incomplete joint penetration can be caused by incorrect welding parameters and poor welding technique.
4. Incomplete Fusion
Incomplete fusion occurs when the weld metal does not fully coalesce with the base material during welding. Incomplete fusion can reduce weld strength drastically because there is no metallurgical bond between the weld metal and the base metal where incomplete fusion is present. Incomplete fusion can also be a geometric stress concentrator and can also have higher localized rates of corrosion than the parts of the weld that do not have incomplete fusion.
“Incomplete fusion can reduce weld strength drastically”
Incomplete fusion can be spotted visually by a welding inspector if it occurs on the root or face surface of the weld joint. Incomplete fusion can occur within the weld joint, however, nondestructive means other than visual examination will be required to discover it. To spot lack of fusion, welding inspectors can look for unusual weld bead profiles and doing a fingernail check. Lack of fusion can be caused by many factors, improper welding technique and improper welding parameters are two examples. Incomplete fusion is also referred to as “lack of fusion”.
5. Arc Strikes
“Causes of arc strikes include improper welding technique and improper grounding”
Arc strikes are marks on the part or structure being welded outside of the weld zone that are created by accidental rapid discharge of an electrical arc. Arc strikes, although usually small, can have large, negative results. Since an arc strike is typically small and happens fast, the volume of the base material that received the arc strike will heat and cool rapidly. This can result in the formation of an extremely hard and brittle microstructure that could be prone to cracks. Arc strikes also typically leave an indentation on the base material. This can be a stress concentrator, and it can also take away from the material’s original thickness, reducing its strength.
Arc strikes can be very easily detected by a welding inspector so long as visual access to the surface of the base material is not obstructed. The welding inspector must also know where to look. While much arc striking occurs somewhere near the weld, it may not always occur there. Sometimes it can occur near the ground clamp and not the welding electrode. Causes of arc strikes include improper welding technique and improper grounding.
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