Welding Defects and Visual Inspection

Welding Defects and Visual Inspection

Welding Defects and Visual Inspection: Welding students often ask questions such as: Which defect contributes to joint failure?

Which ones may pass inspections?

Visual Inspection

Are there jobs on which weld defects are permitted? Knowing the construction and use of the weldment helps the welder answer these questions. In general, the welder’s goal should be to avoid all defects; they all contribute to weld and joint failure.

 

 Minor allowances may be permitted if the work is not critical. Little tolerance is permitted in
critical or code work because high strength is necessary due to load conditions of heat, pressure, or stress.

The criticality of a discontinuity is one way of assessing the importance of classifying it as a defect. The actual
repair of a discontinuity may create more problems and increase residual stresses than if the defect were left alone. Is the discontinuity linear (cracklike) or nonlinear (spherical
porosity, or tungsten inclusion)? Is the end condition sharp (cracklike), or does it have a radius (undercut)? 

Does the discontinuity break the surface or is it subsurface? Higher
stresses will be localized on surface opening discontinuities. Is the discontinuity longitudinal to the load or transverse to the load? 

Will the loading be fatigue or impact or simply a static load? What is the ambient temperature of the weldments? The engineer will take all these issues into
consideration when determining the design of the weldments, materials, welding procedures, acceptance criteria, and which code or specification to follow. If the welder expects to be recognized as a professional, he or she will always strive to do work that is sound and of

 

good appearance. The inability to do so with the high-quality
equipment available suggests carelessness on the part of
the welder. It will surely lessen the regard that the shop
supervisor and other workers have for the welder.
Because the welder is watching every inch of the weld as it
is being made, he or she is in the best position to do the visual inspection. Visual inspection needs to be done before
welding with the proper joint fit-up and selection of materials. It should be done during the welding after tacking, root
pass, fill passes, and cap passes. Visual inspection should
also be done after welding is completed to determine weld
dimensions, overall part dimensional accuracy, and whenever post-weld heat treatment is required. 

The American Welding Society has a certification program that recognizes those people who have work experience and have
passed a multiple-part test covering welding fundamentals,
code interpretation, and practical inspection techniques.
Each portion of this three-part test has a maximum 2-hour
time limit. 

However, weld quality cannot be “inspected in.” It must be built in. Weld quality is built in by each
person who is involved with the project. 

As a professional welder, you should be properly trained for the work you are
doing. If it is code work, you will have to take a certification test to demonstrate the required welding skills. 

Some companies will conduct knowledge tests that may include your ability to recognize weld discontinuities or defects. A professional welder should have available the welding
procedure for the work being done, and in many cases, the code requires the procedure to be displayed and the welder educated on its use. 

Since the welder will be required to
determine if the acceptance criteria have been met, he or she will require tools to measure the weld size and joint geometry.

Are available from sources such as the American Welding Society. For a welder doing fillet welds perhaps all that is required is the appropriate fillet weld gauge.  the proper use of fillet gauges.

 

Handheld Scanner Technology Includes the Palm TM Organizer

 

Visual inspection methods and tools have not changed much over the last 50 years. However, there is a
dramatic change occurring in the equipment that is now available to assist the person inspecting welds. Generically speaking, these devices are known as handheld weld scanners. By simply aiming the scanner at a joint preparation or finished weld and activating it, the operator quickly obtains
a multitude of measurements and validates their geometry against preset thresholds.

The handheld scanner then supplies data via visual displays, computer-saved records, and strip chart printouts.
Typical features measured on the prepared joint include