Common Weld Faults
This term is used to describe the failure of the filler and base metal to fuse together at the root of the joint. Bridging occurs in groove welds when the deposited metal and base metal are not fused at the root of the joint. The frequent cause of incomplete penetration is a joint design which is not suitable for the welding process or the conditions of construction. When the groove is welded from one side only, incomplete penetration is likely to result under the following conditions.
- The root face dimension is too big even though the root opening is adequate.
- The root opening is too small.
- The included angle of a V-groove is too small.
- The electrode is too large.
- The rate of travel is too high.
- The welding current is too low.
Lack of Fusion
Lack of fusion is the failure of a welding process to fuse together layers of weld metal or weld metal and base metal. The weld metal just rolls over the plate surfaces. This is generally referred to as overlap. Lack of fusion is caused by the following conditions:
- Failure to raise to the melting point the temperature of the base metal or the previously deposited weld metal.
- Improper fluxing, which fails to dissolve the oxide and other foreign material from the surfaces to which the deposited metal must fuse.
- Dirty plate surfaces.
- Improper electrode size or type.
- Wrong current adjustment.
Undercutting is the burning away of the base metal at the toe of the weld. Undercutting may be caused by the following conditions:
- Current adjustment that is too high.
- Arc gap that is too long.
- Failure to fill up the crater completely with weld metal.
Slag inclusions are elongated or globular pockets of metallic oxides and other solids compounds. They produce porosity in the weld metal. In arc welding, slag inclusions are generally made up of electrode coating materials or fluxes. In multilayer welding operations, failure to remove the slag between the layers causes slag inclusions. Most slag inclusion can be prevented by:
- Preparing the groove and weld properly before each bead is deposited.
- Removing all slag.
- Making sure that the slag rises to the surface of the weld pool.
- Taking care to avoid leaving any contours which will be difficult to penetrate fully with the arc.
Porosity is the presence of pockets which do not contain any solid material. They differ from slag inclusions in that the pockets contain gas rather than a solid.
The gases forming the voids are derived form:
- Gas released by cooling weld because of its reduced solubility temperature drops.
- Gases formed by the chemical reactions in the weld.
Porosity is best prevented by avoiding:
- Overheating and undercutting of the weld metal.
- Too high a current setting.
- Too long an arc.
Visual Inspection (VT)
Visual inspection is a non-destructive testing (NDT) weld quality testing process where a weld is examined with the eye to determine surface discontinuities. It is the most common method of weld quality testing.
Advantages of nondestructive weld quality testing:
- Inexpensive (usually only labor expense)
- Low cost equipment
- No power requirement
- Quick identification of defects and downstream repair costs due to issues that weren’t caught early
- Inspector training necessary
- Good eyesight required or eyesight corrected to 20/40
- Can miss internal defects
- Report must be recorded by inspector
- Open to human error
Visual Weld Quality Testing Steps
- Practice and develop procedures for consistent application of approach
- Inspect materials before welding
- Weld quality testing when welding
- Inspection when weld is complete
- Mark problems and repair the weld
Visual Weld Equipment
- Weld hand held fillet gauge: measure -
- flatness of the weld
- convexity (how the weld is welded outward)
- concavity (how the weld is rounded inward)
- Protective lenses with pocket viewer and shade lens for use when observing the welding process
- Magnifying glass per the code in your area
- Chisel and hammer for spatter and slag removal before the weld is inspected
- Temperature device (Tempelstick, Pyrometer) to determine the preheating, interpass and post-heating temperatures.
- Magnet to indicate the type of material being welded
- Tape measure
Visual Inspection Before Welding
- Check drawings
- Look at weld position and how ti corresponds to the specification. Watch the vertical direction of travel
- Check welding symbols
- Does procedure align with local codes and the weld specification
Weld Material Inspection
- Do the materials purchased match the specification for base metal size and type? Check electrode size, gas selection and grade.
- Check materials for defects. Look for contaminants such as rust, scale, mill, lamination etc.
- Are materials prepared for correct angles
Follow these weld quality testing steps for assembly inspection:
- Check for fit
- Alignment of fixtures and jigs. Check cleanliness (look for spatter from previous jobs)
- Check quality if tack welds are used. The tack weld must be made with the same electrode as the main weld (s).
- Check use of pre heat to slow the cooling rate and to minimize distortion
- Check for damage (cables, ground clamps, electrode holder).
- Check arc voltage
- Check amperage meter for range against specification
Visual Inspection During Welding
- Check electrodes for size, type and storage (low hydrogen electrodes are kept in a stabilizing oven)
- Watch root pass for susceptibility to cracking
- Inspect each weld pass. Look for undercut and required contour. Ensure the weld is cleaned properly between each pass.
- Check for craters that need to be filled
- Check weld sequence and size. Gauges are used to check size.
Inspection After Welding
- Check weld against code and standards
- Check size with gauges and prints
- Check finish and contour
- Check for cracks against standards
- Look for overlap
- Check undercut
- Determine if spatter is at acceptable levels